Biomass distribution, maturity acceleration and yield in drought-stressed common bean cultivars

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Common bean ( Phaseolus vulgaris L.) is an important food crop grown under rainfed conditions in Latin America where drought is a major limiting factor for production. The objective of this study was to assess the role of phenological adjustment and shoot biomass distribution on seed yield of drought-stressed common bean. Four cultivars differing in growth habit, gene pool origin, and contrasting responses under drought, were tested during 2001 at two locations in Mexico: Cotaxtla, Veracruz (lowlands) where the effect of terminal drought (TD) (end-of-season) was evaluated, and Texcoco, State of Mexico (highlands), where the effects of intermittent and terminal drought were evaluated. Seed yield, plant shoot biomass, and days to flowering and to physiological maturity were recorded. Leaf relative water content (RWC) was recorded after the onset of the intermittent drought (ID) treatment in Texcoco. The drought intensity index was 0.37 in Cotaxtla compared to 0.49 and 0.58 under TD and ID, respectively in Texcoco. Days to flowering and to physiological maturity showed a negative and significant relationship with seed yield. Under drought stress, a significant reduction in the harvest index was observed in susceptible cultivars. All cultivars showed higher values of shoot biomass accumulation, pod and seed number, seed weight and RWC at the basal nodes of the plant across locations and moisture treatments. Cultivar Pinto Villa exhibited the highest biomass accumulation and seed yield across treatments and locations. Significant reduction in number of days to maturity was observed under drought, mainly in resistant cultivars, Pinto Villa and G4523. Maturity acceleration, coupled with a high seed filling rate, contributed to lessen the impact of drought stress in resistant common bean cultivars.