comparison of perithecium dimensions of ophiostoma ulmi and o. novo-ulmi, the causal agents of dutch elm disease

dutch elm disease is one of the most destructive vascular wilt diseases in the world. ophiosatoma ulmi and o. novo-ulmi had been the most important causal agents of the dutch elm disease in the last century. so, in order to manage of disease, their identification and distinction is necessary. these fungal species were distinguished based on morphological, physiological and molecular characters. perithecium dimensions of fungal isolates such as: neck length, bowl width and their ratio, on the mea, are the most important primer factors for their distinction. in this study, neck length, bowl width and their ratio for isolates of fungal causal were estimated in vitro. in this research, every isolate with two standard isolates of a and b type was cultured on mea supplemented by powder of elm wood and was inoculated in temperature 20°c. the results of estimating perithecium dimensions were showed, the isolates had significant difference, so that isolates of o. novo-ulmi to have higher neck length (290-640 micrometer) and shorter bowl width (70-100 micrometer) than o. ulmi were distinguished. neck length to bowl width ratio for the isolates of o. ulmi and o. novo-ulmi was also calculated 2.76 and 5.87, respectively. the potential using of perithecium dimensions of fungal isolates as one of primer morphological factors to distinguish isolates of the causal agent or agents dutch elm disease in iran was discussed in this paper.