Characterization of Coniella granati Isolates Causing Pomegranate Decline in Italy

Abstract

Coniella granati, the causal agent of pomegranate crown rot, twig blight, and fruit decay, is an emerging worldwide pathogen with a heavy impact on pomegranate cultivation. In this study, we report the rapid spread of the fungus in Italian pomegranate orchards associated with crown rot symptoms and provide new results on fungal development, baseline sensitivity to different fungicides, and intraspecific variability by analyzing 11 isolates, representative of populations of the pathogen from comparable pomegranate orchards in different regions of Italy. In vitro assays showed that 25 to 30°C was the optimal range for both colony growth and conidial germination, corroborating the results previously obtained for Californian and Greek isolates. According to the baseline sensitivity assay on the response of colony growth and conidial germination to 10 fungicides, fludioxonil, thiophanate-methyl, tebuconazole, and cyprodinil were the most effective. Random amplified polymorphic DNA (RAPD) analysis, carried out using fourteen 10-mer primers, showed very low intraspecific variability (similarity coefficient >0.95), probably as a result of the recent spread of the pathogen in Italy and the uncommon occurrence of the sexual process as a source of genetic variability. In summary, this study provides new knowledge on C. granati that will be helpful for improving pomegranate crown rot management.

Keywords: Pilidiella granati; RAPD; crown rot; fungicides; variability.