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Disease and abiotic stress are important factors limiting bean production wherever beans are grown. The development of bean cultivars having resistance to these stresses is a cost-effective and sustainable means to address these constraints. During the past 20 years, the Bean/Cowpea Collaborative Research Support Project (B/C CRSP) has supported common bean cultivar development and germplasm improvement programs in the USA and developing countries. Plant breeders have developed and released in Central America and the Caribbean bean cultivars and germplasm with one or more of the following traits; resistance to bean golden yellow mosaic virus (BGYMV), bean common mosaic necrotic virus (BCMNV), rust, web blight and common bacterial blight (CBB) and greater tolerance to high temperatures. In the highlands of Mexico and Ecuador bean cultivars with resistance to anthracnose, rust, root rots and bean common mosaic virus (BCMV), greater biological nitrogen fixation and improved adaptation to intermittent drought have been released. The bean breeding programs in East Africa have developed and released bean cultivars and germplasm with resistance to BCMNV, rust and bruchid seed weevils. Participation in the B/C CRSP has permitted USA bean breeding programs to develop and release bean cultivars and germplasm with resistance to BGYMV, BCMNV, anthracnose, rust, CBB, architectural avoidance to white mold and greater yield potential. Numerous plant breeders, plant pathologists and agronomists from developing countries have received advanced degree training in the USA, which has enhanced the capacity to develop improved bean cultivars for Latin America and Africa. The lack of sustainable seed production and delivery systems continues to limit the impact of the release of improved bean cultivars in many parts of Latin America and East Africa.

Diseases are a major constraint to production of beans in developing countries, reducing yields and seed quality. Contributing factors include poor disease management, lack of resistant cultivars, and the limited availability of certified disease-free seed. From the outset the Bean/Cowpea Collaborative Research Support Program (CRSP) has emphasized integrated disease management, and breeding for resistance to bean rust (Uromyces appendiculatus), common bacterial blight (Xanthomonas campestris (=X. axonopodis) pv. phaseoli) (CBB) and web blight (Thanatephorus cucumeris (anamorph Rhizoctonia solani)) (WB). Later in the 1990s, angular leaf spot (Phaeoisariopsis griseola) (ALS), and virus induced bean common mosaic (BCM) and bean common mosaic necrosis (BCMN) became more widespread and epidemic. The research included development of disease-resistant germplasm and studies of pathogenic variation and epidemiology. During the early 1990s bean golden yellow mosaic (BGYM), became a major disease of common bean in the Caribbean and Central America. No cultivar resistant to the gemini virus causing BGYM was available in the Dominican Republic (DR) and pesticides were used to reduce transmission of the virus by white flies (Bremisia tabaci) biotype A. A change in the bean-production system to limit reproduction of the vector through a host-free period and concentrate the bean growing season to a four month period reduced BGYM significantly. Improved resistant cultivars and disease management resulted in high yields and self-sufficiency of beans in the DR. Evidence for co-evolution of the pathogens causing ALS, CBB, and rust in the two major bean gene pools (Andean and Middle American) was found. Variation in the WB pathogen on bean indicated independent genetic populations and the presence of different anastosmosis subgroups. WB disease management practices should be designed for the sub-group of the pathogen. Seed transmission was found to be a significant source of R. solani inoculum. Specific (Ur-9 gene) and adult-plant resistance (Ur-12 gene) to rust was identified for PC-50 (Andean origin) in the DR, and the genes were mapped. A mobile rust nursery was developed to monitor races of rust in a region and assist in resistance-gene deployment in bean germplasm and varieties. DNA based diagnostic methods were developed to differentiate X. campestris pv. phaseoli from X. campestris pv. phaseoli var fuscans (prevalent in East Africa) and P. griseola isolates. DNA hybridization methods also were developed to identify BGYM and bean golden mosaic viruses. Research in USA and East Africa has helped define bean common mosaic virus (BCMV) and bean common mosaic necrotic virus (BCMNV) as separate viruses and has demonstrated that BCMNV appears to be indigenous to Africa. Serological tools were developed that assist in the detection and identification of potyviruses, BCMV and BCMNV. These tools are now used worldwide.