Overview

This e-library lesson will focus on breeding resistant strawberries to the fungus Verticillium dahliae, common name Verticillium wilt. This is a serious fungal disease that can result in a loss of 50% or more of a strawberry harvest when grown in infested soil . This lesson is written for undergraduate and graduate students who are currently studying plant pathology or the management of crop disease. The main goal is to provide an example of how a cultivar can be made more resistant to a plant pathogen with the use of plant breeding methods.

Since 1930 the University of California, Davis, has been developing strawberry cultivars that are adapted to the agricultural industry and regional farms. Developing cultivars that require fewer inputs are of significant economic importance in agronomy. Developing a crop resistant to a disease is beneficial for horticulturists since less labor and chemicals are needed for a high yield.⁶

In commercial strawberry cultivars, complete resistance to V. dahlia is extremely rare. The majority of Californian strawberry cultivars are highly susceptible to it.² Over the last 18 years of plant breeding for strawberry cultivars with a high degree of resistance and horticultural traits, strawberry cultivars with at least moderate resistance grew to 53.8% of the strawberry germplasm being measured in the study. Each plant was rated from 1 to 5 based on symptoms of V. dahliae in comparison to control plants over the length of the study.

• The lowest ranking was 1 meaning severe stunting or death
• A ranking of 3 indicated moderate damage and signs of tolerance
• The highest ranking was 5 indicating no disease symptoms

After completing this lesson you should be able to:

• Explain the importance of strawberry resistance to Verticillium dahliae
• Examine the process for family selection and direct genotypic evaluation for resistance
• Describe how the plants were graded for stages of Verticillium dahliae infection