Ahmad Azeem, Mbofung Gladys Y, Acharya Jyotsna, Schmidt Clarice L, Robertson Alison E
Department of Plant Pathology and Microbiology, Iowa State University, Ames, Iowa, United States of America.
PLoS One. 2015 Nov 24;10(11):e0143553. doi: 10.1371/journal.pone.0143553. eCollection 2015.
Clavibacter michiganensis subsp. nebraskensis (Cmn), the causal organism of Goss's wilt and leaf blight of maize, can be detected in the phyllosphere of its host prior to disease development. We compared the morphology and pathogenicity of 37 putative isolates of Cmn recovered from asymptomatic and symptomatic maize leaves. Thirty-three of the isolates produced mucoid orange colonies, irrespective of the source of isolation and all but four of these isolates were pathogenic on maize. The remaining 4 isolates recovered from asymptomatic leaves had large fluidal yellow colonies, and were non-pathogenic on maize. Isolates varied in their aggressiveness on a susceptible hybrid of maize but no significant differences in aggressiveness were detected between epiphytic isolates and those recovered from diseased maize tissues. The genomics of Cmn is poorly understood; therefore as a first step to determining what genes may play a role in virulence, we compared 33 putative virulence gene sequences from 6 pathogenic and a non-pathogenic isolate recovered from the phyllosphere. Sequence polymorphisms were detected in 5 genes, cellulase A, two endoglucanases, xylanase B and a pectate lyase but there was no relationship with pathogenicity. Further research is needed to determine what genes play a role in virulence of Cmn. Our data show however, that the virulence factors in Cmn likely differ from those reported for the closely related subspecies michiganensis and sepedonicus.
密执安棒形杆菌内布拉斯加亚种（Cmn）是玉米戈斯枯萎病和叶枯病的致病病原体，在病害发展之前就能在其寄主的叶际中检测到。我们比较了从无症状和有症状玉米叶片中分离得到的37株假定的Cmn菌株的形态和致病性。其中33株菌株产生黏液状橙色菌落，无论分离来源如何，除4株外，所有这些菌株对玉米都具有致病性。从无症状叶片中分离得到的其余4株菌株具有大的流质黄色菌落，对玉米无致病性。这些菌株对一种易感玉米杂交种的侵染力各不相同，但在附生菌株和从患病玉米组织中分离得到的菌株之间未检测到侵染力的显著差异。人们对Cmn的基因组学了解甚少；因此，作为确定哪些基因可能在毒力中起作用的第一步，我们比较了从叶际中分离得到的6株致病菌株和1株非致病菌株的33个假定毒力基因序列。在5个基因中检测到序列多态性，即纤维素酶A、两种内切葡聚糖酶、木聚糖酶B和一种果胶酸裂解酶，但与致病性无关。需要进一步研究以确定哪些基因在Cmn的毒力中起作用。然而，我们的数据表明，Cmn中的毒力因子可能与密切相关的密歇根亚种和马铃薯环腐亚种所报道的不同。
