Morphological and genome characterization of Alternaria alternata causing blueberry (Vaccinium corymbosum L.) leaf spot in Peru

Abstract

Blueberries (Vaccinium corymbosum L.), valued for their nutritional benefits and economic significance, have become Peru's leading agro-export crop. However, intensive cultivation can lead to phytosanitary problems if not addressed promptly, posing a serious threat to blueberry production. This study aimed to isolate and identify the causal agent of leaf spot symptoms initially observed in blueberries cultivated in Peru, marking the first formal documentation of its presence in the country. In 2022, leaf spot symptoms were recorded on V. corymbosum cv. Biloxi, in the north of Lima, Peru. Field observations revealed necrotic, sunken spots on leaves and fruits, with 4.84% of leaves diseased and 1.28% of fruits affected. Pathogen isolation and microscopic studies identified Alternaria alternata as the primary causal agent, which was confirmed by genome sequencing using Oxford Nanopore Technology. Pathogenicity tests demonstrated the fungus' ability to reproduce symptoms identical to those observed in the field, fulfilling Koch's postulates. Under experimental conditions, disease severity increased over time, with the affected leaf area ranging from 9.35% to 25.61% between 7 and 14 days post-inoculation. This study establishes A. alternata as a pathogen of blueberries in Peru and provides essential insights for future research and strategies to mitigate its impact on the industry.