Heat-tolerant Tomato Research Articles

Drought stress had a predominant effect over heat stress on three tomato cultivars subjected to combined stress

BackgroundAbiotic stresses due to environmental factors could adversely affect the growth and development of crops. Among the abiotic stresses, drought and heat stress are two critical threats to crop growth and sustainable agriculture worldwide. Considering global climate change, incidence of combined drought and heat stress is likely to increase. The aim of this study was to shed light on plant growth performance and leaf physiology of three tomatoes cultivars (‘Arvento’, ‘LA1994’ and ‘LA2093’) under control, drought, heat and combined stress.ResultsShoot fresh and dry weight, leaf area and relative water content of all cultivars significantly decreased under drought and combined stress as compared to control. The net photosynthesis and starch content were significantly lower under drought and combined stress than control in the three cultivars. Stomata and pore length of the three cultivars significantly decreased under drought and combined stress as compared to control. The tomato ‘Arvento’ was more affected by heat stress than ‘LA1994’ and ‘LA2093’ due to significant decreases in shoot dry weight, chlorophyll a and carotenoid content, starch content and NPQ (non-photochemical quenching) only in ‘Arvento’ under heat treatment. By comparison, the two heat-tolerant tomatoes were more affected by drought stress compared to ‘Arvento’ as shown by small stomatal and pore area, decreased sucrose content, ΦPSII (quantum yield of photosystem II), ETR (electron transport rate) and qL (fraction of open PSII centers) in ‘LA1994’ and ‘LA2093’. The three cultivars showed similar response when subjected to the combination of drought and heat stress as shown by most physiological parameters, even though only ‘LA1994’ and ‘LA2093’ showed decreased Fv/Fm (maximum potential quantum efficiency of photosystem II), ΦPSII, ETR and qL under combined stress.ConclusionsThe cultivars differing in heat sensitivity did not show difference in the combined stress sensitivity, indicating that selection for tomatoes with combined stress tolerance might not be correlated with the single stress tolerance. In this study, drought stress had a predominant effect on tomato over heat stress, which explained why simultaneous application of heat and drought revealed similar physiological responses to the drought stress. These results will uncover the difference and linkage between the physiological response of tomatoes to drought, heat and combined stress and be important for the selection and breeding of tolerant tomato cultivars under single and combine stress.

Identification of miRNAs and their targets in wild tomato at moderately and acutely elevated temperatures by high-throughput sequencing and degradome analysis.

MicroRNAs (miRNAs) are 19–24 nucleotide (nt) noncoding RNAs that play important roles in abiotic stress responses in plants. High temperatures have been the subject of considerable attention due to their negative effects on plant growth and development. Heat-responsive miRNAs have been identified in some plants. However, there have been no reports on the global identification of miRNAs and their targets in tomato at high temperatures, especially at different elevated temperatures. Here, three small-RNA libraries and three degradome libraries were constructed from the leaves of the heat-tolerant tomato at normal, moderately and acutely elevated temperatures (26/18 °C, 33/33 °C and 40/40 °C, respectively). Following high-throughput sequencing, 662 conserved and 97 novel miRNAs were identified in total with 469 conserved and 91 novel miRNAs shared in the three small-RNA libraries. Of these miRNAs, 96 and 150 miRNAs were responsive to the moderately and acutely elevated temperature, respectively. Following degradome sequencing, 349 sequences were identified as targets of 138 conserved miRNAs, and 13 sequences were identified as targets of eight novel miRNAs. The expression levels of seven miRNAs and six target genes obtained by quantitative real-time PCR (qRT-PCR) were largely consistent with the sequencing results. This study enriches the number of heat-responsive miRNAs and lays a foundation for the elucidation of the miRNA-mediated regulatory mechanism in tomatoes at elevated temperatures.

Evaluation of potential morpho-physiological and biochemical indicators in selecting heat-tolerant tomato (Solanum lycopersicum Mill.) genotypes

A few degrees in temperature above the optimum can cause a considerable yield loss in tomatoes. A research experiment was conducted in which three tomato genotypes of (Solanum lycopersicum Mill.), ‘Suncherry Extra Sweet’ (Suncherry), ‘Walter’, and ‘CLN-2498d’, were evaluated for response to moderate high temperature at the reproductive stage. High temperature reduced the total number of fruits per plant, fruit size, number of seeds per fruit, seed setting, and relative ovule viability. However, high temperature increased proline accumulation and membrane thermo-stability in plant parts of the investigated genotypes. Fruit size and the number of seeds per fruit were reduced in all the genotypes, with the greatest reduction occurring in Suncherry. Similarly, viability of male and female gametes was also reduced in all of the investigated genotypes due to high temperature injury. The reduction in seed setting due to high temperature was greatest in ‘Suncherry’ and ‘Walter’, and least in ‘CLN-2498d’. Likewise, ovule viability was least reduced in ‘CLN-2498d’. The genotypes accumulating higher proline concentrations in reproductive parts and with enhanced membrane thermo-stability under high temperature likewise produced the highest fruit yield, and hence, exhibited high temperature tolerance.

Screening and validation of tomato genotypes under heat stress using Fv/Fm to reveal the physiological mechanism of heat tolerance

Cultivation of tomatoes at high temperatures negatively affects growth and yield. Our aim was to screen tomato genotypes under heat stress for differences in the maximum quantum efficiency of photosystem II (Fv/Fm) and uncover the physiological traits for heat tolerance in a three-step process. Initially, 67 tomato genotypes were ranked according to Fv/Fm. Two genotypes with higher Fv/Fm (heat-tolerant group) and two genotypes with lower Fv/Fm (heat-sensitive group) were selected from the initial screening. Second, the physiological responses of the four genotypes to seven days of heat stress (36/28°C) were analyzed in detail. Third, pollen germination and fruit set of the four genotypes were investigated at high temperature conditions in the field. The results showed that the heat-tolerant group maintained higher leaf pigment content and higher total phenolic content (TPC) than the heat-sensitive group under heat stress. The heat-tolerant group maintained unaltered stomata and pore area and net photosynthesis rate (PN) but increased stomatal conductance (gs) under heat stress compared with the control. Chloroplasts in the heat-tolerant group maintained a normal shape, whereas the chloroplasts in the heat-sensitive group became swollen with decomposed starch grain after heat stress. The heat-tolerant group exhibited a higher pollen germination rate (%), longer pollen tube length and higher fruit set rate compared with the heat-sensitive group at high temperatures in the field. Thus, we concluded that Fv/Fm is an early indicator of heat stress tolerance and that the responses of tomatoes to heat stress were identical in widely different growing conditions. The stay-green trait, improved ability of stomata regulation and higher contents of reactive oxygen species scavengers seemed to be part of the protective mechanisms in heat-tolerant tomatoes.

Heterosis and General Combining Ability Study on Heat Tolerant Tomato (Lycopersicon esculentum Mill)

A study was carried out to estimate heterosis and general combining ability on heat tolerant tomato ( Lycopersicon escullentum Mill). The experiment was conducted at the Teaching and Research Farm of Department of Crop Production and Horticulture Modibbo Adama University of Technology, Yola. (latitude 9o18′N) gene action governing inheritance of characters in tomato ( Lycopersicon escullentum Mill) under high temperature stress. The experiment was conducted at the Teaching and Research Farm of Department of Crop Production and Horticulture Modibbo Adama University of Technology, Yola. (latitude 9o 18'N and long 12o 15'E) and the Teaching and Research Farm of Adamawa State University, Mubi (latitude 10o 03'N and long. 13o 07'E) all in Adamawa state of Nigeria. Fourteen entries consisting of six parents and eight crosses developed by crossing two males (testers) and four females (lines) following line x tester design were evaluated in three replications in a Randomized Complete Block Design (RCBD) in two locations. Ten plants where randomly sampled for recorded observation. Data were collected from the following characters; trichome count, plant height at 60DAT, number of leaves per plant at 60DAT, number of fruits per plant, weight of fruits per plant % damaged fruits and number of days to final harvest. Data were subjected to biometrical analysis. Result of the analysis of variance indicated highly significant difference for all characters among entries except weight of fruits per plant. The result suggested the presence of genetic variability among the tomato genotypes under study. Significant difference were observed in the combining ability analysis of variance in all the agronomic characters under study except for trichome count suggesting both additive and non-additive genetic effects were important in governing this characters under study with more preponderance of additive effects. The cultivars, Cherry, Currant, UC28B and RomaVF were identified as the best general combiners and the best yielders in terms of number of fruits per plant with appreciable tolerance to heat damage. N and long 12o 15′E) and the Teaching and Research Farm of Adamawa State University, Mubi (latitude 10o 03′N and long. 13o 07′E) all in Adamawa state of Nigeria. Fourteen entries consisting of six parents and eight crosses developed by crossing two males (testers) and four females (lines) following line x tester design were evaluated in a Randomized Complete Block Design (RCBD) with three replications. Ten plants where randomly sampled for recorded observation. Data were collected on Trichome count, plant height at 60DAT, number of leaves per plant at 60DAT, number of fruits per plant, weight of fruits per plant % damaged fruits and number of days to final harvest. Data were subjected to biometrical analysis. Result of the analysis of variance indicated highly significant difference for all characters among entries except weight of fruits per plant. The result suggested the presence of genetic variability among the tomato genotypes under study. Significant difference were observed in the combining ability analysis of variance in all the agronomic characters under study except for trichome count suggesting both additive and non-additive genetic effects were important in governing this characters under study with more preponderance of additive effects. The cultivars, Cherry, Currant, UC28B, and RomaVF were identified as the best general combiners and the best yielders in terms of number of fruits per plant with appreciable tolerance to heat damage. However, Currant x Roma vf and Cherry x Golden roma exhibited some level of heterosis in number of leaves, number of flower clusters, number of fruits per plant and plant height. Cherry and Currant, though identified as having highest performance in all characters under study are not commercially acceptable but could be utilized in breeding programs for improvement of tomatoes with required agronomic characteristics. However, UC28B, Roma vf and Golden roma are genotypes that have shown greater performances in all the agronomic characters which could be used for commercial cultivation. Furthermore, Currant x Roma vf and Cherry x Golden roma are desirable segregates that can be used to develop improved tomatoes with required agronomic characteristics through recurrent selection by backcrossing.

Study of heterosis in heat tolerant tomato (Solanum lycopersicum) during summer

An experiment was conducted at the Vegetable Research Field of Olericulture Division, Horticulture Research Cente, Bangladesh Agricultural Research Institute (BARI), Gazipur during May to October 2008 to study heterosis using eight parents viz., P1, P2, P3, P4, P5, P6, P7, and P8. Most of the combinations showed better parent heterosis for earliness. Eight crosses showed positive heterosis for flower production. The highest heterotic effect for fruit set (%) was found in the cross P6 × P7 (62.59%) followed by that in P7 × P8 (60.49%) and P1 × P7 (40.00%). For fruits per plant, 8 crosses provided more than 15 % heterosis over better parent. Considering fruit yield per plant, higher degree of heterosis was manifested by 24 hybrids over better parent ranging from 13.58 to 282.63 %. Cross combination P4 x P7 showed the maximum significant positive heterosis followed by P6 x P7 (187.84 %), P4 x P8 (166.97 %), P3 x P7 (146.08 %), P3 xP6 (103.92 %), and P1 X P7 (100.45 %) and the minimum in P4 x P6 (13.58 %). For viable pollens, P3 x P5 (20.56 %) exhibited the highest positive heterosis. In case of shelf life, the highest heterosis was observed by the cross P3 x P6 (22.78 %) followed by that in P4 x P6 (22.29 %) and P2 x P6 (14.40 %). For fruit flesh thickness, 12 hybrids exhibited more than 10 % heterosis. Pollen tubes as well as viable pollens showed positive correlation with fruit set. DOI: http://dx.doi.org/10.3329/bjar.v38i3.16980 Bangladesh J. Agril. Res. 38(3): 531-544, September 2013

Expression of a gene encoding β‐ureidopropionase is critical for pollen germination in tomatoes

Global warming has seriously decreased world crop yield. High temperatures affect development, growth and, particularly, reproductive tissues in plants. A gene encoding β-ureidopropionase (SlUPB1, EC 3.5.1.6) was isolated from the stamens of a heat-tolerant tomato (CL5915) using suppression subtractive hybridization. SlUPB1 catalyzes the production of β-alanine, the only β-form amino acid in nature. In the anthesis stage, SlUPB1 expression in CL5915 stamens, growing at 35/30°C (day/night), was 2.16 and 2.93 times greater than that in a heat-sensitive tomato (L4783) cultivated at 30/25°C or 25/20°C, respectively. Transgenic tomatoes, upregulating SlUPB1 in L4783 and downregulating SlUPB1 in CL5915, were constructed, and the amount of β-alanine measured by liquid chromatography-electrospray ionization-mass spectrometry in the transgenic overexpression of SlUPB1 was higher than that of L4783. However, the β-alanine in the transgenics downregulating SlUPB1 was significantly lower than the β-alanine of CL5915. Pollen germination rates of these transgenics were analyzed under different developmental and germinating temperatures. The results indicated that germination rates of transgenics overexpressing SlUPB1 were higher than germination rates of the background tomato L4783. Germination rates of transgenics downregulating SlUPB1 were significantly lower than germination rates of background tomato CL5915, indicating the necessity of functional SlUPB1 for pollen germination. Pollen germinating in the buffer with the addition of β-alanine further indicated that β-alanine effectively enhanced pollen germination in tomatoes with low SlUPB1 expression. Together, these results showed that the expression of SlUPB1 is important for pollen germination, and β-alanine may play a role in pollen germination under both optimal and high temperatures.

Effects of Temperature and Water Stress on Growth, Yield and Physiological Characteristics of Heat-tolerant Tomato

Effects of Temperature and Water Stress on Growth, Yield and Physiological Characteristics of Heat-tolerant Tomato

Genetic characterization of heat tolerant tomato (Solanum lycopersicon) genotypes by SRAP and RAPD markers

We employed RAPD and sequence-related amplified polymorphism (SRAP) markers to evaluate polymorphisms in 15 tomato (Solanum lycopersicon) genotypes that were obtained from a tomato breeding program. Four local tomato genotypes selected from the Sanliurfa province (Southeastern Anatolia Region of Turkey), 10 heat-tolerant tomato genotypes, received from the Asian Vegetable Research and Development Center, and a sample of S. pimpinellifolium were genotyped with RAPD and SRAP markers. Eleven SRAP primer combinations were used and 66 bands were scored. The number of bands scored per primer combination ranged from three to 12, with a mean of six alleles per primer combination. All fragments scored for each primer combination were polymorphic. The percentage of polymorphic products ranged from 25 to 80%. The 15 tomato genotypes were screened for RAPD markers using 50 primers in a PCR-based DNA amplification procedure; 46 primers produced clear and good amplification. Ten of these 46 primers amplified monomorphic fragments in the tomato genotypes. A dendrogram was constructed by combining data from the RAPD and SRAP analyses. Similarity ratios of genotypes ranged from 0.87 to 0.99. The dendrogram was divided into two branches; the first main branch included only genotype CL 5915, and the second main branch included all the other genotypes.

Developmental and heat stress-regulated expression of HsfA2 and small heat shock proteins in tomato anthers

The high sensitivity of male reproductive cells to high temperatures may be due to an inadequate heat stress response. The results of a comprehensive expression analysis of HsfA2 and Hsp17-CII, two important members of the heat stress system, in the developing anthers of a heat-tolerant tomato genotype are reported here. A transcriptional analysis at different developmental anther/pollen stages was performed using semi-quantitative and real-time PCR. The messengers were localized using in situ RNA hybridization, and protein accumulation was monitored using immunoblot analysis. Based on the analysis of the gene and protein expression profiles, HsfA2 and Hsp17-CII are finely regulated during anther development and are further induced under both short and prolonged heat stress conditions. These data suggest that HsfA2 may be directly involved in the activation of protection mechanisms in the tomato anther during heat stress and, thereby, may contribute to tomato fruit set under adverse temperatures.

Response of superoxide dismutase isoenzymes in tomato plants (Lycopersicon esculentum) during thermo‐acclimation of the photosynthetic apparatus

Seedlings of Lycopersicon esculentum Mill. var. Amalia were grown in a growth chamber under a photoperiod of 16 h light at 25 degrees C and 8 h dark at 20 degrees C. Five different treatments were applied to 30-day-old plants: Control treatment (plants maintained in the normal growth conditions throughout the experimental time), heat acclimation (plants exposed to 35 degrees C for 4 h in dark for 3 days), dark treatment (plants exposed to 25 degrees C for 4 h in dark for 3 days), heat acclimation plus heat shock (plants that previously received the heat acclimation treatment were exposed to 45 degrees C air temperature for 3 h in the light) and dark treatment plus heat shock (plants that previously received the dark treatment were exposed to 45 degrees C air temperature for 3 h in the light). Only the heat acclimation treatment increased the thermotolerance of the photosynthesis apparatus when the heat shock (45 degrees C) was imposed. In these plants, the CO(2) assimilation rate was not affected by heat shock and there was a slight and non-significant reduction in maximum carboxylation velocity of Rubisco (V(cmax)) and maximum electron transport rate contributing to Rubisco regeneration (J(max)). However, the plants exposed to dark treatment plus heat shock showed a significant reduction in the CO(2) assimilation rate and also in the values of V(cmax) and J(max). Chlorophyll fluorescence measurements showed increased thermotolerance in heat-acclimated plants. The values of maximum chlorophyll fluorescence (F(m)) were not modified by heat shock in these plants, while in the dark-treated plants that received the heat shock, the F(m) values were reduced, which provoked a significant reduction in the efficiency of photosystem II. A slight rise in the total superoxide dismutase (SOD) activity was found in the plants that had been subjected to both heat acclimation and heat shock, and this SOD activity was significantly higher than that found in the plants subjected to dark treatment plus heat shock. The activity of Fe-SOD isoenzymes was most enhanced in heat-acclimated plants but was unaltered in the plants that received the dark treatment. Total CuZn-SOD activity was reduced in all treatments. Darkness had an inhibitory effect on the Mn-SOD isoenzyme activity, which was compensated by the effect of a rise in air temperature to 35 degrees C. These results show that the heat tolerance of tomatoplants may be increased by the previous imposition of a moderately high temperature and could be related with the thermal stability in the photochemical reactions and a readjustment of V(cmax) and J(max). Some isoenzymes, such as the Fe-SODs, may also play a role in the development of heat-shock tolerance through heat acclimation. In fact, the pattern found for these isoenzymes in heat-acclimated Amalia plants was similar to that previously described in other heat-tolerant tomato genotypes.

Pollen grains of heat tolerant tomato cultivars retain higher carbohydrate concentration under heat stress conditions

Abstract Exposure to high temperatures (heat stress) causes reduced yield in tomatoes (Lycopersicon esculentum), mainly by affecting male gametophyte development. Two experiments were conducted where several tomato cultivars were grown under heat stress, in growth chambers (day/night temperatures of 31/25 °C) or in greenhouses (day/night temperatures of 32/26 °C), or under control (day/night temperatures of 28/22 °C) conditions. In heat-sensitive cultivars, heat stress caused a reduction in the number of pollen grains, impaired their viability and germinability, caused reduced fruit set and markedly reduced the numbers of seeds per fruit. In the heat-tolerant cultivars, however, the number and quality of pollen grains, the number of fruits and the number of seeds per fruit were less affected by high temperatures. In all the heat-sensitive cultivars, the heat-stress conditions caused a marked reduction in starch concentration in the developing pollen grains at 3 days before anthesis, and a parallel decrease in the total soluble sugar concentration in the mature pollen, whereas in the four heat-tolerant cultivars tested, starch accumulation at 3 days before anthesis and soluble sugar concentration at anthesis were not affected by heat stress. These results indicate that the carbohydrate content of developing and mature tomato pollen grains may be an important factor in determining pollen quality, and suggest that heat-tolerant cultivars have a mechanism for maintaining the appropriate carbohydrate content under heat stress.

`Amalia': A Medium-fruit-size, Heat-tolerant Tomato Cultivar for Tropical Conditions

The caribbean tropical climate is characterized by two distinct seasons; winter (November to April) and summer (May to October). Winter temperatures range between an average minimum of 17 oC and an average maximum of 27 oC. Summer temperatures (averages minimum 21 oC and maximum 31 oC) delay tomato (Lycopersicon esculentum Mill.) fl owering (Atherton and Harris, 1986) and give problems with fruit setting (Geisenberg and Stewart, 1986). Over 80% of the total annual rain (1300 to 1400 mm) occurs in summer and in combination with high temperatures, this produces ideal conditions for the development of early blight [Alternaria solani (Ell. and Mart.) Jones and Grout] disease. Early blight constitutes a serious restraint for tomato production in tropical countries like Cuba (Izquierdo, 1982), Costa Rica (Calvo et al., 1990), and India (Kalloo and Banerjee, 1993) and the Atlantic coast of southern U.S. (Foolad et al., 2000). As a consequence, tomato cannot be profi tably cultivated in the summer in Caribbean tropical areas. ‘Amalia’ combines heat tolerance with early blight resistance and can be cultivated profi tably in May through October, maintaining an excellent performance in wintertime, (November to April) thus extending the tomato season for almost the whole year. ‘Amalia’ may also be useful to tomato breeders as source for breeding heat tolerant hybrids or improved inbred lines.

Floral characteristics of heat-tolerant and heat-sensitive tomato ( Lycopersicon esculentum Mill.) cultivars at high temperature

The responses of a heat-sensitive (Pusa Ruby) and a heat-tolerant (CL-1131) tomato cultivar to four different temperature regimes were investigated to identify floral characteristics affected by high temperatures. There was an earlier anthesis in cultivar CL-1131 than in Pusa Ruby at 35/30°C (day/night) regime. The flower bud number of the first four trusses and total flower number at 35/30°C were significantly lower than at normal temperatures (22/17°C) in Pusa Ruby but not in CL-1131. Stigma exsertion at high temperatures (28/23°C) was the same in both cultivars. Many floral anomalies such as stigma exsertion without anthesis, empty flowers and persistent flowers without fruit-set were also observed in the 35/30°C regime. Antheridial cone splitting was not observed. The use of stigma exsertion and antheridial cone splitting as criteria for selecting against fruit-set at high temperature may be misleading. Therefore, these characteristics alone should not be used for selecting for heat tolerance in tomato.

Increased Yield of Heat-tolerant Tomatoes with Deep Transplanting, Morning Irrigation, and White Mulch

Studies were conducted in Fall 1994 and Summer 1995 to determine growth and yield response of heat-tolerant tomatoes (Lycopersicon esculentum Mill.) to transplant depth, time of daily irrigation, and polyethylene mulch color. Five-week-old tomato transplants were planted to a depth of either 7.5 or 15.0 cm, drip irrigated every other day for 2.5 h starting at either 7:30 am or 2:30 pm for 80 d following transplanting, and mulched with white-surface (white on black) or black polyethylene. Soil temperatures were recorded daily at 4:00 pm for 21 d from the beginning of fruit set (2 weeks following transplanting) until the tomato canopy shaded the mulch surface. Transplanting tomatoes to a depth of 15.0 cm significantly increased marketable yield in both years and the total yield in 1 year of this study. Mean fruit mass was not influenced by transplant depth, but plant dry mass was significantly increased by deeper transplanting in 1995. Morning irrigation increased the marketable and total yields and mean fruit mass in both years and plant dry mass in 1995. White-surface mulch had a similar effect on yield and fruit mass. Soil temperature was significantly lower at the 15.0-cm depth than at 7.5 cm in both years. Morning irrigation and white-surface polyethylene mulch also significantly reduced soil temperature in both years.

Insect Pests and Impact on Late-Season Tomato in Arkansas

The recent release of heat-tolerant tomato cultivars has resulted in increased interest in expanding fresh market tomato from historically early production to late summer and fall in Arkansas. Although insects are generally of minor importance in early production, much concern exists with the greater numbers of insects occurring later during the season. Insect frequency and impact on tomato were determined in studies conducted in northwestern and southern Arkansas in 1993 and 1994. The corn earworm, Helicoverpa zea (Boddie), was the most damaging insect in both locations during both years. Corn earworm larvae were detected throughout the study and caused extensive fruit damage. At the northwestern location, 81.6% of all harvested fruit was damaged by corn earworm larvae in 1993. Although thrips were present at both locations throughout the season, no plants infected with tomato spotted wilt virus were detected. Other potential insect threats, i.e., stink bugs, flea beetles and tomato pinworms, had no apparent effect on late-season production. Corn earworm management is well developed for early tomato production and should be easily adapted to late-season production. This should insure the success of late-season tomato production in Arkansas.

The relationship between yield and the antioxidant defense system in tomatoes grown under heat stress.

Four putative heat-tolerant tomato (Lycopersicum esculentum) cultivars (Tamasabro, Heat Wave, LHT-24, and Solar Set) and one putative heat-sensitive tomato cultivar (Floradade) were grown in the field under non-stress (average daily temperature of 26 degrees C) and heat-stress (average daily temperature of 34 degrees C) conditions. At anthesis, approximately five weeks after being transplanted to the field, leaf samples were collected for antioxidant analyses. Yield was determined by harvesting ripe fruit seven weeks after the collection of leaf samples. Heat stress resulted in a 79.1% decrease in yield for the heat-sensitive Floradade, while the fruit yield in the heat-tolerant cultivars Heat Wave, LHT-24, Solar Set, and Tamasabro was reduced 51.5%, 22.1%, 43.8%, and 34.8% respectively. When grown under heat stress, antioxidant activities were also greater in the heat-tolerant cultivars. Superoxide dismutase (SOD) activity increased up to 9-fold in the heat-tolerant cultivars but decreased 83.1% in the heat-sensitive Floradade. Catalase, peroxidase, and ascorbate peroxidase activity increased significantly in all cultivars. Only Heat Wave showed a significant increase in glutathione reductase in response to heat stress but all heat-tolerant cultivars exhibited significantly lower oxidized ascorbate/reduced ascorbate ratios, greater reduced glutathione/oxidized glutathione rations, and greater alpha-tocopherol concentrations compared to the heat-sensitive cultivar Floridade. These data indicate that the more heat-tolerant cultivars had an enhanced capacity for scavenging active oxygen species and a more active ascorbate-glutathione cycle and suggest a strong correlation between the ability to up-regulate the antioxidant defense system and the ability of tomatoes to produce greater yields when grown under heat stress.

Effect of Air and Root-zone Temperatures on Physiological Characteristics and Yield of Heat-tolerant and Non Heat-tolerant Tomato Cultivars.

Comparative studies on photosynthesis (Pr), transpiration (E), stomatal conductance (Gs), and yield of heat-tolerant tomato (Lycopersicon esculentum Mill. cv. Shuki) and non heat-tolerant one (cv. Sataan) at 2 air (40°/23° and 22°/16°C) and 4 root (15°, 20°, 25°and 30°±0.5°C) temperatures were carried out. Physiological characters were measured at the vegetative, flowering and fruiting stages of growth. Pr, E and Gs of 'Shuki' at high air and root-zone temperatures were significantly higher than those of 'Sataan' at the seedling, flowering and fruiting stages but no significant differences were observed at low air temperatures. Yield of 'Shuki' was significantly higher than that of 'Sataan' at all root-zone and high air temperatures but not at low air temperatures. Yield correlated significantly with photosynthesis at high air temperatures but no correlation was observed at low air temperatures.

Comparison of mineral absorption and nutrient composition of heat-tolerant and non heat-tolerant tomato plants at different root-zone temperatures

SummaryDifferences in water and mineral absorption and leaf mineral content between a heat-tolerant tomato (Lycopersicon esculentum Mill. cv. Shuki) and a non heat-tolerant one (cv. Sataan) were compared at four root-zone temperatures (RZT); 15, 20, 25 and 30°C. Experiments were conducted at two air temperatures; high (40/23°C) and low (22/16°C) day/night temperatures. Increasing RZT increased water and mineral uptake (N, P, K, and Ca) and total leaf N, P, K and Mg contents at the high and low air temperatures, however, the uptake was more pronounced at the higher air temperature. A significantly greater mineral uptake was recorded for ‘Shuki’ than for ‘Sataan’, at the high day/night air temperature, but no significant differences were observed at the low day/night air temperatures. On the other hand, leaf P, K, Ca , and Mg contents of ‘Sataan’, was higher than that of ‘Shuki’, the heat-tolerant type, at all RZT and at the high day/night air temperatures and this may be attributed to a tissue dilution eff...

Relationship between Some Physiological Characters and Yield of Heat-Tolerant, Non-Tolerant, and Tropical Tomato Cultivars Grown at High Temperature.

The relationships between physiological characters; photosynthesis (Pr), transpiration (E), stomatal conductance (Gs), and yield of three heat-tolerant tomato (Lycopersicon esculentuin Mill.) cvs. Shikiaka, Shuki and Ohio 7663, non heat-tolerant cv. Sataan; and two tropical cvs. Owusu-Bioh and Wosowoso, grown at 40°/23°C day/night temperatures were examined.Physiological characters were measured at air temperatures of 20°, 30°, and 40°C. Pr for heat-tolerant cultivars pooled at the seedling stage (57 leaves) was significantly greater than non heat-tolerant cultivars at 20° and 40°C. Pr, E, and Gs, at the flowering and early fruit development stage (1315 leaves) were significantly higher in the heat-tolerant cultivars compared to the other cultivars at all temperatures. Pr at the seedling stage did not significantly correlate with yield but Pr, E and Gs were significantly correlated with fruit yield at the flowering and early fruit development stage. A linear relationship between Pr and Gs and between E and Gs revealed a close and significant consequential relationship between E and Pr. Regressions among physiological variables were not homogenous among/between cultivars. Regressions between Pr, E, Gs, and yield were heterogenous among/between cultivars. Heat-tolerant cultivars had greater yields than the other cultivars. The results indicate that yield significantly and positively correlated with Pr, E. and Gs.