| Summary: | 碩士 === 國立臺灣大學 === 植物病理學研究所 === 87 === In Taiwan, plant disease caused by Phytophthora spp. was very seriously and among them, Phytophthora parasitica are the most important pathogen. It was shown that there are variations in the pathogenicity , virulence, morphology of sporangia and size of oospores isolated from different host species. This implies that there might be differentiation among this P. parasitica isolates. To understand if there were differentiation in their genotype and the possible relationship between differential genotype and host range, screening for suitable molecular probe have been done in our laboratory to setup the DNA fingerprints system in P. parasitica.
There are two kinds of retrotransposon: PARTN1 and PARTN2 in P. parasitica by the result of Lee’s master thesis ( Lee, 1998), and the Southern blots patterns were different from one another. It was considered that PARTN1 or PARTN2 have some potential to be DNA fingerprinting probe. An ideal DNA fingerprinting probe should be stable in the organism, repeatable, and isolates among P. parasitica are distinguishable. Therefore, the genetic stability of PARTN1 when P. parasitica replicated through asexual stage to 5 generations was detected. It was found that the Southern blots patterns were all the same from parent to their asexual progenies, and PARTN1 and PARTN2 in P. parasitica should be very stable. In addition, the genetic stability when P. parasitica replicated through sexual stage was also detected. It was found that these heterothallic oospores share the genotype from their parents. Some of the bands response to Mendelian rules and indicated the transposition of PARTN1 and PARTN2 were not found in these progenies.
However, there are several bands not found in the parent in inducible homothallic oospore progenies. We don’t know these additional bands were the genetic variation of P. parasitica themselves or the result of transposition. Besides the result of inducible homothallic oospore progenies, the transposition of PARTN1 or PARTN2 was not found.
Also, using PARTN1 as molecular probe (denoted as PARTN1p) to distinguish P. parasitica isolates from different plant hosts was detected. We found the DNA fingerprints pattern different from their host isolates. 46 isolates were divided into 27 genotype when DNA fingerprints was analysis from the size 2 to 6 kb. Compared to Ann’s pathogenicity test (1995) and the results of Chern et al.（1998）, some special isolates like tobacco, diffenbachia, and loquats share the same genotype in each of their host. PARTN1 are genetic stable, easy to distinguish the P. parasitica isolated genotypes and are considered good to be the probe of DNA fingerprints.
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