Phomopsis Seed Infection Effects on Soybean Seed Phenol, Lignin, and Isoflavones in Maturity Group V Genotypes Differing in Phomopsis Resistance

Abstract

Research on factors controlling production and quality of soybean seed phenolics is very limited. The objective of this research was to evaluate phenolic compounds (total phenol, lignin, and isoflavones), and cell wall boron (B) in seed of susceptible (S), moderately resistant (MR), and resistant (R) soybean genotypes to phomopsis seed decay disease under irrigated and non-irrigated conditions. Seeds were evaluated at harvest maturity stage (R8) and 15 days after harvest maturity to test for weathering effects. Results showed that the concentration of seed phenolic compounds was significantly (P ≤ 0.05) higher in R and MR genotypes than S genotypes under irrigated and non-irrigated conditions. Cell wall boron percentage was significantly higher and total boron was significantly lower in S genotypes than MR and R genotypes. The current research demonstrated that genotypes with higher phomopsis seed infection had lower phenolic compounds, indicating a possible association of these compounds with disease defense mechanism. The higher cell wall B percentage in S genotypes indicated a possible involvement of boron in phenolic metabolism and phomopsis resistance. The decrease in phenolic compounds concentrations in S genotypes in seed collected 15 days after R8 indicated the weathering effects on seed coat and cell wall deterioration. Soybean breeders may be able to use phenolics as phenotypic trait and biomarkers for selecting soybean genotypes for higher resistance and for higher seed nutritional qualities.