Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 5/18/2006
Publication Date: 7/1/2006
Citation: Kousik, C.S. 2006. Sources of resistance to the watermelon downy mildew pathogen (Pseudoperonospora cubensis) in us plant introductions (PI). Phytopathology. 96:S63
Technical Abstract: Downy mildew caused by Pseudoperonospora cubensis is an emerging disease in watermelon (Citrullus lanatus) growing regions in the southeastern US. A new project to evaluate US plant introductions (PI) for resistance to downy mildew and transfer these traits into cultivated watermelons was recently started. A sporangial suspension (10 to the 4th power/ml) of a local P. cubensis isolate was used to inoculate plants of 13 C. colocynthis and 30 Parecitrullus fistulosus PI. Three known resistant C. lanatus var. lanatus PI and susceptible Crimson Sweet and Annans Yok Neam (Cucumis melo) were included as checks. Plants were placed in dew chambers at 18 degree C for 24 hr following inoculation. Disease ratings were recorded on a 1-9 scale (1=no lesions, 9=>80% covered by lesions). Variability in ratings within PI was observed. All susceptible checks had ratings > 6. Two of the resistant C. lanatus var. lanatus checks, one P. fistulosus (PI 540911) and one C. colocynthis (PI 386019) had mean ratings below 3 and were considered resistant. No sporulation was observed on leaves of these PI compared to abundant sporulation on the susceptible checks. Further evaluation of resistant PI with different P. cubensis isolates needs to be conducted to determine durability of resistance.