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Growth Analysis of a Sorghum Hybrid and its Parents¹

Growth rate, leaf area index, net assimilation rate, and distribution of dry matter among aboveground plant parts were determined for sorghum [Sorghum bicolor (L.) Moench] hybrid ‘RS 610’ and its parents throughout the growing season in a replicated field experiment. Dry weight and leaf area were measured twice weekly before flowering and weekly thereafter. The hybrid developed faster than its parents. It had greater leaf area than its parents until 1 week prior to flowering, and less leaf area than its parents thereafter. The hybrid had greater total dry weight than its parents throughout the growing season. The crop growth rate (CGR) of the hybrid was greater than that of either parent from emergence to panicle initiation, while net assimilation rate and relative growth rate did not differ among genotypes at this period. RS 10 outyielded its parents in grain, and had more kernels per panicle than the female parent, but did not differ from the male parent in this characteristic. The yield superiority of RS 610 was attributed mainly to the combination of the high CGR of the female parent during grain filling with the effective conversion of dry matter to grain of the male parent. More rapid seedling growth and a longer grain filling period were also advantages of the hybrid over its parents.

Key Words: Crop growth rate • Net assimilation rate • Heterosis • Harvest index • Grain sorghum • Sorghum bicolor (L.) Moench • Hybrid vigor

² Former NSF graduate fellow, Texas A&M Univ. (present address, ICRISAT, 1-11-256 Begumpet, Hyderabad 500016, A.P., India), and research geneticist, USDA-ARS, College Station, TX 77843.

Received for publication September 13, 1976.