Screening for resistance to anthracnose (Colletotrichum gloeosporioides Penz) in Allium cepa and its wild relatives

Colletotrichum gloeosporioides is an airborne disease which causes significant yield losses in shallots (A. cepa var. ascalonicum) grown in the tropics. Breeding for resistance to this disease in shallots has been scarcely carried out and has been primarily focussed on Allium cepa material. Wild species related to shallot might provide sources of resistance and therefore a screening of this material was carried out. Three different isolates of C. gloeosporioides originating from Brazil, Nigeria and Indonesia, were used in the screening procedure. The accessions screened of A. cepa and A. oschaninii were most susceptible to the three isolates. Partial resistance was observed in accessions of A. altaicum, A. fistulosum, A. galanthum, A. pskemense and A. roylei. The highest level of resistance was found in accessions of A. galanthum and A. fistulosum, A. roylei was highly resistant to the Brazilian isolate but very susceptible to the Nigerian and Indonesian isolates. A genetic analysis of the resistance present in A. roylei to the Brazilian isolated revealed that it is dominantly inherited and most probably determined by more than one gene.