Growth-defence carbon allocation is complementary for enhanced crop yield under drought and heat stress in tolerant chickpea genotypes

Non-structural carbohydrates (NSC) are major substrates for primary and secondary plant metabolism with various functions including growth, storage of carbon (C) and energy, osmotic adjustment and synthesis of antioxidants for defence against biotic and abiotic stresses. The allocation of C to growth and defence molecules is labelled antagonistic because it is perceived that limited photosynthates produced under stress is allocated preferentially to defence molecules at the expense of growth, leading to the development of the growth-defence trade-off concept. Several studies and literature reviews have provided evidence both in support and against the growth-defence trade-off. Therefore, it remains unclear whether the allocation of NSC to storage and defence molecules is at the expense of plant growth, especially in annual or short-lived flowering plants. This article reviews literature on sugar and antioxidant metabolism in tolerant/desi and sensitive/kabuli genotypes of chickpea under drought and heat stress conditions. The results show that some of the desi genotypes and drought and heat stress tolerant genotypes accumulated greater NSC, proline or antioxidant enzymes and produced higher biomass and seed yield than kabuli and sensitive genotypes under stress. This is new evidence to support the view that plants accumulate NSC and secondary metabolites and grow at the same time under drought and heat stress conditions which implies complementary allocation of C to growth and defence metabolism. Understanding the growth-defence trade-off and its application is important as it affects plant growth, seed yield, and plant fitness in both natural ecosystems and crop improvement programmes in agriculture.