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ARS Home » Northeast Area » Frederick, Maryland » Foreign Disease-Weed Science Research » Research » Publications at this Location » Publication #418863
Research Project: Diagnostics and Biological Approaches for Management of Emerging Oomycete Plant Pathogens

Location: Foreign Disease-Weed Science Research

Title: Effect of pH on germination and infection by Phytophthora kernoviae oospores

Author
item Puig, Alina
item DODGE, STEPHEN - Former ARS Employee
item WIDMER, TIM - Former ARS Employee

Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2025
Publication Date: 12/18/2025
Citation: Puig, A.S., Dodge, S., Widmer, T. 2025. Effect of pH on germination and infection by Phytophthora kernoviae oospores. Journal of Plant Pathology. https://doi.org/10.1007/s42161-025-02085-9.
DOI: https://doi.org/10.1007/s42161-025-02085-9

Interpretive Summary: Phytophthora kernoviae is a pathogen with a wide host range. It produces large numbers of oospores, which could easily be moved in soil debris and result in the introduction of the pathogen to new locations. To better understand the conditions under which P. kernoviae oospores will germinate, oospores were incubated in solutions over a range of pH levels (3.6, 5.4, 6.9, 9.3, 11.9). Germination was significantly associating with pH (P <.001), ranging from 20% at the lowest pH (3.6) to 84% at the highest pH (11.9). To determine the effect of soil type on infection and detection of P. kernoviae, three different soils (pH 4.2, 5.2, and 7.4) were infested with oospores (1, 10, 100, and 1000 oospores / cc soil) and baited with Rhododendron ponticum leaves. Disease development, as measured by proportion of symptomatic leaf baits, differed based on soil under inoculum concentrations of 1, 100, and 1000 oospores / cc soil (P<.05). No leaf disks became infected in the lowest pH soil (pH 4.2) at any of the inoculum concentrations tested. Infection in the slightly alkaline soil (pH 7.4) ranged from 0 to 89.2% across the inoculum concentrations, and 3.3 to 100% in the pH 5.2 soil. No infection was observed in the lowest pH soil. When the low pH soil was ammended with CaCo3, which raised the pH from 4.2 to 6.1, nearly all leaf disks (90%) became infected.This study provides useful information on the biology of P. kernoviae oospores, which can play in important role in the long distance spread of this pathogen.

Technical Abstract: Phytophthora kernoviae is a pathogen that affects a wide range of trees and shrubs. It produces large numbers of viable structures called oospores, which are resistant to adverse conditions and can be easily transported to new locations in plants or soil debris. To determine how pH (i.e. acidity/alkalinity) affects oospores, a study was done looking at the ability of oospores to germinate in solutions ranging from acidic to alkaline, and their ability to infect leaf disks in acidic, neutral, and alkaline soils. Results showed that the oospores tolerated alkaline conditions, but not acidic conditions. No plants became infected in acidic soil despite the pathogen being present. This improved understanding of P. kernoviae oospores will be used in risk analyses to determine the likelihood of this pathogen becoming established in certain locations based on the soil conditions present. and 3.3 to 100% in the pH 5.2 soil. No infection was observed in the lowest pH soil. When the low pH soil was ammended with CaCo3, which raised the pH from 4.2 to 6.1, nearly all leaf disks (90%) became infected.This study provides useful information on the biology of P. kernoviae oospores, which can play in important role in the long distance spread of this pathogen.