25038 Managing Cucurbit Downy Mildew (Pseudoperonospora cubensis) with Disease Monitoring and Cultivar Resistance

Tuesday, August 9, 2016: 8:30 AM
Valdosta Room (Sheraton Hotel Atlanta)
Wesley L Kline , Rutgers University, Millville, NJ
C. Andrew Wyenandt , Rutgers University, Bridgeton, NJ
In 2014 and 2015, 11 and 14 cultivars respectively were evaluated for tolerance to downy mildew. Plots were one row 4.5 meters long and 1.5 meters between beds and arranged in a randomized complete block design with four replications. Plots were hand seeded (1 seed/hole) at 30 centimeters between plants.

Plots were evaluated for downy mildew development from August through the final harvest in October. Foliage was rated weekly on a scale of 0 to 100 (0.0 = no downy mildew; 100 = 100% of leaves infected) for downy mildew development. Arcsine-transformed area under disease progress curve (AUDPC) values for downy mildew were calculated for all treatments.

Cucumbers were hand harvested on eleven dates in 2014 and nine dates in 2015. Harvested cucumbers from each plot were weighed to determine total yield. They were then graded into one of five classes, counted and weighed: Fancy, No. 1, Large, Small and Culls

There were significant differences among the cultivars for both yield and fruit number in both years. Dasher II, Mongoose, Python, Speedway and Thunder had significantly higher fruit number than Seminis 4220, Tasty Green and Marketmore 76 in 2014 and Dasher II Mongoose and Python had higher yields than all others in 2015. Python had a higher marketable yield than Marketmore 76, Seminis 4220, Seminis 8592 or Tasty Green in 2014, but in 2015 most cultivars did not statistically differ from one another.

The percent marketable fruit in 2014 ranged from 27 to 82%. Python, Seminis 4220 and Mongoose had a significantly higher percent marketable fruit than all cultivars except Intimidator and Tasty Green in 2014. In 2015 percent marketable fruit ranged from 43 to 85%. Marketmore 76 had the highest percent marketable fruit, but was not statistically different from six other cultivars.

In 2014, two cultivars, Marketmore 76 and Mongoose, had significantly higher values under the disease progress curve (AUDPC) which indicates the disease severity was greater for those two. All others were not different from one another. In 2015, Mongoose, Marketmore 76, had the highest values, but they were not statistically different than Speedway or Fanfare. Seminis 4719 and Seminis 4220 had the lowest values, but only differed from the four with the highest values.