Genetic Diversity and Identification of Wilt and Root Rot Pathogens of Tomato in China

Abstract

Fungal wilt and root rot diseases affecting tomato have become prevalent in China in recent years and have caused considerable damage. In 2016 to 2018, symptoms of putative wilt and root rot diseases were observed in several locations in tomato cultivars with resistance to Fusarium oxysporum f. sp. lycopersici races 1 and 2 (FOL race 1 and 2). The objective of this study was to identify the causative agents of wilt and root rot of tomato in China and provide a basis for disease prevention and resistance breeding programs. Based on DNA-sequence analyses of the internal transcribed spacer (ITS) region, 91 isolates from the roots of tomato plants showing symptoms of wilt and root rot were identified, including F. oxysporum (64 isolates), F. solani (11 isolates), F. proliferatum (2 isolates), F. graminearum (2 isolates), F. equiseti (1 isolate), Pythium aphanidermatum (6 isolates), Ascomycota sp. (2 isolates), and Plectosphaerella cucumerina (3 isolates). Fusarium oxysporum accounted for 70.33% of the isolates obtained. In this case, using PCR-based methods for differentiation of F. oxysporum, several formae speciales and races of F. oxysporum were further identified: 7 isolates were identified as FOL race 1, 2 isolates as FOL race 2, 35 isolates as FOL race 3, and 13 isolates as F. oxysporum f. sp. radicis-lycopersici (FORL). Pathogenicity tests revealed 55 isolates of tomato wilt and root rot pathogens to be virulent. This study demonstrated that FOL race 3 was the most widespread and highly virulent race among these tomato pathogens in China, followed by FORL. Therefore, the development of resistant varieties of tomato against FOL race 3 and FORL would considerably aid the urgent need to develop effective disease management strategies.