Identification and pathogenicity of fungal agents of root and crown rot of some cucurbit crops in shahrood region

The root and crown rot is one of the most important diseases of cucurbits in the world including Iran. In order to identify the causal agents of wilting and root and crown rot of cucurbits (watermelon، musk melon and cantaloupe) in Shahrood، investigations and collection of diseased samples were made in various fields of Shahrood، Mayamai and Biargomand regions during 2009-2010. After disinfection with sodium hypochlorite (1%)، pieces of infected tissues were cultured on potato dextrose agar (PDA) medium and /or pieces of infected tissues were cultured on PDA، CMA-PARPH and CMA-PARP media without disinfection. Isolates producing spores were purified with single spore method while isolates which did not produce spores، were purified using hyphal tip method. For pathogenicity tests، seedlings grown in green house were dipped in fungal spore suspension (106/ ml) by root dip method for spore producing fungi while in the case of isolates that did not produce spores، pathogenicity test was performed by placing small pieces of young culture of inoculum around crown and roots of plants being tested. According to the morphological، macroscopic and microscopic characteristics adapted from standard keys، pathogenic isolates were identified as Fusarium solani، F. oxysporum f. sp. melonis، F. oxysporum f. sp. niveum، F. equiseti، Phytophthora nicotianae and Rhizoctonia solani. F. oxysporum was the dominant isolated fungus. The results also showed that F. solani and F. oxysporum could be isolated during all growth stages of plants (seedling up to fruiting stages) and these species were widely spread throughout the region. All of these fungi are reported for the first time from melon fields of Shahrood.