Importance of Growth Regulators and Growth Retardants on Growth, Yield and Economics of Pigeonpea (Cajanus cajan L.): A Review

Pigeonpea (Cajanus cajan L.) is a notable pulse crop that is cultivated in the tropical and subtropical zones, which is regarded not only in terms of food security but also in terms of improved soil fertility and as a source of income among the smallholder farmers. Its productivity is, however, low because of biotic and abiotic stresses, bad crop management and low adoption of better agronomic practices. The concept of using plant growth regulators (PGRs) and growth retardants has been seen as a successful method to stimulate crop growth, crop yield and economic benefits by controlling physiological and morphological characteristics. PGRs, including auxins, gibberellins and cytokinins, are used at different stages of growth to induce the division of cells, elongate cells, flowering, pod development and uptake of nutrients. Chlormequat chloride (CCC), paclobutrazol and maleic hydrazide are growth retardants that regulate excessive vegetative growth and enhance flowering and modify assimilate partitioning in favor of reproductive organs. Concentration, timing and environmental conditions are optimized to ensure that there are good responses in various agro-ecological conditions. Research has demonstrated that the use of moderate amounts of PGRs and retardants improves yield parts, such as the number of pods per plant, the number of seeds per pod, seed weight and overall yield. They also enhance photosynthetic performance, biomass growth, protein level and harvest index by inhibiting apical dominance and enhancing reproductive growth. By and large, growth regulators and retardants enhance productivity, profitability and efficiency of resource utilization in pigeonpea farming, but optimization to suit the regions is critical to reap the long-term gains.