1.8.40
HOST RANGE DETERMINANTS IN COLLETOTRICHUM DESTRUCTIVUM

S AMER1, S ABU EL SOUOD1, P BOWYER2, J KEON2 and JA LUCAS2

1Faculty of Science, Department of Botany, Tanta University, Tanta, Egypt; 2IACR-Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Long Ashton, Bristol BS18 9AF, UK

Background and objectives
Colletotrichum is one of the most important genera of plant pathogenic fungi, responsible for damaging leaf spot, anthracnose and post-harvest diseases of a wide variety of host plants grown in both temperate and tropical environments. Colletotrichum spp. differ in the extent of their host range, but some are specific to particular plant species or cultivars. C. destructivum is one of several fungal species which are capable of causing anthracnose diseases in lucerne (alfalfa, Medicago sativa). We are studying the pathogenicity of C. destructivum isolated from alfalfa towards other legumes such as lentil and cowpea, as well as to alfalfa. In particular we are interested in factors determining host range and lesion development on different legume species.

Results and conclusions
Antifungal saponins occur in many plant species and may provide a preformed chemical barrier to plant pathogenic fungi. The ability to enzymatically degrade these compounds is a host-range determinant in some fungi. Mutants of C. destructivum altered in the production of saponinase enzymes and in sensitivity to saponins have been produced. Such mutants have reduced pathogenicity to some legume hosts. Further analysis using a combination of microscopic, biochemical and molecular genetic approaches is being conducted. The potential role of glucosidase enzymes degrading saponins in influencing host range and pathogenicity in this host-pathogen interaction is discussed.