Available at: https://digitalcommons.calpoly.edu/theses/3407
Date of Award
6-2026
Degree Name
MS in Agriculture - Crop Science
Department/Program
Horticulture and Crop Science
College
College of Agriculture, Food, and Environmental Sciences
Advisor
Shashika Hewavitharana
Advisor Department
Horticulture and Crop Science
Advisor College
College of Agriculture, Food, and Environmental Sciences
Abstract
Strawberry production in California is significantly impacted by soilborne pathogens that reduce plant productivity and increase management costs. This research addressed management of these pathogens through two independent approaches: evaluation of host resistance in strawberry cultivars and assessment of sanitation practices for reducing pathogen movement between fields.
Macrophomina root rot, caused by Macrophomina phaseolina, was evaluated over two growing seasons (2024–2025 and 2025–2026) using field trials at California Polytechnic State University, San Luis Obispo. In Year 1, disease incidence varied widely among genotypes, with mortality ranging from 1.3% to 88.8% and an average mortality of 26.4%. Area under the disease progress curve (AUDPC) values ranged from 0 to 3,691.3, indicating substantial variation in disease progression among cultivars. In Year 2, mortality ranged from 0.0% to 54.3%, with an average mortality of 15.1% at the time of analysis. Several cultivars consistently exhibited low disease levels across both years, while others showed high susceptibility, highlighting significant genetic variation in host response.
Verticillium wilt, caused by Verticillium dahliae, was evaluated under natural field infestation during the same two growing seasons. A total of 81 genotypes were assessed in Year 1 and 92 genotypes in Year 2. In Year 1, mortality ranged from 2.3% to 90.2%, with an average mortality of 47.0%. In Year 2, evaluations are ongoing; as of 14 May 2026, mortality ranged from 0% to 4.6%, with an average of 2.3%. These results further demonstrate substantial variation in susceptibility among strawberry genotypes and emphasize the importance of host resistance for managing Verticillium wilt.
A separate sanitation study was conducted to evaluate current practices and the efficacy of sanitizing agents for reducing pathogen presence on contaminated surfaces. A survey of industry stakeholders in the Santa Maria district, representing approximately 93% of regional strawberry acreage, was used to characterize sanitation practices, perceived effectiveness, and barriers to adoption. Respondents generally considered sanitation to be effective for reducing pathogen movement, but identified time and cost as major limitations. Field evaluations showed that soil accumulation on equipment was greatest in wheel wells, undercarriage areas, and bumpers, and that complete removal of visible soil could be achieved in approximately 15 minutes using high-pressure washing. Laboratory assays evaluating sanitizing agents against Fusarium oxysporum f. sp. fragariae race 1 and M. phaseolina demonstrated variable efficacy among treatments and isolates, with bleach, ethanol, Lysol®, and MG 4-Quat® consistently reducing F. oxysporum recovery, and ethanol showing the most consistent inhibition of M. phaseolina.
Collectively, these findings provide insight into host resistance and sanitation practices as independent components of soilborne disease management in strawberry production systems.