Genetic transformation of the tropical forage legume Stylosanthes guianensis with a rice-chitinase gene confers resistance to Rhizoctonia foliar blight disease

Stylosanthes guianensis is a diverse tropical and subtropical forage legume of great potential. Foliar blight disease, caused by Rhizoctonia solani AG-1, can be a significant constraint to the legume’s production in some areas. The pathogen has a broad range of host plant species, and can survive as sclerotia for long periods in soil or plant debris. No sources of resistance in Stylosanthes are known. Cost-effective disease management strategies are, therefore, needed for this host-pathogen system. Chitinases, which catalyze the hydrolysis of the b-1,4 linkages of the N-acetyl-D-glucosamine polymer chitin of fungal cell walls, are expressed in plants in response to infections by pathogens and some abiotic stresses. In this study, a basic chitinase-encoding gene, isolated from rice, was introduced into the widely distributed S. guianensis accession CIAT 184, using Agrobacterium tumefaciens. A 1.1-kb rice genomic DNA fragment containing the chitinase gene was cloned into a transformation vector, pCAMBIA2301. The vector carried the CaMV 35S promoter, the neomycin phosphotransferase (nptII) gene and the gusA reporter gene. The presence of the chitinase gene in transgenic Stylosanthes plants was determined by dot blot analysis. Transgenic plants expressed higher levels of resistance to R. solani than did control plants. Progenies of a selfed transgenic plant showed segregation for resistance at a ratio of 3:1.