| The species identification, biological characteristics, the monitoring and inheritance of metalaxyl-resistance, and the biological characters and their inheritance of the metalaxyl-resistant (Mtr) mutants of the pathogen causing cotton boll blight in Anhui were studied in detail, respectivel)? and the results were reported in this paper. Fifty-eight Phtyophthora isolates were obtained from the diseased cotton boils collected from 10 different localities. Xuanchen, Wuhu, Wuwei, Wangjiang, Hefei. Feidong, Chuzhou. Shouxian. Haibei and Shuxian in Anhui, and the cultural character, morphology, physiological characteristics, pathogenicity and host range of the isolates were investigated, respectively. The results showed that all of these isolates were homothallic. with antheridia mostly amphigynous, paragynous in the minority. The sporangia were conspicuously papillate and deciduous in water with pedieal short. The maximum temperature for mycelial growth in culture was below 35 ~C. They were sensitive to malachite green and pathogenic to cotton, ramie and other host plants. According to the results and the main tabular keys to the identification of the species of Phytophthora. all of these isolates were identified as Phyrophthora boehmeriae Sawada, suggesting that this species was the pathogenic organism causing cotton boll blight in Anhui. The resistance to metalaxvl of the isolates of the causal organism of cotton boll blight from different districts in Anhui Province was investigated and the results 3 indicated that the EQ0 of metalaxyl to the tested isolates ranged from 0.0083 I.L gIml to 0.079 1 ti g/ml with average as 0.0268 i g/ml, which was obviously below 0.03 76 t gIml, the average of EQ0 for control isolates sensitive to metalaxyl. No metalaxyl-resistant isolates were observed. It was suggested that the tested isolates of the pathogen causing cotton boU blight in Anhui were all sensitive to metalaxyl. In other words, metalaxyl would be still effective for the control of cotton boll blight in the district at present and in the near future. The result also showed that there was obvious locality difference among the isolates tested in the sensitivity to metalaxvl. The metalaxyl tolerance of WH serial isolates from Wuhu was the strongest and the metalaxyl-sensitivity of SX serial isolates from Shouxian was the highest among the isolates tested. Based on the species identification and metala.xyl-resistance monitoring, the metalaxyl-resistant (MtT) mutants of Phytophthora boehmeriae, the causal organism of cotton boll blight in Anhui were obtained by mutagenizing with metalaxyl and the inheritance of metalaxyl-resistance of Mtr mutant in P boehmeriae was investigated in vitro. It was found for the first time that there were three patterns as follows on the inheritance of metalaxyl-resistance of Mtr mutants in P boehmeriae. (1)Mtr character was inherited steadily in both asexual and sexual progenies, which suggested that the character was probably controlled by the steadily-inherited mitochondrial genes in cytoplasm. (2)Mt?character showed continuing variation in single-zoosporous progenies. (3)Mtr character reverted to be metalaxyll-sensitive (Mts) in the first single-zoospore generation. The latter two patterns could be combined as the unstably-inherited mode, in which Mtr character might be controlled by the unstably-inherited mitochondrial genes in cytoplasm. The results mentioned above indicated that there was diversity on th... |
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