Identification and virulence of Fusarium falciforme and Fusarium brachygibbosum as causal agents of basal rot on onion in Mexico

Abstract

Fusarium basal rot is a major disease of onion production in Mexico. Recently, Fusarium falciforme and F. brachygibbosum were reported as two new causal agents of basal rot of onion in Mexico. However, little is known about the pathogenicity and virulence of these pathogens on this crop globally. The virulence (severity of disease) of F. falciforme and F. brachygibbosum isolates recovered in Culiacan Valley (Sinaloa, North-west Mexico) was determined and compared with isolates of F. oxysporum collected from the same crop and region. Two pathogenicity tests were conducted on onion under controlled conditions, one on onion bulbs, and another on onion seedlings of the cv. ‘Carta Blanca’. All of the isolates were pathogenic on onion, indicating that these three Fusarium species are a serious threat to production of this crop in the Culiacan Valley. The isolates showed significant differences in virulence, with F. falciforme the most aggressive at the bulb stage and F. brachygibbosum the most aggressive at the seedling stage, compared with F. oxsyporum. The isolates of these three species caused similar symptoms including yellowing and darkening of the vascular tissues on onion plants, highlighting the need for a specific diagnostic tool to discriminate among members of the species complex. This information is valuable for resistance breeding programmes, to reduce the devastating effects of Fusarium basal rot of onion in Mexico and worldwide.