| The effects of ultraviolet rays on mutagenizing metalaxyl resistance, the effects of on biochemical characteristics of Phytophthora boehmeriae, biochemical characteristics of metalaxyl-resistant (Mtr) mutants of P.boehmeriae and isoenzyme electrophoreses were studied systemically in this paper based on mutagenizing resistence of P. boehmeriae to metalaxyl. 1. The metalaxyl-resistance mutagenesis was carried with ultraviolet rays to mycelium discs, ultraviolet rays to zoospore, ultraviolet rays + metalaxyl to mycelium discs, metalaxyl to mycelium discs, metalaxyl to zoospores methods. The result showed that the mutants could be obtained by applying the two methods, i.e. metalaxyl to mycelium discs and metalaxyl plus ultraviolet ray to mycelium discs, but not by the other methods. 2. The effects of ultraviolet rays on the biochemical characteristics of P. boehmeriae were studied, and the results indicated that the zoospores of P. boehmeriae could be inactivated obviously by irradiating with 30W ultraviolet light 50cm away from the culture dishes tested and that 95% germination of zoospores could be restrained by 30W ultraviolet light treatment for 40sec.The mycelium growth from mycelium discs of P. boehmeriae were inhibited mostly by 30W ultraviolet light treatment for 20min. Afterwards, the inhibitive rates were decreased with the rise of the treatment time, which showed that the mycelium discs of P. boehmeriae had produced flexibility to ultraviolet rays after being irradiated by certain dosage of ultraviolet light. Between ultraviolet-patient isolates and parental isolates there was obvious difference in colony morphology but not in the sensitivity to metalaxyl. Moreover, the growth rates, oospore production, growth states of ultraviolet-patient isolates in different pH and temperature were obviously less than those of the wild parental isolates, suggesting that the adaptability of P. boehmeriae to the environment was depressed by the ultraviolet rays, and that the ability of sexual reproduction was affected notably by the ultraviolet rays.3.Biological characteristics of Mtr mutants of P.boehmeriae were studied, and the results showed that resistance levels of Mtr mutants to metalaxyl were over 498 times of those of the parental isolates. There was greatly difference between Mtr isolates and their parental isolates in colony morphology, but no difference in the adaptation scope at different pH and temperature. The growth rates of Mtr isolates were obviously lower than those of the parental wild isolates at the same pH and temperature. It also indicated that the oospore production of Mtr isolates was obviously less than those of the parental isolates, and that the mycelium production of Mtr isolates was a little reduced compared to those of the parental isolates in liquid culture. The results suggested that the adaptability of Mtr isolates to environment was reduced and so did the sexual reproduction of Mtr isolates while they produced metalaxyl-resistance.4. The variations of isozyme spectra of esterase (EST), peroxidase (POD) polyphenol oxidase (PPO), catalase (CAT) and soluble protein of P. boehmeriae mutants were studied systemically by applying polyacrlamide gel electrophoresis (PAGE) and isoenzyme analytic technique, and the enzyme activity of POD and PPO of the Mtr isolates of P.boehmeriea by applying the spectrophotometry. The results showed that PPO activity of Mtr isolates had increased in some degree compared to parental isolates, and that one band of isozyme spectrum of POD was found related to the character of the metalaxyl-resistance in the mutants. And at least one band of isozyme spectora of souble protein was found in mutants related to the character of metalaxyl-resistance too. The results showed that isozyme spectra of EST, PPO and CAT were different in tested isolates, but that there were no bands observed relative to the metalaxyl-resistance.The results mentioned above provided necessary theoretic foundation and experimental evidences for clarifying the mechanism of metalaxyl-r... |
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