Diseases cause severe losses (20–100%) to yield and quality of common bean (Phaseolus vulgaris L.) worldwide. Our objectives were to describe major bean disease problems in the Americas and review progress achieved in breeding for resistance. We also describe strategies to integrate genetic improvement for resistance to multiple diseases with cultivar development. Common bacterial blight, halo blight, and bacterial brown spot are the major bacterial diseases. Angular leaf spot, anthracnose, root rots, rust, and white mold are severe fungal diseases. Bean common mosaic virus (BCMV), Bean golden mosaic virus (BGMV), Bean golden yellow mosaic virus (BGYMV), and Beet curly top virus (BCTV) are important viral diseases. Breeding for resistance to one or two diseases at a time is emphasized. Backcross, pedigree, and bulk‐pedigree methods of breeding are used. The use of molecular markers has gradually increased. Substantial progress has been made in breeding and genetics of resistance to most of these diseases; however, improvement in resistance to bacterial brown spot, halo blight, root rots, and web blight has been slow and localized. Furthermore, cultivars with high levels of resistance to one or more quantitatively inherited diseases (e.g., common bacterial blight and white mold) are rare. Breeding strategies for simultaneous and integrated genetic improvement of multiple qualitatively and quantitatively inherited resistances and cultivar development are briefly described.

Onion (Allium cepa) is an economically important crop in the United States, generating over $900 million annually in farm receipts from 2000 to 2004 (88). U.S. onion production area ranges from 65,000 to 70,000 hectares annually, with over 80% of the summer production (54,000 hectares) in the western states. On average, 53 million metric tons of onion bulbs are harvested annually from nearly 3 million hectares worldwide. A significant portion of the U.S. and world supply of onion seed is produced in the western United States, primarily in the Pacific Northwest (124). The genus Allium includes various economically important cultivated species, including the bulb onion, chive (A. schoenoprasum), garlic (A. sativum), and leek (A. porrum) (10). At least 18 other Allium species are consumed as fresh vegetables, pickled, or used as flavoring. However, the bulb onion is the most economically valuable species. On average, worldwide production of garlic is valued at about 10% that of the bulb onion (10). Leek and bunching onion are the next most valuable species, with production concentrated in Europe and the Orient, respectively. Bunching onion (A. fistulosum) production also is important in some areas of the United States, such as California. The distinctive flavor or odor of Allium spp. is produced when plant tissues are bruised or cut, and the enzyme alliinase hydrolyzes S-alk(en)yl cysteine sulfoxide precursors to form volatile sulfur compounds (10). Onion, garlic, and their relatives, although primarily grown for food, are also used in traditional medicine, including the treatment of chicken pox, the common cold, influenza, measles, and rheumatism. Antimicrobial characteristics of alliums are likely the result of sulfur compounds. Research has demonstrated that extracts of onion and garlic decrease sugars, lipids, and platelet aggregation, and enhance fibrinolysis in blood, indicating that alliums may help prevent arteriosclerosis and other cardiovascular diseases (111).

Under favorable weather conditions white mold causes 100% loss of yield and quality of susceptible common bean (Phaseolus vulgaris L.) cultivars. The disease is endemic and widespread in North and South American countries including the United States, Canada, Argentina, and Brazil. Our objective was to review progress achieved in identifying sources of resistance in Phaseolus species, genetics, and breeding for resistance to white mold. We also describe an integrated genetic improvement strategy for resistance to the pathogen with germplasm enhancement and cultivar development using multiple‐parent crosses and gamete selection methods of breeding. Substantial progress has been made in understanding pathogenic variation in the white mold fungus, developing screening methods, identifying sources of resistant germplasm, genetics of resistance, and introgressing resistance from the secondary gene pool, and breeding for resistance to white mold. Also, molecular marker‐assisted selection for partial resistance is practiced. However, development of white mold resistant common bean cultivars in most market classes has been slow and localized. Breeding strategies for simultaneous and integrated genetic improvement of qualitatively and quantitatively inherited resistances to white mold and cultivar development are briefly described.

Sclerotium populations of Sclerotinia scierotiorum were germinated sclerotium in both crops. An apothecium variable during this 3-yr study; however, sclerotia did not continued to produce ascospores in the field for about 7 days. accumulate in increasing numbers in fields planted to Apothecium production was less beneath the open bush susceptible dry edible bean (Phaseolus vulgaris) cultivars canopy of dark red kidney Charlevoix and the upright semidespite annual white mold epidemics. Populations ranged vine canopy of small white Aurora when compared to between one and three sclerotia/kg air-dried soil in bean production beneath the dense compact bush canopy of Great fields. A 3-yr crop rotation did not reduce sclerotium Northern (G.N.) Code P #92 and the dense viny canopies of populations significantly. A low sclerotium population of G.N. U I #59 and G.N. Tara. Over 90% of the apothecia were 0.2/ kg soil produced sufficient inoculum (ascospores) to located either adjacent to the plant or on the side of the infect 46% of the plant canopy during 1975. Sclerotia were irrigation furrow, regardless of plant growth habit. An redistributed within a field by irrigation water. During irrigation application every 5 days increased apothecium August, numerous sclerotia germinated to form 11-14 and 7production, especially beneath Tara, when compared to a 10-II apothecia/m 2 in bean and sugar beet fields, respectively, day irrigation frequency. Each apothecium produced about An average of two apothecia were produced by each 2.3 X 106 ascospores under laboratory conditions.

Iris yellow spot virus (IYSV) is an emerging and potentially devastating disease of onion that was recently detected in Colorado and other onion producing regions in the western United States. In annual surveys, IYSV was confirmed in one of 18 fields (5.6%) in 2001, four of 24 (16.7%) in 2002, and 41 of 56 (73.2%) in 2003. IYSV was confirmed on volunteer onions in 2003 at all four locations where IYSV was observed in the onion crop the previous year. The disease was detected in six of seven western Colorado onion fields surveyed in 2003, but was not observed any year in southern or northeastern Colorado. The spatial variability of disease incidence, yield, and plant population also was mapped in two fields in 2003 using the global positioning system and a geographic information system. Disease incidence varied among cultivars, plant population, fields, and location in the field. Distinct disease gradients were observed in both fields with susceptible cultivars Teton and Granero, but not in the moderately resistant cultivar Sterling. In fields planted to the susceptible cultivars, disease incidence was highest on the field edges and lowest near the field centers. Plant population was negatively correlated with IYSV incidence in cultivar Sterling (R2 = 0.56, P = 0.003), but not with the susceptible cultivars. Yield of jumbo market class onions, but not total yield, was negatively correlated with increasing IYSV incidence (R2 = 0.37, P = 0.012) in cultivar Teton. Colossal market class yield, but not other yield components, was negatively correlated with IYSV incidence in cultivar Sterling (R2 = 0.28, P = 0.061). The results of these studies indicate the distribution of IYSV is rapidly expanding in Colorado and is associated with a general reduction in bulb size.