J BIGIRIMANA, G DE MEYER, P DE ROP, J POPPE and M HÖFTE

Laboratory of Phytopathology, University Gent, Coupure Links 653, B-9000 Gent, Belgium

Background and objectives
Anthracnose on beans caused by Colletotrichum lindemuthianum is one of the important worldwide diseases of Phaseolus vulgaris. The high diversity of the pathogen[1] remains a major limiting factor for its control. The present study discusses the diversity of this fungus in Burundi and different infection methods to evaluate resistance to C. ;lindemuthianum.

Materials and methods
Different inoculation methods were performed: on seeds, on leaves in a moist chamber and on detached leaves in humid plates. Two developmental stages were compared: primary and first trifoliate leaves, respectively from 10 and 20-day-old bean seedlings. Fourteen C. ;lindemuthianum isolates from different eco-climatic regions of Burundi (Central Africa) were screened. Their virulence was studied on nine varieties of Phaseolus vulgaris. Based on disease symptoms, bean varieties were classified as sensitive, intermediate or resistant to each C. ;lindemuthianum isolate.

Results and conclusions

The results indicate that the 14 C. ;lindemuthianum isolates tested are distributed in 10 different groups based on virulence to nine bean varieties. Races are to be characterized using the 12 differential bean cultivars [2]. Seeds or primary leaf inoculation resulted in the same resistance grouping of bean varieties. This indicates that the fast and easy seed inoculation technique can be used to differentiate bean cultivars. However, bean varieties consistantly displayed more resistance upon trifoliate leaf inoculation than upon primary leaf or seed inoculation. This indicates that evaluation of resistance based on primary leaf or seed inoculation underestimates field resistance of bean varieties. We are currently studying whether induced resistance can improve the performance of sensitive and intermediate bean varieties. Preliminary results have demonstrated that soil treatment with Trichoderma harzianum T39 induces resistance to C. ;lindemuthianum in both sensitive and intermediate bean varieties.

References
1. Balardin RS, Jarosz AM, Kelly JD, 1997. Phytopathology 87, 1184-1191.
2. Pastor-Corrales MA, 1991. Phytopathology 81, 694.