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

植物病原真菌何时何地产生致病性？和“植物病原真菌的致病性是如何进化的？”是植物病理学中的重要问题。为了给这些问题提供证据，本研究主要对番茄枯萎病病原菌番茄枯萎病（Lycopersicon spp.）与尖孢镰刀菌（Fusarium oxysporum）的协同进化进行了研究。在四年的研究中，我们走访了厄瓜多尔，在那里我们发现了野生的L. pimpinellifolium和L. cheesmanii；在墨西哥，我们还发现了2000多年前驯化番茄的原型（L. esculentum）， L. esculentum vars。在意大利的那不勒斯，现代可食用番茄育种于16世纪开始，从无症状的番茄属和根际土壤中收集组织，并从组织和土壤中分离出尖孢镰刀菌。经接种试验，所有菌株对番茄均无致病性，推测为非致病性共生体。基于rDNA-IGS的系统发育分析表明，来自野生番茄属植物的非致病性尖孢菌分离株与致病菌株（番茄属植物尖孢菌）没有系统发育关系。另一方面，从墨西哥原型番茄和意大利食用番茄中分离出的一些非致病性尖孢镰刀菌与病原菌关系密切。这些结果表明，现在的枯萎病菌的起源是墨西哥番茄驯化过程中出现的非致病性共生体。在16世纪以后的现代育种和传播过程中，无致病性的尖孢杆菌对番茄产生了致病性。目前，在世界范围内的番茄果实和种子贸易中，不仅存在着共生的非致病性番茄枯萎菌（E oxysporum F. sp. lycopersici），也存在着番茄枯萎病菌（F. oxysporum F. sp. lycopersici）。

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.