Occurrence of Bacterial Fruit Blotch on Watermelon (Citrullus vulgaris) Caused by Acidovorax citrulli in the Republic of North Macedonia

Abstract

In late summer 2019, Acidovorax citrulli the causative agent of bacterial seedling blight and fruit blotch (BFB) of cucurbit plants was first detected in a commercial watermelon production area in the village of Sopot, Kavadarci, North Macedonia. Later, in the summer of 2019 and also in 2020, A. citrulli was observed on watermelon fruits (Citrullus lanatus L., varieties “Bibo” and “Olakala”) in the Strumica region in the Eastern part of North Macedonia. Initial symptoms included water-soaked, irregular spots on the fruits that appeared greasy and dark olive green, eventually developing into brown lesions. Round, cream-coloured, Gram-negative bacterial isolates were obtained from symptomatic fruit tissue, which were slow-growing, nonfluorescent, aerobic, and oxidase-positive. In recent years, the disease has spread globally, primarily through the inadvertent distribution of contaminated commercial seeds, emerging as a significant pathogen of cucurbitaceous plant species worldwide. Due to costly lawsuits filed by growers against seed companies and the lack of effective management methods, BFB poses a serious threat to the cucurbit industry, particularly to watermelons and melons. Acidovorax citrulli is a seed-borne pathogen and is listed as an A1 quarantine pathogen by EPPO in 2021. Despite the economic importance of the disease, little is known about the basic aspects of A. citrulli pathogenesis in our country. Based on the fruit symptoms, pathogenicity tests, biochemical tests, serological and PCR analyses, the pathogen was identified as Acidovorax citrulli. To our knowledge, based on the current findings, including symptomatology, pathogenicity tests, biochemical characterization and PCR analyses, this is the first detailed study of A. citrulli causing bacterial fruit blotch on watermelon in North Macedonia.