Presence of Plenodomus tracheiphilus in lemon orchards in Campania region and sensitivity to some active ingredients

Lemon cultivation is mainly in the South of Italy (99%), where Campania is the second most important region, with approxi- mately 1,233 hectares representing about 5% of the national production. In Campania there are two lemon crops with Protected Geographical Indication: “Limone costa d’Amalfi” and “Limone di Sorrento”. Mal secco, caused by the fungus Plenodomus tracheiphilus, is a vascular disease representing a limiting factor for lemon production. In 2024, a survey was done in the two main cultivation areas. Visual assessments were carried out on branches sampled from symptomatic plants from four farms, and isolates were obtained from 50 plants. All the isolates were obtained in pure culture, to pro- ceed with the morphological and molecular identification by PCR amplification. Thirty isolates obtained from the samples from different farms have been identified as P. tracheiphilus with 99.9% nucleotide sequence identity. Sensitivity tests were conducted on the thirty isolates with four formulates relating to three fungicide categories. In addition, in vitro tests were carried out to evaluate the resistance to the various active ingre- dients. Field trials were also conducted to verify the effective- ness of the pruning cuts and on the plants of active substances applied with an adjuvant of natural origin based on galacto- mannans extracted from locust bean gum (Ceratonia siliqua). The results suggested that, besides good agronomic practices, the rational management of orchards, such as removing residues and infected organs and using effective phytoiatric interventions, can contribute to controlling the pathogen.