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

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

Improved lettuce establishment by subsurface drip irrigation

Vegetables are grown in the peri-urban zone throughout Australia in diverse soil types and climates. Irrigation allows cropping throughout the year. Competition for water and adverse environmental impacts from irrigation will increasingly influence access to water and the price paid. These forces are particularly strong in the Sydney Region, where improved irrigation techniques are urgently needed. A review of literature showed that sub-surface drip irrigation (SDI) has the potential to achieve high water use efficiency and crop yields, as well as reduce drainage and runoff and the associated environmental risks. However, disadvantages of SDI include ‘tunnelling’, poor soil surface wetting, and risky crop establishment. The research reported in this thesis, evaluated ways to overcome these problems, including a new product (KISSSTM) that has a narrow band of impermeable material below the drip tape, and geotextile above. It was hypothesised that the impermeable layer would create a temporary watertable, from which the upward flux of water would be greater than in conventional SDI and the drainage less. The research questions were: 1. Does an impermeable layer beneath the drip tape (modified SDI) improve surface soil water conditions and crop establishment, compared with conventional SDI? 2. Does the modified SDI (M.SDI) offer any advantage over using conventional SDI (C.SDI) with increasing irrigation amount or frequency? A further objective was to determine how irrigation management with the modified SDI should take account of soil type and evaporative demand. Field experiments at Richmond, NSW compared C.SDI and M.SDI on a sandy soil in autumn (mean pan evaporation 2 mm/day) and spring (mean evaporation 6 mm/day) to investigate lettuce crop establishment. The treatments were two drip tape types (M.SDI, C.SDI) and three irrigation frequencies (1, 2 and 4 times per day). Irrigation application volume was calculated by using a crop factor of 0.4 in autumn. In spring, crop factors of 0.4 and 0.8 were compared. Modified SDI improved crop establishment compared with conventional SDI. The difference in seedling survival was numerically small but significant (p is less than 0.05), indicating a superior environment for establishment in the M.SDI. This was reflected in higher leaf appearance rates in the spring experiment. In both experiments, leaves were longer and wider with the M.SDI, and plant fresh weights were greater at the end of the crop establishment period. The differences in fresh weight were substantial, with the M.SDI system recording average increases over the C.SDI of 16% and 25% in the autumn and spring experiments, respectively. Plants were also more uniform with the M.SDI. In both experiments, plant weight was closely related to volumetric soil water content, regardless of the source of variation in water content: tape type, crop factor, irrigation frequency, or location within the plot. Soil water and plant weight responded to increased irrigation frequency (IF) and crop factor (CF, included in spring only) with both tape types. The effects of CF and IF were additive within tape types. So, whilst the negative effect of reduced irrigation amount can be offset by increased irrigation frequency, the best growth was obtained where both were high. However, for every combination of CF and IF, plant growth with the modified SDI exceeded the conventional SDI. With the combination of high irrigation frequency (4/day) and a high crop factor (0.8), the modified SDI resulted in a 35% increase in plant fresh weight over conventional SDI. Importantly, at high irrigation frequency (4/day) but with only half the amount of irrigation (CF 0.4 versus 0.8), plant weight with modified SDI was similar to conventional SDI (actually 10% greater). Soil water content was also more uniform in the M.SDI treatment. A glasshouse experiment quantified the components of the water balance under irrigation with conventional and modified sub-surface drip irrigation, in sand and sandy loam soils under different evaporation demand. A tension table in the base of each large pot (50x35x5 cm) was used to maintain a suction of -60 cm at the base. Each treatment was subjected to a sequence of different irrigation frequencies, one per two days; and one, two and four per day. Data for drainage and soil water were recorded daily, and averaged over the last three days when daily drainage approached steady-state for any irrigation frequency. The M.SDI system generally resulted in lower drainage than with the C.SDI, regardless of soil type, irrigation frequency, evaporative demand, and irrigation rate. As the amount of daily irrigation (I) was known and equal for all treatments, soil evaporation (Esoil) was estimated from drainage (D) using the simplified soil water balance equation: Esoil = I – D. Thus soil evaporation was the inverse of drainage. The upward flux of water to meet the evaporative demand was greater in the M.SDI, and it was greater with more frequent irrigation. Soil water content and potential were both higher with the M.SDI. They were also higher with frequent irrigation, as in the field experiment. Overall, the M.SDI had less drainage than conventional SDI, greater upward flux of water (soil evaporation), and wetter surface soils. The findings are consistent with the hypothesis that an impermeable layer beneath the drip tape creates a temporary watertable, increasing the upward flux of water. Both the field and glasshouse experiments showed the benefit of dividing the daily irrigation requirement into smaller, more frequent pulses, for both types of drip tape, regardless of the soil types and climates investigated. Whilst increased irrigation amount and irrigation frequency both increased soil water content and plant growth, the best performance was when both irrigation amount and frequency were high. Frequent irrigation (4/day) was essential to obtain the improved crop growth with the M.SDI and a high crop factor in the spring experiment. These positive responses to tape type and irrigation frequency were obtained at relatively low and high evaporative demand (2, 6 mm/day), and in soils with different texture (coarse sand, sandy loam). So the modified drip tape and more frequent irrigation appear to be reliable, broad recommendations. No specific recommendation can be made on the present data regarding irrigation frequency in relation to evaporative demand, although it might be expected that under very high demand more frequent irrigation will be required unless the modified drip tape can be made to hold a greater volume of water against drainage. In relation to the first objectives of the study, it is concluded that the modified SDI (KISSSTM) improves surface soil water content and uniformity, and has the potential to overcome the plant establishment problems associated with conventional SDI. It does so whilst saving water and reducing environmental risk (drainage and/or runoff). With respect to research question 2, irrigating with more water, or more frequently, did improve seedling growth, but the modified drip tape (KISSSTM) retained an advantage in terms of both establishment and growth at any combination of irrigation amount and frequency. Further research is required to develop guidelines for using the M.SDI in specific soils and climates, especially for heavier-textured soils and more extreme evaporation

Key Determinants of the Physiological and Fruit Quality Traits in Sweet Cherries and Their Importance in a Breeding Programme

Australia produces high-quality sweet cherries and generates revenue from local and export markets. Due to increased demand in the markets, the area of sweet cherry production has increased in Australia. Sweet cherry breeding and production have challenges such as self-incompatibility genotypes and phenotyping of agronomic, physiological, and quality traits. Understanding these traits and their interaction with environmental factors would increase production and provide better economic returns for the industry. This review paper covered the challenges of current sweet cherry production, breeding efforts, the basis for understanding of plant traits, the influence of environmental factors on the traits, and opportunities for new sweet cherry breeding in the future. The period of flowering and maturity along with firmness of the fruit are key traits in cherry production. Breeding techniques such as haplotype breeding will contribute to improving breeding efficiency and deliver better cultivars of sweet cherry

Impact of High Temperature and Drought Stresses on Chickpea Production

Global climate change has caused severe crop yield losses worldwide and is endangering food security in the future. The impact of climate change on food production is high in Australia and globally. Climate change is projected to have a negative impact on crop production. Chickpea is a cool season legume crop mostly grown on residual soil moisture. High temperature and terminal drought are common in different regions of chickpea production with varying intensities and frequencies. Therefore, stable chickpea production will depend on the release of new cultivars with improved adaptation to major events such as drought and high temperature. Recent progress in chickpea breeding has increased the efficiency of assessing genetic diversity in germplasm collections. This review provides an overview of the integration of new approaches and tools into breeding programs and their impact on the development of stress tolerance in chickpea