ANDEAN BEANS WITH RESISTANCE TO ANGULAR LEAF SPOT AND VIRULENCE DIVERSITY OF PHAEOISARIOPSIS GRISEOLA IN SOUTHERN AND EASTERN AFRICA

Authors: Pastor Corrales, Marcial; AGGARWAL, V - BRAMPTON, ON, CANADA; CHIRWA, R - CIAT; BURUCHARA, R - CIAT

Submitted to: Bean Improvement Cooperative Annual Report
Publication Type: Trade Journal
Publication Acceptance Date: 4/19/2004
Publication Date: 7/19/2004
Citation: Pastor-Corrales M. A., V. D. Aggarwal, R. M. Chirwa, R. A. Buruchara. 2004. Andean beans with resistance to angular leaf spot and virulence diversity of Phaeoisariopsis griseola in Southern and Eastern Africa. Ann. Rep. Bean Improvement Coop. 47: 129-130.

Interpretive Summary: Large seeded Andean beans are the preferred class of beans in several countries in Eastern and Southern Africa. In this region, where beans are a very important human food and a significant source of protein, the angular leaf spot disease of beans is very widespread and economically important. Our research revealed that CAL 143, an Andean bean that is well adapted and produces high yields in Africa, was free of the angular leaf spot disease during three years that CAL 143 was evaluated under field conditions in Malawi. CAL 143 was also resistant to angular leaf spot under field conditions in South Africa, Tanzania, and Zambia, but it was susceptible in Uganda. This susceptibility was attributed to the presence of a strain of the pathogen in Uganda that was not present in the other countries. Two other Andean bean lines, AND 277 and AND 279, were also resistant under field conditions in Malawi. In order to better understand the angular leaf pathogen, we studied the diversity of 15 isolates collected in Southern and Eastern African countries. These isolates were separated into 9 different groups of strains. Five of six isolates from Malawi and two of seven from Uganda, obtained from large-seeded Andean beans, were denominated Andean because they caused disease only or mostly on large-seeded Andean beans. The other eight isolates from Uganda, Malawi, and the Democratic Republic of Congo, obtained from a small or Medium-seeded Middle American beans, were denominated Middle American because they caused disease on Middle American and Andean beans. CAL 143 has been released as a variety in Malawi.

Technical Abstract: We identified CAL 143 as the first Andean bean with resistance to the angular leaf spot disease in Southern and Eastern Africa. Angular leaf spot, caused by the fungus Phaeoisariopsis griseola, is the most widespread and economically important and disease of beans in Eastern and Southern Africa. This disease is especially severe on the extensively grown large-seeded Andean beans. The large-seeded Cal 143 was resistant to angular leaf spot in Malawi, South Africa, Tanzania, and Zambia, but it was susceptible in Uganda. This was attributed to the presence of strains (races) of P. griseola in Uganda that were not present in the other countries. We identified two additional Andean bean lines, AND 277 and AND 279, with resistance to angular leaf spot in Malawi. We also characterized the virulence diversity of 15 isolates of P. griseola from Southern and Eastern Africa into 9 different races. Five of six isolates from Malawi and two of seven from Uganda, obtained from large-seeded Andean beans, were characterized into four different races denominated Andean because they caused angular leaf spot only or mostly on large-seeded Andean cultivars. The other eight isolates from Uganda, Malawi, and the Democratic Republic of Congo, obtained from a small or Medium-seeded Middle American beans, were characterized into five different races denominated Middle American because they caused angular leaf spot on both, Middle American and Andean cultivars. CAL 143 was resistant or intermediate under greenhouse conditions to all but one of 15 isolates of the pathogen from Southern and Eastern Africa; it was susceptible to an isolate from Uganda obtained from a medium-seeded Middle American bean.