G. Selles’s research while affiliated with Instituto de Investigaciones Agropecuarias and other places

In the Aconcagua Valley, Chile, a 4-year research (2007/11), has been carried out to evaluate the response of table grape cultivar 'Flame Seedless' to different volumes of irrigation water. The experimental site was a commercial orchard of 'Flame Seedless' grafted on Freedom rootstock, located in the Aconcagua valley (70°41'23"W; 32°47'20.9"S), Chile. Four irrigation treatments were applied in a factor of: 0.57, 0.89, 1.12 and 1.51 of crop evapotranspiration (ETc), during the seasons 2007/08 to 2010/11. Soil water content was monitored with a capacitive probe in each treatment. Midday stem water potential was also measured (MSWP). The minimum soil available water (SAW) and MSDWP were found in 60% ETc treatment in all seasons, but this did not affect berry size distribution and bunch weight, in comparison with the other treatments. In average, the maximum exportable yield was obtained in the 110% ETc treatment. Exportable yield diminished 12% with application of 60% of ETc. Application of water over 110% ETc diminished yield around 10%. Probably, this was related to poor soil aeration. The water use efficiency changed, on the average, from 7 kg m-3 of exported fruit at 60% ETc to 2.3 kg m-3 with water applied at 150% ETc.

Even though storage condition of the fruit has an effect on consumption condition, the postharvest physiology has a mayor influence in the quality of the fruit. The objective of this work was the development of a model to predict the postharvest life of the fruit as the response to specific climate and agricultural practices (irrigation and nutrition). During 3 years (2010-2012) preharvest factors were characterized for 42 sites and their consequent postharvest evolution evaluated for fruit storability during 25, 35 and 45 days at 4-5°C. The data were collected during 3 seasons, and was analyzed through principal components (PCA) and multi-variable regression of the partial least squares (PLS). The postharvest condition of the fruit was affected by Ca and N in the pulp, spring irrigation, and oil content of the fruit. Water deficit above 40% of irrigation requirements affected the shelf-life of the fruit.

‘Hass’ avocado is the most important avocado variety cultivated worldwide. In Chile alone, there are nearly 40,000 ha, distributed between the IV and VI regions, with production areas located close to both the coast and to the hills. Given the increasing competitiveness of fruit export markets, the quality of organoleptic attributes is a key issue in consumer acceptance. The quality of avocados is related to many attributes, especially oil content and firmness (among others), and these attributes are influenced by storage, growing and environmental conditions, as well as the stage of maturity/ripening.

A field study was conducted in the Aconcagua Valley (Chile) with the cultivars 'Crimson Seedless' and 'Thomson Seedless', using linear variable differential transformers (LVDT), also called electronic dendrometers. Two irrigation treatments were employed: 100% ETc and 50% ETc. Four plants per treatment were equipped with LVDT both in the trunk and berries and their diameters were measured every 30 min. Stem, leaf and bunch water potentials (Ψ) were also measured. In both irrigation treatments, Crimson Seedless and Thompson Seedless trunk growth ceased at the beginning of veraison, independent of the plant water status. On the daily scale, trunk contraction and recovery were earlier than those of the berry. At berry stage I berry shrinkage began two to three hours later and recovered 7-8 hours later than the trunk. At fruit stage III, berry recovery began only two to five hours later than the trunk, probably due to phloem transport of water and sugars to the berries in that stage. There was no reverse water flow from the berries to the plant, because a water potential gradient (ΔΨ) favoring the berry was maintained.

In the Aconcagua Valley, Chile, a 5-year research (2007/2012), has been carried out to evaluate the response of table grape 'Thompson Seedless' vines to different volumes of irrigation water. The experimental site was a commercial orchard of 'Thompson Seedless' grafted on Freedom rootstock, located in the Aconcagua valley (70°41'23"W. Long. and 32°47'20.9"S. Lat.), Chile. Four irrigation treatments were applied: 60, 90, 120 and 140 percent of crop evapotranspiration (ETc) during the seasons 2007/08 to 2010/11, and 40, 54, 92 and 108% of Etc in the last season (2011/12). Soil water content was monitored with a capacitive probe in each treatment. Midday stem water potential was also measured. Soil available water as a result of irrigation treatments affected berry size distribution. A linear relationship between berry size and SAW was found. The bunch weight was also affected by a lower application of water (60% ETc). Maximum exportable yield was obtained in the 120% ETc treatment. Table grape production was lowered either by a water application of less than 90% ETc or more than 120% ETc. In the former case, yield reduction may be related to soil water deficit. In the latter case it may be related to poor soil aeration. The water use efficiency changed, on the average, from 7 kg/m3 of exported fruit at 40% ETc to 2.3 kg/m3 with water applied at 140% ETc.

The objective of this study was to define the soil available water depletion (SAWD) in avocado, in order to use it as a criterion for irrigation programs in soils of fine texture and low aeration capacity. To determine appropriately the fraction of soil SAWD we performed three independent trials: Trial 1: We evaluated two treatments: T1, irrigation to 100% ETc and then without irrigation for 13 days, until the SAWD reached 60%; and T2: daily irrigation replacing 100% of the evapotranspiration of the crop (ETc). Trial 2: We evaluated three fractions of SAWD before irrigating again: T1:5%; T2:30% and T3:60%. Trial 3: We monitored the SAWD variation in seven orchards of adult avocados. SAWD was monitored using a capacitive probe to determine which percentages of SAWD changed the velocity of water extraction by the trees. Decreases of SAWD up to 60% before irrigating did not affect the plant water status measured as midday stem water potential (MSWP). Also, stomatal conductance (gs) and yield was not affected. According to our results, avocado transpiration is maintained with low soil humidity. This may indicate that avocado has less stomatal regulation compared to other species. It could be related to the environmental conditions in which these species evolved. This characteristic of avocados, which may sometimes be a limiting factor, may provide an advantage in irrigation management in soils with low air capacity, since it will allow decreasing soil water content without producing stomatal closure, thus improving the oxygen flow in this type of soil.

The effect of flooding on young grapevine plants grafted onto two rootstocks: Harmony and Freedom was evaluated. Grafted and non-grafted plants were grown in plastic pots under normal and flooding conditions. Flooding condition was obtained by keeping the water three cm above the soil and the oxygen diffusion rate (ODR) was 0.2 μg O 2 cm -2 min -1 : In control ODR was 1.7 μg O 2 cm -2 min -1 . Net CO 2 assimilation and stomata conductance were evaluated in developing and mature leaves. In general, at the beginning of flooding, plants grafted on Harmony showed a rapid reduction in net CO 2 assimilation. This reduction reached a minimum after at seven days of flooding treatment. By contrast, the plant grafted on Freedom did not show any reduction on net CO 2 assimilation until seven days of flooding. This indicates that this last rootstock confers to the scion a tolerance to hypoxia. On the other hand, the reduction in net CO 2 assimilation was well correlated with dry matter production and leaf area in both rootstocks. Harmony grafted plants presented the highest reduction (54%) in dry matter accumulation, while Freedom grafted plants presented 36% of reduction. After the flooding treatment, a significant increase in the accumulation of P was found in plants grafted on Harmony. This raises questions on the role of this element in the plant metabolism under low oxygen conditions. Finally, after the results obtained in dry matter reduction under flooding condition, we conclude that in 'Sultanina' grafted plants, Freedom rootstock induced a better tolerance to hypoxia than Harmony. INTRODUCTION A low oxygen concentration in the soil produces an adverse environment in the rhizosphere which in turn induces hypoxia in roots, limiting growth and development of the root system (Drew, 1997; Sauter, 2013). Hypoxia is an important problem in the Aconcagua valley, where 30% of the Chilean table grape industry is concentrated. In this valley almost 70% of the soils have a high proportion of clay and present high bulk density, high soil compaction and low water infiltration (Ferreyra et al., 2011). These soil characteristics favor soil saturation during the growing season, limiting the soil air capacity, the root penetration and finally the grape production (Stępniewski and Stępniewska, 2009). One of the ways to reduce the effect of hypoxia is the use of adequate rootstocks, but in Chile this practice has not been extensively used because phylloxera is not a problem. At present almost 90% of the grapevine plantations in Chile are non-grafted (CIREN-ODEPA, 2008), however interest for grafting is rapidly increasing due to the nematodes attacks in the new plantations and the deleterious effects of abiotic stresses like drought (Iacono et al., 1998) and hypoxia (Bornscheuer, 2003). Harmony and Freedom are the most popular rootstocks used in Chile (Muñoz and

The effect of flooding on young grapevine plants grafted onto two rootstocks: Harmony and Freedom was evaluated. Grafted and non-grafted plants were grown in plastic pots under normal and flooding conditions. Flooding condition was obtained by keeping the water three cm above the soil and the oxygen diffusion rate (ODR) was 0.2 μg O2 cm-2 min-1: In control ODR was 1.7 μg O2 cm-2 min-1. Net CO2 assimilation and stomata conductance were evaluated in developing and mature leaves. In general, at the beginning of flooding, plants grafted on Harmony showed a rapid reduction in net CO2 assimilation. This reduction reached a minimum after at seven days of flooding treatment. By contrast, the plant grafted on Freedom did not show any reduction on net CO2 assimilation until seven days of flooding. This indicates that this last rootstock confers to the scion a tolerance to hypoxia. On the other hand, the reduction in net CO2 assimilation was well correlated with dry matter production and leaf area in both rootstocks. Harmony grafted plants presented the highest reduction (54%) in dry matter accumulation, while Freedom grafted plants presented 36% of reduction. After the flooding treatment, a significant increase in the accumulation of P was found in plants grafted on Harmony. This raises questions on the role of this element in the plant metabolism under low oxygen conditions. Finally, after the results obtained in dry matter reduction under flooding condition, we conclude that in 'Sultanina' grafted plants, Freedom rootstock induced a better tolerance to hypoxia than Harmony.

During the 2008/09 and 2009/10 seasons, net radiation (Rn), latent heat flux (LE), sensible heat flux (H), soil heat flux (G), and crop evapotranspiration (ETc =LE, where λ is latent heat of vaporization) were measured on a drip-irrigated Thompson Seedless vineyard trained on an overhead trellised system ("parronal español"). The experiment was located in Calle Larga, Aconcagua valley, Chile (32°52'40" S, 70°37'45" O, 795 m s.n.m.). LE and H were measured by an eddy correlation system, and reference evapotranspiration (ETo) was calculated using the FAO-Penman-Monteith method. Results indicated that the closure error (ratio of LE+H to Rn-G) decreased as canopy light interception increased (CLI). With 22% CLI closure error was around 20-30%. Over 74% CLI, closure error was around 10 to 20%. Higher closure error with low CLI can be attributed to errors on measurement of G. At 22% CLI the energy partition relative to Rn were 13, 45 and 13% for LE, H and G, respectively. With higher CLI ( 98%), LE, H and G were 81, 0.1 and 1% of Rn respectively. Derived crop coefficients (Kc = ETa/ETo) under an overhead trellised system are higher than those proposed by FAO 56 for table grapes, from near veraison to end of the season. Kc values from budbreak to harvest period increased linearly as CLI increased (Kc = 0.0137*CLI(%) -0.1492).