Knight Noel L, Sutherland Mark W, Martin Anke, Herde Damian J
Centre for Systems Biology, Faculty of Sciences, University of Southern Queensland, Toowoomba, QLD, 4350, Australia.
Department of Agriculture, Fisheries and Forestry Queensland (DAFFQ), Leslie Research Centre, Toowoomba, QLD, 4350, Australia.
Plant Dis. 2012 Nov;96(11):1661-1669. doi: 10.1094/PDIS-12-11-1050-RE.
Assessment among cereal genotypes of relative seedling resistance to the crown rot pathogen Fusarium pseudograminearum has been primarily based on visual discoloration of the leaf sheaths. This study is the first to investigate the relationship between the widely used visual rating of seedling leaf sheath discoloration and the degree of colonization of these tissues by the pathogen, based on quantitative polymerase chain reaction (qPCR) of fungal DNA using primers specific for the translation elongation factor α sequence. Fourteen-day-old seedlings of four hard white spring wheat genotypes which differ in their degree of resistance to the pathogen, based on the expression of visible symptoms, were inoculated using a droplet method and assessed weekly from 7 to 35 days after inoculation (dai) for both discoloration and fungal DNA content per unit of tissue weight. Both visual assessment of disease symptoms and qPCR of fungal biomass indicated significant differences between the partially resistant and susceptible wheat genotypes from 14 dai. Visual discoloration of leaf sheath tissues was strongly correlated with fungal biomass estimated by qPCR in all four genotypes; however, this correlation became weaker with increasing time after inoculation. Significant correlations between these parameters were indicated at 14, 21, and 28 dai whereas, by 35 dai, the correlation was not significant. Evaluation of plants at 14 dai provided a rapid test which gave clear discrimination between lines for both parameters and was the time point of closest correlation between fungal colonization and disease symptoms. Symptom expression at all times following inoculation was accompanied by tissue infection, and at no time was symptomless infection observed under this screening environment. These qPCR results confirm that visual assessments of disease symptoms reflect the extent of tissue colonization by the pathogen in recently colonized tissues and confirm the validity of visual assessments for disease rating in high-throughput screening of breeding materials.
对谷类基因型相对幼苗抗冠腐病病原菌（禾谷镰刀菌）的评估主要基于叶鞘的视觉变色情况。本研究首次基于使用针对翻译延伸因子α序列的特异性引物对真菌DNA进行定量聚合酶链反应（qPCR），来探究广泛使用的幼苗叶鞘变色视觉评级与病原菌在这些组织中的定殖程度之间的关系。根据可见症状的表现，选取了四种对该病原菌抗性程度不同的硬粒白春小麦基因型的14日龄幼苗，采用滴液法接种，并在接种后7至35天每周评估叶鞘变色情况以及每单位组织重量中的真菌DNA含量。对疾病症状的视觉评估和真菌生物量的qPCR均表明，从接种后14天起，部分抗性和易感小麦基因型之间存在显著差异。在所有四种基因型中，叶鞘组织的视觉变色与通过qPCR估算的真菌生物量密切相关；然而，随着接种后时间的增加，这种相关性变弱。在接种后14、21和28天，这些参数之间存在显著相关性，而到接种后35天，相关性不显著。在接种后14天对植株进行评估提供了一种快速检测方法，能清楚地区分两个参数的不同品系，并且这是真菌定殖与疾病症状之间相关性最紧密的时间点。接种后任何时候的症状表现都伴随着组织感染，在这种筛选环境下未观察到无症状感染。这些qPCR结果证实，对疾病症状的视觉评估反映了病原菌在最近定殖组织中的组织定殖程度，并证实了在育种材料高通量筛选中进行疾病评级的视觉评估的有效性。
