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Rice blast
Rice blast,caused by the ascomycete fungus Pyricularia grisea (teleomorph:
Magnaporthe grisea), is a principal
disease of rice worldwide, which can be destructive under favorable condition.
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| Over one thousand
isolates of Pyricularia grisea from
rice in the United States, especially from Arkansas, the main rice production
state in U.S., were examined for vegetative compatibility, MGR586 DNA
fingerprint diversity, and mating type based on hybridization with the mat1-1
and mat1-2 sexual mating type alleles. The
collections contained both archived and contemporary field isolates
representative of the known MGR586 lineages and races that occur throughout the
United States. Complementary nitrate nonutilizing (nit)
or sulfate nonutilizing (sul)
mutants were used to assess vegetative compatibility in P.
grisea. There was a complete
correspondence between vegetative compatibility groups (VCGs), MGR586 lineage,
and mating type among contemporary isolates (collected between 1991 and 2004)
from Arkansas, Louisiana, Missouri, Mississippi, and Texas; all isolates in
MGR586 lineages A, B, C, and D belonged to VCGs US-01, US-02, US-03, and US-04,
respectively. In addition, all isolates tested in VCGs US-01 and US-04 had the mat1-1
mating type allele whereas those in VCGs
US-02 and US-03 had the mat1-2 allele.
The strict association of independent markers during this sample period was
consistent with a strictly asexual mode of reproduction. However, examination of
archived isolates collected in the 1970s and 1980s and contemporary isolates
revealed an incongruent relationship between the independent markers. MGR586 C
and E isolates were vegetatively compatible which indicated that multiple robust
MGR586 delineated lineages could be nested within certain VCGs. Although
isolates in lineages C and E were vegetatively compatible, they were
of opposite mating type. Several hypotheses, including recombination, could
account for the incongruence between the various markers. Among the eight MGR586
lineages (A through H) that occur in the United States, all isolates in lineages
A, D, E, G, and H had the mat1-1 allele,
whereas isolates in lineages B, C, and F had the mat1-2 allele. Nit mutants can be recovered relatively easy
from P. grisea and
should allow large numbers of individuals within a population to be assessed for
vegetative compatibility. VCGs may prove to be an effective multilocus marker in
P. grisea.
Thus, VCGs should be a useful means for characterizing genetic structure in
populations of the rice blast fungus worldwide, provide a useful genetic
framework to assist in interpreting molecular population data, and may provide
insight into potential sexual or asexual recombination events. |
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