Temporal Dynamics of Neonectria ditissima Spore Release From Whole and Shredded Branches of ‘Gala’ and ‘Fuji’ Apple Cultivars

ABSTRACT European canker (EC), caused by Neonectria ditissima , is one of the major threats to apple production in temperate and subtropical highland regions, where pruning residues represent an important source of inoculum. This study monitored the temporal dynamics of N. ditissima spore release from whole and shredded branches, with and without visible EC symptoms, obtained from training prunings of ‘Gala’ and ‘Fuji’ apple trees during the 2023–2025 growing seasons in high‐altitude orchards of southern Brazil. Whole and shredded branches were placed separately in spore‐trap boxes, and microscope slides were replaced weekly to quantify airborne ascospores and conidia. Shredding was performed using a hydraulic mower. Ascospores were consistently the dominant spore type, exhibiting higher release magnitude and frequency than conidia across all treatments and both cultivars. Whole symptomatic branches were the most productive inoculum source, displaying the highest ascospores and conidia release peaks, particularly in ‘Gala’. Shredding reduced spore output but did not eliminate inoculum viability, as shredded symptomatic branches continued to release substantial quantities of spores throughout the evaluation period. Whole and shredded asymptomatic branches also released ascospores and conidia, although at lower intensities, suggesting the presence of latent infections and confirming that the absence of visible symptoms does not preclude inoculum production. Spore‐release peaks in all treatments occurred during periods with rainfall, highlighting moisture as a key environmental factor for maturation of perithecia and sporodochia and spore discharge. The superior spore release capacity of ‘Gala’ under all conditions indicates that this cultivar may act as a regional inoculum resource in areas where EC is endemic. These findings underscore the need for improved EC management strategies, particularly regarding pruning‐residue handling. The persistence of viable inoculum in symptomatic and asymptomatic tissues, even after shredding, demonstrates that residue destruction or removal is essential to reduce disease pressure and limit pathogen spread within and between orchards.