Identification of soybean accessions with high germinability in high-temperature environments
Soybean [Glycine max (L.) Merr.] seed produced in high-temperature, high-humidity production environments is prone to have substandard germination. Hardseededness, wrinkled seed coats, and infection by Phomopsis longicolla Hobbs are all known to affect soybean seed germinability. Ancestors of modern U.S. soybean cultivars may lack the necessary variability to impart high germinability to new cultivars without the introgression of new genetic diversity. The purpose of this research was to identify soybean germplasm possessing positive traits affecting high seed germinability for seed produced under high-temperature environments, such as in the early soybean production system (ESPS) of the midsouthern United States. Seed was produced in the ESPS for 486 U.S. plant introductions (PI), 25 ancestral lines of U.S. cultivars, and four U.S. cultivars at Stoneville, MS, in 2002 and 2003. Standard and accelerated-aging germination percentages, hardseededness, seed coat wrinkling, and incidence of P. longicolla were estimated for each line. Based on the 2002 and 2003 field data, 42 PIs were selected for further testing, along with three cultivars, in two greenhouse temperature regimes (36° and 42°C) at Stoneville, MS, in 2005. Standard field germinations for the 25 ancestral lines ranged from 26 to 82%. Sixty-three accessions were identified as having a mean standard field germination of 90%, <10% hard seed and P. longicolla infection, and 10% wrinkled seed coat. Genotypes with excellent seed traits have now been identified for soybean breeders to use in developing improved cultivars with high seed germinability for use in high-temperature production environments.