Park S-Y, Milgroom M G, Han S S, Kang S, Lee Y-H
Department of Agricultural Biotechnology, Center for Fungal Genetic Resources, Seoul National University, Seoul, Korea.
Phytopathology. 2008 Apr;98(4):436-42. doi: 10.1094/PHYTO-98-4-0436.
A previous study of the diversity and population structure of the rice blast fungus, Magnaporthe oryzae, over a 20-year period in Korea, found novel fingerprint haplotypes each year, and the authors hypothesized that populations might experience annual bottlenecks. Based on this model, we predicted that M. oryzae populations would have little or no genetic differentiation among geographic regions because rice blast is commonly found throughout Korea each year and M. oryzae would have to disperse from small populations surviving annually between rice crops. To test this hypothesis, we sampled M. oryzae from rice fields in eight provinces in Korea in a single year (1999). In four provinces, we sampled from a set of rice cultivars commonly grown in commercial fields (group I); because of low disease incidence in four other provinces, we could not sample from commercial fields and instead sampled from scouting plots of different cultivars set up for detecting new pathotypes of M. oryzae (group II). All isolates were genotyped with DNA fingerprint probes MGR586 and MAGGY, a telomere-linked gene family member TLH1, the PWL2 host specificity gene and mating type. Fingerprint haplotypes clustered into two distinct lineages corresponding to the two sets of cultivars (groups I and II), with haplotype similarities of 71% between lineages and >76% within lineages. Isolates from the same cultivar within group I were genetically differentiated among locations, and isolates within the same location were differentiated among cultivars. Differentiation for TLH1 and PWL2 was significant (P < 0.03), but not as strong as for fingerprint markers. Similar analyses were not possible among group II isolates because too few isolates were available from any one cultivar. All isolates were in the same mating type, Mat1-1, ruling out sexual reproduction as a source of novel haplotypes. When the 1999 samples were compared with the historical samples from the previous study, haplotypes of group I formed a separate cluster, while those of group II clustered with haplotypes from the historical sample. Altogether, geographic subdivision, monomorphism of mating type, and correlation of haplotypes to sets of cultivars are not consistent with the hypothesis of repeated turnover of haplotypes. Instead, the previous correlations of haplotypes to year might have been caused by inadequate sampling of haplotypes each year, highlighting the need for studies of population genetics to be conducted with systematic samples collected to address specific questions.
此前一项针对韩国稻瘟病菌Magnaporthe oryzae的多样性和种群结构开展的为期20年的研究发现，每年都会出现新的指纹单倍型，作者据此推测种群可能每年都会经历瓶颈期。基于此模型，我们预测，稻瘟病菌种群在地理区域间几乎没有或不存在遗传分化，因为每年韩国各地都会普遍发现稻瘟病，且稻瘟病菌必须从每年在水稻作物之间存活的小种群中扩散开来。为了验证这一假设，我们于1999年在韩国八个省份的稻田中采集了稻瘟病菌样本。在四个省份，我们从商业田块中常见的一组水稻品种中采样（第一组）；由于其他四个省份的发病率较低，我们无法从商业田块采样，而是从为检测稻瘟病菌新致病型而设立的不同品种的侦察田中采样（第二组）。所有分离株都用DNA指纹探针MGR586和MAGGY、端粒连接基因家族成员TLH1、PWL2寄主特异性基因以及交配型进行了基因分型。指纹单倍型聚为两个不同的谱系，分别对应两组品种（第一组和第二组），谱系间单倍型相似性为71%，谱系内相似性大于76%。第一组内来自同一品种的分离株在不同地点间存在遗传分化，同一地点内的分离株在不同品种间也存在分化。TLH1和PWL2的分化显著（P < 0.03），但不如指纹标记的分化强烈。由于任何一个品种的第二组分离株数量太少，无法进行类似分析。所有分离株都属于同一交配型Mat1-1，排除了有性繁殖是新单倍型来源的可能性。当将1999年的样本与先前研究中的历史样本进行比较时，第一组的单倍型形成了一个单独的聚类，而第二组的单倍型与历史样本中的单倍型聚类在一起。总体而言，地理细分、交配型的单态性以及单倍型与品种组的相关性与单倍型反复更替的假设不一致。相反，之前单倍型与年份的相关性可能是由于每年对单倍型的采样不足导致的，这突出表明有必要通过收集系统样本开展种群遗传学研究以解决特定问题。
