Management of Phytophthora cinnamomi using fungicides and host plant defense inducers under drought conditions: A case-study of flowering dogwoods

Authors: NEUPANE, KRISHNA - Tennessee State University; Alexander, Lisa; BAYSAL-GUREL, FULYA - Tennessee State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2021
Publication Date: 2/1/2022
Citation: Neupane, K., Alexander, L.W., Baysal-Gurel, F. 2022. Management of Phytophthora cinnamomi using fungicides and host plant defense inducers under drought conditions: A case-study of flowering dogwoods. Plant Disease. 106:475-485. https://doi.org/10.1094/PDIS-04-21-0789-RE.
DOI: https://doi.org/10.1094/PDIS-04-21-0789-RE

Interpretive Summary: Phytophthora root rot is considered one of the most destructive pathogens of ornamental crops and root rot disease symptoms are often exacerbated by drought conditions. However, little is known about the efficacy of common fungicides in water deficit conditions. USDA and Tennessee State University scientists in McMinnville,TN tested nine fungicides for control of Phytophthera root rot in water-stressed dogwood seedlings. Based on plant growth, leaf chlorophyll content, measurements of greenness, and damage to plant roots, they determined that Subdue MAXX, Signature Xtra and Empress Intrinsic provided the highest level of control when used as either preventative or curative treatments. This study will help growers perform successful management of Phytophthora root rot in woody ornamental crops during drought or water deficit conditions.

Technical Abstract: Phytophthora cinnamomi Rands is considered one of the most destructive pathogens of ornamental crops. Different fungicides and host plant defense inducers were tested for their efficacy in managing Phytophthora root rot in drought conditions. In this study, the drought conditions were maintained by evaluating the moisture holding capacity of the pine bark in a 10.2 cm nursery container. Four controls and nine different treatments were used in two trials for this greenhouse study. All treatments were drench applied as a preventative or curative treatment. Seedlings were artificially inoculated with P. cinnamomi. Regular irrigation was carried out using overhead irrigation for one month after inoculation. Irrigation was regulated by drip irrigation after the first month. A moisture level of 15-18% of total moisture holding capacity was maintained using the gravimetric method throughout the drought period. Physiological parameters of the seedlings were recorded a week after seedlings were drought stressed. In both trials of preventative and curative treatments, all treatments were able to suppress the disease significantly except Orkestra Intrinsic. Orkestra Intrinsic had a disease severity statistically similar to the inoculated and stressed control in trial 1 of the curative treatment. Net photosynthesis, stomatal conductance, and leaf moisture potential were significantly greater in seedlings treated with Subdue MAXX, Signature Xtra and Empress Intrinsic in both trials of preventative and curative treatments. Effective quantum yield of Photosystem II was significantly lower in the inoculated stressed control in both trials of preventative and curative treatment. Net chlorophyll content through the SPAD meter showed higher values for Subdue MAXX treated seedlings compared to the non-inoculated non-stressed controls in trial 1 as both a curative and preventative application. In trial 2, Subdue MAXX and Signature Xtra were the best as curative treatments, whereas Empress Intrinsic, Interface and Subdue MAXX were the best as preventative treatments for higher chlorophyll content. This study will help growers perform successful management of Phytophthora root rot in woody ornamental crops during drought or water deficit conditions.