油茶炭疽病菌潜在侵染源及分子进化机制研究

Anthracnose is a major disease of tea-oil trees in China, causing enormous economic losses. The major casual agents are species in the fungal genus Colletotrichum. Our recent preliminary results based on sequences at four gene fragments indicated that at least five species in this genus could cause anthracnose on tea-oil trees. In addition, new and undescribed species may exist and there is phylogenetic evidence for hybridization between some of the species. At present, the relative virulence of these species and their hybrids on tea-oil trees are unknown. In addition, the potential sources of strains causing anthracnose on tea-oil trees remain to be defined. One potential source is other host plants in nearby fields. Understanding the potential sources of infection and the virulence properties of these pathogens will significantly enhance our ability to design sustainable control strategies against anthracnose on tea-oil trees. Here we propose to sample strains of Colletotrichum from both tea-oil trees and other host plants in nearby fields and forests, obtain their genotypes using multiple gene sequences and microsatellite markers, and conduct cross-infection experiments using representative tea-oil tree cultivars and fungal pathogen species/genotypes. Our analyses will identify genetic variation within and among populations, the intraspecific and interspecific relationships among Colletotrichum species between tea-oil trees and other host plants, and their relative specificity in host-pathogen interactions. The research results will provide the theoretical foundation for developing sustainable methods to control anthracnose in tea-oil trees. The approaches and methods developed here can also help guide our managements of other plant infectious diseases.

油茶炭疽病是我国油茶产区的一种重大病害，造成严重经济损失。我们前期的研究发现：①油茶炭疽病由多种炭疽属真菌引起，并且这些炭疽属真菌种内存在重组、种间存在杂交现象；②海南五指山的油茶（油茶苗购于江西长埠）炭疽病菌具有独特的基因型，但与江西长埠或中国内陆其它油茶炭疽病菌共享部分等位基因。我们据此提出一种假说：当地植物（包括当地油茶）炭疽病菌转移到油茶树上，或当地植物炭疽病菌与油茶炭疽病菌之间存在重组或杂交。目前，除了已知油茶组织中潜伏的炭疽病菌能再次引起病害发生外，其它寄主植物的炭疽病菌是否也可以侵染油茶，以及这些病菌之间的遗传关系尚不清楚。为了证明提出的假说，本项目采用多基因序列分析和微卫星标记方法，研究我国油茶及其它寄主植物炭疽病菌群体内和群体间以及种内和种间的基因交流和遗传变异规律，探明油茶炭疽病菌潜在侵染源植物种类，揭示此类病菌的分子进化机制，为可持续控制油茶炭疽病提供理论依据。

油茶是我国特有的木本食用油料树种，具有极高的经济价值、生态功能和社会效益。目前我国油茶林面积6700万亩，年产茶油量约60万吨，2018年全国油茶产业总产值达到1024亿元。油茶产业是贫困地区精准扶贫的支柱产业，习近平总书记曾多次考察调研油茶产业扶贫情况。油茶炭疽病是我国油茶种植区的主要病害，可引起油茶大量落果、落蕾，造成油茶籽减产20%左右，重病区可达40%以上，造成巨大经济损失。本研究基于课题组前期研究工作基础，主要研究不同地理群体的油茶树及不同寄主植物的炭疽病菌株之间的基因流和遗传变异规律，找出我国有哪些油茶炭疽病菌潜在侵染源植物种类，揭示油茶炭疽病菌的分子进化机制。.我们通过研究取得了重要的结果：①油茶炭疽病病原种类复杂多样、分布范围广；②油茶炭疽病菌潜在侵染源植物种类丰富；③Colletotrichum fructicola是油茶炭疽病的主要流行致病菌；④ C. fructicola在油茶与其它寄主植物之间既有无性交流也存在遗传重组和显著的遗传分化现象。⑤致病菌Colletotrichum siamense在油茶与其它寄主植物之间和不同地理群体之间存在基因流。⑥炭疽病菌C. fructicola、C. siamense和C. camelliae 3个不同的物种之间存在基因重组现象，并且具有有性生殖的炭疽病菌更容易进化对杀菌剂产生抗药性；⑦研究发现丝列原活化蛋白激酶基因PMK1和转录因子BZIP10参与调控病菌对不同寄主植物的致病性。⑧发明了一种拮抗油茶多种新炭疽病原菌的菌株及其应用方法。研究结果对联合林业、农业整体考虑油茶及其它寄主植物来制定油茶炭疽病可持续控制策略，减少炭疽病造成的经济损失具有重要的指导意义。