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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Disease and Pest Management Research Unit » Research » Publications at this Location » Publication #403055
Research Project: Disease Management in Small Fruit and Nursery Crops Based on Knowledge of Pathogen Diversity, Biology, and Environmental Effects

Location: Horticultural Crops Disease and Pest Management Research Unit

Title: Greater rate of nitrogen fertilizer application increases root rot caused by Phytophthora cinnamomi and P. plurivora in container-grown rhododendron

Author
item MESTAS, ANGIE - Oregon State University
item Weiland, Gerald - Jerry
item Scagel, Carolyn
item Davis, Elizabeth
item Mitchell, Jesse
item Beck, Bryan

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2023
Publication Date: 7/19/2023
Citation: Mestas, A., Weiland, G.E., Scagel, C.F., Davis, E.A., Mitchell, J.N., Beck, B.R. 2023. Greater rate of nitrogen fertilizer application increases root rot caused by Phytophthora cinnamomi and P. plurivora in container-grown rhododendron. Plant Pathology. https://doi.org/10.1111/ppa.13776.
DOI: https://doi.org/10.1111/ppa.13776

Interpretive Summary: Root rot, caused by many Phytophthora species, decreases the health of rhododendrons produced in nurseries. Optimizing nitrogen (N) fertilizer is often used to improve nursery stock quality, but there is little information on how N fertilizers influence root rot caused by these pathogens. To understand the impact of N fertilizer and pathogen species on root rot development, rhododendrons were grown with no, low, or high rates of N and inoculated with two Phytophthora species. Nitrogen application increased disease symptoms and restricted nutrients, regardless of Phytophthora species. Nurseries frequently apply high amounts of N to promote fast growth. However, our results show that this can make root rot worse when pathogens are present. Although decreasing N can reduce the number of diseased plants, this may also increase the risk for selling apparently asymptomatic plants with low levels of infection.

Technical Abstract: Phytophthora root rot, caused by many Phytophthora species, decreases the health of rhododendrons produced in nurseries. Optimizing nitrogen (N) fertilizer is often used to improve nursery stock quality, but there is little information on how N fertilizers influence root rot caused by these pathogens. To understand the impact of N fertilizer and pathogen species on root rot development, rhododendrons were grown with no (0 g N/pot), low (1.04 g N/pot), or high (3.12 g N/pot) rates of N and inoculated with either P. cinnamomi or P. plurivora. Noninoculated plants at low and high N rates had greater biomass, leaf greenness, and enhanced N, potassium, magnesium, phosphorus, sulfur, and manganese uptake compared to plants grown with no N. When either Phytophthora species was present, N application increased aboveground disease symptoms (wilting, chlorosis, reduced stomatal conductance and biomass), but had no effect on root rot severity belowground. In addition, Phytophthora cinnamomi restricted uptake of several nutrients while P. plurivora had less influence on nutrient uptake. Nurseries frequently apply high amounts of N to promote fast growth. However, our results show that this can exacerbate root rot when P. cinnamomi or P. plurivora is present. Although decreasing N can reduce the number of overtly symptomatic plants, this may conversely increase the risk for selling apparently asymptomatic plants with low levels of infection. Additional studies are needed to determine how N fertilization influences Phytophthora root rot for a broader range of rhododendron cultivars and nursery crop species.