Increasing yields of legume crops in drought-stressed environments

Delivering a reliable food supply to a growing population demands crop production systems that are robust in the face of the increasingly unpredictable climatic conditions. Globally, average yield losses due to abiotic stress (eg. drought and extreme temperatures) are estimated to be >50% for most major crops. PI Biosciences (PIB) has identified an approach, exploiting advances in the understanding of plant stress signalling, to ameliorate abiotic stress. PIB's 'Alethea' technology is a mixture of chemicals that are analogues of compounds that are important in crop physiology and biochemistry, which can be formulated together with micronutrients to produce innovative foliar spray products that are economically and environmentally sustainable, and socially acceptable.

Foliar sprays of Alethea confer salinity tolerance by altering multiple plant hormone signalling pathways (Wargent et al 2013). A previous BBSRC CASE studentship (BB/G01793X/1) confirmed that Alethea pre-treatment significantly changed the transcriptome, including significant up-regulation of some isozymes of superoxide dismutases, a key anti-oxidant enzyme. This work provides a solid base for developing new anti-drought products, but further fundamental understanding is needed to deliver more robust technologies.

PIB's commercial assessment is that grower uptake of anti-stress products will be most successful if targeted to key periods of vulnerability in specific crops. This research programme builds on knowledge of drought effects in soybean, where pod number per plant is the main yield determinant and early pod expansion is regarded as critical. Since mechanistic understanding of drought effects on pod development remains limited, the project will start with fundamental physiological research.

In Years 1 and 2, critical phenological stage(s) for soybean sensitivity to drought will be determined (review of existing literature followed by targeted experiments). Drought treatments of varying severity will be imposed in controlled environments (Lancaster) at defined crop developmental stages, to measure hydraulic and chemical determinants of pod growth. The significance of crop water and carbon status in affecting phytohormones and mediating pod abortion will be tested by manipulating leaf water status (plants grown at different humidities) and carbohydrate supply (stem sucrose feeding). Pods will be sampled for a comprehensive suite of analyses (antioxidant systems, metabolites and phytohormones).

Year 3 experiments will use large-scale glasshouse facilities (Rothamsted Research) to test responses in cultivars differing in drought tolerance, and evaluate whether gibberellin signalling determines pod yield under drought. Pod gibberellin levels under different water regimes will be determined and gibberellin biosynthesis inhibitors (previously demonstrated to increase pod and seed number) will be applied at defined developmental stages. Since leaf elongation of gibberellin-insensitive wheat was insensitive to high soil impedance, a consequence of drying soil (Coelho et al. 2013), drought responses of gibberellin-insensitive soybean will be measured.

Year 4 plans clearly depend on previous progress. We aim to exploit partners' links in Brazil to determine if the physiological understanding gained can explain yield of water-limited crops grown in the field (e.g. through LEC's close collaboration with the University of Lavras or PIB's use of Brazil for field trials).