Spatial Pattern of Strawberry Powdery Mildew (Podosphaera aphanis) and Airborne Inoculum

Area of Science:

• Plant Pathology
• Agricultural Entomology
• Environmental Science

Background:

• Strawberry powdery mildew, caused by Podosphaera aphanis, significantly impacts crop yield.
• Understanding the spatial distribution of airborne conidium concentration (ACC) is crucial for disease management.

Purpose of the Study:

• To analyze the spatial patterns of airborne inoculum and disease incidence of strawberry powdery mildew.
• To determine the relationship between ACC and disease incidence.
• To assess the feasibility of optimizing sampling strategies for risk estimation.

Main Methods:

• Collected data on disease incidence and ACC from 15 strawberry fields over four years (2006-2009).
• Employed statistical methods including variance-to-mean ratio, index of dispersion, negative binomial, Poisson, binomial, and beta-binomial distributions.
• Utilized Taylor's power law and Spatial Analysis by Distance Indices to characterize spatial heterogeneity and association.

Main Results:

• A linear relationship was observed between percent leaf area diseased and daily ACC, while ACC and disease incidence followed an exponential curve.
• Airborne inoculum concentration (ACC) exhibited significantly higher heterogeneity than disease incidence.
• Despite higher heterogeneity in ACC, both inoculum and disease showed weak aggregation, suggesting well-distributed inoculum initiates epidemics.

Conclusions:

• Strawberry powdery mildew distribution is weakly aggregated, with low overall heterogeneity.
• The low heterogeneity of airborne inoculum allows for accurate mean ACC estimation using a single sampler per field.
• Findings support the development of improved sampling schemes for better strawberry powdery mildew risk assessment.