Relationships between Changes in the Heading Date and Yield-related Traits of Sweet Sorghum (Sorghum bicolor Moench) in the Northern Area of Japan

Relationships between days after sowing to heading (DAS-H) and dry matter yield of main stem, between DAS-H and dry matter yield-related traits involving total leaf number, number of elongated internodes, main stem length and diameter among 14 sweet sorghum cultivars in the northern area of Japan were investigated in 1991. Changes in heading date and yield-related traits of eight cultivars were investigated from 1991 to 1993. In 1991, significantly positive linear correlations among cultivars were observed between DAS-H and dry matter production of main stem, and between DAS-H and yield-related traits. Some cultivars had large flexibility in heading date for 3 years. For example, cv. Wray had 88 days after sowing to heading (DAS-H88) in 1991 and DAS-H 125 in 1993. Using the cumulative average temperature from seeding to heading, the difference was 585 degree days. The relative orders of heading date among varieties were unstable. Some varieties including Rio, Wray and Keller showed medium maturity in 1992, but matured early in 1991 and matured late in 1993. Highly positive correlations were observed between DAS-H and yield, and between DAS-H and yield-related traits each year, whereas for combined 3 years data, lowered correlation coefficients were obtained for both cases.