Altitudinal effects on <i>Stylosanthes guianensis</i> at a low latitude site. 2. Seed Production

Seed production of five selections of Stylosanthes guianensis var. guianensis was studied in Bali, Indonesia (latitude 8° 30' S) with a series of harvests at three sites of increasing altitude and rainfall: (1) Sesetan, 10 m, (2) Kuwum, 280 m and (3) Pekarangan, 1000 m. Seed yield of cv. Graham, CPI 34906, cv. Cook and cv. Endeavour was maximal at Sesetan with yields of 109, 39, 38 and 166 g/m2 respectively, whilst cv. Schofield, which flowered little at low altitude, produced 12 g/m2 at Pekarangan. Optimum time of harvest varied from 26 April for cv. Graham at Sesetan to 1 November for cv. Schofield at Pekarangan. Yield stability over sites was greatest in cv. Graham, in which increased number of florets per spike at high altitude partially compensated for negative altitudinal effects on spike density. Disease reduced yields of cv. Cook and cv. Endeavour at Kuwum and Pekarangan and the incidence of rainfall at advanced stages of crop development reduced spike density and seed maturation. It is suggested that the high seed yields attained at the low altitude, low latitude Sesetan site were attained via (1) vigorous vegetative growth and a longer duration of floral induction resulting in high bud site density, (2) high bud site fertility, (3) high seed set (co. 70-80 %), (4) high seed weight and (5) little or no disease or insect damage. The greater synchrony of flowering at higher latitude sites may be less critical for high levels of seed production than the greater length of crop development available at low latitudes