The objective of this research was to evaluate the effect of drought and Phomopsis on seed composition constituents in Phomopsis susceptible (S), moderately resistant (MR), and resistant (R) soybean genotypes grown under irrigated and non-irrigated environments. Genotypes of maturity group (MG) III and V were grown under field conditions in 2003 and 2005. Seed protein, oil, fatty acids, sugars, and minerals were evaluated in seeds harvested at harvest maturity (R8) and 15 days after harvest maturity (delayed harvesting). The results showed that seed protein and oleic acid were higher in S than in MR or R genotypes at 15 days after harvest maturity in MG III in non-irrigated soybean. For MG V genotypes, seed protein, oil, and oleic acid were higher and linoleic and linolenic acids were lower in MR and R than in S in irrigated and non-irrigated soybean at harvest maturity and 15 days after harvest maturity. In MG III genotypes, seed sucrose, raffinose, and stachyose were higher in MR and R than in S genotypes in irrigated soybean at maturity only. In irrigated or non-irrigated soybean, seed sucrose, raffinose, and stachyose were higher in R than in MR or in S in MG V in 2003 and 2005 at harvest maturity or 15 days after harvest maturity. Seed minerals were also altered in MG III and V. This research demonstrated that seed composition components were altered by drought and Phomopsis and the degree of alteration depended on the level of resistance of the genotype and MG.
