The 2012 ASHS Annual Conference

Monosporascus root rot or vine decline caused by Monosporascus cannonballus is widely distributed in the major cucurbit crop growing areas in Korea. Most watermelon, muskmelon and Oriental melon crops are grown in plastic greenhouses in the southern part of the country where the spread of the disease is severe. First isolated in 1993 from the diseased roots of the bottle gourd-grafted watermelon plants, M. cannonballus has been found in wilted plants of muskmelon grown in greenhouses with temperatures often higher than 30 ^oC. The high temperature greenhouse growing conditions favor disease development on muskmelon plants especially during the fruit ripening stage. Because of this disease, the stable and sustainable production of muskmelon crops has been a challenge to many growers. As an effort to develop new cultivars resistant to M. cannonballus, various germplasm materials of Cucumis melo (muskmelon) including commercial lines and hybrids were evaluated in this study. Seeds were surface sterilized in 3% Clorox for 20 minutes and rinsed in sterile water under a laminar flow transfer hood. After seed coat removal, the naked seeds were cultured on agar medium with the pathogen (M. cannonballus) inoculums. Among the 42 genetic materials (28 commercial varieties, 9 accessions, 8 germplasms including domestic lines) tested, the seedlings of 'Rio Gold' and 'Tokyo Early' showed resistance to the pathogen, while seedlings of 'Busan 914' and 'Busan 920' showing only a partial resistance. The rest of the genetic materials were susceptible to the disease. Findings of this study may well be used for further selection and breeding of new muskmelon cultivars resistant to M. cannonballus.