Stability of soybean yield through different sowing periods

Soybean yield is highly affected by sowing period and there are significant productivity losses when sowings are done outward a relatively restricted period in many regions of Brazil. Breeding cultivars less sensitive to phot operiod and to temperature variations is desirable for adaptation to wider sowing period and wider latitude range and also make irrigated soybean cult ivation possible during the fall-winter seasons in frost free regions. The possibility of selecting high yielding and stable lines for yield during va rious sowing periods was studied by analyzing the behavior of 100 non-selec ted advanced lines (F-9 and F-10), from each one of all possible biparental crosses involving the genotypes BR85-29009, OCEPAR 8, FT-2, and BR-13. Exp eriments were set up in a completely randomized design with single-plant hi ll plots and received supplementary irrigation. Sowing was on Sept 27, Oct 20, Nov 17, and Dec 17 in 1993/94 and Sept 20, Oct 20, Nov 17, and Dec 14 i n 1994/95 at Londrina, PR, Brazil. Procedures of regression analysis and mi nimum variance among planting date means were efficient for selecting stabl e lines during the four sowing seasons. It was possible to select stable an d high yielding genotypes through the four sowing periods in all the crosse s. No specific cross was clearly better to produce a greater number of stab le genotypes.