EFFECTS OF SOIL DROUGHT DURING THE GENERATIVE DEVELOPMENT PHASE OF FABA BEAN (VICIA-FABA) ON PHOTOSYNTHETIC CHARACTERS AND BIOMASS PRODUCTION

The effects of periods of drought occurring during different phases of reproductive growth of faba bean (Vicia faba L.) cv. Yichang Dabai on dry matter production, seed yield, photosynthetic rate and stomatal size were investigated in pot experiments in 1987/88 and 1988/89 at Xichang Agricultural College, China. Six treatments were imposed: no drought (control), and drought from floral initiation to first flowering (D1), from first flowering to full bloom (D2), from full bloom to initiation of pod-set (D3), from initiation of pod-set to full pod-set (D4), and from full pod-set to maturity (D5). Photosynthetic rate, chlorophyll content, leaf area, stomatal pore breadth, biomass and seed yield were decreased by all drought treatments, but stomatal frequency and respiratory rate were increased. The light saturation point for photosynthesis was decreased from 950 mumol/m2/s (PAR) to 570 mumol/m2/s (PAR) in leaves from drought-stressed plants, which also showed maximum stomatal opening between 08.00 and 11.00 h followed by progressive stomatal closure. The response of faba bean to drought varied during the different reproductive growth stages. Plants subjected to drought at stage D1 were less affected than those at other stages, while plants at stage D4 were most sensitive to drought, which reduced seed yield by c. 45% in 1987/88 and by c. 43% in 1988/89 relative to the control plants, suggesting that stage D4 is the stage of reproductive development most sensitive to soil drought in the faba bean.