Statistical optimization of synnema production fromOphiostoma novo-ulmi

Dutch elm disease caused by Ophiostoma novo-ulmi is one of the most important forest diseases affectingelms on a worldwide level. Most cultures of Ophiostoma spp. growing on agar media do not producesynnema unless a few pieces of elm wood or elm wood extract are included. Considering to the high woodcarbon-to-nitrogen (C:N) ratio, the effect of low amount of nitrogen and high carbon have evaluated onsynnema production (SP). Response surface methodology (RSM) based on Box-Behnken factorial design(BBD) was performed to optimize the interaction of sucrose and L-asparagin concentrations to increase SP.The results showed a quadratic model with a low p-value to explain the changes in SP as a function of C:Nratio, pathogenicity and time. Based on the coefficient of determination (R۲) and mean absolute error, theRSM model provided a good quality prediction for the SP with all independent variables. According to theRSM model, the maximum production of synnema by O. novo-ulmi can be obtained for ۸۶.۹۴ of thepathogenicity under the ۱۸.۰۹:۱ of C:N ratio during ۱۸.۵ days. The results showed that the SP was enhanced۳.۵-۷.۰ times after optimization in comparison to control. Dendrogram constructed of tested O. novo-ulmiwith UPGMA clustering method on the basis of SP during ۲۰ days (with ۵ intervals) revealed ۲ main-groupsand several sub-groups for fungal samples, but higher similarities observed between fungal samples afteroptimization. This finding could be used to induce SP in large scale for pathogenicity tests andmorphological studies.