Abstract

Two experiments were conducted to determine the importance of photosynthetic leaf area and panicle size on fina1 grain weight (FGW) in sorghum (Sorghum bicolor Moench). The first experiment consisted in defoliating the three upper (U), intermediate (M), and lower (L) leaves and different combinations (U+M, U+L, M+L, U+M+L), plus a check, at three different times post-anthesis (0, 10 and 20 days). The second experiment consisted in partially removing 0, 20, 40, 60, and 80% of the panicle at the same three times. Experiments were conducted during the spring-summer season of 1989 in Rio Bravo, Tamnulipas, México, using hybrid RB-4000. Results indicated that U and M leaves contributed the most to FGW at anthesis, as their defoliation reduced FGW by 11 and l5% compared to the check. If upper or intermediate leaves were defoliated 10 or 20 days post-anthesis, FGW was reduced by 2S and 2%, respectively. Combined defoliation (U+M, U+M, M+L) during anthesis or 10 days arter reduced FGW more, with tbe treatment U+M+L having the greatest reduction in FGW at any time. Removal of portions of the pnnicle increased FGW, the largest effect being detected during anthesis, followed by 10 and 20 days after.