Pestalotiopsis kenyana causes leaf spot disease on Rhododendron agastum in China

Abstract

Rhododendron agastum, a well-known flower with significant aesthetic and medicinal value, belongs to the Rhododendron genus in the Ericaceae family. In April 2023, a leaf spot disease on R. agastum plants was found in the Baili Azalea Forest Area in Guizhou province, China. Approximately 400 plants were surveyed, and the incidence of leaf spot on R. agastum leaves was 20%. The damaged leaves had gray-white irregular diseased spots with black-brown margins and black conidiomata on the surface of the spots. When the disease is severe, the leaves fall. Leaf spot disease is a serious problem for rhododendrons, reducing their ornamental value and causing significant economic losses. To identify the pathogen, we conducted pathogen isolation and pathogenicity study. The pathogen was identified as Pestalotiopsis kenyana by morphological features and combined analysis of multiple genes (ITS, tef1-α, and Tub2). Koch's postulates was tested by isolating and reidentifying the pathogen from inoculated plants, showing that P. kenyana was the causative agent of the disease. To our knowledge, this is the first report of P. kenyana causing leaf spot in R. agastum. This study gives important information for the identification and control of the leaf spot disease caused by P. kenyana.