SEED PRODUCTION POTENTIAL IN BRED POPULATIONS AND CULTIVARS OF SETARIA-SPHACELATA

Poor seed production is a major limitation to use of the winter-green cultivar Setaria sphacelata cv. Narok and the botanical variety splendida. Six experimental varieties with yields and winter-greenness comparable to Narok, but which had shown evidence of higher tiller fertility and three experimental varieties bred to incorporate botanical fertility into var. splendida, were compared with cvv. Nandi, Narok and Kazungula and another winter-green accession, for seed production. The study was conducted over a two-year period, when swards were 4-6 years old. Seed production was assessed on a continuous basis and comparisons made at peak seed production. Mean cleaned-seed yields of Nandi, Narok and Kazungula were 89, 57 and 293 kg/ha/annum, respectively. Five of the six winter-green experimental varieties yielded 100-260 kg/ha/annum, 2-4 times as much cleaned seed as did Narok. The three experimental varieties derived from var. splendida averaged 118-156 kg/ha/annum. For most varieties, germination 6 months after harvest exceeded 50%. Seed yield was strongly correlated with seed weight per unit length of ripe inflorescence but, unexpectedly, only weakly correlated with inflorescence number. This was associated with a strong negative correlation between inflorescence length and number, which is considered to be an attribute of the sample of populations studied rather than a general phenomenon. At peak seed yield, 25-72% of inflorecences were at a preripeness stage and would not have contributed to seed yield. The data on seed yield of old stands of these experimental setaria varieties contributed to the decision to release for commercial use the cultivars Splenda and Solander.