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2 Dry Bean Breeding and Production Technologies
Phillip N. Miklas James D. Kelly and Karen A. Cichy
Production practices and trends Production practice Production trends
Bean genetics Bean species Gene pools Wild bean germplasm
Breeding procedures and practices Breeding procedures − hybridization
Breeding methods Seed multiplication
Breeding for specific traits Breeding for yield Disease resistance Abiotic stress tolerance Breeding for direct harvest systems Symbiotic nitrogen fixation (SNF) Processing quality Micronutrient content Niche markets Organic dry beans Slow darkening (SD) pinto beans Heirloom beans
Genomic research and transgenic beans Genomic research Transgenic beans
INTRODUCTION
Common bean (Phaseolus vulgaris L.) includes a wide array of edible dry bean seed types that differ in size, shape, and color and are known collectively as dry beans; and the many horticultural pod types that also vary in color, size, shape, and flavor known collectively as snap, or garden, or green beans. The major focus of this chapter will be on dry bean breeding, but many of the characteristics discussed are common to both horticultural types. Common bean is a self‐pollinated diploid crop (2n = 2x = 22) with a small genome size of approximately 587 million base pairs distributed along 11 chromosomes (Schmutz et al. 2014). The breeding systems used to improve the crop and the genetic structure of the varieties released to farmers is dependent on the pollination system and flower structure. Varieties are highly inbred homozygous pure lines that maintain their genetic integrity and stability for generations. Bean varieties do not ‘run out’ or change due to genetic drift, but perceived changes due to inadvertent seed mixtures that go undetected, low levels of outcrossing in the field, and the accumulation of seed borne bacterial, fungal and/or viral pathogens can occur. More subtle changes may result in differential performance from changes in climate or from the emergence of new pathogen strains to which the variety is not adapted or lacks resistance. Since beans are an inbreeding species, with no effective mechanism to transfer pollen, hybrid bean varieties are not a viable option at this time.
The first dry bean breeding program in the US was established at Michigan State University (formerly Michigan State College) in the early 1900s (MSU 2009). This was followed by the establishment of a breeding program at the University of Idaho in 1925 (Singh et al. 2007). The most recent bean‐breeding program was established at North Dakota State University in the early 1980s. Currently, there are four public bean‐breeding programs at major land grant Universities, four USDA‐ARS programs that focus on bean genetics and pathology and four private companies actively working on bean breeding. The reader is referred to a few reviews where different aspects of bean breeding are summarized (Kelly 2004, 2018; Miklas et al. 2006; Singh et al. 2007; Beaver and Osorno 2009; Singh and Schwartz 2010; Kelly and Bornowski 2018; Beaver et al. 2020).
PRODUCTION PRACTICES AND TRENDS
Production practice
Dry beans are a short season crop that matures in 85–100 days. Consequently, beans are produced largely in northern states or at higher elevations in the intermountain and western states. Approximately 70% acreage planted to beans in the US is grown under rainfed conditions in the East, Midwest, and Upper Midwest, whereas essentially all western production in semiarid states is grown under irrigation. Yields reflect the availability of water resources and the highest yields are produced in irrigated regions. The major production areas and seed types grown in these states are shown in Figure 2.1. Beans are grown as a row crop in all states, and row widths vary by location, irrigation systems, and harvest methods. In recent years, growers in the Midwest have moved from wider 70–75 cm to narrower 35–55 cm row spacings as newer varieties are more upright, thus better suited for direct harvest. To optimize productivity and better utilize water in western states, growers tend to plant higher plant population densities in 55 cm row spacing. Few producers drill beans (18–25 cm rows), because it often results in shorter, more difficult‐to‐harvest plants and inconsistent yield advantages.
US planting time depends on the speed of warm up in the spring and the length of growing season. Beans require soil temperatures of 13 °C at 5 cm depths to ensure favorable germination and growth. Dates can vary from mid‐May in the Pacific Northwest and Upper Midwest to mid‐June in the East and Midwest to early July in California, which has a longer growing season. Seeding rates vary by seed types; small‐seeded navy and black beans at 40–60kg/ha; medium‐seeded pintos, red beans at 50–65 kg/ha; and larger‐seeded kidney and cranberry beans