A study which probed the occurrence and quantitative variations hepatotoxic microcystin in a Sub Saharan drinking freshwater reservoir was carried out between November 2014 and March 2015. Results reveal the presence of MCYST-YR, MCYST-LR, MCYST-RR, MCYST-LA and MCYST-LF variants either in cells collected directly from bloom or toxic isolates cultured under laboratory conditions. Two minor microcystin congeners (MCYST-(H)YR) and (D-Asp, Dha) MCYST-RR) were identified, but not quantified. Variants dominance were in the order MCYST-LR > MCYST-RR > MCYST-YR > MCYST-LA > MCYST-LF across sampling sites. Maximum and minimum concentrations of quantified MCYSTs congeners were (489.25, 50.95 µg toxin/g DW), (98.92, 9.11 µg toxin/g DW), (140.25, 12.07 µg toxin/g DW), (56.99, 6.20 µg toxin/g DW) and (50.46, 3.65 µg toxin/g DW) for MCYST-LR, MCYST-YR, MCYST-RR, MCYST-LA and MCYST-LF, respectively. Analysis of variance (ANOVA) revealed there was a high significant difference between mean microcystin concentrations across sampling sites (p < 0.05).

A significant number of people around the world suffer from illnesses that are related to the consumption of unsafe vegetable crops. Early identification of waterborne microbial pathogens affecting vegetable crops can be an important step towards the control of disease. Microbial pathogens secrete extracellular metabolic volatiles or molecular biomarkers that affect the yield and quality of vegetable crops. These secreted compounds can be investigated using several applied analytical techniques, such as metabolomics, proteomics and other ‘omics’ tools. Currently, it is possible to use these approaches to characterize a broad range of specialized metabolites present in vegetable crops affected by waterborne and soilborne microbial pathogens. Such approaches may be used to determine molecular biomarkers, which can subsequently be exploited for the diagnosis of microbial pathogens that affect vegetable crops. Molecular biomarkers are involved in complex pathogenic biological processes involving mechanisms of pathogenesis and could be of great interest in the field of metabolomics. This review investigates disease diagnostic strategies and emerging analytical metabolomics techniques for waterborne microbial pathogens in vegetable crops. These will be vital in building comprehensive and more reliable data regarding the nature of secreted proteins and other specialized metabolites in vegetable crops and will lead to an increased understanding of the interactions between the host and pathogenic oomycetes, fungi, bacteria and viruses.

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