Inducing terminal drought stress using potassium iodide (KI) for screening castor germplasm with good root traits

Abstract

Castor is cultivated as a rainfed crop in southern India and experience terminal drought stress with cessation of monsoon. Stem reserves are an important source of carbon for grain filling when current photosynthesis is inhibited by drought and mobilization of stem reserves towards economic yield is an important trait in selection for terminal drought tolerance. Potassium iodide (KI), a chemical contact canopy desiccant which induce leaf desiccation by reducing chlorophyll content is used to induce drought stress for assessing variability in stem reserve mobilization. During kharif, 2015-16, in RG 1826, a genotype selected for drought tolerance, KI was sprayed @ 0.2-1.0% at 50% filling of primary spikes or 1.0-3.0% at 50% filling of tertiary spikes separately as two sets. 1.0% spray at both stages recorded total leaf desiccation, less seed yield reduction in primary (16%) and tertiary (29%) order spikes. Hence, 1.0% KI is the optimum concentration to screen castor genotypes for terminal drought stress tolerance. During laterabi, 2016-17, 12 germplasm lines with known drought tolerance (stress from 30-90 DAS) and root growth characters along with two checks were sown and at 50% filling of tertiary spikes, KI was sprayed @ 1.0%. Promising genotypes with high stem reserve mobilization were identified.