Detection of Monosporascus cannonballus from melon plants using PCR

Root rot and vine decline caused by Monosporascus cannonballus is a major challenge for melon production world-wide. In recent years، a disease suggested to be related to this pathogen was observed 1-2 weeks prior to harvest in many melon production areas across Iran. In this study، melon plants with symptoms of chlorosis، wilting، decline and/or sudden death were collected from melon growing areas. Pieces of the roots with rot symptoms or discoloration were surface-sterilized and placed on PDA culture medium. DNA was extracted from the rest of the sterilized roots and used in polymerase chain reaction (PCR) using specific primers designed from ribosomal DNA of M. cannonballus. The pathogenicity of the fungus for 24 of its isolates was examined on a muskmelon genotype، Zard-e-Garmsar. In addition، the presence of M. cannonballus was tested on the symptomless melon plants at early growing stages as well as those inoculated with this pathogen using the specific primers. The presence of M. cannonballus was confirmed in 95 melon samples (63% of total samples tested) based on the morphological criteria of the isolated fungus and molecular techniques، where a unique band specific to this pathogen was amplified in diagnostic PCR. M. cannonballus was also detected in the roots of symptomless and inoculated melon plants as early as 2 days post-inoculation. This study demonstrated that M. cannonballus is the major causal organism for melon collapse in all sampling regions and that the pathogen is detectable in melon plants suspected of infection using molecular tools at early growth stages.