VG07070 Nitrogen & lettuce diseases

The objective of this study was to determine if the rate and form of Nitrogen increases lettuce susceptibility to disease.

Initial experiments were conducted to determine the susceptibility of 21 lettuce varieties to Downy Mildew.

Varieties were deemed resistant, moderately resistant and susceptible.

Four varieties were used to assess the growth of lettuce in response to various rates of Nitrogen prior to inoculation studies with Downy Mildew.

Lettuce seedlings were watered with Potassium nitrate, a commonly used nursery fertilizer.

Lettuce seedlings were inoculated with Downy Mildew and the incidence and disease severity were assessed 20 days after tinoculation. Fresh weight was also recorded.

Results :

• Results showed that there was a significant varietal difference in susceptibility to Downy Mildew.
• Although varieties Lily and Boomerang showed no infection by Downy Mildew, cv. Constanza was significantly more susceptible to the disease at the highest rate of Potassium Nitrate. Infection also occurred when watered with Calcium Nitrate.
• Assessment of fresh weight indicated that there was a combined detrimental effect of high Nitrogen and infection by Downy Mildew on growth of lettuce.
• Growth of cv. Constanza was reduced following infection with Downy Mildew and application of high rates of Poptassium Nitrate.
• More disease occurred on lettuce plants when high rates of N were applied as Potassium Nitrate.
• Applying higher rates of Nitrogen did not improve plant growth and can increase susceptibility of certain lettuce varieties to disease.

Acknowledgments :

The project VG07070 was formed by Government agencies, private industry, universities and international researchers, to benchmark disease predictive models for major vegetable crops.

Funding was provided by Australian vegetable growers (through the R & D levy) and the Department of Primary Industries, Victoria. The Australian Government provides matched funding for all HAL’s R&D activities.