The basis of chickpea heat tolerance under semi-arid environments

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

Amplitude scintillations on earth-space propagation paths at 2 and 30 GHz

Amplitude scintillation measurements were made simultaneously at 2.075 and 30 GHz on earth-space propagation paths over elevation angles in the range 0.4 to 44 deg. The experiment was performed as the Applications Technology Satellite (ATS-6) was moved slowly from a synchronous position over Africa to a new synchronous position over the United States. The received signal, variance, level, covariance, spectra and fade distributions are discussed as functions of the path elevation angle. These results are also compared wherever possible with similar measurements made earlier at 20 and 30 GHz

Effects of atmospheric turbulence on microwave and millimeter wave satellite communications systems

A model of the microwave and millimeter wave link in the presence of atmospheric turbulence is presented with emphasis on satellite communications systems. The analysis is based on standard methods of statistical theory. The results are directly usable by the design engineer

Power law relationships for rain attenuation and reflectivity

The equivalent reflectivity, specific attenuation and volumetric backscatter cross section of rain are calculated and tabulated at a number of frequencies from 1 to 500 GHz using classical Mie theory. The first two parameters are shown to be closely approximated as functions of rain rate by the power law aR to the b power. The a's and b's are also tabulated and plotted for convenient reference

Amplitude scintillation at 2 and 30 GHz on earth space paths

Extensive amplitude scintillation measurements were made simultaneously at 2.075 and 30 GHz on earth-space propagation paths. These measurements were performed as the Applications Technology Satellite (ATS-6) was moved slowly from a synchronous position over India to a new synchronous position over the United States. The variance, path loss, covariance, and spectra are discussed as functions of the path elevation angle. These results are also compared with earlier simultaneous scintillation measurements at 20 and 30 GHz during the movement of ATS-6 to its position over India

Science and Engineering Technical Assessments (SETA) Program

This document summarizes all activities performed under CTO#5 of the Science and Engineering Technical Assessments (SETA) Contract

Chickpea Abiotic Stresses: Combating Drought, Heat and Cold

Chickpea is an important legume providing dietary proteins to both humans and animals. It also ameliorates soil nitrogen through biological nitrogen fixation. Drought, heat and cold are important factors among abiotic stresses limiting production in chickpea. Identification, validation and integration of agronomic, physiological and biochemical traits into breeding programs could lead to increased rates of genetic gain and the development of better adapted cultivars to abiotic stress conditions. This chapter illustrates the effects of stresses on chickpea growth and development. It also reviews the various traits and their relationship with grain yield under stress and proposes recommendation for future breeding

Effect of high temperature on the reproductive development of chickpea genotypes under controlled environments

High temperature during the reproductive stage in chickpea (Cicer arietinum L.) is a major cause of yield loss. The objective of this research was to determine if that variation can be explained by differences in anther and pollen development under heat stress. Therefore the effect of high temperature during the pre- and post-anthesis periods on pollen viability, pollen germination in a medium, pollen germination on the stigma, pollen tube growth and pod set in a heat tolerant (ICCV 2 92944) and a heat sensitive (ICC 5912) genotype was studied. The plants were evaluated under heat stress and non-heat stress conditions in controlled environments. High temperature stress (29/16˚C to 40/25˚C) was gradually applied at flowering to study pollen viability and stigma receptivity including flower production, pod set and seed number. This was compared with a non-stress treatment (27/16˚C). The high temperatures reduced pod set by reducing pollen viability and pollen production per flower. The ICCV 92944 pollen was viable at 35/20˚C (41% fertile) and at 40/25˚C (13% fertile), while ICC 5912 pollen was completely sterile at 35/20˚C with no in vitro germination and no germination on the stigma. However, the stigma of ICC 5912 remained receptive at 35/20˚C and non-stressed pollen (27/16˚C) germinated on it during reciprocal crossing. These data indicate that pollen grains were more sensitive to high temperature than the stigma in chickpea. High temperature also reduced pollen production per flower, % pollen germination, pod set and seed number

Chickpea and temperature stress

Chickpea is an important food grain legume and an essential component of crop rotations throughout the world. However, the adaptation and productivity of chickpea is often limited by low and high temperatures. Cold stress generally occurs in the late vegetative and reproductive stages across the geographical areas of chickpea production. Cold and freezing temperatures (−1.5°C to 15°C) are considered a major problem during the seedling stage of winter-sown chickpea in Mediterranean areas and autumn-sown crops in temperate regions (Singh, 1993). South Australia and parts of north India are most affected by chilling temperatures at flowering (Berger et al., 2011). On the other hand, high day and night temperatures (>30/16°C) may cause damage during the reproductive stage on winter-sown chickpea in Mediterranean inseason rainfall areas, south Asia and spring-sown regions (Berger et al., 2011). In chickpea, temperature is a major environmental factor regulating the timing of flowering thus influencing grain yield (Summerfield et al., 1990; Berger et al., 2004). Both low and high temperatures can limit the growth and grain yield of chickpea at all phenological stages..

Field response of chickpea (Cicer arietinum L.) to high temperature

High temperature is an important factor affecting chickpea growth, development and grain yield. Understanding the plant response to high temperature is a key strategy in breeding for heat tolerance in chickpea (Cicer arietinum L.). This study assessed genetic variability for heat tolerance in chickpea and identified sources of heat tolerance that could be used for crop improvement. One hundred and sixty-seven genotypes were grown in two environments (heat stressed/late sown and non-stressed/optimal sowing time) in 2 years (2009–2010 and 2010–2011) at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, India. Large genetic variation was observed for phenology, growth, yield components and grain yield. While phenology (assessed as days to first flower, days to 50% flowering and days to first pod) was negatively correlated with grain yield at high temperature; plant biomass, pod number, filled pod number and seed number per plant were positively correlated. Genotypes were classified into short and long duration groups based on their maturity. Days to first flowering (DFF) of long duration genotypes were negatively associated with grain yield under stressed conditions in both years compared with medium to short duration genotypes. However, genotypes varied in their heat sensitivity and temperatures ≥35 °C produced yield losses up to 39%. A heat tolerance index (HTI) classified the genotypes into five groups: (i) stable heat tolerant (>0.5), (ii) moderately heat tolerant (0.1–0.49), (iii) stable heat sensitive (−ve values), (iv) heat tolerant to moderately sensitive (−0.10 to 1) and (v) heat sensitive to moderately tolerant (−0.5 to 0.4). Pod characteristics, including days to first pod and pod number per plant, were correlated with grain yield whereas canopy temperature depression (CTD) was generally not correlated. Heat tolerant genotypes in a range of maturities were identified that could be used to improve the heat tolerance of chickpea