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Published on: October 28, 2021
Shedding Light on Races of the Spinach Fusarium Wilt Pathogen, Fusarium oxysporum f. sp. spinaciae
Alex M Batson1, Sanjaya Gyawali1, Lindsey J du Toit1
1Washington State University Mount Vernon Northwestern Washington Research and Extension Center, Mount Vernon, WA 98273, U.S.A.
Abstract:
Two pathogenicity groups of Fusarium oxysporum f. sp. spinaciae, the causal agent of Fusarium wilt of spinach (Spinacia oleracea), were described recently based on virulence of isolates on proprietary spinach inbreds. In this study, a wide range in severity of wilt was observed for 68 spinach cultivars inoculated with an isolate of each pathogenicity group, with 22 (32.4%) cultivars displaying differential responses to the isolates. In a second set of trials, seven spinach cultivars were inoculated with five isolates of each pathogenicity group. The cultivars had similar wilt responses to isolates within each group. In both sets of trials, the most severe wilt developed on cultivars inoculated with pathogenicity group 2 isolates when daylength was shorter and light intensity lower. To test whether light intensity exacerbates severity of Fusarium wilt, three spinach cultivars were inoculated with two isolates of each pathogenicity group and grown with or without shading. Shaded plants developed more severe wilt than nonshaded plants. This difference in wilt severity was greatest for plants inoculated with pathogenicity group 2 isolates. We propose naming isolates of pathogenicity groups 1 and 2 as races 1 and 2 of F. oxysporum f. sp. spinaciae, respectively, and recommend the cultivars Kiowa (susceptible to both races) and Magnetic (susceptible to race 2 and highly resistant to race 1) as differentials. Results of this study should help breeders screen spinach germplasm for resistance to both races of F. oxysporum f. sp. spinaciae.
Insights
Two races of Fusarium wilt pathogen (Fusarium oxysporum f. sp. spinaciae) were identified in spinach. Race 2 causes more severe disease, especially under low light conditions, impacting spinach cultivation.
Area of Science:
- Plant Pathology
- Crop Science
- Mycology
Background:
- Fusarium wilt, caused by Fusarium oxysporum f. sp. spinaciae, is a significant disease affecting spinach (Spinacia oleracea).
- Recent studies identified two pathogenicity groups within the pathogen based on virulence on specific spinach inbreds.
Purpose of the Study:
- To differentiate and characterize the pathogenicity of Fusarium oxysporum f. sp. spinaciae isolates.
- To investigate the influence of environmental factors, specifically light intensity, on disease severity.
- To propose a race classification and identify differential spinach cultivars for resistance screening.
Main Methods:
- Inoculation of 68 spinach cultivars with isolates from each pathogenicity group.
- Testing seven spinach cultivars with five isolates from each group.
- Evaluating disease severity under varying light conditions (natural vs. shaded).
Main Results:
- Differential wilt responses were observed in 32.4% of cultivars tested.
- Pathogenicity group 2 isolates consistently caused more severe wilt, particularly under shorter daylengths and lower light intensity.
- Shading significantly exacerbated wilt severity, with the effect being more pronounced for pathogenicity group 2.
Conclusions:
- Propose naming pathogenicity groups 1 and 2 as races 1 and 2 of Fusarium oxysporum f. sp. spinaciae.
- Recommend 'Kiowa' (susceptible to both races) and 'Magnetic' (susceptible to race 2, resistant to race 1) as differential cultivars.
- Findings aid breeders in screening spinach germplasm for resistance to both races, crucial for disease management.
