Effects of Maturity and Phomopsis longicolla on Germination and Vigor of Soybean Seed of Near-Isogenic Lines.

Soybean [Glycine max (L.) Merr.] seed quality has declined in the mid-southern United States due to the shift to soybeans that mature during mid August through September as opposed to October to November, which was common in the past. This decline was shown to be related to increased temperatures during seed maturation, increased levels of Phomopsis seed decay (PSD), and potentially maturity per se. In this study, the effects of maturity and Phomopsis longicolla Hobbs, the cause of PSD, on seed quality were evaluated in a field trial of two sets of near-isogenic soybean lines ('Clark' and 'Harosoy'), where the maturity of each line within a set varied. No effects of maturity on germination, accelerated aging germination (AA), or hardseededness were detected. Phomopsis longicolla level had a significant negative effect on germination in both isoline sets. Year had a significant effect on germination in both isoline sets. In addition, year and P. longicolla level had a significant negative effect on AA for the Clark set, and only year had an effect on AA in the Harosoy set. Phomopsis longicolla level, not maturity, was the most significant factor in seed germination and vigor. Therefore, there continues to be a great need to develop varieties of soybeans with resistance to P. longicolla and high germinability when seed are produced in conditions of high humidity and high temperatures. [ABSTRACT FROM AUTHOR]