Rapid growth rate of the human population is driving the increased demand for cultivated soybean [Glycine max (L.) Merrill], a major source of protein and oil in global food, feed, and biofuel production. Increasing yield at a pace faster than traditional breeding methods presently achieve has become a need and future commitment. In soybean, a self-pollinated crop, a possibility to increase yield may result from the development of hybrid cultivars. Researchers have been interested in floral development and pollination, as these factors have a direct impact on maintaining and enhancing crop yields. Soybean breeders also need to understand phenotypic differences in male-sterility loci that could be manipulated for use in hybrid seed production. Among them, the ms9 locus is particularly interesting because it has high insect pollinator attraction, which facilitates its potential use in hybrid seed production. Recent release of multiple genomic tools for soybean, new bioinformatic approaches can be used to identify candidate male-sterility genes and compare their function. This dissertation is organized in chapters dealing with different aspects related to the use of male sterility.

In Chapter 2, we determined that ms9 is a thermosensitive male-sterility locus, influenced by day temperature. Bioinformatic analyses in Chapter 3 identified four homeologs of male-sterility genes from Arabidopsis and rice as candidate genes for ms3, msp, and ms2 loci. A total of 23 candidate genes for the ms9, msp, ms3, and ms2 loci were identified. In Chapter 4, utilizing a similar bioinformatic approach targeting the ms9 locus, we prioritized a list of nine candidate genes for analyses using quantitative real-time polymerase chain reaction (qRT-PCR). Two genes, a small nuclear ribonucleoprotein (snRNP, Glyma03g30880) and an auxin-indole-3-acetic acid (AUX/IAA) responsive gene (Glyma03g31530), had increased expression in fertile and in male-sterile floral phenotypes as day temperature increased from 30 to 35 yC.

Our results will facilitate protocol development to utilize ms9 as the source of male sterility for soybean breeding and hybrid seed production programs. The bioinformatic approaches used, identified for the first time, candidate male-sterility genes in soybean, which allow future elucidation of functional aspects of these candidate male-sterility genes. Finally, polymorphic markers will be designed once the male-sterility gene is confirmed. Marker assisted selection (MAS) programs can be used to identify male-sterile, female-fertile plants prior to flowering. This approach would ultimately improve efficiency of identifying plants for use as female (pod) parent in hybrid seed production.