Submitted to: Biological and Cultural Tests for Control of Plant Diseases
Publication Type: Research Notes
Publication Acceptance Date: 12/15/1998
Publication Date: N/A
Interpretive Summary: Downy mildew is an important disease of muskmelons (cantaloupe, honeydew, etc.). The development and cultivation of varieties that are genetically resistant to the disease is the most environmentally sound and economically desirable method of controlling downy mildew. Good sources of resistance, preferably from a wide genetic pool, must be identified in order for plant breeders to develop these varieties. The U.S. Plant Germplasm Collection represents such a wide genetic pool of muskmelon lines collected from throughout the world. As part of the ARS effort to generate a data base for this collection of muskmelon lines, Agency scientists are systematically testing them for resistance to the most important diseases. These studies report the results of such tests conducted in 1998 to identify resistance to downy mildew. In these tests, two lines contained individual plants that were resistant to the disease. These lines contained resistant individual plants that should be useful genetic sources for the development of new, downy mildew resistant muskmelon varieties.
Technical Abstract: Cucumis melo (muskmelon) plant introductions accessions were tested for resistance to Pseudoperonospora cubensis pathotype 4, the incitant of downy mildew of muskmelon. This report gives the results of tests on 114 PI accessions and four control 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 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 H airbrush at 40 psi. After inoculation, plants were placed in a dark dew chamber at 20C for the sixth day after inoculation, plants were returned to the dew chamber for 18 hr to enhance sporulation, and were rated for RT on the seventh day post-inoculation. PI accessions 13253 and 20486 contained individual plants that were resistant.