欧亚国际

小麦是全世界最重要的作物之一，对全球食品安全至关重要。“Take-all ”根病害是由子囊菌真菌Gaeumannomyces tritici(Gt)致病，可穿透根并毁坏维管系统。形成的黑色坏死斑破坏了养分和水吸收，导致减产达60%。其它密切相关子囊菌真菌品种，例如G. hyphopodioides(Gh),却是对抗“take-all”病的生物控制剂。 

G.hyphopodioides可侵染外皮质根层，但与“Take-all”不同，其不会侵入到中间部位，特征是在菌表面和亚皮下囊泡形成灰色菌丝。

来自英国的科学家研究重点是对高级成像技术进行评估，以对根定植进行真菌检测和精确定量，通过测量光合参数评估对地上部健康的影响。研究中使用了VideometerLab 多光谱成像系统。

图中显示“Take-all”感染小麦幼苗。左侧是原始图像，有红色箭头标示“take-all ”损失，用手工评分；右图是相同图像经‘VideometerLab’分析，将根组织分类为感病(蓝色)和健康(桔色/黄色)。

具体实验步骤：

A 5-week time-course seedling pot bioassay was set up using 250g of soil from Webb’s Field on the Rothamsted Farm, UK.

An artificial inoculum layer derived from PDA plates contained Gt, Gh or an uncolonised control. The pots were baited with 10 seeds of the wheat cultivar‘Hereward’, and kept in a controlled environment room. Each week, the pots were visually assessed for the presence of necrotic lesions, greying and vesicles. The level of infection was recorded as the proportion of roots showing at least one area of fungal colonisation, making this a semi-quantitative method of assessment. Potentially, imaging could provide a more efficient method to assess root colonisation, allowing the affected root area to be accurately quantified and also removing the subjectivity that can be associated with manual scoring. Consequently, a key question was: can multispectral imaging be used to quantitatively assess and distinguish between Gt and Gh seedling root colonisation?

Multispectral imaging was accomplished using a ‘VideometerLab’ imager, a system that uses 19 different wavelengths ranging from UV to the NIR. Training images were taken of healthy roots, and those colonised with Gt or Gh. These training images were used to build statistical transformations, which were subsequently used to score pixels as corresponding to healthy or colonised root tissue. The threshold pixel score chosen ensured that, in the case of Take-all, only the dark black lesions were scored. The ‘VideometerLab’ and visual assessments of Take-all colonised roots showed a significant correlation (Spearman’s Rank, Rs = 0.670, p = <0.001, n =24). Interestingly, whilst low, the Take-all scores for the uninoculated, control plants, were consistently higher using the image-based scoring. It is possible that the ‘VideometerLab’ was detecting other fungal colonisation phenotypes caused by contamination in the soil which were not visible to the human eye. The ‘VideometerLab’ struggled to distinguish the root greying caused by Gh from mild Take-all symptoms and preliminary analysis has shown that the root greying phenotypes associated with the presence of both fungal species have similar pixel scores across all wavelengths. However, the dark necrotic Take-all lesions had a distinct spectral signature, supporting the validity of our method for scoring Take-all.

Prior to harvesting the roots for the imaging described above, a LemnaTec ‘PhenoCenter’ was used to evalsuate the impact of fungal root colonisation on above ground plant health. Specifically, a PAM fluorescence camera was used to evalsuate photosynthetic efficiency in the foliage. This technique is based on the observation that light energy absorbed by photosystem II can be dissipated via three routes: photochemical reactions, dissipated heat or as fluorescence – it’s the competition between these processes which is exploited to quantify photosynthetic parameters. While a small reduction in photosynthetic efficiency was observed for the Take-all infected plants, no significant difference was observed between the Gh and control pots. These are encouraging results as it would be undesirable for Gh to impact photosynthetic efficiency if used as a biocontrol agent.