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Genetic Enhancement of Tomato Crop for Abiotic Stress Tolerance
Abstract
India being the second largest producer of tomato will still fall short of the country's requirement. The main concern is the decreasing productivity due to negative effects of environmental stresses. Production of tomato is subjected to many abiotic stresses, mainly heat and drought. In order to sustain tomato production with present day challenges, we need to have a thorough knowledge of the plant's reaction toward the stress and develop sufficient genetically enhanced varieties or hybrids which are tolerant and capable of mitigating the stress. Here we have made an attempt to address the challenge thrown to the breeders by the changing climatic scenario.
... Tomato is economically one of the most important vegetable crops (Venema et al., 2005) and is widely consumed worldwide (Sadashiva et al., 2013). In fact, as far as commerce is concerned, it ranks second after potato (Jaiswal et al., 2015), occupying an area of 5.0 × 10 6 hectares (ha) with an average production of 37 tons per ha worldwide (FAO, 2014). ...
... Tomato is sensitive to chilling like other plants that originating from subtropical regions (Zhang et al., 2004), and this limits its productivity and geographical distribution (Allen and Ort, 2001;Cao et al., 2015). The crop has an optimal mean daily temperature range between 20 and 25°C, while temperatures under 12°C reduce or inhibit growth (Cao et al., 2015;Sadashiva et al., 2013;Veal et al., 2007). In Southern Europe, seasonal crops such as tomato are usually transplanted to extend the period of cultivation; however, early transplant establishment constitutes a critical stage, exposing plants to the risk of naturally occurring chilling events (Javanmardi et al., 2013). ...
... Cellular membranes are the primary targets under low temperature stress (Gupta and Kaur, 2005;Sadashiva et al., 2013), triggering a cascade of events that induce gene expression modification resulting in physiological and morphological adaptation. Moreover, cold stress causes the production of reactive oxygen species (ROS) (Mittler, 2002) that can cause oxidative damage to DNA, proteins and lipids (Apel and Hirt 2004); on the other hand, ROS increase can modify multiple signaling pathways including early chilling stress response. ...
Six processing tomato seedlings, representative of cultivars widely cultivated over the last 80 years in Southern Europe, were compared to assess the physiological responses to chilling. Low temperature stress was applied for 24 h (1 °C, day and night). PEARSON, the oldest cultivar, reported the highest values of chlorophyll content both using DUALEX (ChlDX = 23.11) and SPAD (ChlSPAD = 35.27) and nitrogen balance index (NBIDX = 29.62) measured with DUALEX, before chilling stress. The cultivar E6203 was the least sensitive to chilling with the highest value of maximal photosystem II (PSII) efficiency (Fv/Fm2 = 0.64) at recovery and visual regrowth score (VS3 = 4.0) at regrowth period. As regards chilling tolerance in terms of maximal PSII efficiency, few differences were observed among the cultivars, apart from C33, that was the most sensitive. On the other hand, a better regrowth was recorded in the modern ones. Strong correlations were found between the different parameters investigated both before (SPAD and DUALEX) and after the chilling stress (maximal PSII efficiency, SPAD and electrolyte leakage). SPAD values at regrowth were shown to be a good indicator of tomato chilling status at regrowth period. Analysis of genetic similarity based on microsatellite markers clearly discriminated modern and old varieties according to the year of release. This information could be useful in breeding programs for new cultivars suitable for early transplant, when chilling injury can happen.
... chilense and L. esculentum var. cerasiforme are drought-tolerant species (Sadashiva et al., 2013). Researches are in progress to clarify molecular pathways on drought response of plants (Sadashiva et al., 2013), and miRNAs can be alternatives to identify drought metabolism, as they play crucial role on abiotic stress response regulating the stress-related mRNAs (Kumar, 2014). ...
... cerasiforme are drought-tolerant species (Sadashiva et al., 2013). Researches are in progress to clarify molecular pathways on drought response of plants (Sadashiva et al., 2013), and miRNAs can be alternatives to identify drought metabolism, as they play crucial role on abiotic stress response regulating the stress-related mRNAs (Kumar, 2014). Determination and functional characterization of stress-related miRNAs and target identification are important in breeding programmes and can contribute to developing new strategies for improving stress tolerance (Barrera-Figueroa et al., 2013). ...
Drought stress has adverse impacts on plant production and productivity. MicroRNAs (miRNAs) are one class of noncoding RNAs regulating gene expression post-transcriptionally. In this study, we employed small RNA and degradome sequencing to systematically investigate the tissue-specific miRNAs responsible to drought stress, which are understudied in tomato. For this purpose, root and upground tissues of two different drought-responsive tomato genotypes (Lycopersicon esculentum as sensitive and L. esculentum var. cerasiforme as tolerant) were subjected to stress with 5% polyethylene glycol for 7 days. A total of 699 conserved miRNAs belonging to 578 families were determined and 688 miRNAs were significantly differentially expressed between different treatments, tissues and genotypes. Using degradome sequencing, 44 target genes were identified associated with 36 miRNA families. Drought-related miRNAs and their targets were enriched functionally by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Totally, 53 miRNAs targeted 23 key drought stress- and tissue development-related genes, including DRP (dehydration-responsive protein), GTs (glycosyltransferases), ERF (ethylene responsive factor), PSII (photosystem II) protein, HD-ZIP (homeodomain-leucine zipper), MYB and NAC-domain transcription factors. miR160, miR165, miR166, miR171, miR398, miR408, miR827, miR9472, miR9476 and miR9552 were the key miRNAs functioning in regulation of these genes and involving in tomato response to drought stress. Additionally, plant hormone signal transduction pathway genes were differentially regulated by miR169, miR172, miR393, miR5641, miR5658 and miR7997 in both tissues of both sensitive and tolerant genotypes. These results provide new insight into the regulatory role of miRNAs in drought response with plant hormone signal transduction and drought-tolerant tomato breeding.
... Currently, tomato (Solanum lycopersicum L.) is considered among the most valuable and economically important horticultural crops (Fondio et al. 2013;Sadashiva et al. 2013), with an annual production of about 180 million tons in 2019 (FAOSTAT 2020). Its production shows an increasing trend with an overall global fruit yield of 182.3 million tons and 1,293,761 tons/year in Morocco in 2019 (FAOSTAT 2019). ...
The present work aimed to investigate the effect of potentially beneficial soil microorganisms in enhancing the tolerance of tomato plants against Verticillium wilt. The autochthonous mycorrhizal fungi "Rhizolive consortium" and plant growth-promoting rhizobacteria (PGPR) boost the growth and development of plants by providing well-adopted strategies and mechanisms to ensure good-quality production and protection to resist different pathogens including Verticillium dahliae. The application of these bio-agents alone and/or in combination with the pathogen was studied to evaluate their impact on tomato crops. In this study, eight treatments were applied: (i) Control, (ii) Rhizolive consortium (M), (iii) ER10 strain (B), (iv) combination of M and B (MB), (v) V. dahliae (V), (vi) Rhizolive consortium + V. dahliae (MV), (vii) ER10 strain + V. dahliae (BV), and (viii) Rhizolive consortium + ER10 strain + V. dahliae (MBV). Co-inoculation of Rhizolive consortium and ER10 strain significantly improved mycorrhizal frequency and intensity, growth and mineral nutrition of tomato plants. Furthermore, stomatal conductance and chlorophyll fluorescence were improved compared to the control. Moreover, the combination of these biostimulants reduced the disease severity and incidence by 26 and 28%, respectively, and the leaf damage index by 69% compared to plants inoculated with V. dahliae. In addition, the Rhizolive consortium alone or combined with ER10 strain resulted in improved antioxidant activities and stress markers. The synergistic interaction between Rhizolive consortium and ER10 strain promoted tomato yield and fruit quality compared to the control. The results highlight the importance of considering these beneficial soil microorganisms to promote plant resistance to Verticillium wilt disease.
... In tomato, various sources which are resistance to drought are identified in wild taxa like LAO429 (S. cheesmaniae Ecuador), LA1334 (S. lycopersicum var. cerasiforme Peru), RF4A (S. pennellii IIHR India), etc. which can be used in the breeding programs to develop drought resistant varieties of tomato [86]. Tests for drought stress tolerance shows that under the drought stress conditions S. pennellii has good ability to increase the water use efficiency when compared to cultivated S. lycopersicum. ...
Future climate change scenarios have become a major threat and limitation for global food production. The rise in greenhouse gases and temperature throughout the globe has caused perturbance in the natural seasonal cycles. This causes a threat to nutritional and calorific food security for the ever-increasing population in the South Asian Countries. Reduction in the amounts of rainfall in the tropics and subtropics has increased the occurrence of drought leading to more frequent water stress affecting the production of crops, including vegetables, which are predominantly grown in the tropical and sub-tropical regions. India is the second-largest producer of vegetables in the world and heavy consumer of vegetables. The mini-review focused on drought stress effects on the vegetable production and photosynthesis, transpiration, water uptake and other metabolic and developmental processes. Grafting, breeding, cultural and biotechnological strategies are used to combat drought stress and will be used in the future to ease the harmful effects of drought stress.
... Tomato (Solanum lycopersicum L.) is economically one of the most important horticultural crops and it is widely consumed worldwide (Sadashiva et al., 2013;Venema et al., 2005), being second only to potato in world commerce (Jaiswal et al., 2015). The organic cropping system (OCS) met significant interest in many areas of the world (De Ponti et al., 2012) due to its ability to increase agricultural sustainability and biodiversity (Mehdizadeh et al., 2013). ...
... Tomato (Solanum lycopersicum L.) is economically one of the most important horticultural crops and it is widely consumed worldwide (Sadashiva et al., 2013;Venema et al., 2005), being second only to potato in world commerce (Jaiswal et al., 2015). The organic cropping system (OCS) met significant interest in many areas of the world (De Ponti et al., 2012) due to its ability to increase agricultural sustainability and biodiversity (Mehdizadeh et al., 2013). ...
... Tomato (Solanum lycopersicum L.) is one of the most important horticultural crops, within which it ranks second after potato in the world commerce (Sadashiva et al., 2013;Ronga et al., 2017). Cultivated on 4.8 × 10 6 hectares (ha) and with an average yield of 37 tons ha −1 (FAO, 2016), tomato is widely consumed also for its content in lycopene and other valuable anti-oxidant compounds (Raiola et al., 2014). ...
Blossom-end rot (BER) is a physiological disorder causing severe losses in tomato crops. Despite its economic importance and the large collection of studies concerning its onset, BER occurrence is still poorly understood, making its prediction and prevention very difficult. Currently, two theories are accredited to explain the BER onset: the first one identifies a reduced root uptake and an aberrant regulation of cellular partitioning of calcium as the major physiopathy agent, while the second one hypothesizes a primary role to abiotic stresses, as they induce reactive oxygen species (ROS) production in the plant, leading to membranes disintegration and loss of cell turgor. To date, there are no unequivocal proofs that allow us to definitively go beyond one of the two hypotheses. Rather, a multitude of genetic, physiological and environmental factors form a complex network of interactions and synergies contributing to BER occurrence. This is why the "multi-disciplinary approach" is maybe the most appropriate one to understand this physiopathy and to develop new and effective BER-contrasting tools with genetic and agronomic methods. This review adopts this kind of approach to investigate the causes of BER and to describe the practices preventing its occurrence, possibly providing the most complete compendium about this disorder to date.
... Each variety preserved by one or more farmers can be deemed to be a subpopulation with high levels of genetic differentiation [21]. This is why it is important to characterize the different genepools of the Latin American tomato by focusing on the fruit [22], tolerance to abiotic [23,24] and biotic stress [25,26], phenotypic and genetic diversity [27,28], performance stability or genotype-environmental interaction [5,6], and even aspects relating to consumer preference [29] in order to describe the phenotypic and genetic diversity of the tomato. In terms of the genepools found in El Salvador, studies on phenotypic and genetic diversity are difficult to find or do not exist. ...
The agromorphological traits and phenotypic variation of mineral content in the fruit were evaluated in eleven tomato accessions from nine communities in El Salvador. The tomato collection was cultivated in a greenhouse with a randomized complete block design with three replications. Plant phenological and fruit traits, as well as the mineral content, were evaluated using atomic-absorption and ultraviolet-visible spectroscopy. In the analysis of variance, significant differences (p < 0.01) among the accessions were determined for agromorphological traits and all mineral elements except Cu. Plant height at 30, 60 and 90 days after transplant, days to flowering and maturating of the fruits, and the number and weight of fruits per plant were useful variables for describing the phenotypic divergences among the tomato accessions. In terms of mineral content, the differences among the accessions were based on Mg, P, S, Fe, Zn and Mn. The weights of the fruits per cluster and per plant and fruit weight presented negative correlations with Ca, Mg, Fe and P (r = -0.67 to -0.71, p < 0.05) and a positive correlation with Na (0.63).
Vitamin K epoxide reductase (VKOR) exists widely in the chloroplasts of higher plants and plays important roles in redox regulation. However, investigations of plant VKOR function have primarily focused on VKOR from Arabidopsis, and knowledge concerning this function is therefore quite limited. In the present study, Solanum lycopersicum was used to study the function of VKOR. Transcription level analysis revealed that SlVKOR expression was up-regulated by salt or drought stress. To investigate the function of SlVKOR in plants further, we generated sense and antisense transgenic Solanum lycopersicum homozygotes at T2 generation plants. Compared to WT plants, the leaf-discs of the SlVKOR over-expression plants retained a much higher percentage of chlorophyll after salt or drought treatment; whereas the antisense transgenic plants displayed an opposite response. The over-expression plants displayed lower levels of H2 O2 and O2 ·(-) than WT plants, whereas antisense plants accumulated considerably more H2 O2 and O2 ·(-) . The activities of reactive oxygen scavenger enzymes, including SOD, POD, APX, and CAT, were consistent with the accumulation of reactive oxygen species. Based on these results, we suggest that SlVKOR is involved in resistance to salt or drought stress.
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Fruit set of 6 genotypes of tomato ( Lycopersicon esculentum Mill) ranged from 50% (BL6807) to l% (L401) in the summer and from 93% (BL6807) to 78% (L401) in the spring. Flower drop was significantly higher in the summer for each cultivar, except for BL 6807 where there was no difference. All genotypes had significantly more underdeveloped ovaries in the summer and generally less normal pollen, smaller fruit, and less seed per fruit. Although these variables were related to low fruit set at high temperatures, they were not primarily responsible for this character.
Leaf heat tolerances of ‘Saladette’ (heat tolerant) and ‘UC-82B’ (less heat tolerant) tomato ( Lycopersicon esculentum , Mill) were evaluated after heat acclimation. When plants of both genotypes were grown in a temperature regime below 30°C, there was no difference in heat tolerance. When plants of both genotypes were exposed to a temperature regime of 35° (day/night), ‘UC-82B’ could reach a higher level of heat tolerance, similar to ‘Saladette,’ but ‘UC-82B’ required 6 cycles of high temperature exposure, whereas ‘Saladette’ needed only a single cycle.
Sugars, acids and their interactions were important to sourness, sweetness, and overall flavor intensity in tomato ( Lycopersicon esculentum Mill.). Fructose and citric acid were more important to sweetness and sourness than glucose and malic acid, respectively. The pH was a better objective measure of sourness than titratable acidity. An interaction between glucose and citric acid on sweetness was observed. Quantitative differences in 11 volatile compounds were found among the cultivars. Several of these volatiles were significantly related to variation in the flavor characteristics studied. Three compounds (peaks (20–21), 51, and 75) appeared to be more important to the “tomato-like” character.
The effect of temperature on CO 2 fixation was studied in 2 tomato ( Lycopersicon esculentum Mill.) cultivars; the heat-sensitive “Roma VF” and the heat-tolerant “Saladette". A decrease in apparent photosynthesis was found in both cultivars after plant exposure for various lengths of time to temperatures of 35° to 40°C. An increase in temperature also increased transpiration and raised the CO 2 compensation point. The decrease in photosynthesis after a short exposure to high temperature was due to an increase in mesophyll resistance and, to a lesser extent, to an increase in stomatal resistance to CO 2 diffusion. Saladette was less affected by high temperature and had a slightly greater photosynthetic capacity than the heat-sensitive Roma VF, after pretreatment at high temperature.
The result series of our irrigation experiment, made between 1977-1997, using two tomato varieties, can demonstrate the effect of different cultivation and environmental factors on yield. The yields of two studied tomato varieties are presented by the different fruit size, yield results of 4 different water supplies and yield results during 21 years. According to the average results of these 21 years, the increasing of yield quantity was observed in case of two varieties thanking to the irrigation, which proves the necessity of regular irrigation. According to the yield quantity of non irrigated plants and the effect of irrigation different crop year categories can be assigned. In most of the years (app. 55-66 %) regular irrigation is required but in part of the years (20-25 %) irrigation can be ineffective. The accumulated amount of rainfall during growing season, taken as function of accumulated amount of average temperature, can suitably present the environmental conditions of tomato and also notice the expectable crop results. Irrigation can be more important between 20 June and 10 August.
Environmental-induced phenotypic variation in plants is often considered to be a functional response that maximizes fitness in heterogeneous environments. Lycopersicon chilense, a tomato species endemic to Atacama Desert, shows altitudinal phenotypics variations in their natural environments, which could be due to different soil water availabilities. It is hypothesized that (a) seeds coming from populations of different environments, cultivated in the same environment, will have similar phenotypes, if populations are not genetically differentiated, and that (b) the different populations subjected to two drought levels should vary their phenotypic constitution with respect to the control groups. The responses of twenty phenotypic traits to different irrigation levels were studied in nine wild populations of Lycopersicon chilense. Seeds were collected from populations along an altitudinal gradient (from 20 m to 3,075 m), transferred to a common environment and grown under three soil water conditions: low (80 % FC), moderate (40 % FC) and severe (20 % FC). In spite of the climatic differences in their natural habitat the phenotypic responses of plants growing in the same environment was similar in the nine populations. Significant differences among populations were only observed in three out of twenty traits (fruit fresh weight, fruit volume and number of seeds per fruit). Soil water deficit induced a phenotypic response in twelve characters; among these: root dry weight, cover, number of seeting fruits and number of seeds per fruit showed the highest significance. An interaction between population and drought treatment was found only for fresh weight of fruits, fruit volume and number of seeds per fruit. Our data indicate that the phenotypic response does not differ among populations growing under similar environmental conditions. Probably the phenotypic response of L. chilense in their natural habitats is related to physiological and metabolic adjustment rather than genetic variation.
Yield and quality are the primary goals of most plant breeding programs. Both of these general characteristics are multifaceted and extremely complicated. This complexity and a frequent negative relationship between them makes it difficult to deal successfully with them simultaneously in a breeding program.
Selected F 3 and F 4 lines of different origin were evaluated at high temperature (26° night and 35°C day) in the greenhouse along with several known heat-sensitive and heat-tolerant tomato ( Lycopersicon esculentum Mill.) cultivars. A number of the selected lines had fruit set comparable to the tolerant cultivars Saladette, Ohio 7663, BL 6807, and Chico III. The expected greater fruit set of the tolerant cultivars vs. that of the sensitive cultivars was observed. High fruit set in this study was not associated with high seed number in the majority of tolerant cultivars evaluated.
Field studies were conducted on a Typic Xerorthents Entiosols soil (Hanford sandy loam) to determine the response of two cultivars of processing tomatoes ( Lycopersicon esculentum Mill.) to trickle irrigation applied at three percentages of evapotranspiration (ET) to either the top of the plant row or between the beds using a traveling irrigation system. Irrigation was terminated when fruits were either 30% or 70% red (14 or 7 days before harvest). Yields of red tomatoes and total tomatoes increased with increasing trickle irrigation water. The concentrations of soluble solids (SSC) and total solids (TS) and pH decreased with increasing trickle irrigation rates, while color, fruit size, and acidity increased, as did the yield of SSC and TS per hectare. Placement of trickle irrigation on the plant row was more favorable than placement in the furrow between the beds for yield and quality characteristics. Trickle irrigation to 70% ET terminated 7 days before harvest produced responses similar to conventional furrow irrigation. Although statistically these treatments could not be compared directly to conventional furrow, all traveling trickle irrigation rates were superior in water use efficiency to that of the conventional furrow irrigation. Trickle irrigation rates of 35% ET, 70% ET, and 105% ET did not differ in water use efficiency. Chemical names used: 2( a -naphthoxy)- N , N -diethyl propionamide (napropamide); S -propyl butylethiocarbamate (pebulate).
Fruit set and fruit development of seeded, naturally seedless, and growth-regulator-induced seedless tomatoes ( Lycopersicon esculentum Mill. cv. Azes), were examined under 17°, 22° and 27°C day temperatures, all with natural daylight and constant 10° night temperature. The best seeded fruit set and development were at 22° day temperature. A high positive correlation (r = 0.9) was found between number of seeds per fruit and fruit size with a day temperature of 27°; there was a lower but still positive correlation with lower temperature. Seedless fruit developed, and attained marketable weight (above 40 g), only when the inflorescences had been sprayed with 20% β naphthoxyacetic acid (B-NOA). Day temperature also affected fruit shape. At 27° the fruit was almost globe-shaped, but at the lower temperatures the fruit became more oblate. Fruit puffiness was particularly related to lack of fertilization resulting from flower emasculation or to lower day temperature affecting set of seed-deficient fruits. “No-Seed” treatment led to green jelly production and pointed blossom-end in fruits, under all temperature regimes.
A study was undertaken to determine a) if genotypic responses for fruit set and pollen viability in tomatoes ( Lycopersicon esculentum Mill.) exposed to high temperatures are related, and b) if pollen viability at high temperature could be used to screen tomato plants for better performance in high-temperature environments. Fruit set, pollen germination, and pollen tube length varied among tomato sources exposed to 40C for 60 min, and both pollen germination ( r = 0.988***) and pollen tube length ( r = 0.815**) correlated positively with fruit set. Differentiation among tomato sources for increased pollen viability at high temperature was accelerated by increasing the temperature at which flowers were exposed from 40 to 48C. Pollen viability has a major role in determining the fruit set of tomatoes at high temperatures and can serve as a basis of screening for tomato plants that will potentially produce higher fruit yield in high-temperature environments.
High-temperature responses of heat-tolerant tomato ( Lycopersicon esculentum Mill. cvs. Saladette, PI 262934, BL6807, S6916, CIAS161, and VF36) were studied at 38/27°C day/night temperature. Flower production was reduced in all cultivars except BL6807 which partitioned a greater proportion of total assimilates to the flowers. Only ‘Saladette’ and VF36 showed a total lack of stigma exsertion, which in effect is functional male sterility. Pollen production was reduced in all cultivars, and there was a lack of pollen dehiscence. Several techniques were used to evaluate gamete viability. There was poor agreement among the 3 methods used to assess pollen viability. ‘Saladette’ suffered the least reduction for in vitro germination but had the greatest loss in seed set when high-temperature pollen was used. Seed set is probably the most reliable method to measure gamete viability. CIAS 161 and S6916 had the least reduction in pollen viability according to seed set criteria. Ovule viability is much more difficult to adequately evaluate. According to seed set criteria PI 262934 ovules suffered the least damage due to high temperatures. Whether the male or female gamete was affected more severely depended on genotype. Pollen viability was greatly reduced in PI 262934 but ovule viability was less severely affected. In BL6807 ovule viability was more severely reduced than pollen viability.
Heritabilities (h 2) and genetic correlations between percent fruit set, yield, and fruit weight were estimated from one summer planting each in Florida and Puerto Rico of 100 S, tomato (Lycopersicon esculentum Mill.) families from a synthetic population. Single-location h 2 was high for all traits. Across-locations h 2 was low for yield, intermediate for fruit set, and high for fruit weight. Genotype × environment interaction (G × E) was 1) the only significant component of variance for yield, 2) somewhat important for fruit set, and 3) not an important variance component for fruit weight. The greater importance of genetic variance compared to G × E variance explains why across-location heritabilities for fruit weight and fruit set were high. Genetic correlations between fruit set and weight were strongly negative, while those between yield and set were large and positive. Yields under high temperatures may increase with selection for fruit set, but a reduction in fruit weight would be expected in this population and those with similar genetic correlations.
The salt tolerance locus SOS1 from Arabidopsis has been shown to encode a putative plasma membrane Na /H anti-porter. In this study, we examined the tissue-specific pattern of gene expression as well as the Na transport activity and subcellular localization of SOS1. When expressed in a yeast mutant deficient in endogenous Na transporters, SOS1 was able to reduce Na accumulation and improve salt tolerance of the mutant cells. Confocal imaging of a SOS1–green fluorescent protein fusion protein in transgenic Arabidopsis plants indicated that SOS1 is localized in the plasma membrane. Analysis of SOS1 promoter–-glucuronidase transgenic Arabidopsis plants revealed preferential expression of SOS1 in epidermal cells at the root tip and in parenchyma cells at the xylem/symplast boundary of roots, stems, and leaves. Under mild salt stress (25 mM NaCl), sos1 mutant shoot accumulated less Na than did the wild-type shoot. However, under severe salt stress (100 mM NaCl), sos1 mutant plants accumulated more Na than did the wild type. There also was greater Na content in the xylem sap of sos1 mutant plants exposed to 100 mM NaCl. These results suggest that SOS1 is critical for controlling long-distance Na transport from root to shoot. We present a model in which SOS1 functions in retrieving Na from the xylem stream under severe salt stress, whereas under mild salt stress it may function in loading Na into the xylem.
Hybrids With Other Solanum Species In contrast to the normal meiosis of hybrids within Lycopersicon, meiosis in hybrids involving the more distantly related Solanum species is partially disrupted. Observations in this area are based primarily on F1 L. esculentum x S. lycopersicoides hybrids, of which the first were synthesized by Rick (1951). Detailed studies were conducted on comparative chromosome morphology and associations in the 2x and 4x intergeneric hybrids (Menzel 1962, 1964, Menzel and Price 1966). Chromosome behavior during early prophase of the 2x hybrid is relatively normal: chromosomes are completely synapsed and form normal synaptonemal complexes at pachytene. However, occasional inversion or deficiency configurations are observed, and the total pachytene complement length of S. lycopersicoides is nearly 1.5 times that of the cultivated tomato. Chromosomes 4, 9, and 10 of S. lycopersicoides were found to be longer than the corresponding chromosomes of L. esculentum, and the resultant bivalents showed unequal pairs. During meiosis, 2x hybrids undergo reduced chiasma formation and produce about four univalents/cell at metaphase I. In 4x allotetraploids, pairing occurs preferentially among homologous chromosomes, resulting in mostly bivalents and a few multivalents. The 4x hybrids also exhibit greater pollen fertility than diploids, and produce a few viable seeds. In allotriploid (sesquidiploid) hybrids, consisting of two genomes of L. esculentum and one of S. lycopersicoides, preferential pairing of the L. esculentum homologues produces 12 bivalents, with the S. lycopersicoides chromosomes forming 12 univalents (Rick et al. 1986). In addition, the condensation of S. lycopersicoides chromosomes during early diakinesis of the sesquidiploids is significantly delayed with respect to their L. esculentum counterparts. These observations of incomplete chromosome pairing and lack of synchronization during meiosis indicate the chromosomes of L. esculentum and S. lycopersicoides are homeologous.
A short period at an average temperature of 10° C. during the early growth of tomato plants increased the number of flowers on the first inflorescence. The yield of these plants, whose vegetative apex was removed after the first inflorescence, was approximately 25% greater than that of similar unchilled controls. Fruit number was increased still more ; average fruit weight diminished, and there were fewer very large fruit of low market value. Similar increases in yield were obtained from plants sown throughout the year, except from a September sowing when there was no increase. Chilling delayed harvesting by about four days with summer sowings and rather more in winter, but had little effect on the duration of the harvesting period.Increase in flower number may not have been the only cause of the increased yield. The possibility of a direct effect of the cool period on yield is discussed.The cultivar Minicraigella was more suitable than Minipotella for growing as a single-inflorescence plant since it produced fewer oversize fruit and the fruit ripened more quickly.
Two crops of tomatoes, grown in bags of peat, were supplied with 60,80,100 and 120% of the water requirement estimated from solar radiation integrals for 12 weeks after planting. Restricting water to 60% and 80% of the requirement controlled vegetative vigour but reduced final yield by about 20% and 4% respectively. These decreases were mainly because of a reduction in fruit size rather than number. Overwatering had little effect on yield but caused Mn deficiency. As restricted watering reduced the water content of the fruit, so.the dry matter, sugar, acid and potassium concentrations in the fresh material increased; this was particularly marked in plots receiving only 60% of the water requirement. The response to the treatments disappeared 4-5 weeks after they were discontinued. Retention of six extra leaves in one crop had no effect on yield. The data suggest that watering should be restricted to 80% or less of the estimated requirement in order to achieve a significant improvement in the flavour components of the fruit.
To reduce stem elongation in young cucumber and tomato plants, the effect of a low- temperature pulse (LTP) in connection with day break was investigated. For cucumber an LTP at the end of the night was superior to an LTP application at the start of the daily light span or at the time of change-over, and reduced the final plant height by 24% compared with the control plants. An LTP at the beginning of the daily light period reduced tomato plant height by 28%. In both species additional effects of ah LTP application, such as reduced plant growth (dry weight) and development (number of leaves, leaf-petiole length), were also observed. In tomato flowering was delayed. Consequently, time to first harvest was delayed. However, LTP affected neither early yield nor quality of tomatoes or cucumbers.
Experiments in glasshouse and controlled environment facilities investigated the effect of different fruit removal and lighting/shading treatments on the pattern of tomato yields. While the removal of flowering trusses resulted in a yield loss about eight weeks later, there was little loss in cumulative yield as assimilates were distributed to neighbouring trusses. In the growth room experiment, increased photosynthetic photon flux density (PPFD) for one week resulted in a period of increased yield from 4-6 weeks after the start of the treatment, followed by suppressed yields due to smaller fruits on subsequent trusses. However, neither fruit load nor assimilate availability appeared to be responsible for the fluctuations in yield recorded within the glasshouse crop. In this experiment fruit size remained fairly consistent (except when fruit removal treatments were applied), whereas the number of fruits picked per week exhibited much greater variability. This was the case even when all trusses were pruned to leave five fruits, and so was not due to a cycle in the number of fruits set per truss. The flushes in yield were found to be a consequence of a hastening of fruit maturation.
Fireball, Hot Set and Porter were compared at 35 degrees C. day and 25 degrees C. night temperatures and at 22 degrees C. day and 18 degrees C. night temperatures. In the high-temperature conditions, Porter gave the highest yield of fruit. At the lower, more normal temperature for tomato growing, Fireball had the highest fruit yield and Porter the lowest. (Abstract retrieved from CAB Abstracts by CABI’s permission)
To assess whether cycles in the weekly pattern of tomato yields were due to the pattern of fruit load on plants, truss-removal and truss-pruning treatments were applied to individual rows within glasshouse compartments. When the pattern of fruit load was stabilized by pruning all trusses to five fruits, fruit size increased although the pattern of yield was similar to that from control rows. Furthermore, imbalances in fruit load caused by truss removal did not cause cyclical fruit production. The effect of temperature on the pattern of yield was investigated by raising air temperature within compartments by about 4.5 K for one week on two occasions. High yields were initially recorded following the start of the high temperature pulse but low yields were subsequently recorded. Overall, there was no significant effect of the treatment on cumulative yields over the course of the experiment. The results show that changes in air temperature are important in determining the pattern of tomato yields. Fruit temperatures were recorded with thermal-imaging equipment and thermistor sensors inserted into fruits. Fruit temperatures in excess of 35°C were recorded, although fruit temperatures were only slightly above air temperatures when averaged over longer periods. Fruits at the south end of the rows were on average 1.9 K warmer than the air compared with 0.9 K warmer in the middle of the rows. For accurate predictions of the pattern of yield, fruit temperatures should be considered.
Crop-scale and controlled environment experiments were carried out to explore the effects of short periods or "pulses" of high temperature on fruit quality defects, uneven ripening and softness for two standard round UK tomato cultivars Solairo and Espero. Elevated temperatures were achieved by manipulating glasshouse heat and vent set points. Heat pulses were applied over 3 or 7 d to explore the impacts of duration, in 1999, and magnitude for a range of mean temperatures 20.4 (control), 22.2, 24.2 and 25.9°C over 3 d in 2000. Fruit defects and yields were significantly increased in the week immediately following the end of a heat-pulse treatment. This demonstrated that i) the development of uneven ripening and softness was confined to fruits between mature green and colour stage 4/5 and that ii) the potential commercial impact of these defects was compounded by the higher yields. Pulse durations of 7 d compared with 3 d exacerbated the incidence of uneven ripening and increased yield but had little additional effect on fruit softening. Strong positive linear relationships were found for the dependence between the key fruit defects and pulse magnitude in the range 20.4-25.9°C. The incidence of uneven ripening increased at a rate of 2.7 units of score and fruit firmness decreased by 0.07 N mm-1 per °C rise in mean pulse temperature. Fruit detached at mature green and placed in controlled environment conditions at constant light and humidity with air temperatures of 20.2, 22.9 and 26.8°C exhibited similar incidences of defect compared with attached fruits sampled from the crop-scale experiments. Future studies could utilise the detached fruit model system to elucidate the mechanisms involved in high temperature induced softness and uneven ripening. To provide an estimate of commercial damage, relationships between percentage Class I uneven ripening fruits and pulse temperature and magnitude were formulated. A heat-pulse lasting 3 d and with a mean temperature of 23.0°C was sufficient to cause a 10% loss of Class I fruit. This temperature regime was lower than previously considered harmful by growers. Implications for predicting the likely impact of high temperature events are discussed.
November-sown tomato crops in NFT were grown at 11–16°C night air temperatures to investigate the possibility of using lower temperatures in order to save fuel. Fruiting was delayed at the lower air temperatures but the final yield and total crop values were increased, provided the lower temperature was restricted either to the period up to or following the onset of fruit picking. The former was preferable because more fuel was saved. The time intervals between the flowering of successive inflorescences and the time between flowering and fruit ripening within an inflorescence depended on air temperature, both processes having a temperature coefficient (Q10) of 1.7. The effect of low air temperature regimes on these two components of crop production is therefore predictable. Root temperatures were increased by up to 12°C above the ambient of ≃ 15°C, either from flowering to picking or from picking onwards in various combinations with the air temperatures. Increasing root temperature up to picking resulted in small reductions in yield and quality of early fruit. During the fruiting phase, however, root heating increased final yield by about 10% over 20 weeks of picking. The economic data suggest that lower night air temperatures than those currently used and higher root temperatures, related to growth phase, would increase the profitability of the tomato crop.
The response of glasshouse grown tomatoes, cv. Counter, to day/night temperature regimes was examined in two consecutive years. In both years three day/night temperature regimes, with the same average 24-hour temperature, were applied in duplicate, i.e. high/low, equal, and low/high. Differences in temperature were maintained from three days after planting (4 December 1984 and 3 February 1986) until 13 May 1985 and 1 May 1986, respectively. Plant development (increase in number of trusses) was not affected.by the temperature regime. Growth in length of the stem was strongly reduced by a lower day temperature. In the first experiment the crop at the low day temperature treatment was damaged by leaf scorch, most likely caused by low transpiration. Consequently, early yield was lower for this treatment. In the second experiment no leaf scorch occurred and no significant differences in early yield were found. Final yield and average fruit weight, until 1 July for both experiments, were higher at the higher night temperature. Shelf life of the fruits and internal quality was not influenced by the temperature regime. Thus, the length of a tomato plant can be manipulated by the difference between day and night temperature, while development and early yield depend greatly on the average 24-hour temperature. Final yield can be higher at higher night temperature and the same average temperature because the crop is more robust. Temperature control based on average 24-hour temperat-ure can be used to minimize energy. consumption and, together with other growth factors, to optimize financial yield.
Volatile components of field-and glass greenhouse-grown tomatoes (Lycopersicon esculentum MILL., variety, V. R. Moscow) of different maturities were studied by gas-liquid and thin-layer chromatography. The following components were separated and identified: isobutyl alcohol, isopentyl alcohol, hexyl alcohol, 2-methyl-3-hexanol, isovaleraldehyde, caproaldehyde, benzaldehyde, furfural, isopentyl acetate, isopentyl butyrate, isopentyl isovalerate, butyl hexanoate, hexyl hexanoate, methyl salicylate and α-pinene. Chromatograms were consistent for both field-and greenhouse-grown tomatoes at all stages of maturity. Except for isovaleraldehyde and hexyl alcohol, the biosynthesis of volatile components increased along with the growth of fruit. Isovaleraldehyde and hexyl alcohol, presumed to give the "green leafy" aroma of tomatoes, were found to be in their highest concentrations at the breaker and the large-green stages, respectively.
In a study carried out at Viterbo, 9 drip irrigation treatments and 3 fertilization treatments were compared in a split-plot experiment. Water deficits were imposed by reducing irrigation volumes to 50% or 75% of crop évapotranspiration in 2 growth periods: before or after fruit set. Irrigation deficit in the 1st growth period reduced the number of flowers leading to a decrease in the number of fruits and in the marketable yield. Water deficits improved the quality of fruits increasing soluble solids and acidity. Reducing irrigation by 25% before fruit set and by as much as 50% in the fruit development and ripening stages resulted in no significant decrease of soluble solid yield. Fertilization affected mainly plant vegetative growth, increasing LAI and biomass.
An analysis of major US crops shows that there is a large genetic potential for yield that is unrealized because of the need for better adaptation of the plants to the environments in which they are grown. Evidence from native populations suggests that high productivity can occur in these environments. Genotypic selection for adaptation to such environments has already played an important role in agriculture, but the fundamental mechanisms are poorly understood. Recent scientific advances make exploration of these mechanisms more feasible. -from Author
This chapter evaluates traits for improving crop yield in water-limited environments. The chapter describes the components of yield and the determinants of survival against which the proposed and demonstrated contributions by traits are critically assessed. Both modern and subsistence agriculture are differentiated mainly by the degree of risk that can be tolerated. Many traits have been proposed for improving the performance of drought-affected crops. Putative traits are more effective in enhancing drought resistance and contributing to grain yield in water-limited environments. The potential value of a trait depends upon the crop and the moisture environment in which it is grown. The chapter presents simulation models, which are very powerful tools for critically assessing the value of putative traits. However, more work is needed in the development and testing of suitable models, and in their application for this purpose. Use of near-isogenic populations as opposed to isogenic lines also appears to hold great promise.
Tomatoes are grown in the field wherever climatic conditions will permit economic yields to be attained. Field-produced fruit is used for consumption fresh and for processing. In recent years there has been a considerable increase in land area used for tomato production (Table 13.1), ranging from about 15% in China. Greece. India and North Africa up to 40% in Cuba, Indonesia and West Africa. The extra fruit is mainly intended for export to Western Europe, USA and Canada. In many countries there has also been a marked improvement in average yields and quality which are directly attributable to improved understanding and utilization of modern technology.
Desiccation is the extreme form of dehydration. Tolerance of desiccation is acquired by seeds and in resurrection plants, a small group of angiosperms. Desiccation tolerance is the result of a complex cascade of molecular events, which can be divided into signal perception, signal trans-duction, gene activation and biochemical alterations leading to acquisition of tolerance. Many of these molecular processes are also observed during the dehydration of non-tolerant plants. Here we try to give an overview of the gene expression programmes that are triggered by dehydration, with particular reference to protective molecules and the regulation of their expression. Potential transgenic approaches to manipulating stress tolerance are discussed.