SOYBEAN SEED OIL CONTENT - GENETIC-CONTROL UNDER DIFFERENT PHOTOPERIODS

The oil content of soybean (Glycine max (L.) Merrill) seeds is a polyg enic and complex trait that is responsive to environmental effects tha t occur during plant development. Our objective was to study the seed oil content of soybeans developed under diverse photoperiod and temper ature conditions. Three parental inbred lines with classic (BR-13, FT- 2 and BR85-29009) and one with long juvenile flowering type (OCEPAR 8) and the F2, F3, and F9 generations derived from all possible crosses between them (including reciprocals) were sowed in September 27th, Oct ober 20th and December 17th in 1993 in Londrina, Parana State, Brazil (between 23 degrees 08'47'' and 23 degrees 55'46'' latitude S). The Oc tober and December sowing dates are within the period the varietal res earch personnel recommend for sowing soybeans in Parana State. The ana lysis of variance indicated significant differences among sowing dates , among advanced inbred lines, and the sowing date x inbred line inter action. Seed oil content increased from September to October and decre ased from October to December in all materials, but the reduction was greater in FT-2 and OCEPAR 8 among the parentals. The additive genetic Variance (D) or additive variance among linked genes (DI) was signifi cant for all crosses and sowing dates. Genotype x microenvironment int eractions were important in some crosses. The additive [d] effects wer e greater in September and October, and the additive x additive intera ction [i] was important in October among the mean genetic parameters. Significant dominance effects [h] were more frequent in December and O ctober, often in direction of the increased seed oil content. The heri tability estimates ranged from 15 to 43%, with the highest values obta ined in September. The prediction of cross potential to generate highe r seed oil inbred lines indicated that selection is likely to be succe ssful in most crosses. The highest proportion of inbred lines with see d oil percentage above the standard (lines with more than 22% seed oil content) was for BR85-29009 x OCEPAR 8 in September, FT-2 x OCEPAR 8 in October, and in BR85-29009 x OCEPAR 8 and BR-13 x OCEPAR 8 in Decem ber.