Abstract
Cassava will have a vital role to play, if food security is to be achieved in Sub-Saharan Africa, especially Central and East Africa. The whitefly Bemisia tabaci poses a major threat to cassava production by small holder farmers in part due to their role as a vector of cassava mosaic begomoviruses (CMBs) and cassava brown streak ipomoviruses (CBSIs). In the present study untargeted metabolomics has been used as a tool to assess natural variation, similarities and attempts to identify trait differentiators among an East African cassava diversity panel that displayed tolerance/resistance to the effects of Bemisia tabaci infestation. The metabolome captured, was represented by 1529 unique chemical features per accession. Principal component analysis (PCA) identified a 23% variation across the panel, with geographical origin/adaption the most influential classification factors. Separation based on resistance and susceptible traits to Bemisia tabaci could also be observed within the data and was corroborated by genotyping data. Thus the metabolomics pipeline represented an effective metabotyping approach. Agglomerative Hierarchical Clustering Analysis (HCA) of both the metabolomics and genotyping data was performed and revealed a high level of similarity between accessions. Specific differentiating features/metabolites were identified, including those potentially conferring vigour to whitefly tolerance on a constitutive manner. The implications of using these cassava varieties as parental breeding material and the future potential of incorporating more exotic donor material is discussed.
Highlights
These low abundant features are close to the limit of detection and present high variability and poor reproducibility across replicates (RSD>30%)
The final data matrix contained 1530 unique chemical features (S1 Fig), one being the internal standard. At this stage chemical features grouped under the same peak-cluster (PC) group were treated independently, and clustering of adducts, in-source fragments or multiple charged species was considered later for identification and characterisation purposes
The most promising candidates within the 5CP collection, which represent a subset of national collections, as potential sources of both whitefly and disease resistance seem to be concentrated in the Ugandan and Tanzanian lines (Table 1) which are the ones presenting the highest level of duplication and homology
Summary
The funders were involved in the provision of plant material, decision to publish and preparation of the manuscript. Plant breeding relies on the selection of accessions carrying desirable agronomic and consumer traits. This is not always a straightforward task, especially when the resolution or sensitivity of the phenotyping methodology is low or heavily influenced by environmental factors. The robustness of phenotyping criteria for assessing disease resistance in cassava has been already addressed, and has highlighted the effects of the environment on the visible symptoms of disease [1] and on the development rate of its vector, the whiteflies [2].
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