Bean Anthracnose: Virulence of Colletotrichum lindemuthianum Isolates from Burundi, Central Africa.

The diversity of Colletotrichum lindemuthianum is a major limiting factor in control of anthracnose on bean (Phaseolus vulgaris), and race characterization of this pathogen is an important tool in breeding programs. Race characterization has been carried out on isolates from North, Central, and South America; Europe; and Asia, but little or no information exists on the diversity of C. lindemuthianum in Africa. In this work, 12 isolates from the major bean-growing areas of Burundi, Central Africa, were characterized. Their virulence was tested on 12 bean differential cultivars (1) and on 4 bean cultivars commonly grown in Burundi: 2 from local germ plasm (Muyinga-1 and Urubonobono) and 2 from Colombia (A 321 and Calima). Detached unifoliate bean leaves from 8-day-old plants were placed on a humid surface in trays and sprayed until runoff with a suspension of 10 spores ml. Trays covered with transparent plastic sheets to keep a minimum relative humidity of 92% were incubated at 20°C. Seven days after inoculation, symptoms were evaluated for severity on a scale of 1 to 9. Leaves scored as 1 to 3 were considered resistant. Races were characterized according to a numerical binary system (1). Nine races were identified: 9, 69, 87, 384, 385, 401, 448, 449, and 485. Seven of these races (9, 69, 87, 384, 401, 448, and 485) were described for the first time in Africa. Races 401 and 485 have not yet been reported in the literature. The most susceptible differential cultivars were Michelite, PI 207262, To, and Mexico 222. Muyinga-1, Urubonobono, and A 321 were sensitive to nine, six, and five races, respectively. There is a high diversity of C. lindemuthianum in Burundi, and the local germ plasm tested is very susceptible to the characterized races. Breeding programs in Burundi should focus on lines and cultivars, such as Tu, AB 136, G 2333, and Calima, that are resistant to all the races characterized in this study. Reference: (1) M. A. Pastor-Corrales. Phytopathology 81:694, 1991.