Development Of Heat Tolerant Cultivars Research Articles

Character Association Study in Maize Hybrids Developed through Integration of Rapid Cycle Genomic Selection and Doubled Haploid Technology for Heat Stress Tolerance

Heat stress is becoming a major constraint for maize production; therefore heat stress resilience has emerged as an important aspect in maize hybrids targeted for post rainy spring season. Selection of genotypes based on high grain yield under heat stress condition is often misleading and the identification of secondary traits also associated with grain yield may help in development of heat tolerant cultivars. Hence, the present research work to study the association of traits was conducted during summer and kharif 2018 and rabi 2018-19 at Bheemarayanagudi and Raichur using 111 testcross progenies of doubled haploids derived from C1, C2 and C3 cycles of multi-parental synthetic population 1 and 2 improved through rapid cycle genomic selection for heat stress tolerance. The phenotypic correlation analysis under heat stress and optimal conditions, number of kernels per cob and cob girth exhibited the strong positive association with grain yield per plant. Further, under early spring condition number of kernels per cob, cob length, cob girth and 100 grain weight recorded the strong positive association with grain yield per plant. However, when considering across heat stress, early spring and optimal conditions, the grain yield per plant showed positive and significant strong to moderate association with the traits viz., number of kernels per cob, cob length and cob girth under all the seasons. In addition, days to 50% silking showed significant negative correlation with grain yield per plant under heat stress and optimal condition. Hence, the simultaneous selection criteria for the genotypes that exerts early silking, higher number of kernels per cob, higher cob girth and lengthy cob should be the priority of breeders to achieve higher grain yields in maize under heat stress condition as well as optimal conditions.

Molecular insights into mechanisms underlying thermo-tolerance in tomato.

Plant productivity is being seriously compromised by climate-change-induced temperature extremities. Agriculture and food safety are threatened due to global warming, and in many cases the negative impacts have already begun. Heat stress leads to significant losses in yield due to changes in growth pattern, plant phonologies, sensitivity to pests, flowering, grain filling, maturity period shrinkage, and senescence. Tomato is the second most important vegetable crop. It is very sensitive to heat stress and thus, yield losses in tomato due to heat stress could affect food and nutritional security. Tomato plants respond to heat stress with a variety of cellular, physiological, and molecular responses, beginning with the early heat sensing, followed by signal transduction, antioxidant defense, osmolyte synthesis and regulated gene expression. Recent findings suggest that specific plant organs are extremely sensitive to heat compared to the entire plant, redirecting the research more towards generative tissues. This is because, during sexual reproduction, developing pollens are the most sensitive to heat. Often, just a few degrees of temperature elevation during pollen development can have a negative effect on crop production. Furthermore, recent research has discovered certain genetic and epigenetic mechanisms playing key role in thermo-tolerance and have defined new directions for tomato heat stress response (HSR). Present challenges are to increase the understanding of molecular mechanisms underlying HS, and to identify superior genotypes with more tolerance to extreme temperatures. Several metabolites, genes, heat shock factors (HSFs) and microRNAs work together to regulate the plant HSR. The present review provides an insight into molecular mechanisms of heat tolerance and current knowledge of genetic and epigenetic control of heat-tolerance in tomato for sustainable agriculture in the future. The information will significantly contribute to improve breeding programs for development of heat tolerant cultivars.

Morpho-Physiological Traits and Functional Markers Based Molecular Dissection of Heat-Tolerance in Urdbean.

Urdbean (Vigna mungo L. Hepper) is one of the important pulse crops. Its cultivation is not so popular during summer seasons because this crop is unable to withstand excessive heat stress beside lack of humidity in the atmosphere. Therefore, a panel of 97 urdbean diverse genotypes was assessed for yield under stress and non-stress conditions with an aim to identify heat tolerant genotypes. This study identified 8 highly heat tolerant and 35 highly heat sensitive genotypes based on heat susceptibility index. Further, physiological and biochemical traits-based characterization of a group of six highly heat sensitive and seven highly heat tolerant urdbean genotypes showed genotypic variability for leaf nitrogen balance index (NBI), chlorophyll (SPAD), epidermal flavnols, and anthocyanin contents under 42/25°C max/min temperature. Our results showed higher membrane stability index among heat tolerant genotypes compared to sensitive genotypes. Significant differences among genotypes for ETR at different levels of PAR irradiances and PAR × genotypes interactions indicated high photosynthetic ability of a few genotypes under heat stress. Further, the most highly sensitive genotype PKGU-1 showed a decrease in different fluorescence parameters indicating distortion of PS II. Consequently, reduction in the quantum yield of PS II was observed in a sensitive one as compared to a tolerant genotype. Fluorescence kinetics showed the delayed and fast quenching of Fm in highly heat sensitive (PKGU 1) and tolerant (UPU 85-86) genotypes, respectively. Moreover, tolerant genotype (UPU 85-86) had high antioxidant activities explaining their role for scavenging superoxide radicals (ROS) protecting delicate membranes from oxidative damage. Molecular characterization further pinpointed genetic differences between heat tolerant (UPU 85-86) and heat sensitive genotypes (PKGU 1). These findings will contribute to the breeding toward the development of heat tolerant cultivars in urdbean.

Breeding, genetics, and genomics for tolerance against terminal heat in lentil: Current status and future directions

AbstractHeat stress at terminal stage in lentil is one of the major factors causing drastic yield loss. Development of heat tolerant cultivars is one of the ways to tackle this problem. However, heat stress tolerance is a complex trait in nature and many morphological, physiological, biochemical, and metabolic changes are responsible for heat stress tolerance in lentil. Therefore, in the past years, efforts have been made to know genetics and genomics of heat stress tolerance in lentil. In this review, we discussed current progress on breeding, genetics, and genomics including quantitative trait locus (QTL) mapping, transcriptomics, proteomics, and network of metabolic pathways for heat tolerance and future directions for developing heat tolerant cultivars in lentil.

Coordinated regulation of three kinds of thermotolerance in tomato by antioxidant enzymes

Although the relationship between basal (BT), acquired (AT) and maintenance of acquired thermotolerace (MT) has been illustrated in a heat resistant tomato genotype and sensitive tomato genotypes, whether more resistant and sensitive tomato genotypes are satisfied with the rule and the relationships of antioxidant enzymes (AE) activity in three kinds of thermotolerance are not known. Here, we have observed the intension of three kinds of tomato thermotolerance is associated with AE activities. The priming and enhancement of thermotolerance was temperature dependent with stronger thermotolerance priming by moderately high temperatures than warmer temperatures. Interestingly, AE activity also showed significantly higher in seedlings under moderately high temperature than ones at warmer temperatures. While after the first optimized priming of different high temperatures combined with secondary priming for a reasonable period, AE activity and its thermotolerance further enhanced. Surprisingly, these optimized acclimation treatments showed no difference in AE activity and MT intension, suggesting that secondary priming could supply gaps produced by the first priming of warmer high temperatures, through enhancing AE activity. Additionally, the basal heat resistant genotypes showed stronger AE activity and thermotolerance (AT and MT) than sensitive genotypes. Results from this study will provide insights into understanding mechanism behind regulating tomato thermotolerance and facilitate the development of heat tolerant cultivars.

POTENTIAL OF F3:4 SEGREGATING WHEAT POPULATIONS FOR TOLERANCE TO HEAT STRESS

Heat is one of the major abiotic stresses that affect wheat yield and quality in many parts of the world. To overcome this problem, the development of heat tolerant cultivars has been shown to be one of the main targets of breeding programs, especially for the conditions of Central Brazil. The present study was developed with objective of identifying promising populations for tolerance to heat stress, in order to obtain lines adapted to the conditions of Central Brazil. The experiment was carried out in the summer of 2011 in Coimbra/MG where 36 segregating populations with different numbers of families per population were evaluated in an augmented block design, determining the cycle, plant height and grain yield. Genetic variability for heat tolerance was observed among the wheat populations. The vegetative development stage of wheat was more sensitive to the effect of heat stress. The most promising segregating populations were IAC364/BRS207, IAC24/Alianca IAC24/Pioneiro that associated high yield with a large number of families selected among the most productive, demonstrating the possibility of selecting heat stress-tolerant lines.

Susceptibility of Faba Bean (Vicia faba L.) to Heat Stress During Floral Development and Anthesis

Experiments were conducted over 2 years to quantify the response of faba bean (Vicia faba L.) to heat stress. Potted winter faba bean plants (cv. Wizard) were exposed to temperature treatments (18/10; 22/14; 26/18; 30/22; 34/26 °C day/night) for 5 days during floral development and anthesis. Developmental stages of all flowers were scored prior to stress, plants were grown in exclusion from insect pollinators to prevent pollen movement between flowers, and yield was harvested at an individual pod scale, enabling effects of heat stress to be investigated at a high resolution. Susceptibility to stress differed between floral stages; flowers were most affected during initial green‐bud stages. Yield and pollen germination of flowers present before stress showed threshold relationships to stress, with lethal temperatures (t 50) ˜28 °C and ~32 °C, while whole plant yield showed a linear negative relationship to stress with high plasticity in yield allocation, such that yield lost at lower nodes was partially compensated at higher nodal positions. Faba bean has many beneficial attributes for sustainable modern cropping systems but these results suggest that yield will be limited by projected climate change, necessitating the development of heat tolerant cultivars, or improved resilience by other mechanisms such as earlier flowering times.

Determination of heat tolerance of interspecific (Cucurbita maxima x Cucurbita moschata) inbred line of squash ‘Maxchata’ and its parents through photosynthetic response

Development of heat tolerant cultivars is the need of hour to combat the challenges of global warming and food supply to increasing population. This study was conducted to determine the extent of heat tolerance of newly developed interspecific inbred line of squash named as ‘ Maxchata ’ through comparing its photosynthetic attributes with its parents C. maxima and C. moschata . Plants of these three cultivars were subjected to three different temperatures i.e 30 ° C day/ 25 ° C night as control, 37 ° C day/ 32 ° C night as moderate heat stress and 42 ° C day/ 37 ° C night as severe heat stress, for seven days. Results showed that various gas exchange attributes like photosynthetic rate ( P N ), stomatal conductance (g s ) and transpiration rate (E) as well as chlorophyll florescence (F v /F m ) all dropped significantly in the studied cultivars with increasing temperature, while intercellular CO 2 concentration ( Ci ) increased pointing to the nonstomatal limitations. Further, chlorophyll pigments also degraded with heat shocks resulting in more Chl a to b ratio and decreased chlorophyll carotenoids ratio. However, these trends were more abrupt in C. maxima , chased by ‘ Maxchata’ and then C. moschata . Hence, C. moschata had the best photosynthetic machinery to sustain the heat regimes, followed by ‘ Maxchata ’, while, C. maxima was the most susceptible. So, ‘ Maxchata ’ with some degree of heat tolerance has the ability to cope with the climate change.