Submitted to: Biological and Cultural Tests for Control of Plant Diseases
Publication Type: Research Notes
Publication Acceptance Date: 10/8/1997
Publication Date: N/A
Interpretive Summary: Downy mildew is an important fungus disease that attacks the foliage of muskmelons (cantaloupe, honeydew, etc.). The development and cultivation of varieties that are genetically resistant to the disease is both environmentally sound and economically feasible. Good sources of resistance, preferably from a wide genetic pool, must be identified in order for plant breeders to develop these varieties. Muskmelons grown fro seeds representing genotypes from all over the world collected by the U. S. Plant Introduction Station were tested for resistance to the disease. Twenty-one muskmelon lines were found with better resistance than the susceptible control variety, and some may serve as useful sources for the development of new muskmelon cultivars with resistance to the disease.
Technical Abstract: Cucumis melo (muskmelon) plant introductions (PIs) were tested for resistance to Pseudoperonospora cubensis pathotype 4, the incitant of downy mildew of muskmelon. This report gives the results of tests on 245 PIs and four check cultivars. Field plots of two to five 10-leaf-stage plants of each entry were inoculated by spraying the adaxial leaf surfaces with 20,000 sporangia per ml using a Micro Ulva. Ratings for downy mildew reaction type (RT) were made approximately 19 days post-inoculation using a 1-4 scale of increasing resistance. Those entries in which one or more plants had a RT equal to or greater than 2 were retested in replicated glasshouse trials. Four replicates of six plants each were inoculated at the 2-expanded-leaf stage with 5,000 sporangia per ml using a Paasche Type airbrush at 40 psi. After inoculation, plants were placed in a dark dew chamber at 20C for 18 hr, then transferred to a glasshouse bench for five days. On the sixth day after inoculation, plants were retured to the dew chamber for 18 hr to enhance sporulation. Twenty-one PIs wre significantly more resistant than the susceptible check.