| The physiology,ecology,monitoring and inheritance of resistance to metalaxyl of the pathogen causing tobacco black shank were studied systematically in vitro,respectively,by the methods of gathering,isolating,purifying,identification,inducing of sporangia,partnership culture,artificial inoculation,and colony growth rate tests. The results were summarized as follows:1. Sixty-nine Phytophthora isolates were obtained from over three hundred diseased tobacco stems collected from ten different localities,i.e. Bozhou, Guoyang, Xuxian, Taihe, Lixin, Guzhen, Fengyang. Hefei,Shexian,and Wuhu in Anhui Province. The results showed all of these isolates were heterothallic,with amphigynous antheridia and pathogenic to tobacco. The sporangia were mostly spherical or subspherical,caduceus,and conspicuously papillate,with pore narrow and pedical short,and the asymmetry shape ones frequently appeared. The maximum temperature for mycelial growth in vitro was beyond 35,below 40. The sixty-nine isolates were all identified as Phytophthora nicotinae Breda de Haan var. nicotianae Waterhouse (equal to Phytophthora parasitica Duster var. nicotianae Waterhouse),according to the tabular keys to the species of Phytophthora. The result indicated that this species was the pathogenic microorganism of tobacco black shank in Ahui Province.2. The mode of pore extrusion release was concluded as the release process of zoospores of Phytophthora nicotinae var. nicotianae and the modes of germination of zoospores were reduced to two types for the first time,direct germination fashion,and indirect germination fashion. In addition, the direct mode was reduced further to two fashions, i.e. monopole germination and multipolar germination,based on the results of detail observation through microscope in the dissertation.3. The method of partnership-culturing for 2-3 weeks on -sitosterol L-trytophan medium in darkness at 25 could be used to determine mating type of Phytophthora nicotinae var. nicotianae.4. AT mating type was predominant in the isolates of Phytophthora nicotinae var. nicotianae from Anhui,A0 mating type was in the next place,and other mating types were not observed by the method of partnershipculture in vitro on 3 -sitosterol L-trytophan medium,suggesting that sexual propagation of Phytophthora nicotinae var. nicotianae might not be taken place frequently,and the composition of different pathogenicity isolates was steady in Anhui. According to the results of AI mating type not being observed,Anhui might not be the origin center of Phytophthora nicotinae var. nicotianae. The results showed further that the mating type distribution Phytophthora nicotinae var. nicotianae on geography in Anhui was in line with the law of the mating type distribution of Phytophthora nicotinae in China.5. The effects of inoculation methods,tobacco varieties and isolates on the pathogenicity of Phytophthora nicotianae var. nicotianae were studied systematically by means of three-factor randomized block design. The results showed that pathogenicity of Phytophthora nicotianae var. nicotianae were influenced by integrated factors,and inoculation methods were the maximum effect factor. The results indicated that the important order of the effects of the factors was inoculation methods > tobacco varieties > isolates. Among the different combinations of inoculation method, tobacco varieties and isolates, the pathogenicity from the combination of wounded-inoculation + Hongda + pnBZ-8 was the most significant and that from the combination of unwounded-inoculation + NC89 + pnSX-3 was the weakest. The effect of interaction of inoculation methods and tobacco varieties was significant at 0.05 levels,while the other interaction effects were not significant. The method of inoculation with mycelium dish on wounded tobacco stem was the ideal method of pathogenicity test,since this method was simple and convenient,and could reflect the pathogenicity level of Phytophthora nicotianae var. nicotianae.6. The studies on pathogenicity differentiation of Phy...
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