台灣疫病菌PHYTOPHTHORA PARASITICA 之基因型研究(二)

Phytophthora parasitica Dastur (=
Phytophthora nicotianae Breda de Haan),
being able to attack a wide variety of plants,
is a very notorious plant pathogen in the
central and southern Taiwan. Crops of great
economical importance such as citrus,
tobacco, dieffenbachia, lily, cymbidium, etc.,
all are targets of this pathogen. It has been
shown that there are variations in the
morphology, pathogenicity, and virulence
among P. parasitica isolated from different
host species, indicating that differentiation
may have arisen in P. parasitica isolated
from different host species. The purpose of
this study was to analyze the genotypes of P.
parasitica by DNA fingerprinting. To
search for probes appropriate for DNA
fingerprinting analysis, 20 clones were
randomly selected from the genomic library
of P. parasitica . Subsequently, DIG-labeled
probes were prepared from each clone and
used in genomic Southern hybridization.
Besides, the possibility that retrotransposon
may serve as a genetic marker was also
investigated at the same time. Fortuitously,
results obtained from the latter approach
have been very inspiring. It has been found
that there indeed exist Ty1-copia
retrotransposons in P. parasitica, as revealed
by the presence of reverse transcriptase
sequences. Analysis by genomic Southern
hybridization using retrotransposon sequence
as a probe indicated that polymorphisms
exist among P. parasitica isolates tested. To
determine its genetic stability, RNA was
prepared from this fungus and analyzed by
Northern hybridization as well as reversetranscriptase-
polymerase chain reaction.
No signal was detectable, indicating that this
retroelement is unable to transpose. In
addition, the genetic stability of this sequence
throughout the asexual and sexual
reproduction cycles of P. parasitica is now
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being investigated as well.