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Chickpea (Cicer arietinum L.) is an important grain legume. Global warming and changes in cropping systems are driving chickpea production to relatively warmer growing conditions. Studies on the impact of climate change on chickpea production highlighted the effect of warmer temperatures on crop development and subsequent chickpea yield. For example, the yield of chickpea declined by up to 301 kg/ha per 1˚C increase in mean seasonal temperature in India. Assessment of whole plant response, particularly flowering and grain filling in warmer environments, in the field is generally an effective screening method. The identification of heat tolerant genotypes can help adapt chickpea to the effects of warmer temperatures. In this study, 167 chickpea genotypes were screened in heat stressed (late season) and non-stressed (normal season) conditions in the field during 2009-10 (year 1) and 2010-11 (year 2) at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), India. The aim of these experiments was to screen chickpea germplasm in contrasting chickpea growing seasons for high temperature tolerance. Plant phenology (days to first flowering, days to 50% flowering, days to first pod, and days to maturity), growth (plant height, plant width and biomass at harvest) and grain yield including pod number per plant, filled pod number per plant and seed number per plant were recorded in both seasons. There was large and significant variation for phenology, growth, grain yield and yield traits. Pod numbers per plant and harvest index are the two key traits that can be used in selection for breeding programs. The genetic variation was also confirmed by canopy temperature depression and the Heat Tolerance Index (HTI). Furthermore, using daily maximum and minimum temperature during the growing period, temperature for chickpea developmental stages (vegetative, flowering and grain filling phases) was calculated for both seasons to understand genotype × environment (G × E) interaction. In addition, sensitivity of male and female reproductive tissues to high temperature is important to explain the effect of heat stress on the reproductive phase. Therefore, field experiment was conducted at ICRISAT under stressed condition (late season) during 2011. The aim of these experiments was to study genetic variation in male reproductive tissue (anther, pollen), its function (pollen germination and tube growth) and pod set. Pollen fertility, in vitro pollen germination, in vivo pollen germination and pod set was examined under different temperatures. The field experiment was compared with controlled environments (stressed and non-stressed conditions). Both anthers and pollen grains showed more structural abnormalities such as changes in anther locule number, anther epidermis wall thickening and pollen sterility, rather than function (e.g. in vivo pollen tube growth). Clearly, chickpea pollen grains are more sensitive to high temperature than the stigma in both the field and controlled environments. Both studies suggested that the critical temperature for pod set was ≥37˚C in heat tolerant genotypes (ICC 1205; ICC 15614 and ICCV 92944) and ≥33˚C for heat sensitive genotypes (ICC 4567; ICC 10685 and ICC 5912). Implementation of molecular breeding in chickpea improvement program depends on the understanding of genetic diversity. Diversity Array Technology (DArT) is a micro-array based method allowing for finding of DNA polymorphism at several thousand loci in a single assay. The aim of this research was to investigate the genetic diversity between the167 chickpea genotypes using DArT markers. Based on 359 polymorphic DArT markers, 153 genotypes showed polymorphism. A dendrogram derived from cluster analysis based on the genetic similarity coefficient matrix for the 153 genotypes was constructed. There were nine groups (group 1-9) identified from dendrogram. The genotypes were collected from 36 countries and ICRISAT breeding lines were also included in the germplasm. Based on eleven quantitative traits (days to first flowering, days to 50% flowering, days to first pod, days to physiological maturity, plant height, plant width, plant biomass, pod number per plant, filled pod number per plant, seed number per plant and grain yield) observed in the field, the diversity groups were arranged under stressed and non-stressed conditions for two years and their relationship of origin was also studied. The group 9 (ICRISAT breeding lines) produced highest grain yield under non-stressed and heat stressed followed by group 3. Those breeding lines were crossbreeds from the ICRISAT’s breeding programs and released in different countries at different times. Furthermore, characterisation of ICRISAT screening environments using 29 years of temperature data was done to understand the chickpea growing season for future breeding programs. Association analysis was conducted on chickpea genotypes evaluated in the field screening for high temperature tolerance. Eleven quantitative traits observed in the field under heat stressed and non-stressed conditions were analysed to understand the genetic control of heat tolerance through marker-trait association. Under heat stress, 44 DArT markers were associated with grain yield and pod characteristics such as total pod number, filled pod number and seed number. A DArT marker was associated with three or four traits and may be efficiently used in improvement of more than one trait at a time. The associated markers for the traits like plant height, plant width, pod number and grain yield were found in the genomic regions of previously reported QTLs. In addition, many genomic regions for phenology, biomass and grain yield under heat stressed and non-stressed conditions. The number of markers significantly associated with different traits was higher under heat stress, suggesting that many genes are present that control plant response to high temperature in chickpea. Four populations, ICC 1356 x ICC 15614; ICC 10685 x ICC 15614; ICC 4567 x ICC 15614 and ICC 4567 x ICC 1356 of F1s, F2s along with their parents were assessed in the field in 2011 at heat stressed condition (late season). The objective of this experiment was to study the inheritance of heat tolerance. Days to first flowering (DFF), pod number per plant (TNP), filled pod number per plant (NFP), seed number per plant (NS) and grain yield per plant (GY) was recorded. Estimates of broad sense heritability for the traits DFF, TNP, NFP, NS and GY were calculated for all four crosses. In this study, parents were heterogeneous for heat response. At extreme high temperature (>40˚C) the population, especially ICC 4567 x ICC 15614, set pods and gave higher grain yield compared with other crosses. The adaptation of chickpea to high temperature may also be improved using more exotic parents to combine allelic diversity for flowering time, pod number, filled pod number, seed number per plant and grain yield. High temperature clearly has an influence on plant growth, development and grain yield. The research has identified heat tolerant sources of chickpea and also found the impact of high temperature on the male reproductive tissue. Studying genetic diversity using DArT markers and understanding diversity group with agronomic traits provided the basis of chickpea response to high temperature. Further research is needed from populations of chickpea crosses using late generations. This will enable the development of heat tolerant chickpea cultivar. |
