Fusarium wilt caused by members of the Fusarium oxysporum species complex: challenging the concept of forma specialis

Abstract

Members of the Fusarium oxysporum species complex (FOSC) are pathogens that cause wilt and rot in ornamentals, vegetables, fruit crops, and legumes of agricultural importance in tropical and temperate regions worldwide. Although pathogens of the F. oxysporum morphotype obtained from plants showing wilt and rot symptoms are grouped into formae speciales based on pathogenicity toward the host of origin, bioassays and genomic studies reveal the fragility of this concept. The lack of host specificity may lead to inadequate management of agricultural crops. This Thesis comprises five chapters that: (i) investigate the etiology of Fusarium wilt in Brazil; and (ii) evaluate the pathogenicity of members of the FOSC in crops such as passion fruit, tobacco, common bean, cowpea, tomato, and banana. Through molecular phylogeny analyses, cross-inoculation bioassays, and evaluation of morphological markers, species of the FOSC present in Brazil were identified. It was demonstrated that they can induce typical wilt symptoms in different hosts, regardless of the plant from which the isolate was obtained. The results challenge the forma specialis concept by showing that virulence is not host-specific, nor is it related to the species. The phenomenon of pathogenicity can be explained by the transfer of virulence genes among elements of population. This study contributes to the understanding of the etiology of Fusarium wilt in Brazilian agroecosystems, providing support for management strategies, diagnosis, and breeding programs aimed at resistance.