Analysis of the evolutionary history of phytopathogenic fungi of tomato based on gene genealogies

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When and where did plant pathogenic fungi generate pathogenicity?' and 'How has pathogenicity been evolved in plant pathogenic fungi?' are important questions in plant pathology. In order to give evidences to answer these questions, we focused mainly on the coevolution between Lycopersicon spp. (tomatoes) and Fusarium oxysporum, the wilt pathogen of tomato in this study. During the four research years, we visited Ecuador where we could find wild L. pimpinellifolium and L. cheesmanii, Mexico where domestication of tomato occurred more than 2000 years ago and still we can find prototype edible tomato (L. esculentum), L. esculentum vars. ceraciforme and creole, and Naples in Italy where modern breeding of edible tomatostarted in 16th century, collected tissues from symptomless Lycopersicon spp. and rhizosphere soil, and isolated Fusarium oxysporum from the tissues and the soil. All of the isolates showed no pathogenicity on tomatoes by inoculation test and were supposed to be non-pathogenic symbionts. Phylogenetic analysis against the isolates based on rDNA-IGS revealed that non-pathogenic F. oxysporum isolates from wild Lycopersicon spp. carried no phylogenetic relationship with the pathogenic strains (F. oxysporum f. sp. lycopersici). On the other hand, some of the non-pathogenic F. oxysporum isolates from Mexican prototype tomatoes and Italian edible tomatoes showed close relationship between the pathogen. These suggested that the ancient of the present wilt pathogen was the non-pathogenic symbiont which emerged during the domestication of tomato in Mexico. The non-pathogenic E oxysporum have got pathogenicity to tomato during the modern breeding and distribution after 16th century. Now, worldwide trading of tomato fruits and seeds distributes not only the symbiotic non-pathogenic E oxysporum but also F. oxysporum f. sp. lycopersici, the wilt pathogen of tomato.