Mycosphaerella ribis in Blackcurrant: Overwintering Sources of Inoculum and Spore Release Patterns

Area of Science:

• Plant Pathology
• Mycology
• Horticulture

Background:

• Mycosphaerella ribis causes Mycosphaerella leaf spot in blackcurrants.
• Disease management requires understanding inoculum sources and spore release dynamics.
• Previous studies have not fully characterized fruit lesions or detailed spore release patterns in organic systems.

Purpose of the Study:

• To investigate disease symptoms, inoculum sources, and spore release patterns of Mycosphaerella ribis.
• To observe Mycosphaerella leaf spot development in organic blackcurrant plantations without fungicide application.
• To develop predictive models for spore release based on environmental factors.

Main Methods:

• Three-year field study in organic blackcurrant plots.
• Spore trapping of ascospores (from leaf litter) and conidia (from overwintering fruit stalks).
• Development and validation of degree-day models incorporating rainfall and leaf wetness duration for spore maturation and release prediction.

Main Results:

• Both foliar and fruit lesions were observed.
• Ascospores were released from bud break to mid-July (peak before that), while conidia were released from bud break to early August (peak late May to mid-July).
• Dry conditions and nighttime moisture suppressed spore release; models accurately predicted release based on specific environmental triggers.

Conclusions:

• Mycosphaerella ribis poses a threat to both blackcurrant foliage and fruit.
• Understanding the distinct sources and timing of ascospore and conidia release is vital for effective disease control.
• Predictive models based on degree-days and weather patterns can aid in timing sanitary measures to reduce primary inoculum.