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枯萎病菌致病力的变化可能是连作条件下甘蓝枯萎病严重发生的重要原因之一。本研究在建立适度感染的人工病圃的基础上连续种植甘蓝5茬,每茬收获后随机采集土样。利用驹田氏培养基通过稀释平板法对连作土壤中尖孢镰刀菌种群数量的监测结果表明,连作后尖孢镰刀菌的数量由第二茬后的3.047×104cfu.g-1土壤增加到第五茬收获后的1.608×105cfu.g-1土壤。对各茬后所分离30株甘蓝枯萎病菌(Fusarium oxysporum f.sp.conglutinans,Foc)的培养性状的观察结果表明,连作后Foc菌株在菌落形态、菌落扩展速率和产孢量等方面均发生明显的变化。用浸根法进行的致病力测定结果表明,随着连茬次数增加,弱致病力菌株占总供试菌株的比例逐渐变小,到第三茬后由第一茬的6.7%下降为0;而强致病力菌株的比例逐渐上升,由第一茬后的6.7%上升到第四茬后的16.7%。利用11条寡聚核苷酸随机引物对受试菌株进行PCR-ISSR扩增,结果显示从第三茬后Foc群体遗传结构出现分化。UPGMA聚类分析结果表明,第三、四和五茬后的Foc菌株都分为A和B两个类群,每个类群又分为Ⅰ和Ⅱ两个亚类群,但同一类群和亚类群中包含不同致病力的菌株,未发现病菌的致病力变化与遗传结构分化之间的相关。
The change of pathogenicity of Fusarium wilt may be one of the important reasons for the severe occurrence of cabbage wilt under successive cropping conditions. In this study, a moderate infection of artificial disease nursery based on the continuous cultivation of cabbage 5 stubble, stubble after harvest random sampling of soil samples. The results of monitoring the population of Fusarium oxysporum in continuous cropping soil by Kudan’s medium by dilution plate method showed that the number of Fusarium oxysporum increased from 3.047 × 104cfu.g-1 soil after the second crop to The fifth crop after harvest 1.608 × 105cfu.g-1 soil. The observation of the culture traits of 30 strains of Fusarium oxysporum f. Sp. Conglutinans (Foc) isolated after each stubble showed that the Foc strains were significantly different in colony morphology, colony expansion rate and sporulation rate after continuous cropping The change. The results of pathogenicity test by root immersion showed that the proportion of weak virulent strains to the total tested strains gradually decreased with the increase of the number of continuous cropping and decreased from 6.7% of the first crop to 0; however, the proportion of strong virulent strains gradually increased from 6.7% after the first crop to 16.7% after the fourth crop. PCR-ISSR amplification of the tested strains with 11 oligonucleotide primers showed that the Foc population differed in its genetic structure after the third crop. UPGMA cluster analysis showed that Foc strains after the third, fourth and fifth crop were divided into two groups A and B, and each group was divided into two subgroups Ⅰ and Ⅱ, but the same group and subgroup contained Different pathogenic strains, no pathogenic changes found in germs and genetic structure of the correlation between.