# Vulnerability of Walnut Pruning Wounds to Fungal Trunk Pathogens and Seasonal Conidial Dynamics of Botryosphaeriaceae in the Maule Region, Chile

## TL;DR

This study examines how pruning wounds in walnut trees affect susceptibility to fungal diseases and how weather influences spore release in Chile.

## Contribution

The study identifies specific fungal species that cause the most damage and shows how wound age and weather conditions influence disease risk.

## Key findings

- Diplodia mutila, Neofusicoccum nonquaesitum, and N. parvum caused the longest lesions in walnut pruning wounds.
- Susceptibility to infection decreased as pruning wound age increased.
- Spore dispersal of Botryosphaeriaceae was positively linked to rainfall and humidity but not maximum temperature.

## Abstract

Branch canker and dieback, caused by Botryosphaeriaceae and Diaporthaceae, is a major disease of walnut (Juglans regia L.) worldwide. In Chile, the impact of pruning wound age and timing on susceptibility to these pathogens in walnut trees remains poorly understood. During June–July (2023) and June–July (2024), this study assessed the effect of pruning wound age of the walnut cv. Chandler on infection by seven fungal species and simultaneously tracked seasonal conidial release of Botryosphaeriaceae spp. in the Maule Region, Chile. Lignified twigs were artificially inoculated at 1, 15, 30, and 45 days after pruning, and necrotic lesion lengths were measured six months post-inoculation. All fungal isolates caused significantly longer lesions than the control (p < 0.0001), with Diplodia mutila, Neofusicoccum nonquaesitum, and N. parvum being the most aggressive. At the same time, Dothiorella sarmentorum and Diaporthe species (Diaporthe australafricana, Di. foeniculina, and Di. patagonica) produced the smallest lesions. Susceptibility decreased with increasing wound age, with a significant interaction between fungal species and pruning wound age. Spore trapping of Botryosphaeriaceae revealed that dispersal was positively associated with rainfall (r = 0.81, p < 0.0001), relative humidity (r = 0.51 to 0.61, p < 0.05) and average temperature (r = 0.32 to 0.58, p < 0.05), but negatively or not significantly correlated with maximum temperature (r = −0.59 to −0.79, p > 0.05). These results demonstrate that rainfall or relative humidity, moderate conditions, and favor conidial release. At the same time, infection risk declines with wound age, underscoring the need to adjust pruning schedules and preventive strategies to reduce disease risk in walnut orchards.