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ItemIncreasing lentil (Lens culinaris) adaptation to acute high temperature for arable croppingDelahunty, Audrey Jane ( 2021)Lentil (Lens culinaris Medik.) is an important crop for providing a source of dietary protein globally and is produced over three distinct agroecological zones; Mediterranean, sub-tropical and temperate. Crop production is constrained by abiotic and biotic stresses, including acute high temperature (HT). For Mediterranean-type climates, such as southern Australia, low and unreliable winter rainfall (200 – 600 mm/year) and frequent acute HT events (heat waves) during the reproductive phase, limit production with yield losses up to 70%. Consequently, increasing the adaptation of commercial lentil varieties within contemporary breeding programs, by utilising global germplasm adapted to HT environments, is the critical next step. This project screened 135 lentil genotypes (global landraces and commercial cultivars) for tolerance to acute HT occurring during the reproductive period. Screening was through a combination of late sowing (summer - chronic and acute HT), controlled-environment (acute HT) and subsequent in-season validation (winter - acute HT), where a daily maximum temperature of greater than 30 degrees Celsius was classified as HT tolerant. Genotypes selected for screening were predominately from regions where HT occurs during the reproductive period (i.e. Mediterranean and sub-tropical). Across HT treatments ranging from acute (3 days) to chronic HT during the reproductive period, we observed that HT caused a 48% reduction in grain yield across genotypes screened, which translated to an average reduction of 0.14 and 0.19% per degree (>30 degrees Celsius) for global landraces and commercial cultivars respectively. We identified 15 landraces and the commercial cultivar, Nipper to have a high level of yield stability under HT. Within the 15 landraces identified, AGG 73838 and 73154 consistently exhibited HT tolerance under the multiple screening strategies employed in this study. The additional 13 landraces were identified within the late sowing field screening process. The identification of these 15 HT tolerant landraces provides a valuable source of material that can be immediately utilised by Australian lentil breeding programs. Optimal screening approaches for HT tolerance were also identified in this study, where field-based and controlled environment screening methods were tested and their utility to breeding programs, assessed. To align with current breeding strategies, several requirements were considered important; 1) reliable methods for identifying genetic diversity to HT response within global material, 2) high-throughput potential and (or) ability to measure parameters efficiently, and 3) methods to enable screening of large populations. Through assessing a range of screening methodologies, we determined that a multi-stage screening process integrating late sowing over spring/summer with subsequent winter validation, is required. This process enables the shortlisting of HT tolerant germplasm from a broad range of material and further validation of phenotype response in field conditions. To rank genotypes based on HT tolerance we determined that the indices, stress tolerant index (STI) and high temperature tolerance index (HTTI), which integrate the absolute and relative response of genotypes within the test population, were an effective means of ranking HT tolerance. The final component of this project assessed the combined effects of available soil water, night-time temperature and carbon dioxide concentration on HT response in lentil, which provided insight to the impact of other abiotic constraints associated with climate change. We determined that for HT, lentil response varied with available soil water and soil type. For lentil grown in a sandy loam soil, when HT and high water occurred together, HT caused a significant reduction in yield (33%), whereas under low water the application of HT did not further reduce yield. In contrast, for a clay soil there was a significant reduction in yield due to HT across both high and low water treatments. This highlights the effect of soil type on crop water availability and the potential variable response to acute HT depending on soil type and rainfall patterns of a growing region. For the impact of high night temperature, we observed no effect of night temperature when it occurs in conjunction with high day temperature. For the collective effect of HT and carbon dioxide concentration, elevated carbon dioxide did not alter the pattern of plant response to acute HT. This suggests that for lentil, the effects of HT are unlikely to be exacerbated or reduced under elevated carbon dioxide levels. Ultimately, this project contributes to the Australian lentil industry by identifying landraces with HT tolerance and through the development of a screening methodology that can be adopted by current breeding programs to increase the HT tolerance of future commercial lentil cultivars.