Integrated breeding approaches for improving drought and heat adaptation in chickpea (Cicer arietinum L.)

Chickpea (Cicer arietinum L.) is a dry season food legume largely grown on residual soil moisture after the rainy season. The crop often experiences moisture stress towards end of the crop season (terminal drought). The crop may also face heat stress at the reproductive stage if sowing is delayed. The breeding approaches for improving adaptation to these stresses include the development of varieties with early maturity and enhanced abiotic stress tolerance. Several varieties with improved drought tolerance have been developed by selecting for grain yield under moisture stress conditions. Similarly, selection for pod set in the crop subjected to heat stress during reproductive stage has helped in the development of heat‐tolerant varieties. A genomic region, called QTL‐hotspot, controlling several drought tolerance‐related traits has been introgressed into several popular cultivars using marker‐assisted backcrossing (MABC), and introgression lines giving significantly higher yield than the popular cultivars have been identified. Multiparent advanced generation intercross (MAGIC) approach has been found promising in enhancing genetic recombination and developing lines with enhanced tolerance to terminal drought and heat stresses.     

Genotypic variability among cotton cultivars for heat and drought tolerance using reproductive and physiological traits

Development of rapid and inexpensive screening tools for heat and drought stress tolerance is needed and will be helpful in cotton breeding programs and selecting cultivars for a niche environment. In this study, several pollen-based traits at optimum and high temperatures and physiological parameters measured during the boll-filling period were used to evaluate variability among the cultivars for heat and drought stresses. Principal component analysis and drought stress response index methods were used to categorize cotton cultivars into three heat and drought tolerant clusters. Based on the combined analysis, PX532211WRF has been identified as heat- and drought-tolerant, and would be expected to perform better under both heat- and drought-stressed environments. A poor correlation between reproductive and physiological indices indicates that screening breeders have to use different traits to screen cultivars for reproductive and vegetative tolerance. Identified traits could serve as valuable screening tools in cotton breeding programs aimed at developing genotypes to a changing climate. Moreover, cultivar-dependent relative scores will aid in the identification of cultivars best suited to niche environments to alleviate the influences of abiotic stresses at both vegetative and reproductive stages.     

Quantitative trait locus mapping of drought and salt tolerance in an introgressed recombinant inbred line population of Upland cotton under the greenhouse and field conditions

Drought and salt tolerances are complex traits and controlled by multiple genes, environmental factors and their interactions. Drought and salt stresses can result in more than 50% yield loss in Upland cotton (Gossypium hirsutum L.). G. barbadense L. (the source of Pima cotton) carries desirable traits such as tolerance to abiotic and biotic stress along with high fiber quality. However, few studies have been reported on mapping quantitative trait loci (QTL) for abiotic stress tolerance using a permanent bi-parental population in multiple tests. The transfer of drought and salt tolerance from Pima to Upland cotton has been a challenge due to interspecific hybrid breakdown. This issue may be overcome by using introgression lines with genes transferred from Pima to Upland cotton. In this study, four replicated tests were conducted in the greenhouse each for drought and salt tolerance along with another test conducted in a field for drought tolerance using an Upland recombinant inbred line population of TM-1/NM24016 that has a stable introgression from Pima cotton. The objectives of the study were to investigate the genetic basis of drought and salt tolerance and to identify genetic markers associated with the abiotic stress tolerance. A total of 1004 polymorphic DNA marker loci including RGA-AFLP, SSR and GBS-SNP markers were used to construct a genetic map spanning 2221.28 cM. This population together with its two parents was evaluated for morphological, physiological, yield and fiber quality traits. The results showed that drought under greenhouse and field conditions and salt stress in the greenhouse reduced cotton plant growth at the seedling stage, and decreased lint yield and fiber quality traits in the field. A total of 165 QTL for salt and drought tolerance were detected on most of the cotton chromosomes, each explaining 5.98–21.43% of the phenotypic variation. Among these, common QTL for salt and drought tolerance were detected under both the greenhouse and field conditions. This study represents the first study to report consistent abiotic stress tolerance QTL from multiple tests in the greenhouse and the field that will be useful to understand the genetic basis of drought and salt tolerance and to breeding for abiotic stress tolerance using molecular marker-assisted selection in cotton.     

Exploring genetic diversity for heat tolerance among lentil (Lens culinaris Medik.) genotypes of variant habitats by simple sequence repeat markers

The study was carried out to assess genetic diversity among 119 lentil genotypes grown in different habitats for heat tolerance using morpho‐physiological and reproductive traits and SSR markers. High‐temperature stress was applied at seedling (35/33°C) and anthesis stages (35/20°C) to study the effects on morpho‐physiological and reproductive traits under hydroponic condition, which was compared with non‐stressed and stressed field conditions. A set of 209 alleles were identified by 35 SSR markers among the genotypes. Genetic diversity and polymorphism information content values varied between 0.0494–0.859 and 0.0488–0.844, with mean values of 0.606 and 0.563, respectively. Genotypes were clustered into nine groups based on SSR markers. Morpho‐physiological and reproductive traits under heat stress were found to be significantly different among SSR clusters. These findings suggest that heat adaptation is variable among the genotypes and the tolerant materials can be evolved through hybridization using parents from different clusters with diverse mechanisms of heat tolerance.     

Wheat cellular thermotolerance is related to yield under heat stress

Cellular thermotolerance in terms of cellular membrane thermostability is often implied as an indication of crop heat tolerance and it is therefore considered as a possible selection criterion for heat tolerance. While there is ample genetic variability for cellular thermotolerance in wheat and other crop plants its relations to yield under heat stress is not sufficiently established. This study was performed to assess the genetic relations in wheat between cellular thermotolerance and yield under heat stress. In one study the co-segregation among cellular membrane thermostability (CMS), yield under chronic heat stress and yield under non-stress conditions was evaluated in a random inbred line (RIL) population of a cross between heat resistant (Danbata) and heat susceptible (Nacozari) cultivars. In a second study the same association was evaluated for yield under heat stress in 49 F₇ breeding lines randomly selected from a breeding program. CMS was assayed in growth chamber grown and heat-hardened seedlings. Yield was evaluated under Mediterranean summer irrigated conditions where chronic heat stress caused a reduction in mean yield of the RIL population by 47% as compared with the normal winter growing conditions (non-stress). The RILs varied significantly (p<0.05) for CMS, biomass and yield under stress and non-stress conditions. The two parent cultivars did not differ in biomass or yield under non-stress (winter) conditions but they widely differed for both traits under heat stress. Yield of RILs under heat stress was well distributed between the extreme values of the parent cultivars. There was a significant RIL by season interaction for biomass (F = 9.74; p<0.0001) and yield (F = 10.08; p<0.0001), indicating specific adaptation to heat stress of certain lines in terms of their productivity. Broad-sense heritability for yield was high and nearly the same in the winter (h ²=0.71)and the summer (h ²=0.67). Broad-sense heritability for CMS was high (h ²=0.74). CMS was positively and significantly (p<0.01) correlated across 98 RILs with biomass (r = 0.60* *) and yield (r = 0.53^**) under stress but rot with biomass or yield under non-stress conditions. The 49 breeding lines varied significantly (p<0.01) for CMS and yield under chronic heat stress in the summer season. CMS and yield were significantly correlated (r = 0.56^**) across lines. Overall the associations between CMS and yield under heat stress were reasonably strong and significant but not perfect. Other factors besides cellular thermostability may support yield under heat stress. CMS alone cannot be used as the exclusive selection criterion for heat tolerance in wheat breeding. lt may be valuable as a supplemental criterion in the final breeding stages or as a rough selection tool to reduce a large population into the most likely heat tolerant core at the early stages of the breeding program.     

Evaluating physiological traits to complement empirical selection for wheat in warm environments

The response of spring wheat to heat stress has been determined in several hot wheat growing environments worldwide on different types of germplasm. Physiological data has been collected to identify potential traits to assist in the empirical breeding for heat tolerance. Initial studies focused on 10 established varieties to determine genetic diversity for heat tolerance, identify association between heat tolerance and traits measured, and evaluate genotype by environment interaction (G x E). Yields from over 40 hot environments were analysed for G x E, and relative humidity (RH) was identified as the major factor determining relative genotype ranking. Further analysis focused on 16 environments: those with low RH and relatively high yields, i.e., over 2.5 t ha^-1. For these environments, mean yield of lines correlated with a number of physiological traits measured in Mexico, including canopy temperature depression (CTD), membrane thermostability, leaf conductance and photosynthetic rate at heading, chlorophyll content during grainfilling, leaf internal CO₂ concentration, and dark respiration. Morphological traits were measured in all environments and the following showed associations with yield: above ground biomass at maturity, days from emergence to anthesis and to maturity, grain number m^-2, and ground cover estimated visually after heading. Subsequent studies focused on breeding material, namely recombinant inbred lines derived from crosses between parents of contrasting heat tolerance, and 60 advanced breeding lines selected for performance under heat stress. The genetic basis for association between heat tolerance and CTD was established by demonstrating a correlation between the two traits in RILs (recombinant inbred lines). Data from RILs, as well as from the 60 advanced lines grown at several international locations, indicated CTD to be a powerful and robust selection criterion for heat tolerance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Traits in Spring Wheat Cultivars Associated with Yield Loss Caused by a Heat Stress Episode after Anthesis

Heat stress resulting from climate change and more frequent weather extremes is expected to negatively affect wheat yield. We evaluated the response of different spring wheat cultivars to a post‐anthesis high temperature episode and studied the relationship between different traits associated with heat tolerance. Fifteen spring wheat (Triticum aestivum L.) cultivars were grown in pots under semifield conditions, and heat stress (35/26 °C) and control treatments (20/12 °C) were applied in growth chambers for 5 days starting 14 days after flowering. The heat stress treatment reduced final yield in all cultivars. Significant variation was observed among cultivars in the reduction in average grain weight and grain dry matter yield under heat stress (up to 36 % and 45 %, respectively). The duration of the grain‐filling period was reduced by 3–12 days by the heat treatment. The reduction in the grain‐filling period was negatively correlated with grain nitrogen yield (r = ?0.60). A positive correlation (r = 0.73) was found between the treatment effect on green leaf area (GLA) and the reduction in yield resulting from heat stress. The amount of stem water‐soluble carbohydrates (WSC) was not related to treatment effects on grain yield or grain weight. However, the treatment effect on stem WSC remobilization was negatively correlated with reduction in grain‐filling duration due to heat stress (r = ?0.74) and positively with treatment effect on grain N yield (r = 0.52). The results suggest that the effect of the heat treatment on GLA was the trait most associated with yield reduction in all cultivars. These findings suggest the importance of ‘stay green’‐associated traits in plant breeding as well as the need for better modelling of GLA in crop models, especially with respect to brief heat episodes during grain filling. There is in particular a need to model how heat and other stresses, including interacting effects of heat and drought, affect duration of GLA after flowering and how this affects source–sink relations during grain filling.     

抗虫棉不同类型品种苗期耐盐理化特性差异研究

 为揭示不同基因型抗虫棉耐盐性差异的生理机制,指导抗虫棉耐盐品种鉴选和盐碱地棉花生产,以耐盐性差异显著的两类转Bt基因抗虫棉品种——耐盐性强的鲁K536、鲁棉研18优选系,耐盐性弱的新棉33B优选系、鲁K1258——为试验材料,利用不同盐分含量砂培与土培试验相结合,比较研究它们苗期的主要理化指标变化。结果表明,在NaCl胁迫下,耐盐性强的品种苗期叶片内的K⁺含量显著高于耐盐性弱的品种,Na⁺含量显著低于耐盐性弱的品种,丙二醛含量也显著低于耐盐性弱的品种,而游离脯氨酸、可溶性糖、类胡萝卜素含量均显著高于耐盐性弱的品种。耐盐性强的品种棉苗的过氧化物酶活性、叶绿素a、b和a+b含量以及净光合速率明显高于耐盐性弱的品种。表明棉花的耐盐性强弱因基因型而异,基因型间的耐盐性差异与丙二醛、脯氨酸、可溶性糖、类胡萝卜素含量和保护酶活性以及盐离子在叶片中累积量的差异有关。     

Response of cotton genotypes to water and heat stress: from field to genes

Cotton is a crop of tropical and subtropical regions but the seed cotton yield is highly influenced by abiotic stresses like drought and heat. Response of cotton genome to abiotic stresses is highly complex and involve many genes. A comprehensive study, involving cotton genotypes developed through conventional and synthetic tetraploid method, was designed to (i) study the introgression of heat and water stress tolerance by using wild relatives (ii) evaluate genetic markers for marker assisted selection against water and heat stress. Two separate experiments for water and heat stress tolerance with a common control were established. Treatments in each experiment include a control and a stress treatment. Heat stress was applied by sowing crop two month earlier than the control treatment, whereas water stress was imposed by withholding alternate irrigation. Analyses of variance depicted highly significant (P ≤ 0.01) effect of genotypes and both stresses on boll retention, boll weight and seed cotton yield. Interaction of genotypes with stress in both experiments was also highly significant (P ≤ 0.01). Genotypes derived from interspecific crosses performed consistently in stress conditions compared to control which prove it a reliable method to introgress stress related genes from wild parents. Four genes reported for water stress tolerance and five genes reported for heat stress tolerance were evaluated by field results for efficient marker assisted selection (MAS). Results verified drought stress genes but heat stress genes could not explain genetic variability caused by heat stress. It is concluded from the results that separate genes may be responsible for heat stress tolerance for vegetative and reproductive stages, therefore, selection criteria should include both the traits.     

滨海盐碱地转基因抗虫棉品种鉴选

为探明转基因抗虫棉的耐盐性，筛选出适合盐碱地种植的抗虫棉高产品种，不同盐分含量砂培试验与滨海盐碱地大田试验相结合。研究了不同基因型抗虫棉的耐盐性及其生育特点和产量表现。结果表明。供试抗虫棉品种间的耐盐性存在差异，但耐盐程度皆十分有限。从不同基因型抗虫棉的耐盐性、出苗成苗率、生长情况和产量等分析。以鲁棉研17、鲁棉研21、鲁536、中棉所45和鲁棉研18综合性状较好，适宜于盐碱地种植，可作为当前盐碱地植棉的适宜品种。     

Expression of seed storage proteins responsible for maintaining kernel traits and wheat flour quality in common wheat under heat stress conditions

Heat stress during grain filling has been documented to decrease wheat grain yield and quality in arid regions worldwide. We studied the effect of heat stress on wheat flour quality in heat tolerant cultivars to define the effects of heat stress on flour quality and to identify germplasm combining traits for heat tolerance and good flour quality. We studied the kernel phenotypic traits, the expression of seed storage proteins (SSPs), and the resulting flour quality under heat and normal conditions. Under heat stress, all cultivars yielded narrow-shaped seeds, and increased protein contents as compared to the control plants grown under normal conditions. The specific sedimentation values used to estimate the gluten quality varied between cultivars. We identified cultivars that could maintain good flour quality under heat stress conditions: ‘Imam’, which possessed the Glu-D1d allele responsible for the suitable bread-making; ‘Bohaine’, which displayed high expression level of SSPs; and ‘Condor’, which possessed slight variations in the ratio of each SSP under heat stress conditions. Combining the desirable traits from these cultivars could yield a wheat cultivar with heat tolerance and good flour quality.     

Assessment of Groundnut under Combined Heat and Drought Stress

In semi‐arid regions, particularly in the Sahel, water and high‐temperature stress are serious constraints for groundnut production. Understanding of combined effects of heat and drought on physiological traits, yield and its attributes is of special significance for improving groundnut productivity. Two hundred and sixty‐eight groundnut genotypes were evaluated in four trials under both intermittent drought and fully irrigated conditions, two of the trial being exposed to moderate temperature, while the two other trials were exposed to high temperature. The objectives were to analyse the component of the genetic variance and their interactions with water treatment, year and environment (temperature) for agronomic characteristics, to select genotypes with high pod yield under hot‐ and moderate‐temperature conditions, or both, and to identify traits conferring heat and/or drought tolerance. Strong effects of water treatment (Trt), genotype (G) and genotype‐by‐treatment (GxTrt) interaction were observed for pod yield (Py), haulm yield (Hy) and harvest index (HI). The pod yield decrease caused by drought stress was 72 % at high temperature and 55 % at moderate temperature. Pod yield under well‐watered (WW) conditions did not decrease under high‐temperature conditions. Haulm yield decrease caused by water stress (WS) was 34 % at high temperature and 42 % under moderate temperature. Haulm yield tended to increase under high temperature, especially in one season. A significant year effect and genotype‐by‐environment interaction (GxE) effect were also observed for the three traits under WW and WS treatments. The GGE biplots confirmed these large interactions and indicated that high yielding genotypes under moderate temperature were different to those at high temperature. However, several genotypes with relatively high yield across years and temperature environments could be identified under both WW and WS conditions. Correlation analysis between pod weight and traits measured during plant growth showed that the partition rate, that is, the proportion of dry matter partitioned into pods, was contributing in heat and drought tolerance and could be a reliable selection criterion for groundnut breeding programme. Groundnut sensitivity to high‐temperature stress was in part related to the sensitivity of reproduction.     

Phenological Development–Yield Relationships in Dry Pea in Semiarid Mediterranean Conditions

Dry pea (Pisum sativum L.) growers in the semiarid Mediterranean region require cultivars that are both early maturing and high yielding. However, negative relationships between these two characteristics limit their simultaneous improvement. A better understanding of the relative importance of the developmental stages in determining yield would assist in pea improvement. Sixteen dry pea cultivars were grown for 2 years under semiarid Mediterranean conditions (Maru, north Jordan) in order to see if differences in growing degree days (GDD) to flowering and GDD from planting to physiological maturity exist and to study their relationships with seed yield. Seed yield was negatively correlated with GDD to maturity, but not significantly correlated with GDD to flowering. Increasing GDD to flowering resulted in higher seed yield, while increasing seed fill duration had little effect. Rapid seed fill rate was positively correlated with seed weight and negatively correlated with seed fill duration. These results indicate that Mediterranean-adapted cultivars would have preflowering periods lasting as long as possible, followed by short seedfill periods. Simultaneous selection for early maturity and a relatively long time to flowering is recommended for the development of early-maturing, high-yielding cultivars adapted to semiarid Mediterranean environments.     

棉花苗期耐低钾能力筛选指标研究及其与产量、品质的关系

以长江流域下游棉区的12个棉花主栽品种为研究材料,在人工气候室水培和田间种植条件下进行棉花苗期耐低钾能力筛选指标研究。结果表明,低钾会放大棉花苗期关于钾素吸收利用和光合碳同化等生理特性上的品种间差异幅度。土壤严重缺钾时会显著降低棉花铃数、铃重及衣分,其中铃数响应土壤缺钾最为敏感,而在铃重组成中纤维质量对土壤缺钾的响应幅度大于棉子质量。通过对比基于棉花苗期不同生理指标和最终产量与品质指标的筛选结果,发现综合考虑棉花苗期叶片SuSy活性、SPAD值和单株叶片生物量3项指标的低钾胁迫系数对棉花最终产量与品质的耐低钾能力具有较好的预测效果。通过试验筛选出低钾敏感型棉花品种泗杂3号和耐低钾型棉花品种泗棉3号,二者可作为进一步研究低钾环境下棉花产量、品质形成机理的理想试验材料。     

Heat stress affects vegetative and reproductive performance and trait correlations in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis>)

High ambient temperature has adverse effects on plant vegetative and reproductive development and reduces crop yield. To better understand the importance of male and female fertility for tomato fruit set ability under high temperature conditions and to test whether heat tolerance levels among and between reproductive and vegetative traits of genotypes correlate with each other, 13 tomato cultivars were subjected to long-term moderate heat (LTMH) or short-term heat shock (STHS), depending on the trait that was evaluated. LTMH caused significant decrease in performance of nearly all reproductive traits, i.e. pollen viability, pollen number, female fertility, seeded-fruit set and flower number per inflorescence, but not in inflorescence number. Considerable variation was found among cultivars, both under control and LTMH conditions. The cultivars Nagcarlang, Saladette and Malintka 101 produced a higher percentage of viable pollen under LTMH. For fruit set under LTMH condition, only cultivars that had been previously reported as being heat-tolerant produced fruits with seeds. STHS negatively affected vegetative traits concerning seedling survival and membrane stability. Correlation analysis revealed relationships between various traits within the control and heat treatments, but not between the two. Under heat stress fruit set was positively correlated with pollen viability, as well as with flower number per inflorescence. However, no significant correlations were found between vegetative and reproductive traits. Our data highlight the prominent role of pollen viability for tomato fertility under LTMH growth conditions. The observed variation in thermotolerance among different cultivars offers the possibility to decipher underlying physiological and genetic mechanisms.     

Genetic variation in salt tolerance at the seedling stage in an interspecific backcross inbred line population of cultivated tetraploid cotton

Soil salinity reduces cotton growth, yield, and fiber quality and has become a serious problem in the arid southwestern region of the Unites States. Development and planting of salt-tolerant cultivars could ameliorate the deleterious effects. The objective of this study was to assess the genetic variation of salt tolerance and identify salt tolerant genotypes in a backcross inbred line (BIL) population of 142 lines from a cross of Upland (Gossypium hirsutum) × Pima cotton (G. barbadense) at the seedling growth stage. As compared with the non-saline (control) conditions, seedlings under the salinity stress (200 mM NaCl) showed a significant reduction in all the plant growth characteristics measured, as expected. Even though the two parents did not differ in salt response as measured by percent reduction, significant genotype variations in the BIL population were detected for all traits except for leaf number. Based on percent reduction of the traits measured, several BILs were more salt tolerant than both parents. The results indicate that transgressive segregation occurred during the process of backcrossing and selfing even though both parents were not salt tolerant during seedling growth. Coefficients of correlation between all the traits were significantly positive, indicating an association between the traits measured. The estimates of broad-sense heritability were 0.69, 0.46, 0.47, 0.43, and 0.49 for plant height, fresh weight of shoot and root, and dry weight of shoot and root, respectively, indicating that salt tolerance during cotton seedling growth is moderately heritable and environmental variation plays an equally important role. The overall results demonstrate that backcrossing followed by repeated self-pollination is a successful strategy to enhance salt tolerance at the seedling stage by transferring genetic factors from Pima to Upland cotton.     

Divergent strategies displayed by potato (Solanum tuberosum L.) cultivars to cope with soil drought

The physiological responses of potato (Solanum tuberosum L) cultivars to soil drought at the tuberization phase and their impact on agronomically important traits were investigated in potted plants under semi‐controlled conditions. Genotype‐dependent responses of potato to water deficiency were evaluated on two pairs (tolerant/sensitive) of Polish cultivars. Each pair of cultivars had a similar genetic background but was extremely different in terms of drought tolerance evaluated on the basis of loss of tuber yield under field conditions. The results clearly indicate different mechanisms of tolerance to water deficiency and the ability to recover from soil drought in two tolerant but genetically unrelated cultivars. When subjected to soil drought, the cultivar Gwiazda had low rates of transpiration and photosynthesis and low levels of stomatal conductance due to hypersensitivity to ABA, but its maximal photochemistry efficiency and PSII performance index were unchanged. Another strategy was displayed by the dehydration‐avoidant cultivar Tajfun, which kept the stomata partially open. Thus, the plants were able to retain a relatively high rate of photosynthesis over transpiration. The parameters measured for cultivar Tajfun for photosynthesis and transpiration were the same after plant rewatering, similar to the control plants. This was not the case for the cultivar Gwiazda. The ability of plants to regenerate after soil drought relief appears to be a good indicator of potato susceptibility to soil drought and allows the yield of potato tubers to be predicted. The physiological traits identified in closely related potato cultivars but differed in their drought tolerance seem to be useful for genetic engineering and breeding programmes.     

The effect of spot blotch and heat stress on variation of canopy temperature depression,chlorophyll fluorescence and chlorophyll content of hexaploid wheat genotypes

Spot blotch, caused by Cochliobolus sativus (Ito and Kurib.) Drechsler ex Dastur, and heat stress are two important stresses of bread wheat (Triticum aestivum L.) causing substantial yield reduction in the warm areas of South Asia. These two stresses put pressure on at least 25 million hectares of wheat areas worldwide. This study was conducted to examine variation in physiological traits and its association with heat and spot blotch. Eleven diverse bread wheat genotypes were evaluated in replicated field trials under spot blotch epidemics and heat stress conditions in 2006 and 2007 at Rampur, Nepal. Canopy temperature depression (CTD), chlorophyll fluorescence (CF), chlorophyll content, percent disease leaf area, yield and yield components were recorded. Heat and spot blotch individually reduced CTD, CF, chlorophyll content, grain yield (GRY), and thousand kernel weight (TKW), with greater reductions recorded under combined stress. Genotypes showing lower GRY or TKW loss due to spot blotch also exhibited lower yield loss due to heat stress or combined heat and disease stress, suggesting an association between tolerance mechanisms to the stresses. The physiological traits chlorophyll content, CF and CTD showed higher correlations with GRY and TKW than with area under disease progress curve (AUDPC) suggesting their potential application in screening for heat and spot blotch tolerant genotypes. Genotypes with lower disease showed the highest values for chlorophyll content, CF and CTD. Our findings provide new information on the relationship of these physiological traits with spot blotch resistance and heat tolerance when examined in the same study. The physiological traits studied have potential application in integrative indirect selection criteria for improving spot botch and heat tolerance in wheat.     

Drought stress‐induced changes in starch yield and physiological traits in potato

Drought stress is an important limitation for potato (Solanum tuberosum L.) production as potato depends on appropriate water availability for high yields of good quality. Therefore, especially in the background of climate change, it is an important goal in potato breeding to improve drought stress tolerance. In this study, 34 European starch potato cultivars were evaluated for drought stress tolerance by growing under well‐watered and long‐term drought stress conditions in rainout shelters in 2 years’ pot trials. Besides yield, six physiological traits, that is free proline content, osmolality, total soluble sugar content, chlorophyll content (SPAD), cell membrane stability and crude protein content, were determined in leaves sampled during vegetative growth and during flowering to investigate their association with drought tolerance. ANOVA revealed significant treatment effects for all physiological traits and increased genotypic effects at flowering. The sensitivity of physiological traits to drought was significantly higher during flowering than during vegetative growth. Drought stress decreased starch yield significantly (p < .001), on average by 55%. Starch yield was significantly influenced by genotype and genotype × treatment interactions. Stress tolerance index (STI) calculated from starch yield ranged from 0.26 (sensitive) to 0.76 (tolerant) with significant genotype effects (p ≤ .001). STI correlated positively with cell membrane stability (r = .59) and crude protein content (r = .38) and negatively with osmolality (r = ?.57) and total soluble sugar content (r = ?.71). These contrary correlations suggest a dual adaptation strategy in potato under long‐term drought stress conditions including increased membrane stability combined with an increased osmolality due to an increased soluble sugar content.     

Application of Stress Indices for Heat Tolerance Screening of Common Bean

Common bean is adapted to relatively cool climatic conditions and temperatures of >30 °C during the day or >20 °C at night result in yield reduction. The long‐term goal of breeding for heat tolerance is the development of germplasm with improved field level tolerance under variable temperature conditions. Using previously developed stress indices, this study presents results from high temperature screening of 14 genotypes in both the greenhouse and field in Puerto Rico. A total of three sets of paired trials were conducted in the field and in the greenhouse under high temperature (stress) and lower temperature (low‐stress) conditions. The geometric mean (GM), stress tolerance index (STI) and stress susceptibility index (SSI) were used to evaluate the genotypic performance under stress and low‐stress conditions. The results indicate that it was possible to identify superior genotypes for heat tolerance based on their stress indices. In this evaluation of heat tolerance indices, STI and GM, although correlated, were found to be effective stress indices for the selection of genotypes with good yield potential under stress and low‐stress conditions.