Growth, Yield and Photosynthetic Activity of Vigna radiata L. Grown at Different Temperature and Light Levels

Two varieties of mungbean (Vigna radiata L.), BARImug 2 (M2) and BARImug 3 (M3) were grown under 1) 12-h light at 700 mumol m(-2) s(-1) (HL) at 30degreesC/12-h darkness at 25degreesC (HL+LT), 2) 12-h HL at 40degreesC (HT)/12-h darkness at 25degreesC (HL+HT) and 3) 12-h light at 200 mumol m(-2) s(-1) (LL) at HT/12-h darkness at 25degreesC (LL+HT), and their growth, yield and photosynthetic activities were analyzed. The plants grown under LL+HT were the tallest followed by those grown under HL+HT and HL+LT, in this order. The leaf area was the largest under HL+LT followed by LL+HT and HL+HT. In general, the plants grown under HT had lower biomass compared with those grown at LT. Grain yield was zero (no pod setting) under HL+HT in both varieties, but that under LL+HT was 30-40% of that under HL+LT. M3 produced higher grain yield as well as higher biomass than M2 under both HL+LT and LL+HT. The yield reduction under LL+HT was primarily due to the substantial reduction in the number of pods per plant as well as number of seeds per pod. HT decreased the photosynthetic CO2 assimilation rate (Pn), and the plant under HL+HT had lower Pn than those under HL+LT. The heat acclimation of photosynthetic apparatus was considered to proceed more easily under HL than under LL, because the photochemical efficiency of PSII (Fv/Fm) and quantum yield of PSII electron transport (FDelta/F'm) after heat shock at 50degreesC were greatly higher in the plants grown under HL+HT than those under HL+LT. It was concluded that HL at HT inhibited pod setting but accelerated the heat acclimation of photosynthetic apparatus of mungbean.