Patterns of osmotic adjustment in pigeonpea - its importance as a mechanism of drought resistance

Osmotic adjustment (OA) is considered as an important physiological mechani sm of drought adaptation in many crop plants. The present investigation was aimed at assessing the importance of OA in improving productivity under dr ought. Using two automated rain-out shelters, 26 extra-short-duration pigeo npea [Cajanus cajan (L.) Millsp.] genotypes were grown with irrigation duri ng the growth period or with water deficit imposed from flowering until mat urity. Mean leaf Psi s(100) (60-92 DAS) under drought correlated significan tly (r(2) = 0.72**; n = 26) to the mean OA (60-92 DAS) and contributed 72% of the genotypic variation in OA. Significant genotypic variation was obser ved in the initiation of OA, the duration of OA and the degree of OA. Based on the measured QA at 72, 82, and 92 days after sowing (DAS), genotypes we re grouped into five different clusters. Genotypic differences in total dry matter production under drought were positively associated with OA at 72 D AS (r(2) = 0.36**, n = 26). Significant positive relationship between OA at 72 DAS and grain yield under drought was found (r(2) = 0.16*; n = 26). How ever, OA towards the end of pod filling phase, i.e. at 92 DAS, had a signif icant negative relationship with grain yield under drought (r(2) = 0.21*; n = 26). Genotypic differences in grain yield under drought was best explain ed using stepwise multiple regression to account for differences in OA at 7 2, 82, and 92 DAS (r(2) = 0.41**; n = 78). The degree of OA at 72 and 82 DA S contributed positively to the grain yield, whereas OA at 82 DAS contribut ed negatively to this relationship. (C) 2000 Elsevier Science B.V. All righ ts reserved.