Data from: Sex at the origin: an Asian population of the rice blast fungus Magnaporthe oryzae reproduces sexually.

Sexual reproduction may be cryptic or facultative in fungi and therefore difficult to detect. Magnaporthe oryzae, which causes blast, the most damaging fungal disease of rice, is thought to originate from South-East Asia. It reproduces asexually in all rice-growing regions. Sexual reproduction has been suspected in limited areas of South-East Asia, but has never been demonstrated in contemporary populations. We characterized several M. oryzae populations worldwide both biologically and genetically, to identify candidate populations for sexual reproduction. The sexual cycle of M. oryzae requires two strains of opposite mating types, at least one of which is female-fertile, to come into contact. In one Chinese population, the two mating types were found to be present at similar frequencies and almost all strains were female-fertile. Compatible strains from this population completed the sexual cycle in vitro and produced viable progenies. Genotypic richness and linkage disequilibrium data also supported the existence of sexual reproduction in this population. We resampled this population the following year, and the data obtained confirmed the presence of all the biological and genetic characteristics of sexual reproduction. In particular, a considerable genetic reshuffling of alleles was observed between the two years. Computer simulations confirmed that the observed genetic characteristics were unlikely to have arisen in the absence of recombination. We therefore concluded that a contemporary population of M. oryzae, pathogenic on rice, reproduces sexually in natura in South-East Asia. Our findings provide evidence for the loss of sexual reproduction by a fungal plant pathogen outside its centre of origin.

真菌的有性生殖可呈隐蔽性或兼性特征，因此难以被检测发现。引发稻瘟病——危害水稻最严重的真菌病害——的稻瘟病菌（Magnaporthe oryzae），被认为起源于东南亚地区。该菌在所有水稻种植区均以无性生殖方式繁衍。东南亚部分区域曾被怀疑存在有性生殖，但从未在当代种群中得到证实。为筛选出具备有性生殖潜力的候选种群，本研究对全球多个稻瘟病菌种群开展了生物学与遗传学特征分析。稻瘟病菌的有性生殖周期需要两种交配型相反的菌株相互接触，且其中至少一种菌株为雌性可育型。在一处中国种群中，两种交配型菌株的出现频率相近，且几乎所有菌株均为雌性可育型。该种群中的亲和性菌株可在体外（in vitro）完成有性生殖周期，并产生具有活力的子代。基因型丰富度与连锁不平衡（linkage disequilibrium）数据同样证实了该种群存在有性生殖。次年我们对该种群进行了重新采样，所得数据进一步确认了其具备有性生殖的全部生物学与遗传学特征。尤为关键的是，两年间观测到等位基因发生了显著的遗传重组重排。计算机模拟分析证实，若不存在重组事件，本次观测到的遗传学特征几乎不可能自然产生。据此我们得出结论：在东南亚自然生境中，感染水稻的稻瘟病菌当代种群确实能够进行有性生殖。本研究结果为真菌植物病原物在起源中心之外丧失有性生殖能力提供了实证依据。