Effect of Leaf Wetness Duration, Temperature, and Conidial Inoculum Dose on Apple Scab Infections

Area of Science:

• Plant Pathology
• Mycology
• Horticultural Science

Background:

• Apple scab, caused by Venturia inaequalis, is a significant disease affecting apple production.
• Understanding the environmental factors influencing disease development is crucial for effective management strategies.

Purpose of the Study:

• To investigate the impact of Venturia inaequalis inoculum dose and leaf wetness duration on apple scab symptom development.
• To determine the relationship between environmental conditions and apple scab infection severity.

Main Methods:

• Apple seedlings ('Idared' × 'Golden Delicious') were inoculated with varying concentrations of Venturia inaequalis conidia.
• Seedlings were subjected to different leaf wetness durations at controlled temperatures (6, 11, 16, 22°C).
• Disease incidence was assessed based on scab lesions per plant.

Main Results:

• Disease incidence increased with inoculum doses up to 81.2 × 10^3 conidia/ml across all tested temperatures.
• Higher temperatures (22°C) resulted in lower disease incidence compared to cooler temperatures.
• Increasing leaf wetness duration, particularly doubling the C3 curve duration, significantly elevated disease incidence.

Conclusions:

• Both inoculum dose and leaf wetness duration are critical factors in apple scab development.
• Optimal infection conditions involve moderate temperatures and sufficient leaf wetness duration, with a threshold around 150-200% of the C3 curve.
• Effective disease management requires careful consideration of these environmental parameters to minimize apple scab outbreaks.