GUIDING THE DEVELOPMENT OF COMMON BEAN CULTIVARS WITH DURABLE RUST RESISTANCE BASED ON THE GENETIC DIVERSITIES OF THE PATHOGEN AND ITS HOST

Authors: Pastor Corrales, Marcial - Talo; Aime, Mary; STEADMAN, J - UNIV OF NEBRASKA

Submitted to: World Cowpea Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2004
Publication Date: 4/1/2005
Citation: Pastor-Corrales M.A., Aime A.C. and Steadman J.R. 2005. Guiding the development of common bean cultivars with durable rust resistance based on the diversity of the rust pathogen and its common bean hosts. International Edible Legume Conference in conjunction with IV World Cowpea Congress. Durban, South Africa. 17 - 21 April 2005.

Interpretive Summary: The common bean, consumed in the form of seeds of dry beans or as green pods of snap beans, is the most important legume crop in the world. One of the most damaging diseases of this crop is called common bean rust. This disease caused by a fungus has been difficult to control because the rust pathogen has many strains some of which overcome genetic resistance in bean. The genetic diversity of the rust fungus is not well understood. In this research, the genetic diversity of the bean rust fungus was determined by DNA typing and by testing the virulence (disease causing ability) of different strains of rust on different bean varieties. We discovered that the genetic differences among the rust fungus strains correlate directly with differences in the bean plant, roughly dividing into two main groups. Based on these differences, varieties of common bean are being bred that are resistant to the main strains of the rust pathogen. This research will be used by plant breeders and pathologists to develop varieties of common bean that are resistant to common bean rust.

Technical Abstract: The common bean includes wild populations and cultivars. The diversity of wild beans and cultivars is organized into large-seeded Andean and small and medium-seeded Middle American gene pools. We have analyzed the virulence and genetic diversity of the common bean rust pathogen, Uromyces appendiculatus, using differential cultivars and molecular markers, to determine if the diversity of this pathogen parallels the diversity of its host. Results using differential cultivars revealed many virulence phenotypes in the pathogen; however, these segregated in two distinct groups, one Andean and another Middle American that mirrored the diversity of their host. Andean phenotypes were only or mostly pathogenic on Andean beans while Middle American phenotypes were pathogenic on both groups of cultivars, although they exhibited a preference for Middle American beans. The same two groups of isolates were also analyzed with molecular markers, which revealed the same patterns of diversity at the genetic level. Based on these results, we are developing bean germplasm lines combining complementary rust resistance genes from Middle American and Andean beans. We have recently released bean germplasm lines with two genes from Middle American beans and two genes from Andean beans. These bean lines were effective against all known virulence phenotypes of the bean rust pathogen under greenhouse and field conditions.