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Research |
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Genetic differentiation of Magnaporthe oryzae populations from scouting plots and commercial rice fields in Korea
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Authours
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Sook-Young Park, M. G. Milgroom, S. S. Han, Seogchan Kang, and Yong-Hwan Lee |
Title |
Genetic differentiation of Magnaporthe oryzae populations from scouting plots and commercial rice fields in Korea |
Journal |
Phytopathlogy, 2008 (98) ~ |
Abstract
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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 Iand 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. |
Link
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