E S Mwangi, E G Gatebe, M W Ndung'u


Sclerotinia sclerotiorum (Lib.) de Baryis an ubiquitous phytopathogenic fungus capable of infecting a wide varietyof vegetables, ornamentals, and field crops causing significant quality and yield losses. Plants susceptible to thispathogen encompass 75 families, 278 genera, and 408 species (Boland and Hall, 1994). The general inability ofeconomically important crops to develop germplasm resistant to this pathogen has focused attention on the needfor a more detailed understanding of the pathogenic factors involved in disease development.S. sclerotiorum wasstudied to determine the impact of culture media representing disparate carbon to nitrogen sources and ratios onmycelial growth, oxalate accumulation, and culture pH. The three parameters exhibited significant variations withrespect to the differing preference for the nutrient sources and ratios; most oxalate accumulated on high CN (75:1)nutrient media, the intermediate CN (35:1) nutrient media exhibited the best growth potential, while the highestoxalate–to-biomass ratio occurred on poor CN (3.6:1) nutrient media and pH raised in low (10:1) and poor (3.6:1)nutrient media. Further, we made an attempt to identify the potential regulators for oxalate metabolism byanalyzing metabolites present in the culture filtrate. HPLC analysis of the culture filtrate revealed 6 – 17 peaks.Nine peaks were identified as acetate, citrate, succinate, malate, oxalate,oxaloacetate, succinate,glycolate, andindole-3-acetic acids (IAA).Acetate, oxalate and malate were present in all the culture filtrates but in varyingamounts.The other metabolites were not detected in some of the culture filtrates. Taken together, these resultsindicate that; 1) oxalate production did not correlate with growth; 2) oxalate accumulation and regulation isdependent on nutritional conditions and; 3) the decrease in culture pH was independent of oxalate accumulation.The most potent oxalogenic CN media has an important influencer as a tool for biogeochemical particularly if usedwith other parameters such as high growth rate and biomass accumulation. Secondly, such studies may lead toidentification of most commendable media for laboratory assay and the rational design of strategies toregulate/depress oxalate accumulation and reduce its availability in plant foods.


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