Strawberry Powdery Mildew Caused by Podosphaera aphanis: Fungicide Resistance and Host Plant Resistance

<p>Strawberry powdery mildew, caused by <em>Podosphaera aphanis</em>, affects leaves, fruit, and runners of strawberry plants. Infected leaves have reduced photosynthetic capability and infected fruit become unmarketable. Both of these factors translate to economic loss for the grower and therefore merit taking measures to control the disease. One objective of this study was to evaluate the resistance developed in populations of strawberry powdery mildew to chemical control measures. A fungicide assay was developed to evaluate the efficacy of six treatments (penthiopyrad, quinoxyfen, myclobutanil, trifloxystrobin, cyflufenamid, fluopyram + trifloxystrobin) for control of the disease. Nineteen isolates of strawberry powdery mildew were collected from Balico, Salinas, Watsonville, San Luis Obispo, Santa Maria, Ventura, and Oxnard CA and tested through the assay. The number of isolates resistant to each treatment was: penthiopyrad (7), quinoxyfen (6), myclobutanil (7), trifloxystrobin (2), cyflufenamid (1), fluopyram + trifloxystrobin (0). This documents resistance in <em>P. aphanis</em> to multiple chemicals used for its control. Documentation of any resistance is novel in California and novel worldwide with resistance to Fungicide Resistance Action Committee (FRAC) codes 7 and 13. Another objective of this study was to evaluate host plant resistance to strawberry powdery mildew. Twelve cultivars were evaluated in a winter greenhouse trial, sixteen cultivars in a summer greenhouse trial, and the ten cultivars shared in both trials were also evaluated in two fields. The cultivars found to be most susceptible to mildew infection were BG 3.324 and Royal Royce. The cultivars found to be the least susceptible to mildew infection were Fronteras, San Andreas, and Sweet Ann. The cultivars evaluated represent more than 55% of the state’s acreage and the host plant resistance information will be a valuable tool to growers looking to culturally control powdery mildew.</p>

Name thesis:degree_name

MS in Agriculture - Plant Protection Science

Year dc:date.available

2020

Author dc:creator

• Palmer, Michael G

Contributors dc:contributor

• Gerald Holmes
• Horticulture and Crop Science
• College of Agriculture, Food, and Environmental Sciences

• Strawberry
• Powdery Mildew
• Fungicide Resistance
• Host Plant Resistance
• Plant Pathology

Identifier

10.15368/theses.2020.147

OAI identifier oai:identifier

oai:digitalcommons.calpoly.edu:theses-3746