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

Summary

When walnut trees are pruned, the resulting wounds are exposed to dangerous fungi that can cause branch die-back and significantly reduce crop yield. This research found that freshly cut pruning wounds are most vulnerable to infection, especially from aggressive fungi like Diplodia mutila, but this vulnerability decreases over time. The fungi spread their spores mainly during wet winter months when rainfall and humidity are high, so timing pruning operations to avoid these periods and protecting wounds with fungicides could substantially reduce disease losses in walnut orchards.

Background

Branch canker and dieback caused by Botryosphaeriaceae and Diaporthaceae fungi represent a major disease threat to walnut (Juglans regia L.) production worldwide, including in Chile where disease incidence ranges from 10-40%. Pruning is a common orchard practice that creates wounds vulnerable to pathogen invasion, but the temporal dynamics of wound susceptibility in walnut remain poorly characterized.

Objective

This study evaluated how pruning wound age affects susceptibility to infection by Botryosphaeriaceae and Diaporthaceae species in walnut cv. Chandler, and monitored seasonal conidial dispersal patterns of Botryosphaeriaceae to identify high-risk infection periods in the Maule Region of Chile.

Results

All fungal isolates produced significantly longer lesions than controls, with Diplodia mutila, Neofusicoccum nonquaesitum, and N. parvum being most aggressive (51.8, 42.1, and 46.2 mm respectively on fresh wounds). Susceptibility decreased markedly with wound age, declining by approximately 40-60% by day 45 post-pruning. Botryosphaeriaceae spore dispersal was strongly positively correlated with rainfall (r=0.81) and relative humidity (r=0.51-0.61) but negatively with maximum temperature (r=-0.59 to -0.79), with over 50% of annual spore release occurring during winter months.

Conclusion

Fresh pruning wounds are most vulnerable to infection, particularly by aggressive Botryosphaeriaceae species, with susceptibility decreasing progressively over 45 days. Winter rainfall periods coincide with peak spore release, creating high-risk conditions for infection. These findings support adjusting pruning schedules and implementing protective strategies during high-risk periods to reduce disease incidence in walnut orchards.
  • Published in:Microorganisms,
  • Study Type:Field Experimental Study,
  • Source: 10.3390/microorganisms13102407, PMID: 41156865
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