RELATIONSHIPS BETWEEN CHANGES IN THE HEAD ING 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 mat ter yield of main stem, between DAS-H and dry matter yield-related tra its involving total leaf number, number of elongated internodes, main stem length and diameter among 14 sweet sorghum cultivars in the north ern area of Japan were investigated in 1991. Changes in heading date a nd yield-related traits of eight cultivars were investigated from 1991 to 1993. In 1991, significantly positive linear correlations among cu ltivars were observed between DAS-H and dry matter production of main stem, and between DAS-H and yield-related traits. Some cultivars had l arge flexibility in heading date for 3 years. For example, cv. Wray ha d 88 days after sowing to heading (DAS-H88) in 1991 and DAS-H125 in 19 93. Using the cumulative average temperature from seeding to heading, the difference was 585 degree days. The relative orders of heading dat e among varieties were unstable. Some varieties including Rio, Wray an d Keller showed medium maturity in 1992, but matured early in 1991 and matured late in 1993. Highly positive correlations were observed betw een DAS-H and yield, and between DAS-H and yield-related traits each y ear, whereas for combined 3 years data, lowered correlation coefficien ts were obtained for both cases.