甘薯(瘟)青枯菌致病类群及分布的研究

PATHOGENIC GROUPS OF SWEET-POTATO PSEUDOMON AS SOLAN ACEARUM AND ITS DISTRIBUTION AND DEVELOPMENT

1984—1986年从我国南方甘薯瘟病区收集109个菌株,根据各菌在惠红早、广薯15、华北48和金薯120等鉴别品种上的侵染程度,可分为2个菌群和4个亚群(Ⅰ-A、Ⅰ-B、Ⅱ-C和Ⅱ-D),其中Ⅰ-B亚群出现频率高达41.3%。对温度反应显示,Ⅱ群菌株对华北48和金薯120的强致病起点适温分别为21±1℃和26±1℃。调查表明,感病品种连作地以Ⅰ群菌占优势,换用并连茬抗病品种后,Ⅱ群菌随之发生,4—5年后占绝对优势,其频率为87.8—100%。用Ⅰ群菌株连续2次接种抗病品种后,子代出现Ⅱ群菌频率达91%以上。

109 isolates of Pseudomonas solanacearum collected from sweet potatodiseased areas in the south of China from 1984 to 1987 could be divid-ed into 2 groups,4 subgroups(Ⅰ-A,Ⅰ-B,Ⅱ-C and Ⅱ-D)based on their infectivity on differential cultivars Huihongzao,Guangshu 15,Huabei 48 and Jinshu 120.Among them Ⅰ-B Subgroap was the predomi-nant(41.3%).Reactions of isolates to d fferent temperature showedthat the lowest temperature for group Ⅱ to severely infect cvs.Huabei48 and Jinshu 120 was 21±1℃ and 26±1℃,respectively. Investigations on the distribution and development of the bacteriumgroups in diseased fields showed that group Ⅰ predominated in the dis-eased fields of successively growing susceptible cultivars,whereas Ⅱoccurred when resistant cultivars were grown alternatinely and reachedabout 87.8—100% in 4—5 years.The fact that group Ⅱ in theoffspring population from group Io ccurred at a frequency over 91% whengroup I was used for inoculation of resistant cultivars in vitro succes-sively 2 times explained that mild pathogenic bacteria group variatedtoxicically when it infected resistant cultivars in soil and successivecultivation of resistant varieties might led to a directional accumlationof stroger pathogenic bacteria group and finally loss their resistance.