Cross Pathogenicity of Fusarium Oxysporum f. Sp. Betae On Sugar Beet and Common Bean.

Fusarium wilt, also known as Fusarium yellows, is caused by the fungus Fusarium oxysporum. Fusarium oxysporum is a vascular pathogen with a broad host range including common bean (Phaseolus vulgaris L.) and sugar beet (Beta vulgaris L.) with formae speciales (f. sp.) defined by the ability to cause disease on a specific host. Hence, Fusarium wilt of common bean is caused by F. oxysporum f. sp. phaseoli and Fusarium yellows on sugar beet caused by F. oxysporum f. sp. betae. Both pathogens occur throughout the sugar beet and common bean production areas in the United States where sugar beet is often grown in rotation with common bean. Often isolates of F. oxysporum are tested for pathogenicity only on the host they were isolated from; therefore, it is not known whether isolates of f.sp. betae can be pathogenic on common bean, or f. sp. phaseoli pathogenic on sugar beet; which has implications regarding common bean and sugar beet crop rotations. Our objective is to determine if isolates of F. oxysporum f. sp. betae are cross-pathogenic to common bean. We inoculated common bean with 52 isolates of F. oxysporum f. sp. beta along with 4 isolates of F. oxysporum f. sp. phaseoli, (used as controls) to common bean (Viva) and sugar beet (FC716) in the greenhouse using a root dip assay and assessed disease severity based on a disease index scale (1-9 for common bean; 0-5 for sugarbeet).  No F. oxysporum f. sp. betae isolates showed cross-pathogenicity to common bean, nor were the F. oxysporum f. sp. phaseoli controls cross pathogenic to sugar beet. These results suggest that common bean does not serve as a host for F. oxysporum f. sp. betae, and that crop rotation with bean and sugar beet can be a useful method of control.