Date of Award

5-2025

Degree Name

MS in Agriculture - Crop Science

Department/Program

Horticulture and Crop Science

College

College of Agriculture, Food, and Environmental Sciences

Advisor

Gerald Holmes

Advisor Department

Horticulture and Crop Science

Advisor College

College of Agriculture, Food, and Environmental Sciences

Abstract

Strawberry production in California is limited by plant diseases such as Macrophomina root rot (MRR) caused by Macrophomina phaseolina, Verticillium wilt (VW) caused by Verticillium dahliae, and Botrytis fruit rot (BFR) caused by Botrytis cinerea. Current disease management strategies are compromised due to fumigant regulations or ineffective disease management practices. This thesis investigated methods to potentially improve the management of these three diseases. Two host plant resistance evaluations for MRR and VW were conducted for the 2022-2023 and 2023-2024 growing seasons. Sixty-three strawberry genotypes were screened in both years. All plants were exposed to the pathogen via artificial (M. phaseolina) or naturally occurring (V. dahliae) inoculum. A wide range of plant resistance to MRR and VW was observed. The three most resistant cultigens (cultivars and elite breeding lines) to MRR based on final plant mortality were ‘UCD_Mojo’, ‘PE.13.119.024’, and ‘152x18’. The three most resistant cultigens to VW based on final plant mortality were ‘UCD_Mojo’, ‘UC_Eclipse’, and ‘152x18’. Variation in disease pressure between years highlights the importance of multi-season screening across diverse environmental conditions. A survey of BFR levels in commercial strawberry fields that were not treated and treated with fungicides was conducted in Santa Maria, CA in 2023 and 2024. BFR incidence was recorded weekly in the field and postharvest following 7 days at 34°F. Weather stations at each field location measured temperature, leaf wetness duration, and calculated the BFR risk factor using the Strawberry Advisory System (StAS) developed by the University of Florida. In 2023, the average in-field BFR incidence was 4.0% (treated) vs. 7.7% (untreated), and the average postharvest BFR incidence was 3.8% vs. 7.2%. In 2024, the average in-field BFR incidence was 2.5% vs. 6.7%, and the average BFR postharvest incidence was 2.1% vs. 4.6%, respectively. Screening new strawberry genotypes against MRR and VW should be ongoing as part of a standard process for determining the susceptibility of currently grown and potentially new cultivars. Additional research under more diverse weather conditions is necessary to verify the impacts of reducing fungicide use in BFR management and to validate the use of StAS in making fungicide use decisions in California fields.

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