BROAD SPECTRUM RESISTANCE TO DRY BEAN RUST DISEASE DISCOVERED IN AFRICAN LANDRACE CULTIVARS

Dry edible bean production provides a banquet for fungal pathogens to feast upon. Small-holder subsistence farmers in poorer countries suffer the most from these uninvited guests, because they cannot afford fungicides or other technologies, such as disease resistance, to combat the pathogens. The major fungal diseases plaguing dry bean producers in Sub-Saharan Africa and worldwide are rust, angular leaf spot, anthracnose, and root rots. Our aim is to provide resource poor farmers with dry bean cultivars harboring resistance to one or more of the prevalent bean diseases that negatively affect their livelihoods.

One focus of our Feed the Future Grain Legumes Project has been to evaluate a large panel of accessions for resistance to the aforementioned diseases. The panel consists of old landraces and new cultivars representing the large seeded ‘Andean’ bean types produced around the world. Large-seeded beans are the preferred type in Africa. The greatest progress made thus far has been in the identification of broad spectrum resistance to rust in large seeded landrace cultivars that originate from Tanzania. These landraces, with confirmed resistance in field trials in Africa and the US, provide breeders with a valuable source of rust resistance for improving large-seeded African cultivars used by small-holder farmers. Another set of materials with broad spectrum resistance to rust was found within lines from the Ecuadorian National Program (INIAP), through work conducted in collaboration with the Feed the Future Legume Innovation Lab USAID project.

The identification of dry bean accessions with broad spectrum resistance to rust disease is an exciting discovery. Our project has already initiated crosses with these materials to transfer the resistance into other susceptible cultivars and dry bean market classes (yellow, red mottled, white, tan, etc.) for small-holder farmers in Sub-Saharan Africa.

Broad spectrum resistance to the devastating bean rust disease in Africa. Photograph A compares a Tanzanian landrace with broad spectrum resistance (left) to a susceptible accession (right). Notice the reduced biomass and vigor of the susceptible line. Photograph B shows typical rust symptoms, including necrotic leaf spots and fungal pustules, on susceptible dry bean leaves. Both images are from the Cedara Agricultural Research Station, Kwazulu Natal Province, South Africa. (Photo credits: Talo Pastor-Corrales, USDA-ARS Beltsville; 2013)