Tolerance to Monosporascus Root Rot and Vine Decline in Melon (Cucumis melo L.) Germplasm

Abstract

We conducted a field screening of melon (Cucumis melo L.) cultigens to identify potential sources of host-plant resistance to Monosporascus cannonballus Pollack & Uecker. Seed were sown in Speedling trays with inoculated or noninoculated media. Plants were transplanted into a field known to be highly infested with M. cannonballus. Cultigens were arranged in a randomized complete block with three replications in each treatment (fumigated/noninoculated, nonfumigated/inoculated). Vine decline (1 = no symptoms to 5 = dead vines) was rated at 78 and 90 days post-transplanting. Disease symptoms were most severe and occurred earliest in the inoculated, nonfumigated plots. However, natural infection by M. cannonballus occurred in the fumigated plots, as all root samples collected contained perithecia. The majority of cultigens (85%) showed moderate to severe vine decline symptoms. Mean vine decline ratings of melon types from the spring test, ranked from most tolerant to least tolerant, were: Charentais = Ananas = Galia > Misc. = Honeydew = Mixed > US cantaloupe. A Fall test of the most tolerant cultigens showed similar results, in that Ananas and Charentais types had the highest tolerance; however, Galia types performed poorly, which may be due to the different environmental conditions, or differing fruit loads on the vines in the two tests. `Deltex', an Ananas hybrid, showed the highest tolerance based on vine decline ratings in the two tests.