Impact of Nutritional (C: N Ratio and Source) on Growth, Oxalate Accumulation, and Culture pH by Sclerotinia Sclerotiorum.

Abstract

The phytopathogenic fungi Sclerotinia sclerotiorum, causative of Sclerotinia stem rot of soybean was studied to determine the impact of culture media representing disparate carbon to nitrogen sources and ratios on mycelial growth, oxalate accumulation, and culture pH. The three parameters exhibited significant variations with respect 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 highest oxalate–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 by HPLC analysis of metabolites present in the culture filtrate, which revealed 6–17 peaks. Nine peaks were identified as acetate, citrate, succinate, malate, oxalate, oxaloacetate, succinate, glycolate, and indole-3-acetic acids (IAA). Acetate, oxalate and malate were present in all the culture filtrates but in varying amounts. The other metabolites were not detected in some of the culture filtrates. Taken together, these results indicate that; 1) oxalate production did not correlate with growth; 2) oxalate accumulation and regulation is dependent on nutritional conditions and; 3) the decrease in culture pH was independent of oxalate accumulation. Such studies may lead to identification of most commendable media for laboratory assay and the rational design of strategies to regulate/depress oxalate accumulation and reduce its availability in plant foods.

Key words: biomass, metabolites, mycelial, nutrition, oxalate, Sclerotinia sclerotiorum