2018 ASHS Annual Conference

Irrigation with water containing plant pathogens, such as species of oomycetes, has the potential to induce high levels of root and crown rot in plants. To test the prevalence of these pathogens in early January, the irrigation ponds of a group of local Maryland pick-your-own operations were sampled. These operations harvest a wide variety of crops, including strawberries, apples, pumpkins, and raspberries. Many of these specialty crops are known for being highly susceptible to oomycetes, which can cause heavy economic losses.

Rhododendron leaves were used as a pathogen trap to sample the irrigation ponds for the presence of oomycetes. Once collected, the leaflets were plated and monitored for mycelial growth. Next, differential plating was used to segregate the groups of Phytopythium and Phytophthora cultures. The DNA was extracted from each of the samples and underwent a polymerase chain reaction (PCR). This allowed the samples to be tested using the Blast technique to identify the particular species and isolate of the samples collected. During the spring, the pathogenicity of these particular isolates was tested using strawberries and pumpkins. Each crop was inoculated with a different isolate of the pathogens in a growth chamber and their growth and general health were recorded.

The positive results of the irrigation pond sampling during early January highlighted the resilience of these plant pathogens. These results demonstrate the opportunity for growers to screen their irrigation water for plant pathogens and then deploy preventative measures prior to the growing season.