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Timing of fruit removal affects concurrent vegetative growth and subsequent return bloom and yield in olive (Olea europaea L.)
Abstract
Olive (Olea europaea) demonstrates a high tendency toward alternate fruit production, with significant negative consequences on the industry. Fruit load is one of the main cause-and-effect factors in the phenomenon of biennial bearing, often disrupting the balance between reproductive and vegetative processes. The objectives of the present study were to identify the time range during which heavy fruit load reversibly interrupts the reproductive processes of the following year. The linkage between timing of fruit removal, vegetative growth, return bloom, and fruit yield was studied. Complete fruit removal in cv. Coratina until about 120 days after full bloom (August 15) caused an immediate resumption of vegetative growth. The new shoots grew to twice the length of those on trees that underwent later fruit removal. Moreover, a full return bloom, corresponding with high subsequent yields, was obtained by early fruit removal, while poor or no bloom developed on late-defruited or control trees. Thus, the critical time to affect flowering and subsequent fruiting in the following year by fruit thinning occurs in olive trees even weeks after pit hardening—much later than previously suggested. Furthermore, the data indicate that flowering-site limitation, due to insufficient or immature vegetative growth during the On-year, is a primary factor inducing alternate bearing in olive.
... Indeed, it has been observed that once reproduction starts, the crop will compete with and reduce vegetative growth [15]. This competition has been well recognized in mature trees of several species [16][17][18], including olive [19][20][21][22][23][24]. It is especially prominent in young fruit trees, where the removal of all blossoms or fruit results in dramatic increases in growth with respect to the fruiting trees [25][26][27][28][29]. ...
... The increase in growth was significantly and positively related to the NAA concentration ( Figure 6) and, hence, inversely related to fruit set and yield efficiency (Figure 7). Likewise, early and complete de-fruiting [22] or deflowering performed by hand [31,39] resulted in an increase in vegetative growth of the trees. ...
... This is especially true for olives, which are normally harvested in autumn. This competition is well-known in both mature and young trees of several species, including olive [16][17][18][19][20][21][22][23][42][43][44][45]. In young apple trees, removing flowers/fruits results in very large increases in vegetative growth [25][26][27][28]. ...
In 2019–2020, trials were carried out in both intensive (cultivar Moraiolo) and super-high-density (cultivar Sikitita) young olive orchards to drastically reduce early production and, consequently, accelerate tree growth. Different concentrations of naphthaleneacetic acid (NAA) (0 ppm–control, 20 ppm, 40 ppm, 80 ppm, 160 ppm and 250 ppm) were applied at full bloom (open flowers > 80%), using a shoulder sprayer, and their effects on vegetative growth and reproductive behavior were evaluated, also compared to manually deflowered trees. The treatments with NAA reduced fruit set (down to values close to zero) compared to the control, and the reduction was correlated with the NAA concentration. In particular, 160 ppm virtually eliminated fruit set and thus production in both Moraiolo and Sikitita cultivars. In Moraiolo, 160 ppm NAA and manual deflowering determined similar shoot and trunk growths, which were greater than in control trees. Application of 160 ppm NAA for two consecutive years gave a progressively higher increase in trunk growth compared to the control. In conclusion, in young olive trees, the treatment with 160 ppm NAA at full bloom practically eliminated fruit set and production, with a parallel great increase in vegetative growth. This can be exploited as a powerful technique to accelerate the growth of young olive trees in both intensive and super-high-density orchards, as well as in nurseries. A more rapid transition to the adult stage/size of the trees and to full production of the orchard allows us to anticipate the use of mechanical harvesting and the recovery of the planting investment.
... Fruit number is the main yield component in olive (Trentacoste et al. 2010) and is determined over two seasons. First, potential inflorescence number (i.e., bud number) and bud induction are determined during the shoot growth period in the previous season (Cuevas et al. 1994;Dag et al. 2010). Second, inflorescence structure, flower quality, fruit set, and natural fruit drop occur in the current season (Rapoport et al. 2012). ...
... As the fruit number increases, the assimilates available during the post-fruit set are distributed and shared by more fruits, resulting in reduced assimilate availability per fruit (Trentacoste et al. 2010). Experiments aimed at studying fruit mass and fruit oil concentration determination and their environmental influence usually focus on the post-flowering period (Dag et al. 2010;Fernández et al. 2015). The assumption that fruit mass is determined exclusively after flowering needs to be reviewed. ...
... Most of the shoot growth occurs during the post-fruit set period, determining the total number of axillary buds, i.e., the "number of potential flower sites" (Fernández et al. 2015). The majority of olive research has focused on crop load effects on vegetative growth, which has been widely described as the importance of assimilates on vegetative growth increasing flowering sites the following season (e.g., Dag et al. 2010;Fernández et al. 2015). ...
Olive yield components are first determined during flowering, ovary growth, and fruit set. However, variations of the assimilates available during these important processes have been little studied. The aims of this study were to evaluate the effects of source-sink alterations on (i) production of flowers and their structure, (ii) sink responsiveness source activity, and (iii) the relationship between final fruit mass and flower ovary size. Two levels of shading at 50% and 80% were applied in an orchard cv. Arbequina over three seasons, with two durations: short-period (SP, from harvest up to 20 days after flowering) and long-period (LP, continuous shading from beginning to end of the experimental period). An unshaded Control was included. Control presented the highest fruit yield and was 50% greater than both SP50-LP50, and 80% greater than both SP80-LP80. Fruit number was highly responsive to source-sink alterations. The control and both SP50-LP50 treatments presented similar fruit loads, whereas both SP80-LP80 produced 80% less fruits. Source activity alteration during pre-fruit set affected inflorescence structure. By contrast, during the post-fruit set, it drastically reduced inflorescence production. Fruit mass increased mainly due to fruit growth rate in relation to the assimilate. Reduction in ovary mass due to low source activity during pre-fruit set had a slight influence on final fruit mass when source activity was not limited during the post-fruit set period. Fruit oil concentration was highly conservative across a wide range of source-sink ratios.
... Field experimental studies explaining the effects of deficit irrigation on vegetative and reproductive growth, plant physiology and olive oil quality have been published by several authors (e.g. Anastasopoulos et al., 2011;Dag et al., 2010;Gucci et al., 2019;Rapoport et al., 2004). However, a thorough understanding of the physiological responses of deficit-irrigated trees during the growth season is still lacking. ...
... The former showed a reduction in growth up to 80%. In four-year-old 'Coratina' trees in Israel, under 900 mm annual irrigation, shoot elongation was impeded by crop load and resumed only after harvesting in September (Dag et al., 2010). In addition, Fernandes et al. (2018) found that fruit growth of 11-year-old 'Arbequina' olive trees decreased by approximately 40% under regulated deficit irrigation, compared to fully irrigated trees. ...
Agricultural water demand in the Mediterranean region is expected to increase due to climate change. The application of deficit irrigation practices may improve the efficiency of water use in orchards, by accounting for changes in environmental conditions and in the tree growth. The main goal of this study was to improve our understanding on the effect of deficit irrigation on physiology, morphology, yield, and oil quality of ‘Koroneiki’ olive trees. The effect of two deficit irrigation treatments and three harvest dates on olive yield and oil quality were investigated in a 17-year old, low-density ‘Koroneiki’ orchard in Cyprus, during a high crop load year. For the sustained deficit irrigation (SDI) treatment 70% ETc was applied over the irrigated period, while the regulated deficit irrigation (RDI) consisted of 70% ETc during water-stress sensitive growth stages (shoot growth, flowering, bud initiation) and 35% ETc during water-stress tolerant growth stages (pit hardening, oil accumulation). Environmental conditions and volumetric soil water content of the 70-cm rootzone were monitored. A Kc of 0.37 was derived for the irrigated period from daily water balance computations, excluding rain days. No significant effects of the two irrigation treatments were found on morphology, physiology, fruit yield and oil quality. Midday stem water potential reached − 4 MPa in September as a result of increasing fruit load. Leaf conductance ranged between 65 and 228 mmol m⁻²s⁻¹, with highest values obtained under high soil water conditions and a vapour pressure deficit of 3.6 kPa. Yields were approximately 9 tons ha⁻¹ in both irrigation treatments while water productivity was 1.4 and 1.0 kg oil m⁻³ irrigation water in SDI and RDI, respectively. Maximum phenolic content was found in early December, reaching on average 202 mg kg⁻¹ oil in both irrigation treatments. Overall, irrigation water use in RDI was 32% less than in SDI, whereas oil quality was only affected by the harvest date.
... Indeed, fruit removal from On-Crop trees is effective at inducing flowering, but in citrus it is effective only if it is performed no later than 1-2 months prior to the onset of the flowering induction period (Verreynne and Lovatt, 2009;Martínez-Fuentes et al., 2010;Muñoz-Fambuena et al., 2011). This "memory" of the fruit load persists even longer in olive, where fruit removal is effective only if performed 2 to 3 months before onset of the flowering induction period (Dag et al., 2010;Haberman et al., 2017). Recent findings suggest that fruit-load memory might be controlled by epigenetic mechanisms (Agustí et al., 2019). ...
... Fruit presence is thought to generate a "memory", which can be reversed by fruit removal until a certain time prior to the onset of the flowering induction period, usually 1 month in citrus. However, in olive, the "memory" of fruit load seems to last longer, as fruit removal is effective at inducing a return bloom only if it is performed 2-3 months prior to flowering induction (Dag et al., 2010;Haberman et al., 2017). Fruit-load "memory" has been suggested to be associated with the epigenetic regulation of citrus MADS19, a FLOWERING LOCUS C (FLC) ortholog, which suppresses the expression of FLOWERING LOCUS T (FT) in the vernalization/cold pathway (Agustí et al., 2019). ...
In many fruit trees, heavy fruit load in one year reduces flowering in the following year, creating a biennial fluctuation in yield termed alternate bearing AB). In subtropical trees, where flowering induction is mostly governed by the accumulation of chilling hours, fruit load is thought to generate a signal (AB signal) that blocks the perception of the cold induction. Fruit removal during a heavy-fruit-load year (On-Crop) is effective at inducing flowering only if performed one to a few months prior to onset of the flowering induction period. We previously showed that following fruit removal, content of the auxin indoleacetic acid (IAA) in citrus buds is reduced, suggesting that the hormone plays a role in the AB signal. Here, we demonstrate that fruit presence generates relatively strong polar auxin transport (PAT) in citrus and olive stems. Upon fruit removal, PAT is reduced and allows auxin release from the bud. Furthermore, using immunolocalization, hormone and gene expression analyses, we show that in citrus, IAA level in the bud and, specifically, in the apical meristem is reduced upon fruit removal. Overall, our data provide support for the notion that fruit presence generates an auxin signal in the bud which may affect flowering induction.
... The olive tree reproductive cycle normally begins with initiation of inflorescences from lateral buds at leaf axils of previous season vegetative growth at the end of winter (Haberman et al., 2017;Lavee, 1996). Hence, current season vegetative growth is the platform for the following season flowering and its extent sets the flowering potential (Dag et al., 2010). The magnitude of olive annual flowering and yield varies greatly. ...
... The magnitude of olive annual flowering and yield varies greatly. In most cases, this is attributed to the alternate bearing pattern of olive (Lavee, 2007), in which fruit load inhibits both flowering and vegetative growth (Dag et al., 2010;Samach and Smith, 2013). In "on"-years, trees tend to produce vast numbers of flowers (Martin, 1990). ...
Current trends of intensification of olive cultivation including irrigation and fertigation have dictated a need to reconsider fertilization management practices. We evaluated the long-term effect of nitrogen (N) fertilization level on the productivity of field grown olive trees in an intensively cultivated orchard in order to optimize N fertilization and achieve maximum yields and profits with minimal negative environmental impact. Deficient N fertilization reduced vegetative growth and lowered fruit and oil yields, attributed to down-regulation of flowering intensity and reduced rate of perfect flowers and fruit set. In addition, under low N availability trees appeared to be more susceptible to alternate bearing. The highest N level was the most effective in promoting vegetative growth, but did not induce an increase in yield. An intermediate annual level of 150 kg N hectare −1 was optimal for maintaining highest long-term yield and reducing alternate bearing. The results correspond to previous findings from container-grown trees that N availability significantly affects tree reproductive traits. Proper N fertilization is concluded to be fundamental to successful management of intensive cultivated olive orchards.
... Clear differences among layers were seen in total inflorescence number per position, which decreased dramatically from upper to lower layers in each hedgerow (Table 3) and correlated strongly with irradiance received (Table 8). Dag et al. (2010) demonstrated a strong competitive effect of developing fruits with new shoot growth necessary for forming potential flowering sites, similar to our observations for positions receiving reduced irradiance, and emphasized the critical nature of flowering site number in the olive tree bearing cycle. Since inflorescence number per shoot derives directly from bud number and percentage of floral buds, parameters which showed only minor differences (Table 2), the substantial differences in inflorescence number per layer were produced mainly by differences in total number of reproductive shoots per position, suggested previously by Trentacoste et al. (2015), with lesser shoot level contributions of bud number and percent of buds forming inflorescences. ...
... When correlated with calculated mean daily irradiance, fruit number showed a strongly positive relationship for all studied periods, with the best correlation for mean annual values (Table 8). Fruit removal experiments by Dag et al. (2010) concur with the importance of assimilate-influenced vegetative growth of flowering sites in determining final fruit production. ...
... However, the opposite is also true: once reproduction starts, the crop will compete with, and reduce, vegetative growth and, therefore, vigor, as shown also by modeling (Grossman and DeJong, 1994;Smith and Samach, 2013). This is the case for mature trees of many species (Berman and DeJong, 2003;Costes et al., 2000;Lauri and T erouanne, 1999;Salazar-García et al., 1998;Stevenson and Shackel, 1998), including olive (Castillo-Llanque and Rapoport, 2011;Connor and Fereres, 2005;Dag et al., 2010;Lavee, 2007;Monselise and Goldschmidt, 1982;Obeso, 2002;Rallo and Su arez, 1989). In young trees, the removal of all blossoms or fruits results in dramatic increases in growth relative to the fruiting trees (Chandler and Heinicke, 1926;Embree et al., 2007;Forshey and Elfving, 1989;Mochizuki, 1962;Verheij, 1972). ...
... These results are in line with previous finding that vegetative growth (i.e., vigor) is reduced by the presence of fruit, which compete for resources (Berman and DeJong, 2003;Castillo-Llanque and Rapoport, 2011;Chandler and Heinicke, 1926;Connor and Fereres, 2005;Costes et al., 2000;Dag et al., 2010;Embree et al., 2007;Forshey and Elfving, 1989;Lauri and T erouanne, 1999;Lavee, 2007;Mochizuki, 1962;Monselise and Goldschmidt, 1982;Obeso, 2002;Rallo and Su arez, 1989;Salazar-García et al., 1998;Stevenson and Shackel, 1998;Verheij, 1972). This is not to say, however, that more abundant fruiting cannot be a consequence, rather than the cause, of reduced vigor. ...
Low vigor and early and abundant production are desirable traits for modern tree crops. In olive, most cultivars are too vigorous and cannot be successfully constrained in the small volume allowed by the straddle harvester used in the so-called superhigh-density (SHD) orchards. Only few cultivars appear to have sufficiently low vigor to be suitable for this system. These cultivars combine low vigor with earlier and higher yield. This study investigated the hypothesis that differences in vigor between Arbequina, a low vigor and the most commonly used cultivar in SHD orchards, and Frantoio, a highly vigorous cultivar not suitable for such orchards, are related to their differences in early bearing and consequent differences in dry matter partitioning into fruit. Young trees of both cultivars were deflowered either in 2014, 2015, both years, or neither one, resulting in a range of cumulative yields over the 2 years. Tree trunk cross-sectional area (TCSA) was measured at the beginning of each year. This was closely related to total tree mass, as assessed at the beginning and at the end of the experiment. Cumulative yield, in terms of fruit dry matter, was also assessed. TCSA increased less in fruiting trees in both years. As expected, when not deflowered, ‘Frantoio’ was less productive and more vigorous than ‘Arbequina’. However, there was no difference in TCSA increment when both cultivars were completely deflowered. TCSA increments were closely inversely related to yield across all treatments and cultivars (R²= 0.90). The regressions improved further when data from 2015 only were used (R²= 0.99). The results represent the first quantitative report showing that differences in vigor among cultivars can be completely explained in terms of different dry matter partitioning into fruit, supporting the hypothesis that early bearing is a major cause, rather than merely a consequence, of lower vigor in young ‘Arbequina’ trees. These results provide new understanding on vigor differences across cultivars, which will be useful for breeding and selection of new genotypes. © 2018, American Society for Horticultural Science. All rights reserved.
... Indeed, the plant harvest index can be increased by using deficit irrigation strategies (Morison et al., 2008). In addition to saving water, deficit irrigation strategies can reduce vegetative growth without decreasing yield, i.e., they are effective in decreasing the carbon spent on vegetative growth without decreasing fruit growth as shown previously in olive (Iniesta et al., 2009;Dag et al., 2010;Hernandez-Santana et al., 2017). Thus, under limited available water, fruits augment their already strong carbohydrate sink capacity and have higher priority for assimilates than vegetative organs, leading to a reduced vegetative growth of roots, stem and leaves (Génard et al., 2008;Hacket-Pain et al., 2017). ...
... However, under conditions of water stress, 45SDI trees dedicated most of their A N to fruit growth and oil accumulation (Fig. 3). Other authors working with forest and agronomical species reported similar results (e.g., Dag et al., 2010;Müller-Haubold et al., 2013;Selas et al., 2002;Intrigliolo and Castel, 2007;Hacket-Pain et al., 2017;Hernandez-Santana et al., 2017), demonstrating that the competing sink relationships between vegetative growth (stem or leaves) and fruit production for newly assimilated carbon were dependent on drought. This indicates that the biological costs of reproduction increase strongly under conditions of environmental stress, penalizing vegetative growth but having no detrimental effect on vegetative growth under favourable climatic conditions (Hacket-Pain et al., 2017). ...
... Similarly, reproductive growth competes with, and reduces, vegetative growth, as demonstrated by modeling exercises (e.g., DeJong 1994, Smith andSamach 2013). This is true for mature trees of many species (Stevenson and Shackel 1998, Costes et al. 2000, Berman and DeJong 2003, including olive (Obeso 2002, Connor and Fereres 2005, Lavee 2007, Dag et al. 2010, Castillo-Llanque and Rapoport 2011), but especially for young fruit trees, where removal of all blossoms or fruits results in spectacularly large differences in vegetative growth compared with the fruiting controls (Verheij 1972, Forshey and Elfving 1989, Embree et al. 2007. ...
... Whatever the mechanism for partial compensation of vegetative growth in fruiting trees, the fact that vegetative growth was reduced in close proportion to crop load (Figure 3) suggests that this effect was dominant over possible photosynthetic compensation/downregulation. This agrees with previous findings that vegetative growth is depressed by the presence of fruit, which compete for resources (Verheij 1972, Forshey and Elfving 1989, Stevenson and Shackel 1998, Costes et al. 2000, Obeso 2002, Berman and DeJong 2003, Connor and Fereres 2005, Embree et al. 2007, Lavee 2007, Dag et al. 2010, Castillo-Llanque and Rapoport 2011. ...
It has long been debated whether tree growth is source limited, or whether photosynthesis is adjusted to the actual sink demand, directly regulated by internal and environmental factors. Many studies support both possibilities, but no studies have provided quantitative data at the whole-tree level, across different cultivars and fruit load treatments. This study investigated the effect of different levels of reproductive growth on whole-tree biomass growth across two olive cultivars with different growth rates (i.e., Arbequina, slow-growing and Frantoio, fast-growing), over 2 years. Young trees of both cultivars were completely deflowered either in 2014, 2015, both years or never, providing a range of levels of cumulated reproductive growth over the 2 years. Total vegetative dry matter growth over the 2 years was assessed by destructive sampling (whole tree). Vegetative growth increased significantly less in fruiting trees, however, the total of vegetative and reproductive growth did not differ significantly for any treatment or cultivar. Vegetative growth over the 2 years was closely (R2 = 0.89) and inversely related to reproductive growth across all treatments and cultivars. When using data from 2015 only, the regression improved further (i.e., R2 = 0.99). When biomass was converted into grams of glucose equivalents, based on the chemical composition of the different parts, the results indicated that for every gram of glucose equivalent invested in reproductive growth, vegetative growth was reduced by 0.73-0.78 g of glucose equivalent. This indicates that competition for resources played a major role in determining tree growth, but also that photosynthesis was probably also enhanced at increasing fruit load (or downregulated at decreasing fruit load). The leaf area per unit of trunk cross sectional area increased with deflowering (i.e., decreased with reproductive growth), suggesting that water relations might have limited photosynthesis in deflowered plants, which had much greater canopies. Net assimilation rate (NAR) increased with reproductive growth and decreased with plant size. Net assimilation rate was also negatively correlated with the leaf area per unit of trunk cross sectional area, suggesting that water relations might have contributed to decreasing NAR at increasing plant size.
... If a tree spends more of the available resources into producing fruits, it can only grow less as a result (Grossman and DeJong, 1994). Competition between vegetative and reproductive growth is well established in several tree species (Berman and DeJong, 2003;Costes et al., 2000;Lauri and T erouanne, 1999;Salazar-García et al., 1998;Stevenson and Shackel, 1998) including olive (Castillo-Llanque and Rapoport, 2011;Connor and Fereres, 2005;Dag et al., 2010;Fern andez et al., 2015;Monselise and Goldschmidt, 1982;Rallo and Su arez, 1989). However, very few studies considered young trees and no relationship between tree initial growth and cumulative yield was found (Moutier, 2006). ...
... Trees that spend more energy on production are expected to grow less vegetation because reproductive and vegetative growth compete for the same sources within a tree (Grossman and DeJong, 1994). This competition is well established in several tree species (Berman and DeJong, 2003; Costes et al., 2000;Lauri and T erouanne, 1999;Salazar-García et al., 1998;Stevenson and Shackel, 1998) including olive (Castillo-Llanque and Rapoport, 2011;Connor and Fereres, 2005;Dag et al., 2010;Fern andez et al., 2015;Monselise and Goldschmidt, 1982;Rallo and Su arez, 1989). Most of these studies have focused on mature trees during 1 year. ...
The modern olive industry is increasingly interested in olive cultivars that start producing early and remain relatively small, because they are suitable for super highdensity orchards. Some cultivars are better suited to this than others but it is not clear why. Understanding the mechanisms that lead to early production and reduced canopy size is therefore important. The object of this study was to investigate whether differences in vigor across olive cultivars are related to earliness and abundance of bearing. We analyzed tree growth and productivity in young coetaneous trees of 12 olive cultivars, grown together in the same orchard. Trunk diameter increased over the observation period, reaching significantly different values across cultivars. Canopy volume also increased, reaching 2-fold differences between the minimum and the maximum values. Cumulative yield increased, reaching up to 3-fold differences. When the cumulative yield at the end of the experiment was plotted against the final trunk diameter, no correlation was found. A significant correlation was found when cumulative yield was plotted against the increment in trunk diameter during the observation period for which yield data were collected. This relationship improved (i.e., R² rose from 0.57 to 0.83) when yield efficiency [i.e., cumulative yield per unit of final trunk cross-sectional area (TCSA) or per unit of canopy volume] was used instead of yield. These results clearly showed that trees that produced proportionally more (i.e., higher yield efficiencies) grew less. We conclude that, in young olive trees, vigor is inversely related to early bearing efficiency, which differs significantly across cultivars. The results support the hypothesis that early and abundant bearing is a major factor in explaining differences in vigor across olive cultivars. © 2017, American Society for Horticultural Science. All rights reserved.
... Clear differences among layers were seen in total inflorescence number per position, which decreased dramatically from upper to lower layers in each hedgerow (Table 3) and correlated strongly with irradiance received (Table 8). Dag et al. (2010) demonstrated a strong competitive effect of developing fruits with new shoot growth necessary for forming potential flowering sites, similar to our observations for positions receiving reduced irradiance, and emphasized the critical nature of flowering site number in the olive tree bearing cycle. Since inflorescence number per shoot derives directly from bud number and percentage of floral buds, parameters which showed only minor differences (Table 2), the substantial differences in inflorescence number per layer were produced mainly by differences in total number of reproductive shoots per position, suggested previously by Trentacoste et al. (2015), with lesser shoot level contributions of bud number and percent of buds forming inflorescences. ...
... When correlated with calculated mean daily irradiance, fruit number showed a strongly positive relationship for all studied periods, with the best correlation for mean annual values (Table 8). Fruit removal experiments by Dag et al. (2010) concur with the importance of assimilate-influenced vegetative growth of flowering sites in determining final fruit production. ...
Irradiance received within the olive hedgerow canopy varies with respect to row orientation, spacing and hedge dimensions. These orchard management criteria offer the opportunity for improving productivity based on understanding the responses of yield-determining processes to irradiance. How irradiance influences inflorescence and flower development, the initial steps in fruit formation, are fundamental components of these processes. In this study we evaluated flowering and fruiting parameters in 5 hedgerow positions (defined by hedgerow side and vertical layer above soil) for N–S (North-South) and E–W (East–West) olive hedgerows (cv. Arbequina). The canopy layers and orientations provided a wide gradient of irradiance received and the relationship of estimated mean daily irradiance for annual and for short periods during floral development and initial fruit set was explored. The numbers of inflorescences and fruits per layer increased from the less illuminated base to more illuminated upper canopy layers. Axillary bud number per shoot also increased toward more illuminated positions, while the proportion of floral buds was unresponsive to the irradiance microenvironment at different positions within the hedgerows. Inflorescence length, node and flower number per inflorescence, and perfect flower percentage increased with position illumination. Ovary quality, indicated by ovule differentiation, was consistently high, independent of position, but ovary size showed some slight significant increases with illumination, mainly in the endocarp. Flowers/inflorescence, fruits/fruiting inflorescence and inflorescence and fruit number per position correlated positively and significantly with estimated irradiance similarly for annual and short periods (r range from 0.49 to 0.86). Despite improved flowering parameters with greater irradiance, no consistent differences among positions were found for percentage of inflorescences bearing fruit and fruit number per inflorescence. Instead, our results indicated that different fruit numbers among canopy positions were primarily due to an irradiance effect on vegetative growth, causing more and longer fruiting shoots and therefore more total flowering sites (nodes) per layer, with only a small contribution by inflorescence structure and flower quality.
... It is over all controlled by an interaction between vegetative growth and fruit load. Alternate bearing is a major problem for olive farmers and it had negative effect on production and oil olives industry (Dag et al., 2010 andLavee, 2006). Olive farmers need to the stability of their annual production. ...
... 'Manzanilla') reported by Rallo and Martin [16] and Ramos [8]. The differences in the amount of flower formation are expected, considering the well-documented alternate bearing behavior of the olive tree, and could relate to competition for assimilates and different inhibitory factors [22][23][24][25]. It is possible that the consistent temporal patterns we observed between ON and OFF trees, in spite of the quantitative differences in budburst percentages (Figures 1 and 3), support the hypothesis of separate controls of flowering level and dormancy release. ...
Dormancy release dynamics in olive tree (Olea europaea L.) reproductive buds as affected by cold accumulation, tree bearing status, and budburst temperature was studied under natural and controlled conditions, using both cuttings and container- and field-grown plants. The chilling necessary for dormancy release was acquired at different times within the bud population, presenting a progressive pattern of reproductive budburst. Once sufficient chilling is accumulated, 20 °C is a suitable temperature for reproductive budburst, although higher temperature, e.g., 30 °C, during dormancy release can inhibit budburst. While the bearing status of trees determined the amount of return bloom, dormancy release followed a similar pattern for previously bearing and non-bearing trees. Concurrent with investigating budburst factors, the use of shoot cuttings was tested as a method for olive dormancy release studies by contrasting with results from whole trees. It was found it to be valid for studying reproductive budburst, thus providing a useful method to screen chilling requirements in cultivar evaluation and the breeding programs currently ongoing in this species. However, the method was not valid for vegetative budburst, with varying results between cuttings and the whole plant.
... When studying averages of trees from the same treatment and year, n varied between 10.9 and 28.4 ( Figure 4A,B). A fruit-bearing branch produces far fewer new nodes than one without any fruit load [17]. It should, therefore, be noted that although we studied the same trees during both study years, in each year we chose to measure branches with no fruit. ...
Olive (Olea europaea L.) trees can reach a very old age and still bear fruit. Although traditional groves are planted at low density and are rainfed, many newer groves are planted at higher densities and irrigated. As expected, initial yields per area are larger in high density plantations, yet some farmers claim they experience a reduction in productivity with grove age, even in well maintained trees. In order to test the accuracy of this claim and its underlying cause, we measured several productivity parameters in selected branches of trees in seven sites differing in cultivar (‘Barnea’ or ‘Souri’), location and irrigation regime (rainfed or irrigated) for two consecutive years. For each site (cultivar/location/regime), we compared neighboring groves of different ages, altogether 14 groves. There was no consistent reduction in productivity in older groves. Differences in productivity between irrigated cultivars were mostly due to variation in the percentage of inflorescences that formed fruit. Several parameters were higher in irrigated, compared to rainfed ‘Souri’. Differences in productivity between years within the same grove was mostly due to variation in the percentage of nodes forming inflorescences. We studied the expression of OeFT2 encoding a FLOWERING LOCUS T protein involved in olive flower induction in leaves of trees of different ages, including juvenile seedlings. Expression increased during winter in mature trees and correlated with the percentage of inflorescences formed. The leaves of juvenile seedlings expressed higher levels of two genes encoding APETALA2-like proteins, potential inhibitors of OeFT2 expression. The buds of juvenile seedlings expressed higher levels of OeTFL1, encoding a TERMINAL FLOWER 1 protein, a potential inhibitor of OeFT2 function in the meristem. Our results suggest that olives, once past the juvenile phase, can retain a similar level of productivity even in densely planted well maintained groves.
... The results also demonstrated that from May onwards, HFL in 'Shelly' attenuated the rate of inflorescence development, but it was only from July onwards that this factor repressed, to some extent, the rate of return to flowering. Previous studies performed in fruit tree species such as citrus [44], olive [56] and avocado [47] have pointed to the existence of a critical physiological window of time, after which fruit load (or the "memory" of fruit being present on the tree) effectively represses flowering. A noteworthy point is that whereas in avocado and citrus, flowering induction occurs in parallel to the presence of developing fruit on the tree [44,47] In mango, like in olive, flower induction takes place after the fruit is harvested from the tree [4,48]. ...
Plant flowering is antagonistically modulated by similar FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1 (TFL1) proteins. In mango (Mangifera indica L.), flowering is induced by cold temperatures, unless the tree is juvenile or the adult tree had a high fruit load (HFL) in the summer. Here, we studied the effects of juvenility and fruit load on the expression of four MiFT/TFL1 genes cloned from the mango 'Shelly' cultivar. Ectopic expression of MiFT1 in Arabidop-sis resulted in early flowering, whereas over-expression of MiFT2 and the two cloned MiTFL1 genes repressed flowering. Moreover, juvenility was positively correlated with higher transcript levels of MiFT2 and both MiTFL1s. In trees with a low fruit load, leaf MiFT1 expression increased in winter, whereas HFL delayed its upregulation. MiFT2 expression was upregulated in both leaves and buds under both fruit load conditions. Downregulation of both MITFL1s in buds was associated with a decrease in regional temperatures under both conditions; nevertheless, HFL delayed the decrease in their accumulation. Our results suggest that cold temperature has opposite effects on the expression of MiFT1 and the MiTFL1s, thereby inducing flowering, whereas HFL represses flowering by both suppressing MiFT1 upregulation and delaying MiTFL1s downregulation. The apparent flowering -inhibitory functions of MiFT2 are discussed.
... Por outro lado, um evento climático extremo pode servir como estopim para iniciar uma sincronia na alternância produtiva das árvores da região (GALÁN et al., 2008). Técnicas de cultivo estão sendo aplicadas recentemente com o objetivo de reduzir esse comportamento: irrigação, colheita precoce ou "raleio artificial de frutos" (DAG et al., 2010). ...
oliveira é uma das frutíferas mais antigas utilizadas pelo homem. Seu cultivo remonta a 6.000 anos. É originária de vasta grande área, que abrange desde o Sul do Cáucaso até os planaltos do Irã, Palestina e a zona costeira da Síria, estendendo-se pelo Chipre até o Egito, povoando posteriormente para todos os países que margeiam o Mediterrâneo. O cultivo em sebe representa a grande revolução na cultura do olival, porque permite obter em 10 anos de cultivo a mesma produção acumulada de um olival tradicional de sequeiro em 70 anos. Para os cultivos de superintensivo têm sido propostos inicialmente as variedades de alto rendimento como Arbosana, Arbequina e Koroneiki, que apresentam desenvolvimento limitado (porte médio). Posteriormente, foram lançadas novas variedades de porte baixo mais apropriadas ao cultivo em sebe. São recomendados espaçamentos de 3-4 m x 1,0-1,5 m ao longo das linhas. As árvores prontas para o plantio são pequenas, com cerca de 18 meses, 40-50 cm de altura e um bom sistema radicular. Elas devem ser manejadas com cuidado para mantê-las no tamanho certo para a colheita mecanizada ao longo da linha e para garantir um equilíbrio entre a atividade vegetativa e reprodutiva. A grande vantagem que este sistema apresenta reside no fato das cultivares utilizadas terem uma entrada em produção ultraprecoce, permitindo obter logo elevadas produções entre o 3º e o 5º ano após a plantação. No olival superintensivo, sua colheita mecanizada recorre a máquinas de vindimar cavalgantes automotrizes, possibilitando capacidades de trabalho de 2-3h/h. Também o cultivo em sebe permitir ser podado mecanicamente, visando manter uma copa reduzida. Em razão do exposto, há uma redução significativamente nos custos de produção, pois este sistema em sebe facilmente atinge os 12.000 kg/ha. Vale lembrar que no passado ocorreu a domesticação dessa árvore de porte alto para de porte médio e recentemente para de porte baixo, mas por meio do desenvolvimento de novas cultivares com características de baixo vigor e, ao mesmo tempo, de pouca exigência em frio (fatos parecidos sucederam com a outras espécies vegetais) é possível futuramente ampliar o cultivo em sebe para outras regiões fora de climas subtropical e temperado. Portanto, aquele que decidir cultivar essa cultura de forma superintensiva e conhecê-la em maior profundidade, o livro Tecnologias utilizadas no cultivo em sebe da oliveira (Olea europaea, L.) mecanizada, será de grande interesse e ajuda para o produtor que necessita pôr em prática as várias tecnologias abordadas no mesmo.
... During "on" years, shoot elongation ceased around the flowering or maximum rate of the pit hardening stage. This was most likely due to the assimilate demand for flower formation and fruit growth, as described for well-watered 4-year-old 'Barnea' and 'Coratina' trees grown in Israel [29,45] and 9-year-old 'Arauco' trees grown in Argentina [46], where fruits were manually thinned. [43] found that the pattern of fruit growth was similar in fully irrigated 44-year-old 'Manzanillo' trees and trees where irrigation was withdrawn at the maximum rate of pit hardening in Spain, even though their Ψ s values after the treatments began were significantly different. ...
Climate change is affecting water resources in the Mediterranean region. In olive orchards, irrigation water use efficiency could be increased by accounting for trees’ alternate bearing behaviour and growth-stage sensitivity to drought. The main objective of this study is to examine olive tree phenology, morphology and physiology in “on” and “off” productive years for the improvement of irrigation scheduling. A regulated (RDI) and a sustained (SDI) deficit irrigation treatment were applied in a ‘Koroneiki’ olive orchard in Cyprus. Flowering occurred on 11 May 2019 and on 27 April 2021, which was caused by the lower temperatures in 2019. The Kc for the irrigation season, computed from daily water balance observations, was 0.37 in 2019 (38% canopy cover) and 0.41 in 2021 (62% canopy cover). Irrigation treatments did not significantly affect plant morphology and stem water potentials. In “on” years, shoot elongation ceased early in the season and stem water potential towards the end of September (−4.0 MPa) was lower than in the “off” year. Stem water potential recovery in the September of the “off” year indicated that irrigation could be less than 35% ETc in early fall. Water savings in RDI were 24–32% in “on” and 48% in “off” years relative to SDI, with no statistically significant effects on olive yields.
... Vegetative and reproductive growth in olive trees occur simultaneously for several months during the growing season with competition for carbohydrates between plant organs often occurring. Fruit are considered to be a stronger sink than vegetative shoots, but a reduction in both vegetative and reproductive growth has been observed when fruit load is high (Dag et al., 2010;Fernández et al., 2015;Rosati et al., 2018). The warming study of whole olive trees mentioned earlier using OTCs in southern Spain found that a 4 • C increase in air temperature increased trunk growth and pruning weight over three years, although individual shoot length appeared to be less sensitive to warming (Benlloch--González et al., 2019). ...
Global warming and olive expansion to new regions have increased interest in understanding how air temperature affects olive production. Thus, the objective of this study was to evaluate the responses of oil yield components, total biomass production, and its partitioning to a moderate temperature increase (3–4 °C) during the oil accumulation phase in young olive trees of two olive cultivars (cvs. Arbequina, Coratina). Young, potted olive trees were actively heated by 3–4 °C in open top chambers under outdoor conditions compared to near-ambient temperature in similar control chambers. The trees were warmed from final fruit set to the end of the oil accumulation phase (5 months) in one (2014–15 or 2015–16) or in two consecutive seasons. Oil yield and its components were obtained from fruit harvested at the end of the season, while the vegetative dry biomass produced was estimated from destructive harvests of entire trees before and after a warming period. Glucose equivalents (GE) were also calculated for both oil yield and vegetative growth. Warming during the oil accumulation phase in one season led to some significant temperature x cultivar interactions for oil components. Individual fruit dry weight was reduced by warming to a greater extent in cv. Coratina than in cv. Arbequina, while fruit oil concentration was decreased more in cv. Arbequina. Significant decreases in oil yield were also observed for both cultivars. Warmed trees had a greater net leaf area increase than control trees when heated during the oil accumulation phase for one season (2014–15 or 2015–16), and allocated more GE to vegetative organs than to fruit in 2015–16. However, total tree biomass was not affected by warming. Warming trees the first season led to reduced flowering the following spring, and directly contributed to a temperature x cultivar interaction for fruit number during the second warming period with a 66% reduction in fruit number in warmed trees of cv. Arbequina and very low fruit number in all cv. Coratina trees. In contrast to warming during one season, total tree biomass GE decreased across cultivars when warming was performed in the oil accumulation phase for two consecutive seasons. The results suggest that cultivars should be carefully selected for new, warmer growing regions and that global warming may ultimately reduce oil yields and affect cultivar selection.
... Alternate bearing is an undesirable horticultural trait of many perennial crops, including olive [39]. Alternate bearing yield fluctuations in olive are driven mainly by the negative feedback of fruit load on vegetative vigor and flowering [59,60]. Thus, promoting vegetative growth and flowering during a high fruit load season (on-year) is ultimately the way to reduce the alternate bearing amplitude without reducing overall yields. ...
Phosphorus (P) availability significantly impacts olive tree reproductive development and consequential fruit production. However, the importance of P fertilization in olive cultivation is not clear, and P application is usually recommended only after P deficiency is identified. In order to determine the long-term impacts of continuous P fertilization in intensive irrigated olive cultivation, the growth and production of trees in an intensive orchard with or without P fertilization were evaluated over six consecutive seasons. Withholding of P resulted in significant reduction in soil P quantity and availability. Under lower P availability, long-term fruit production was significantly impaired due to reduced flowering and fruit set. In addition, trees under conditions of low P were characterized by higher alternate bearing fluctuations. Olive tree vegetative growth was hardly affected by P fertilizer level. The impairment of tree productivity was evident in spite of the fact that leaf P content in the treatment without P fertilization did not decrease below commonly reported and accepted thresholds for P deficiency. This implies that the leaf P content sufficiency threshold for intensive olive orchards should be reconsidered. The results demonstrate the negative impact of insufficient P fertilization and signify the need for routine P fertilization in intensive olive cultivation.
... In the first phase, the floral induction process in olive tree is not yet fully clarified. However, the negative effect of developing fruit on flower induction from early stages (Dag et al. 2010) is well known, as in other polycarpic fruit crops. Microscopic development of buds prior to budding and flowering has been described, and the positive effect of winter cold on flowering has been demonstrated (Hartmann and Whisler 1975;Haberman et al. 2017;Ramos et al. 2018). ...
Olea europaea L. (Oleaceae), a traditional oil crop of Mediterranean basin, has been expanded considerably in the last decades to other regions of the world. “Arbequina” is one of the most widely planted cultivars due to its good agronomic and technological attributes, but interannual variability in thermal and rainfall regimes affects its regular fruit production in countries of the Southern Hemisphere, including Uruguay. To better understand the floral mechanisms that regulate fruit set in Southern Hemisphere climatic conditions, our work addresses the “Arbequina” flower functionality and pollen grains presentation along flower life span. In this andromonoecious species, the fruitful perfect flower morphs were evaluated by means of determining functional parameters such as stigmatic receptivity and pollen grain viability in each floral phenological stage, and pollen grain adhesion and pollen tube growth rate in hand pollination treatments. This flower morph did not show functional limitations under Uruguayan climatic conditions for the year in which the study was carried out, but a breeding system expressed by two different functional phases was detected. The first pistillate functional phase, where the stigma is receptive but no pollen release occurs, tends to avoid self-pollination and promotes crosspollination in the same flower. Then, a second perfectly functional phase follows, where the stigma remains receptive and the anthers release their pollen grains. In a self-incompatible olive cultivar such as “Arbequina”, this pollen grain presentation further stresses the importance of combining inter-compatible olive cultivars with synchronized flowering in orchard design, as a first step to ensure fruit set.
... Pistachio kernels are a major sink for K (% 0.85%), hence the level of nuts loads influenced directly the annual K balance in pistachio trees. The absence of fruit, caused either naturally or by removal, allowed the renewal of vegetative growth (Dag et al. 2010;Elloumi, Ghrab, and Ben Mimoun 2014a). Newly grown branches and leaves become the primary sink for K, in the absence of fruit. ...
Under dry and warm environmental conditions, the main Tunisian pistachio cultivar Mateur does not show a normal ‘On/Off’ cycle with highly variable nut yield, which could be affected by the tree nutritional status. In this context, Potassium (K) is considered a key nutritional element for nut development and for yield. The current study investigated the effects of alternate bearing and flower bud removal on seasonal dynamics of potassium in fruiting and non-fruiting branches of mature pistachio trees (cv. Mateur) in arid land. Three disbudding treatments were considered in reference to untreated trees taken as a control (T0): removal of all flower buds for one year (T1), or two successive years (T2) and removal of 50% of flower buds each year (T3). Similar K concentrations were detected early in the season in leaves, current shoot and one-year-old wood for all treatments. Current shoot begin the cycle with higher K concentrations, which declined during the lignification of endocarp and seed growth stages to finally accumulate K during postharvest. Inversely, one-year-old wood stored a large amount of K during the stage I and II of nut development, and became the main sink for K of the bearing shoot. Leaf K concentration explained 75% of yield variation. Yearly removal of 50% of flower buds induced less variation of leaf K concentrations (ranged between 0.5-0.8% DM) with regular nut yield compared to bi-annual On-Off cycle. Thus, under severe climatic conditions, the annual pruning could be applied to improve the nutritional status of pistachio trees.
... Further evidence for this local effect is the production of extended nodes after removing the fruit during an off-year, as was found for Benzioni in 2017. This outcome is likely because the fruits on the neighboring branches act as a robust sink, and the competition for reserves between fruit and vegetative meristems inhibits growth, as has been reported for avocados and olives [28,29]. Although in Hazerim, fruit removal did not affect node length in the off-year, it produced longer branches with more nodes than the control branches. ...
Jojoba (Simmondsia chinensis) is a wax crop cultivated mainly in arid and semi-arid regions. This crop has been described as an alternate-bearing plant, meaning that it has a high-yield year (“on-year”) followed by a low-yield year (“off-year”). We investigated the effect of fruit load on jojoba’s vegetative and reproductive development. For two consecutive years, we experimented with two high-yielding cultivars—Benzioni and Hazerim—which had opposite fruit loads, i.e., one was under an on-year load, while the other was under an off-year load simultaneously. We found that removing the developing fruit from the shoot during an off-year promotes further vegetative growth in the same year, whereas in an on-year, this action has no effect. Moreover, after fruit removal in an on-year, there was a delay in vegetative growth renewal in the consecutive year, suggesting that the beginning of the growing period is dependent on the previous year’s yield load. We found that seed development in the 2018 season started a month earlier than in the 2017 season in both cultivars, regardless of fruit load. This early development was associated with higher wax content in the seeds. Hence, the wax accumulation rate, as a percentage of dry weight, was affected by year and not by fruit load. However, on-year seeds stopped growing earlier than off-year seeds, resulting in smaller seeds and an overall lower amount of wax per seed.
... Since, in fruit trees, reproductive and vegetative growth occur simultaneously for several months, there is a strong competition for the resources available between the reproductive and the vegetative organs of the plant (Forshey and Elfving, 1989;DeJong, 1999;Wünsche and Ferguson, 2005). This competition is well established in mature trees of several species (Stevenson and Shackel, 1998;Costes et al., 2000;Berman and DeJong, 2003), including olive (Monselise and Goldschmidt, 1982;Rallo and Su arez, 1989;Obeso, 2002;Connor and Fereres, 2005;Lavee, 2007;Dag et al., 2010;Castillo-Llanque and Rapoport, 2011), and it is even more striking in young fruit trees, where removing flowers and preventing fruit development results in dramatic increases in vegetative growth (Chandler and Heinicke, 1926;Verheij, 1972;Forshey and Elfving, 1989;Embree et al., 2007). Recently, it has been found that deflowering resulted in strong increments in vegetative growth also in young olive trees, and that this eliminated differences in vigor (i.e. ...
This study investigated the effects of cultivar, fruit presence and tree age on whole-plant partitioning of dry matter and energy equivalents (i.e., glucose equivalents). Young trees of two cultivars characterized by different vigor (i.e., Arbequina, low vigor and Frantoio, high vigor) were either completely deflowered from 2014 to 2017 or never, providing two contrasting levels of cumulated reproductive growth over the following 4 years. Total vegetative dry matter growth over the 4 years was assessed by destructive samplings (whole tree). Plant growth was inversely correlated to reproductive efforts, with Arbequina producing more and growing less than Frantoio. Deflowered trees grew similarly across cultivars, although deflowered Arbequina grew statistically less than deflowered Frantoio by the fourth year, due to abundant flower production. Total reproductive (flowers + fruit) and vegetative biomass production were the same for all cultivars and treatments. Arbequina had a greater distribution of dry matter in directly productive structures (current and one-year-old shoots) and in leaves. This allows it to increase the number of current and following-year production sites, and to save in the resources invested in non-productive sinks (roots, trunk and branches), thus liberating resources for reproductive growth. Greater investments in leaves allow it to intercept more light and thus to increase assimilation. Increased assimilation and increased partitioning towards productive structures, and decreased competition by non-productive structures might contribute to explain the greater early bearing attitude of this cultivar.
... Several TFs and genes belonging to different pathways, directly and/or indirectly involved in the bud meristems transition from both vegetative to the reproductive stage and flower induction to differentiation were identified (Figure 7) [16,63,64]. DEGs analysis sustained a consistent flower induction in July on unloaded branches, together with a higher crop yield in the following year, triggering the alternate bearing. ...
The olive tree (Olea europaea L.) is a typical Mediterranean crop, important for olive and oil production. The high tendency to bear fruits in an uneven manner, defined as irregular or alternate bearing, results in a significant economic impact for the high losses in olives and oil production. Buds from heavy loaded ('ON') and unloaded ('OFF') branches of a unique olive tree were collected in July and the next March to compare the transcriptomic profiles and get deep insight into the molecular mechanisms regulating floral induction and differentiation. A wide set of DEGs related to ethylene TFs and to hormonal, sugar, and phenylpropanoid pathways was identified in buds collected from 'OFF' branches. These genes could directly and indirectly modulate different pathways , suggesting their key role during the lateral bud transition to flowering stage. Interestingly, several genes related to the flowering process appeared as over-expressed in buds from March 'OFF' branches and they could address the buds towards flower differentiation. By this approach, interesting candidate genes related to the switch from vegetative to reproductive stages were detected and analyzed. The functional analysis of these genes will provide tools for developing breeding programs to obtain olive trees characterized by more constant productivity over the years.
... These results are in agreement with other studies made in irrigated conditions by El-Sonbaty et al. (2012), or in dryland conditions by Elloumi et al. (2009). However, this issue remains controversial since several studies indicate that crop intensification reduces alternate fruit bearing (Moriana et al. 2003;Connor and Fereres 2004), while others indicate the opposite effect (Dag et al. 2010;Ben-Gal et al. 2011). ...
The results of a 4-year experiment combining irrigation, N, and K showed that to maintain productivity and tree growth it is necessary to attain a higher leaf N status than current diagnosis standards. To sustain high oil yield and quality and to avoid excessive vigor, a critical N concentration was established for olive trees of 1.94% for leaves sampled in July. A negative relationship was obtained between N leaf concentration and some quality parameters. Above 1.94% N, total phenolic content and oxidative stability fell below 220 mg kg−1 and 10 hr, respectively. In addition, above this N leaf concentration other factors including the alternate bearing index (ABI) and vegetative growth distorted productive and qualitative responses. Moreover, the differential productive response of trees related to alternate fruit bearing status implies that the interpretation of leaf nitrogen content can be more accurate when ABI suggests an ON tree status.
... Despite the advances made in AdaptaOlive v2.0 compared to the original model , some processes still require additional improvements in order to be correctly simulated. Thus, although alternate bearing could have a high impact on olive yield, especially under rainfed conditions, it is not incorporated into simulation models due to limitations in the understanding of its physiological bases, even under current weather conditions (Dag et al., 2010). In addition, other yield limiting factors such as pests and diseases, aspects related to nutrient deficits, different cultivar sensitivity to extreme events, competition with cover crops (seeded or spontaneous), or the effect of weather conditions on oil quality (Mousavi et al., 2019), have not yet been considered. ...
The identification of agricultural adaptation strategies to offset climate change impact requires a detailed knowledge of the response of crop systems under future climatic conditions. To carry out such an analysis for Mediterranean olive orchards, an improved version of the AdaptaOlive simulation model combined with perturbed climate (PC) and sensitivity analysis using impact response surfaces (IRSs) have been applied. As a result, phenology, crop yield and irrigation requirements were projected for olive orchards located at five locations representative of Southern Spain, with contrasting current and future weather conditions. Thus, under near future conditions using Representative Concentration Pathway (RCP) 4.5, large differences in olive yield response were found depending on the location, with an average yield increase of 19% for locations with cold winters, and reductions of 34% for locations with mild winters. Olive yield response could show abrupt changes even for limited changes in weather variables when critical thresholds are exceeded. IRSs and PC enabled the identification of such site-specific thresholds in terms of changes in temperature and rainfall from the baseline conditions. Thus, temperature increases of 3 °C generated null crop damage linked to flowering failure caused by lack of chilling in Jaen or Granada, whereas in Seville the damage was severe in 74% of the years. The analysis of the impacts of water stress and temperature increase on olive yield revealed the critical processes that need to be addressed by promoting adaptation measures. Said processes were not the same for entire analyzed area; in Seville-which has mild winters-cultivars with an earlier flowering date should be recommended, but in Granada-which has cold winters and low rainfall-the introduction of deficit irrigation strategies would be the appropriate recommendation. These results confirm the need to conduct weather sensitivity analyses, as provided by PC and IRSs, in order to develop site-specific adaptation strategies for the Mediterranean olive orchards. This procedure was required due to the non-smooth response to weather components, and the high spatial variability of weather conditions and olive orchard characteristics in Southern Spain.
... The alternate bearing in pistachio, as in all other fruit plants, is governed by both internal and external factors. The internal factors include the genotype and the endogenous hormone balance, whereas the external factors are the environmental conditions encountered by the pistachio tree (Mok and Mok, 2001;Foster et al., 2003;Achard et al., 2006;Al-Shdiefat and Qrunfleh, 2008;Bangerth, 2006;Dag et al., 2010;Gundesli et al., 2019). There are also other factors, such as planting density, irrigation and fertilisation, which may affect the growth and development of the plant (Weinbaum et al., 1994;Brown et al., 1995;Picchioni et al., 1997;Gundesli, 2017). ...
Alternate bearing is a significant economic problem affects the producers, consumers and the economy of a country. Cytokinin-like compounds contents in the different tissues of pistachio trees (Pistacia vera cv. `Uzun') were measured to elucidate the relationship between endogenous cytokinin and flower bud abscission (alternate bearing). Identification and quantification of cytokinin-like compounds and such as Z-type, DHZ-type, and P-type from different physiological stages and tissues were determined using HPLC-ESI-MS/MS (High-performance liquid chromatography-electrospray ionisation tandem mass spectrometry) techniques. Six to eight different cytokinin-like compounds were detected, respectively; Isopentenyl adenine riboside (IPR) and trans-Zeatin O-glucoside (t-ZOG) which were the main isoprenoid cytokinin being the dominant conjugate in all organs of pistachio trees. Leaf and shoot from ‘On’ year trees had higher cytokinin contents significantly than those of “Off” trees in all sampling dates. Interestingly, the relatively high cytokinin activity was recorded before flower bud abscission in the fractions corresponding to that IPR and t-ZOG while the activity dropped considerably at the flower bud abscission period (55 DAFB). Consequently, the strong negative relation between cytokinin and bud abscission could be a first indication of the role of cytokinin-like compounds content in this unique phenomenon of ‘Uzun’ pistachio variety. It was concluded that cytokinin could have an important role in the alternate bearing in pistachio.
... The alternate bearing in pistachio, as in all other fruit plants, is governed by both internal and external factors. The internal factors include the genotype and the endogenous hormone balance, whereas the external factors are the environmental conditions encountered by the pistachio tree (Mok and Mok, 2001;Foster et al., 2003;Achard et al., 2006;Al-Shdiefat and Qrunfleh, 2008;Bangerth, 2006;Dag et al., 2010;Gundesli et al., 2019). There are also other factors, such as planting density, irrigation and fertilisation, which may affect the growth and development of the plant (Weinbaum et al., 1994;Brown et al., 1995;Picchioni et al., 1997;Gundesli, 2017). ...
Alternate bearing is a significant economic problem that affects fruit producers, consumers and the economy of a country. Concentrations of cytokinin (CK)-like compounds in different tissues of pistachio trees ( Pistacia vera ‘Uzun’) were measured to elucidate the relationship between endogenous CKs and flower bud abscission (alternate bearing). Identification and quantification of CK-like compounds of the Z, DHZ and iP types from different physiological stages and tissues were performed using high-performance liquid chromatography–electrospray ionisation–tandem mass spectrometry (HPLCESI-MS/MS) techniques. Five to seven different CK-like compounds were detected, respectively. Isopentenyl adenine riboside (iPR) and trans -zeatin- O -glucoside ( t -ZOG) were the main isoprenoid CKs, as the dominant conjugates in all the analysed organs of pistachio trees. The leaves and shoots of ‘On’-year trees had significantly higher CK contents than those of ‘Off’-year trees on all the sampling dates. Interestingly, the relatively high CK activity was recorded before flower bud abscission in the fractions corresponding to iPR and t -ZOG, while this activity dropped considerably during the flower bud abscission period (55 DAFB). Consequently, the strong negative correlation between CK concentration and bud abscission could be the first indication of the role of CK-like compounds in this unique phenomenon in the ‘Uzun’ pistachio cultivar. It was concluded that CKs could have an important role in the alternate bearing in pistachio.
... Olives have a high tendency to alternate bearing, which results in yield fluctuation [42]. Olive alternate bearing is driven by the inhibitory effect of high fruit load on tree growth and flowering [43,44]. Thus, higher flowering intensity following fruit-bearing is a desirable trait. ...
The olive growing sector is transitioning from traditional to intensive irrigated cultivation, dictating a need to reconsider orchard management practices including fertilization. Potassium (K) is an essential nutrient, typically found in high concentrations in plants. Orchard K fertilization requirements are commonly derived from the disparity between assumed tree requirements and extractable soil K. The long-term impact of insufficient fertilization on K available in the soil, growth, and yield of irrigated field-grown olive trees was evaluated over six consecutive seasons. Withholding of K fertilization led to lower exchangeable and soluble K concentrations in the soil and significantly impaired yield. The reduction in yield was attributed to reduced flowering and fruit set, resulting in a lower fruit number. Tree vegetative growth and flowering quality traits were not affected. In addition, trees not receiving K appeared to be more susceptible to alternate bearing. Following two seasons of omitting K fertilization, leaf K concentration did not decrease below the conventionally accepted sufficiency threshold for olive (0.8%). In spite of this, the trees produced significantly lower yields. Our results suggest that long-term insufficient K fertilization results in reduced soil available K and consequently impairs tree productivity. The results imply that the sufficiency threshold for K in diagnostic leaves should be reconsidered for intensive orchards. Moreover, the current method for K deficiency detection using leaf K concentration may be inadequate for intensive orchards. Integration of other parameters, such as fruit K content, leaf Na, and changes in soil exchangeable K content or sorption energy, may promote a more reliable analysis of orchard K nutritional status.
... Current researches on alternative bearing were focused on the relationship between this natural phenomena and carbohydrate availability, enzymatic and photosynthesis activities. Developing fruits are a sink for carbohydrates at expenses of vegetative growth and for this reason fruit load is considered the main cause of alternate bearing in (Proietti et al., 2006;Lavee, 2007;Dag et al., 2010;Haouari et al., 2011;Annabi et al., 2018), in peach (Di Vaio et al., 2001)), in apple (Cheng et al., 2008), in citrus (Syvertsen et al., 2003) and in apricot (Roussos et al., 2011). Haouari et al. (2011) reported that a reduction of sink demand manipulated the source-sink balance, causing an accumulation of photo-assimilates and a decline of leaf photosynthesis . ...
Girdling practice gained attention as a mean to increase crop yields particularly for alternate bearing plants.
Data published for ligneous are controversial and mechanisms by which girdling regulates plant growth and
photosynthesis for olive tree are still not well elucidated. The physiological modifications induced by shoots
girdling, and their effects on the mobilization of assimilates, on the gas exchanges and on antioxidant activity
were studied in olive leaves of Meski, Picholine, Chetoui and Koroneiki cultivars. From each ‘ON’ and ‘OFF’ trees,
six shoots were selected, 3 of them were girdled and 3 were used as control. Total carbohydrates, alcoholic
(Mannitol) and soluble (Glucose, Fructose and Sucrose) sugars, photosynthesis parameters, total protein and
antioxidant activities in leaves of ‘ON’ and ‘OFF’ trees were analyzed. In girdled shoots a reduction of photosynthetic rate and a greater accumulation of both carbohydrates and antioxidant activities were observed.
Girdling, breaking off the phloematic flow, caused a store of elaborated sap in leaves that inhibited the photosynthetic activity inducing an oxidative stress. Our results confirmed fluctuations in carbohydrates, gas exchanges and antioxidant activities as a direct consequence of girdling and of presence or absence of fruits, and
showed clearly how each olive cultivar responds differently to girdling evidencing that the girdling effects are
cultivar dependent.
... These good performances on experimental plots were corroborated when the model was applied for yield estimation on farm level on sites 6-13. In particular, yield data for these sites exhibited a general trend for alternate bearing that was captured by the model with a good level of agreement with observations, especially considering that physiology of alternate bearing is not still fully understood (Dag et al., 2010). Interestingly, in some case, we observed an interaction between the alternate bearing and the effect of stress events at anthesis that may further depress the expected reduced yield or smooth the expected increased yield (e.g. ...
This paper describes the architecture of a process-based model that simulates on a daily time step growth and development of an olive agroecosystem, including the olive tree and grass cover growth and their competition for water. The key process of the model is the simulation of daily potential biomass increase for olive tree and grass cover that may be reduced depending on water availability. The model includes a phenological sub-model simulating the sequence of olive tree vegetative and reproductive stages for determining changes in biomass allocation and the timing of possible environmental stresses (heat and water stress) that may reduce final yield. The model was calibrated and validated in Tuscany region by exploiting a data set covering heterogeneous climatic features as well as soil types and management practices existing in this region. The results pointed out that the model is able to faithfully reproduce water balance of the system, biomass accumulation and yield of olive tree and grass cover biomass. We concluded that this model is a useful prognostic tool to test the effectiveness of management practices for improving economic viability of olive tree cultivation.
... As previously reported, crop load has a strong influence on water tree requirement (Bustan et al. 2016), shoot growth (Dag et al. 2010), yield and yield components, i.e., oil content and fruit size (Trentacoste et al. 2010). In this context, and given the variability of the crop load on the evaluated trees (variation coefficient of 33.1% Table 3), multiple linear regressions were adjusted, accounting for the crop load and water status of olive trees (Table 2). ...
The intense drought affecting olive production in Northern Chile underscores the need to research non-traditional irrigation strategies to obtain the best crop performance. Accordingly, this study aimed to obtain preliminary data to guide future research on this topic. Different water replenishment levels on crop evapotranspiration (ETc; 13.5, 27.0, 40.5, and 54%) were established in a young orchard, cv. Arbequina, from the end of fruit drop (EFD) to full bloom in the next season. We evaluated the influence of plant water status (Ψstem) and crop load, considered as function of fruit number divided by trunk cross-sectional area, on reproductive and productive variables using multiple linear regressions. Our results show that crop load and Ψstem measured from EFD to harvest affected yield components. Nevertheless, Ψstem had the strongest influence on fruit size, pulp development, oil accumulation, and yield. Oil content and yield were reduced by 54% and 50% for each MPa, respectively, from Ψstem EFD-H − 1.8 MPa, an effect that intensified as crop load increased. During the period of flower development (September–November), the number of flowers per inflorescence and percentage of perfect flowers were reduced when Ψstem was less than − 2.0 MPa. These preliminary results showed that bud differentiation, inflorescence and flower formation are highly sensitive to water deficit.
... Fruit removal scheduled until the middle of the summer, which brings about significant vegetative growth, bloom and fruit yield in the subsequent year (Dag et al., 2010. ...
... For the same pruning intensity, summer pruning resulted in a greater proportion of low vigor shoots compared to watersprouts than with winter pruning (Fig. 2). It is likely that a shift towards less vigorous shoot types occurred with summer pruning due to the well-known reduction in vigorous vegetative growth during fruit growth and olive oil accumulation in the summer months (Dag et al. 2010;Fernández et al. 2015). The timing of pruning had less affect than shoot type on return flowering, and the percentage of flowering base branches was similar on trees pruned in the winter or in the summer for the 3 years after simulated mechanical pruning (Fig. 4). ...
Key message
More vigorous watersprouts and fewer low vigor shoots form as wood age increases at the cutting points with greater canopy pruning depth in olive trees, which reduces return flowering. Such information is relevant to long-term olive orchard pruning strategies in hedgerows.
Abstract
Demographic analysis of growth responses to pruning in fruit trees seeks the quantification of the typology of new shoots originating from the remaining branches. Pruning of hedgerows using mechanical discs is becoming increasingly common in orchards, but little information is available as to how such pruning, which does not discriminate between branch size, wood age at the cutting point, branch type, or position, modifies subsequent new shoot demography. Hence, the experiment described in this study in young olive trees (cv. Arbequina) assessed the following questions: (1) Is the type and growth of new shoots associated with the intensity of mechanical pruning and/or the wood age on which they grow? (2) How many growing seasons does it take for new shoots formed after pruning to flower? The principal hypothesis was that a greater proportion of vigorous watersprouts form compared to low vigor shoots as wood age at the cutting points increases with canopy pruning depth, and that the watersprouts have low flowering potential. Both new shoot growth and return flowering were monitored on exposed supporting wood over several growing seasons after implementing three winter (25W, 50W, and 75W) pruning levels of increasing intensity and one summer pruning (75S) treatment along with an unpruned control (CON). As hypothesized, a greater number and elongation of vigorous watersprouts were found as wood age increased at the cutting points with greater winter pruning intensity, and the watersprouts had low levels of return flowering even 3 full years after pruning compared to the CON. Growth of low vigor shoots was relatively more important than watersprout growth in the severe summer pruning treatment, although 3 years after the summer pruning flowering was not fully recovered. In contrast, the more lightly pruned winter treatments (25W, 50W) did not show significant differences in flowering with the CON at the end of 3 years. Thus, mechanical hedge pruning in olive trees should be light-to-moderate to avoid the formation of watersprouts on older wood, which leads to long-term reductions in flowering.
... Interestingly, previous studies on olive trees have shown that fruit growth has preference over vegetative growth (stem or leaves), especially under water stress (Iniesta et al., 2009;Dag et al., 2010; main sink for new carbon assimilates. Similarly, it has been reported that olive fruits are the main water sinks during water stress periods, and that this decreases in importance under conditions of no water stress (Girón et al., 2015). ...
Yield, the final goal in agricultural systems, is highly determined by fruit growth. However, most works on deficit irrigation did not consider the physiology and dynamics of fruit growth. In this study, we explore the effect of water relations between leaves and fruits on fruit growth in well-watered (WW) and water-stressed (WS) trees in a super-high-density olive orchard (cv. Arbequina) over a full irrigation season (June-October of 2017) in southern Spain. Both leaf and fruit water potential were measured, along with pressure-volume curves. Concomitantly, fruit growth and diurnal changes in six fruits of each irrigation treatment were continuously monitored with fruit gauges, which recorded changes in the equatorial diameter of the fruit. Fruit water status and growth were greatly affected by water stress, the latter recovering markedly, following our regulated deficit irrigation strategy. The gradient between leaf and fruit water potential was positive most of the time for both irrigation treatments, and greater for WS than WW trees, which suggests water flow into the fruit. However, we also observed negative fruit growth in WS which, together with the positive gradient, suggests that water flow from the parent plant to the fruit was insufficient to balance fruit transpiration under conditions of water deficit. Although a strong correlation was found between leaf water potential and the amplitude of fruit contraction in WW trees, this relationship did not hold for WS trees, suggesting a progressive decoupling of fruit water status from leaves as water stress progressed. Accordingly, an osmotic adjustment as evidenced by the analyses of pressure-volume curves occurred in WS fruits towards the end of the season. These results indicate that leaf-fruit water potential measurements may not be sufficient to study fruit-leaf water relationships in the canopy; however, fruit gauges may serve as highly useful instruments to understand the water status and daily dynamics of fruit growth.
... Some cultivars are characterized by high phenolic contents (Coratina), while others highlight more reduced concentrations (Taggiasca). Also the ripening degree reached by the olive fruits belonging to the same cultivar and grown in the same grove determines the characteristics of the extracted oil (Dag et al., 2010). In particular, the green or turning-colour olives give a product characterized by bitter notes due to a higher presence of phenolic components (Oleocanthal). ...
To highlight the effects induced by the direct addition of solid carbon dioxide to olive fruits on oil production and phenol accumulation, olive fruits from the same cultivar with different ripening degrees were used. A part of the olives were obtained from irrigated plants, while the other fraction derived from not irrigated olive trees. The yield of oil extracted from olive fruits belonging the same cultivar and coming from the same orchard increased with the ripening degree of the milled fruits. Furthermore, the olives harvested on the same date from irrigated plants produced more oil than those coming from not irrigated trees. In addition, the addition of carbonic snow to fruits characterized by the same ripening index increased both the yield of oil and the concentration of total phenols dissolved in the extra-virgin olive oils.
... Besides, fruiting branches or shoots differing in vigour, length and age, are normally observed in fruit species, which can result in a large distribution of fruit size. Also, in extreme situations, the occurrence of biennial production patterns might occur, as described in Coffea arabica L. (Bote and Vos, 2016) and Olea europea L. (Dag et al., 2010). ...
... Table 5. The rates of photosynthesis, stomatal conductance (g S ), and transpiration of leaves from different shoot types (''on'' or ''off'') in 10-yearold alternate-bearing 'Nadorcott' mandarin trees during summer of season 1. Davenport, 1987;Verreynne and Lovatt, 2009) and with studies in other alternate-bearing evergreens; e.g., in olive [Olea europaea (Dag et al., 2010)]. The higher number of new vegetative shoots in ''off'' trees affected flowering in the subsequent spring; ''off'' trees had more nodes and more potential sites available from which a flower could develop. ...
The objectives of this study were to improve the understanding of the mechanism of alternate bearing and the role of carbohydrates in 'Nadorcott' mandarin (Citrus reticulata) trees. Selected phenological responses were measured in natural heavy-(''on'') and low-fruiting (''off'') 'Nadorcott' mandarin trees grown under commercial South African production conditions. The relationships with seasonal leaf and root carbohydrate concentrations were evaluated at the shoot-, branch-and tree level over two seasons. Fruit load [R 2 = (L)0.80 and R 2 = (L)0.73 in seasons 1 and 2, respectively; (P < 0.01)] and the number of newly developed vegetative shoots [R 2 = 0.81 and R 2 = 0.78 in seasons 1 and 2, respectively; (P < 0.01)] were the most important determinants of return bloom.
... Effects of LFR on vegetative growth, fruit development, biomass productivity, photosynthetic characteristics of leaves have been studied in many fruit varieties, e.g., olive (Olea europaea L.) (Dag et al. 2010, Martín-Vertedor et al. 2011, Naor et al. 2012, European plum (Prunus domestica L.) (Seehuber et al. 2011), apricot (Prunus armeniaca L.) (Roussos et al. 2011), peach (Prunus persica L. Batsch) (Li et al. 2007), and grape (Vitis vinifera L.) (Rossouw et al. 2017). However, carbohydrates and energy, which are used for vegetative growth, fruit development, and biomass productivity are both the products of photosynthesis in source leaves. ...
In this study, we investigated maximal quantum yield of PSII photochemistry(Fv/Fm),effective quantum yield of PSII photochemistry (ΦPSII), and nonphotochemical quenching (NPQ) of walnut (Juglans regia ‘Xinxin2’) leaves with different leaf-to-fruit ratios (LFRs). The results indicated that the increasing LFR increased the values of Fv/Fm, ΦPSII, and NPQ in leaves on the girdled shoot with one and two leaves, and decreased the values of Fv/Fm and ΦPSII in leaves on the girdled shoot with five leaves, whereas had no effect on the chlorophyll (Chl) fluorescence in leaves on the girdled shoot with three and four leaves. These results indicate that the effects of LFR on Chl fluorescence depend on a LFR range and show a transitional trend transition, and that excessive fruit load accelerates leaf senescence resulting in the destruction of the reaction center in PSII.
... The previous season fruit load is another factor that could affect current season yield. High crop loads in one season are associated with reduced return bloom in citrus (Verreynne and Lovatt 2009), apple (Byers and Carbaugh 2002;Embree and Myra 2007;Meland 2009;Suo et al. 2016), olive (Dag et al. 2010) and pecan (Reid et al. 1993;Rohla et al. 2007). In almonds, spurs (the main bearing structure) that bore fruits in one season are more likely to die the following year than non-bearing spurs and have lower probabilities of return bloom (Heerema et al. 2008;Lampinen et al. 2011;Reidel et al. 2004;Saa and Brown 2014;Saa et al. 2017;Valdebenito et al. 2017b). ...
Key message
From 1 year to the next the number of shoots increases, but their individual size declines. Shoots located in more lightened canopy zones and bearing two fruits maintain productive sustainability.
Abstract
432 shoots in 24 mature trees from three commercial orchards located in the central valley of Chile were inspected for 2 years. Tree canopy was divided into three zones according to light exposure (upper, lower-exposed, lower-shaded). In the first year of the study, six shoots were randomly selected in each canopy zone and divided into three bearing statuses [shoots bearing one fruit (F1), shoots bearing two fruits (F2), and shoots bearing three fruits (F3)]. In the second year, all new shoots (1068) born on the 432 shoots were studied. Specific leaf weight and current-year shoots (CY) characteristics (length, diameter, number of leaves, number of leaflets, leaf area) were evaluated as a function of the previous season fruit load and canopy position of the 1-year-old (1Y) shoots. The results indicated that 1Y shoots located in more light-exposed canopy zones bore on average 0.5 more CY shoots than 1Y shoots in the lower-shaded canopy zone. Specifically, the 1Y shoot probability of bearing CY shoots that had two or three fruits was 72.8% in the upper canopy zone, 44.6% in the lower-exposed zone, and 34.9% in the lower-shaded zone of the canopy, respectively. 1Y shoots in the lower-shaded zone had on average a 7.7% higher probability of dying than 1Y shoots in the upper and exposed positions. In addition, CY shoots born on 1Y shoots exposed to light were on average 2.7 cm longer, more than 1 mm thicker, and had 53.7% greater leaf area than CY shoots born on shaded 1Y shoots. Finally, the results of this study showed that 1Y shoots that had two fruits in the previous season produced CY shoots with the greatest bearing potential in the current and future seasons.
... The inhibiting action of developing fruits on return bloom is well established as a major factor in olive tree biennial bearing (de Almeida, 1940;Lavee, 1986;Dag et al., 2010;Rallo and Cuevas, 2010). Currently, the absence of fruits after full bloom is considered a favorable signal for floral induction, i.e., the first step in the transition of buds from undefined to potential reproductive (Lavee, 1986;Stutte and Martin, 1986;Fernández-Escobar et al., 1992). ...
... For example, some discrepancies were found for some of the simulations of Y oil , ET ( Table 1) and E p (Figure 3), but, considering that the general trends and differences between treatments were captured by the model, we believe that the results are highly acceptable. Some of the divergences between measured and simulated Y oil might be attributed to the fact that the approach followed by OliveCan to simulate alternate bearing is limited, as far as the physiological bases of alternate bearing are not completely understood yet (Connor, 2005;Dag et al., 2010). However, biennial comparisons ( Table 2) only improved slightly the results. ...
Several simulation models of the olive crop have been formulated so far, but none of them is capable of analyzing the impact of environmental conditions and management practices on water relations, growth and productivity under both well-irrigated and water-limiting irrigation strategies. This paper presents and tests OliveCan, a process-oriented model conceived for those purposes. In short, OliveCan is composed of three main model components simulating the principal elements of the water and carbon balances of olive orchards and the impacts of some management operations. To assess its predictive power, OliveCan was tested against independent data collected in two 3-year field experiments conducted in Córdoba, Spain, each of them applying different irrigation treatments. An acceptable level of agreement was found between measured and simulated values of seasonal evapotranspiration (ET, range 393 to 1016 mm year-1; RMSE of 89 mm year-1), daily transpiration (Ep, range 0.14–3.63 mm d-1; RMSE of 0.32 mm d-1) and oil yield (Yoil, range 13–357 g m-2; RMSE of 63 g m-2). Finally, knowledge gaps identified during the formulation of the model and further testing needs are discussed, highlighting that there is additional room for improving its robustness. It is concluded that OliveCan has a strong potential as a simulation platform for a variety of research applications.
... Fruit production proportionally reduced vegetative production in terms of total 2015 new shoots ( Figure 1A). This agrees with previous findings on the depressing effect of fruit production on vegetative production ( Salazar-García et al. 1998, Stevenson and Shackel 1998, Lauri and Térouanne 1999, Costes et al. 2000, Berman and DeJong 2003, including in olive ( Monselise and Goldschmidt 1982, Rallo and Suarez 1989, Obeso 2002 Tree Physiology Volume 00, 2018and Fereres 2005, Lavee 2007, Dag et al. 2010, Castillo-Llanque and Rapoport 2011). Previous studies have not considered whole-plant biomass production across both cultivars and fruit production treatments. ...
The amount of shoot stem (i.e., woody part of the shoot) dry matter per unit shoot leaf dry matter (i.e., the shoot wood to leaf biomass ratio) has been reported to be lower in short shoots than in long ones, and this is related to the greater and earlier ability of short shoots to export carbon. This is important in fruit trees, since the greater and earlier carbon export ability of shoots with a lower wood to leaf biomass ratio improves fruit production. This ratio may vary with cultivars, training systems or plant age, but no study has previously investigated the possible effect of fruit production. In this study on two olive cultivars (i.e., Arbequina, with low growth rate, and Frantoio, with high growth rate) subject to different fruit production treatments, we found that at increasing fruit production, shoot length and shoot wood to leaf biomass ratio were proportionally reduced in the new shoots growing at the same time as the fruit. Specifically, fruit production proportionally reduced total new-shoot biomass, length, leaf area and average shoot length. With decreasing shoot length, shoot diameter, stem mass, internode length, individual leaf area and shoot wood to leaf biomass ratio also decreased. This may be viewed as a plant strategy to better support fruit growth in the current year, given the greater and earlier ability of short shoots to export carbon. Moreover, at the whole-tree level, the percentage of total tree biomass production invested in leaves was closely correlated with branching density, which differed significantly across cultivars. By branching more, Arbequina concentrates more shoots (thus leaves) per unit of wood (trunk, branches and root) mass, decreasing wood to leaf biomass ratio at the whole-tree level. Therefore, while, at the shoot level, shoot length determines shoot wood to leaf biomass ratio, at the canopy level branching density is also an important determinant of whole-tree wood to leaf biomass ratio. Whole-tree wood to leaf biomass ratio is likely to affect the canopy's ability to export carbon (i.e., towards fruits), as shoot wood to leaf biomass ratio affects the carbon export ability of the shoot.
... Such a pattern is common in most olive cultivars (Lavee, 2007). This often occurs because in the "on" year there is low shoot growth, which leads to few potentially reproductive buds for the next year; when crop load is high there is inhibition of floral induction (Dag et al., 2010;Fernández et al., 2015). Consequently, the year-to-year variations in yield are directly related with fruit number per tree of each year (Martín-Vertedor et al., 2011;Trentacoste et al., 2015). ...
An increase in the land area dedicated to super-high density olive orchards has occurred in Chile in recent years. Such modern orchards have high irrigation requirements, and optimizing water use is a priority. Moreover, this region presents low water availability, which makes necessary to establish irrigation strategies to improve water productivity. An experiment was conducted during four consecutive growing seasons (2010-2011 to 2013-2014) to evaluate the responses of yield and water productivity to irrigation cut-off strategies. These strategies were applied after fruit set using midday stem water potential (Ψstem) thresholds in a super-high density olive orchard (cv. Arbequina), located in the Pencahue Valley, Maule Region, Chile. The experimental design was completely randomized with four irrigation cut-off treatments based on the Ψstem thresholds and four replicate plots per treatment (five trees per plot). Similar to commercial growing conditions in our region, the Ψstem in the T1 treatment was maintained between -1.4 and -2.2 MPa (100% of actual evapotranspiration), while T2, T3 and T4 treatments did not receive irrigation from fruit set until they reached a Ψstem threshold of approximately -3.5, -5.0, and -6.0 MPa, respectively. Once the specific thresholds were reached, irrigation was restored and maintained as T1 in all treatments until fruits were harvested. Yield and its components were not significantly different between T1 and T2, but fruit yield and total oil yield, fruit weight, and fruit diameter were decreased by the T3 and T4 treatments. Moreover, yield showed a linear response with water stress integral (SΨ), which was strongly influenced by fruit load. Total oil content (%) and pulp/stone ratio were not affected by the different irrigation strategies. Also, fruit and oil water productivities were significantly greater in T1 and T2 than in the T3 and T4. Moreover, the T2, T3 and T4 treatments averaged 37, 51 and 72 days without irrigation which represented 75-83, 62-76 and 56-70% of applied water compared with T1, respectively. These results suggest that using the T2 irrigation cut-off strategy could be applied in a super-high density olive orchard (cv. Arbequina) because it maintained yields, saving 20% of the applied water.
... In Years 2 and 3, fruit number and yield in unpruned trees were influenced by the previous year fruit load with some tradeoff between fruit number and fruit weight and oil content (Fig. 6). There are indications that the vegetative growth of the unpruned, control trees was also regulated by the fruit load as has been seen in previous studies (e.g., Dag et al., 2010;Fernández et al., 2015). Both trunk and branch growth (Figs. ...
Mechanical pruning has become increasingly common in olive orchards, particularly under high tree densities. Large cutting disks make heading cuts at a single canopy depth without discriminating between branch thickness, size, or type of branch. The objectives of this study were to: (i) quantify the responses of vegetative growth over two growing seasons and yield components over three seasons following different intensities and moments of application of mechanical pruning; and (ii) evaluate some leaf morphology and gas-exchange characteristics of the remaining leaves after pruning. Five year-old olive trees with high crop load (cv. Arbequina) were pruned towards the end of the winter (W) or early summer (S). Three intensities of winter pruning representing different distances (0.25, 0.50, 0.75 m) from the outer canopy surface were applied, while there was only a single summer pruning treatment (0.75 m). The vegetative growth variables measured after pruning included new branch number and length, new leaf number, and increase in trunk cross sectional area. Reproductive variables included fruit and oil yield, fruit number, fruit weight, and oil content per fruit. Growth of new branches increased significantly with winter pruning intensity while delaying pruning to early summer reduced regrowth to the level of the unpruned control. Despite differences in yield in individual years between the unpruned control and the winter pruning treatments, the average yield over the three years after the winter pruning event was similar between all trees. Delaying the intense pruning to summer was associated with some reduction in yield, and moderate winter pruning (0.50 m) appeared to partially reduce alternate bearing. When measured shortly after winter pruning, specific leaf mass of the remaining leaves decreased steadily as the level of winter pruning increased, which is consistent with prior shading within the tree. The leaf net photosynthetic rate per unit mass was also different between pruning treatments. In conclusion, our results contribute to filling the gaps in knowledge related to important aspects of olive tree responses to the intensity and timing of mechanical pruning.
The fruit and seed produced by a small number of crop plants provide the majority of food eaten across the world. Given the growing global population, there is a pressing need to increase yields of these crops without using more land or more chemical inputs. Many of these crops display prominent 'fruit-flowering feedbacks', in which fruit produced early in sexual reproductive development can inhibit the production of further fruit by a range of mechanisms. Understanding and over-coming these feedbacks thus presents a plausible route to increasing crop yields 'for free'. In this review, we define three key types of fruit-flowering feedback, and examine how frequent they are, and their effects on reproduction in a wide range of both wild and cultivated species. We then assess how these phenomenologically distinct phenomena might arise from conserved phytohormonal signalling events, particularly the export of auxin from growing organs. Finally, we offer some thoughts on the evolutionary basis for these self-limiting sexual reproductive patterns, and whether they are also present in the cereal crops that fundamentally underpin global diets.
In this work we present the results obtained in the North-east of Tunisia during the period 2010-2017 relative to the morphological, agronomic and technological study of olive varieties implemented in the National Olive Collection of ‘Oued Souhil’ Nabeul, which includes 42 local and foreign varieties.
The descriptive criteria used in this work for the tree, fruits, pits and leaves are those of International Olive Council (IOC, 1981).
The statistic analysis of data (ANOVA, PCA) allowed the distinction of the most performant varieties which are selected on the basis of the most performant variables like water productivity, olive oil production and their ability to valorize more intensive cultivation systems and their adaptative behavior to water shortage. The Cvs., Chemlali, Chétoui and Galega are among these varieties.
A sufficient and mature vegetative growth is an essential condition for production in the following season and consequently affects the alternate bearing (AB) behavior. However, little is known about its interaction with the crop load and water supply. Herein, we studied the effect of different water regimes and bearing status on the vegetative intensity and flush and its consequence on the flowering parameters of the following season. Rainfed (RF) and fully irrigated (FI) treatments were applied for bearing (ON) and non-bearing (OFF) trees of the ‘Zalmati’ olive orchard in south Tunisia during 2018. The water deficit condition (RF) and the high crop load (ON) have caused a similar decrease in the total node number and shoots length by about 65%. Furthermore, the flowering parameters in 2019, especially the percentage of floral buds (i.e., floral induction intensity), were differentially affected by water supply according to the bearing status of the previous season. FI reduced the percentage of floral buds in 2019 by about 37% for OFF trees, while it increased it by more than four times for the ON trees. Concerning the growth flush, the second (i.e., autumnal) flush seems to respond better to water supply than the first (i.e., spring) one, for both vegetative and flowering parameters. The second flush of growth provided 28% of the total vegetative growth but contributed about 35% to the total number of floral buds for RF OFF trees. Besides, FI makes the first and the second flushes contribute equally to total vegetative growth and to the flowering parameters of the following season. On the other hand, the bearing status of the trees does not affect the contribution of each flush to the total vegetative growth.
Yearly yield fluctuations are normal in fruit trees. Yield alternation might be induced by environmental stresses, but in many fruit tree species yield alternation is an inherent characteristic, resulting in perpetual biennial cycling. Endogenous cues are thought to be the major players in determining the phenomenon, although the genetic basis, if it exists, is still enigmatic. In most cases, alternate bearing is due to inhibition of floral induction, following a heavy fruit load ON year. Understanding of flowering control in model plants has made great progress during recent decades. Due to conservation of many molecular components of the flowering‐control pathways among higher plants, there has also been considerable progress in the identification of these components and in the understanding of their role in fruit trees. In this review, flowering control by exogenous and endogenous cues in Arabidopsis along with updated findings in fruit trees are summarized. The effect of fruit load on flowering‐control genes is also examined. Along with these fundamental traits, more practical aspects, namely mitigation strategies of alternate bearing, are also reviewed. Recent developments in mitigation practices of six representative fruit trees are also summarized. Finally, some basic questions, including the genetic and epigenetic background of alternate bearing, an evolutionary perspective, and possible common mechanisms among various fruit trees, are thoroughly discussed.
In perennial fruit crops, reproductive success and productivity are principally governed by the core event, regular flowering. However, this feature bearing can be influenced by different factors viz. environmental conditions, germplasm, rootstocks, and cultural operations. The phenomenon of irregular bearing is more dominant in perennial fruit crops. In order to ensure regular and quality fruit production it is therefore, imperative to regulate the flowering phenology. The comparative studies conducted by the researchers for understanding the physiological and molecular aspects associated with regular and irregular bearing phenomenon in perennial fruit crops are helpful to understand the crux of flowering, discover the regulatory factors for regularity in bearing. Further, differential gene expression studies allow the identification of key genes related with the regular bearing feature. The identified candidate genes in this regard could be harnessed for selection of desirable parents, hybrids in early nursery stage, thus facilitating the plant breeders through precision breeding approaches. This paper reviews the current understanding of the physiological and molecular basis associated with the flowering phenology along with the impact of different factors on alternate bearing in perennial fruit crops.
Flower bud induction in the olive is a long lasting process, influenced by a number of factors, both internal and external to the tree. Research results seem to confirm the hypothesis of a two-step induction, eventually leading to the onset of flower bud differentiation, which appears to be started at the end of autumn. The paper examines the various aspects of this important issue in olive flower biology, by reviewing a large number of research papers produced over almost a century.
GA 3 scaffold injections applied between May and November to nonbearing olive (Olea europea L.) trees inhibited flowering the following year, increased shoot width when applied in May, June, and July, and increased inflorescence length when applied in November and February. Fruit removal and seed destruction were effective in improving the return bloom in `Manzanillo' olives when done before endocarp sclerification. Depending on-the year, endocarp sclerification takes place 7 to 8 weeks after full bloom (AFB), usually about 1 July. Fruit removal had no effect on flowering when done after this time. Scaffold injection of paclobutrazol applied to bearing trees between May and September did not affect flowering the following year. The results of our research supports the hypothesis that olive flower induction occurs around the time of endocarp sclerification. Chemical names used: gibberellic acid (GA 3 ), (2RS,3RS)-1-(4-chlorophenyl)-4-dimethyl-2-1,2-4-triazol-1-yl) pentan-3-ol(paclobutrazol).
Experiments with olive ( Olea europaea L.) shoot explants were carried out to determine the influence of winter chilling on the release of axillary buds from dormancy. This investigation was designed to explore an alternative explanation for the confusing concept surrounding the role of chilling in olive floral induction. Leafy explants collected from 10 Nov. to 6 Mar. were grown in a greenhouse under mist at 13/24C (night/day) and in a growth chamber at 10/21C (night/day) to determine the end of dormancy. Growth of floral buds from leafy explants was first recorded from 5 Jan. samples. After that date the percentage of developing floral buds and rate of their development increased. Floral bud abscission, increase in bud fresh weight, and simultaneous decrease of relative bud dry weight were associated with growth initiation of floral buds. Manual defoliation of adult trees during the period of shoot explant collection indicated that leaves play a critical role in development once the floral buds had completed dormancy. Supplementary chilling of isolated shoots collected 20 Jan. demonstrated that 7.2C was sufficient to complete chilling requirements, while 12.5C allowed both the completion of chilling requirements and the proper temperature for subsequent floral bud growth. Winter chilling is required to release previously initiated floral buds from dormancy, and we question the previous concept that the role of chilling is to induce olive floral initiation.
Changes in hormone concentrations in leaf, node, shoot tip, and fruit samples of three Turkish olive (Olea europaea L.) cultivars ('Gemlik', 'Memecik', and 'Tavsan Yuregi') were monitored at monthly intervals over two successive years of the alternate-bearing cycle. Concentrations of abscisic acid (ABA), indole acetic acid (IAA), gibberellic acid-like substances (GA), and kinetin-like cytokinin were determined and their relationship to flower bud formation were examined during "on" and "off" years. Results showed significant differences in IAA, ABA, GA3-like, and kinetin-like cytokinins between "on" and "off" cropping years in various tissues of olive trees. Relative balances between GA 3-like and ABA concentrations of tissues appears to exhibit evidence of being a key regulator of floral development and alternate bearing.
Phenological observations in olive tree (Olea europaea L.), on the first reproductive phase (budburst) and the winter chilling temperatures required for its onset, were analysed over a 4-year period (1998 - 2001). Research was carried out on two different cultivars growing in two Mediterranean olive-growing areas: 'Ascolana' in central Italy and 'Picudo' in southern Spain. The two main objectives of the study were: (1) to evaluate the different amounts of winter chilling, and their relationship with the budburst dates in outdoor olive plantations; and (2) to test the validity in the study areas of two chilling calculation methods, the Aron and the Utah method. Results show that for the Spanish cultivar the average chilling requirement of 997 h was approximately half of that recorded for the Italian cultivar (1848 h). Also, the year-to-year variability in chilling accumulation and the reproductive development date was observed to be higher in the Spanish area than in the Italian one, indicating a more consistent and predictable winter chilling response in the latter. As regards the validity of the methods, the Aron method seems to be more appropriate for use in warmer places, since it yielded better results in the Spanish site.
Biennial bearing is a major horticultural and economic drawback of olive (Olea europaea L.) cultivation, which particularly affects the olive oil industry under intensive production systems. The number of fruits per tree in an on-year is a primary determinant of the biennial cycle. While fruit thinning using NAA shortly after full bloom is commonly practiced to increase fruit size in table olives, the extent of its influence on biennial bearing is unknown. In the present study, the ability of that common naphthaleneacetic acid (NAA) treatment (100mg/L, 10 days after full bloom) to alleviate biennial bearing in two oil olive cultivars, Picual and Barnea, was poor, although significant influence on the number of fruit was evident solely in Barnea. Picual seemed less susceptible than Barnea to biennial bearing. Consequently, the effect of a broad range of NAA concentrations (0-320mg/L, 10 days after full bloom) on various yield parameters was investigated during a biennial cycle of Barnea trees. There was a gradual proportional decline in the on-year number of fruits from ∼50000 to 10000/tree in response to increasing NAA concentrations. The number of return fruits in the off-year was reciprocal to the on-year fruit load, but remained relatively small, below 15000/tree. The dynamic relationship between fruit load and fruit size in both on- and off-years was a significant compensation factor in fruit and oil yields. In both cultivars, an on-year fruit load smaller than 20000/tree is likely to provide consistent yearly oil yields ranging from 10 to 12kg/tree. The results demonstrate the possibility of using NAA post-bloom spraying to balance biennial bearing in oil olives.
Olive (Olea europaea L.) is one of the most important crop plants grown in the Mediterranean region. Varying levels of hormones, sugars and mineral nutrient are thought to influence flower bud formation. The objective of this study was to evaluate the changes in endogenous sugar, mineral nutrition and hormone levels in leaf, node and fruit samples of Memecik olive during the induction, initiation and differentiation periods in on (bearing) and off (non-bearing) years. Leaf, node and fruit samples of mature 15-year-old Memecik olive were used. The samples were taken during the induction, initiation and differentiation periods of olive in on (2000) and off (2001) years. Sugar (glucose, fructose and sucrose), mineral nutrient (N, P, K, Ca, Mg, Fe, Zn, Mn and Cu) and hormone [abscisic acid (ABA), indole acetic acid (IAA), gibberellic acid (GA3, GA4) and zeatin (Z)] levels were determined in on and off years. Hormone and sugar levels were measured by gas chromatography and high-performance liquid chromatography. The K, Ca, Mg, Fe, Mn, Zn and Cu levels were quantified by an atomic absorption spectrophotometry. Nitrogen was determined by the Kjeldahl procedure, and P by a spectrophotometric method. The differences in any of the sugar concentrations, with the exception of fructose, were not significant in on and off years. Hormone levels, however, were significantly different in on and off years. Glucose had the highest concentrations in both years, followed by sucrose and fructose, respectively. The highest macro and micro element concentrations were found to be Ca and Fe, respectively. Thus, the results suggest that carbohydrates and mineral nutrients may not have a direct effect to induce flower initiation. However, high GA3 level exhibited an inhibitory effect on floral formation during the induction and initiation periods. On the other hand, the high concentrations of GA4, ABA and certain cytokinin levels may have a positive effect on flower formation in olive during the induction and initiation periods.
The aim of this research was to study flower bud differentiation processes in two oil olive cultivars from Tuscan germplasm (Leccino and Puntino). The effect of fruit-set was studied using 'ON' (with fruits) and 'OFF' (without fruits) shoots. Axillary buds were periodically collected at different phenological stages, from endocarp sclerification (July) until budbreak in the following spring. Thin sections were analysed using histology (apex size), histochemistry (RNA, starch and soluble carbohydrates) and cytokinin immunocytochemistry (zeatin localisation). The micromorphological observations and histochemical procedures did not allow us to distinguish axillary buds sampled from 'ON' and 'OFF' shoots. Cytokinin immunocytochemistry revealed early different localisation patterns between 'ON' and 'OFF' samples. Zeatin accumulated only in 'OFF' axillary bud meristems, particularly in July, when endocarp sclerification of fruits from the previous flowering is taking place. At this time, a strong RNA signal was also observed. Both these signals were correlated with floral evocation, and their coincidence with a phenological stage of development provided a useful tool to determine the time when axillary buds switch from the vegetative to the reproductive phase.
Environmental factors such as suitable light and thermal conditions are essential for the reproductive development of olive buds. However, the tree and its buds have to be in a suitable responsive physiological state in order to respond. Furthermore sufficient well developed buds from the previous season with a good nutritive balance, capable to differentiate are required on the tree. In the present paper, we are demonstrating the changes in the nutritional state of the tree developing in ON and OFF years affecting the responsiveness of the buds and level of vegetative growth to the environmental conditions. After a heavy crop a nutrient dilution occurred and vegetative growth is inhibited. Thus, a following growing season is required to regain a good nutrient balance for generating vegetative growth with sufficient buds responsive to environmental differentiation stimuli for the initiation of the next ON year.
Alternate bearing in olive is largely determined by flowering load. In order to know if there are differences in floral quality related to flower load, and if these differences reinforce or alleviate the alternate-bearing tendency, we compared pistil abortion, floral sink strength and fruit set between “on” and “off” ‘Manzanillo’ olive trees. ‘Manzanillo’ trees with light flowering showed a higher percentage of pistillate inflorescences, higher dry weight and nitrogen content of the flower, and a higher percentage of fruit set. The tree with the lightest flower load had greater ovule longevity than the tree with the heaviest flower load, although differences were not found in the incidence of undeveloped embryo sacs. The results suggest partial compensation of the alternate habit by enhancement of female floral quality and an increase in fruit set when low levels of flowering occur.
A series of experiments were performed to determine the role of the seed and crop load on flower induction in olive. Complete de-fruiting of branches 2–3 cm in diameter as early as 2 weeks after anthesis did not promote flowering in ‘Manzanillo’. Destruction of the seed promoted flower formation compared to seeded controls in both ‘Manzanillo’ and ‘Koroneiki’. Dry matter accumulation and partitioning in both seeded and seed-killed fruit were similar. Carbohydrate demand did not appear to be a primary factor in flower formation. Flowering was promoted in both varieties when the seed was destroyed prior to endocarp sclerification.
IntroductionDefinition of AlternationRepresentative Cases of AlternationHorticultural TraitsCauses of AlternationHorticultural Control of AlternationConclusions
Literature Cited
This paper describes the phenological growth stages of olive trees using the BBCH (Biologische Bundesanstalt, Bundessortenamt, Chemische Industrie) scale. Eight principal growth stages for bud, leaf and shoot development, inflorescence emergence, flowering, fruit development, fruit maturity and senescence and 32 secondary growth stages are described. Advantages of the BBCH scale over other methods are discussed.
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This investigation was designed to characterize phenolic metabolism of the olive cultivar, Hardy's Mammoth, by examining its constitutive tissues. The phenolic profiles of pulp, seed, stone, and new and old season leaves were monitored over two fruiting seasons, to investigate possible relationships between tissues and phenol content and to determine the impact of alternate fruit bearing. No major qualitative differences in phenolic composition were found between the various tissues; however, distinct differences between the tissues with respect to quantifiable phenols were established. Relationships between 2-(3,4-dihydroxyphenyl)ethyl (3E,4E)-4-formyl-3-(2-oxoethyl)hex-4-enoate ester, oleuropein, and hydroxytyrosol in pulp and leaf were identified and found to be related to alternate bearing. Concentrations of 5-caffeoylquinic acid in old season leaves differed dramatically between seasons, confirming earlier studies.
Comparative analyses of reproductive and vegetative tissues of the olive (Olea europaea L. cv. Manzanillo) for endogenous hormones, particularly inhibitors and gibberellin like substances, were made to study the relation between such hormones and thermoinduction of flowering. Qualitative and quantitative changes in gibberellin-like subtance(s) were observed in lateral buds (potential flower buds) but not in leaves or terminal buds (potential vegetative buds) sampled from orchard trees at intervals during the winter and spring. At least two types of gibberellin-like substances were found in extracts of lateral buds; their levels increased progressively during the low temperature induction period, reaching a maximum shortly before floral initiation. Two types of inhibitors were extracted from buds and leaves. A nonacidic type did not change during the induction stage but decreased considerably during the initiation period. An acidic inhibitor, which was identified as an abscisic acid-like substance, was present at a relatively lower level in lateral (flower) buds than in terminal (vegetative) buds during the induction period.It was concluded that winter chilling induces flowering in the olive possibly by altering a balance between endogenous gibberellins and inhibitors, including abscisic acid.Inflorescence development following the winter chilling period was associated with an increase in the level of endogenous inhibitors and gibberellins. Shoot growth, however, was correlated with a decrease in the inhibitor(s) level. A rise in gibberellin-like activity is believed to be a result, not a cause, of shoot growth.