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

Abstract

Two varieties of mungbean (Vigna radiataL.), BARImug 2 (M2) and BARImug 3 (M3) were grown under 1) 12-h light at 700„molm-2 s”1 (HL) at 30°C/12-h darkness at 25”C (HL + LT), 2) 12-h HL at 40°C (HT)/12 -h darkness at 25°C (HL + HT) and 3) 12-h light at 200 jumolm^s-1 (LL) at HT/12-h darkness at 25°C (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 0O2 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 (FA/F’m) after heat shock at 50°C 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.

Keywords

• Chlorophyll fluorescence
• Drymatter allocation
• Photosynthesis
• Pod setting
• Vigna radiata L