W. R. Fehr

We developed stage of development descriptions which we believe apply to all soybean ( Glycine max (L.) Merr.) genotypes grown in any environment. The descriptions apply to single plants or a community of plants and are precise and objective. Vegetative and reproductive development are described separately. Vegetative stages are determined by counting the number of nodes on the main stem, beginning with the unifoliolate node, that have or have had a completely unrolled leaf. Reproductive stages Rl and R2 are based on flowering, R3 and R4 on pod development, R5 and R6 on seed development, and R7 and R8 on maturation. The stage descriptions should enhance soybean research by standardizing descriptions of soybean plant development. The system also will be used by the soybean hail insurance industry for stage determination in adjustment of losses.

Soybean development is a continuous process that begins when a seed germinates and is completed where a mature seed is ready for harvest. During its life, the soybean plant is exposed to many factors that may encourage or retard its development and productivity. Some factors are controlled by nature, such as wind, rain, hail, and frost. But farmers also influence soybean development and productivity by application of pesticides and fertilizers or by the timing and methods of planting, cultivation, and other cultural practices.

In this book, successful plant breeders share their experiences and that of their colleagues. They provide a step-by-step description of the process of cultivar development for a crop species, discuss the alternative strategies that are available at each step of the process, and describe those strategies that have been used most successfully. Crop species were chosen fro this book to represent the major types of cultivars that are grown commercially. The development of asexually propagated cultivars, pure-line cultivars, synthetics, multilines, and hybrids are described in one or more of the chapters. Collectively, the chapters describe the application of all breeding method that are currently used by plant breeders for cultivar development.

Isoflavones in soybean [ Glycine max (L.) Merr.] may have positive impacts on human health. The objective of this study was to determine the role of the genotype, environment, and genotype × environment interactions on isoflavone contents of soybean. Nine isoflavones were measured in six cultivars grown at eight locations during 2 yr. The mean contents of total isoflavones and six of nine individual isoflavones were significantly higher in 1996 than 1995. There were significant differences among locations in one or more years for total and individual isoflavone contents. The year × location interactions were significant due to changes in rank and magnitude among the locations during the 2 yr. The genotype, genotype × year, genotype × location, and genotype × year × location interactions were significant for total and individual isoflavone contents. Despite the significant genotype × environment interactions, the differences between the cultivars with the highest and lowest total and individual isoflavone contents were relatively consistent among the 16 environments. It should be possible to breed for isoflavone content as a quantitative trait in a cultivar development program.