Leaf Spot Disease of Red Clover Caused by Leptosphaeria weimeri (=Longiseptatispora meliloti) in China

Abstract

Red clover (Trifolium pretense) is widely cultivated as an excellent forage and green manure crop. In 2021, a leaf spot disease was discovered in a red clover field in Min County, Gansu Province, China. Symptoms on T. pratense manifested as small white spots that gradually expanded into nearly oval or irregularly shaped gray-white lesions. The causal agent of this new disease was identified as Leptosphaeria weimeri (=Longiseptatispora meliloti) based on morphological identification, pathogenicity tests, and the phylogenetic identification of ITS, LSU, and SSU sequence. The optimal growth temperature was found to be 20 °C under different culture conditions, while the optimal spore-producing temperature was 25 °C. The pH for optimal growth and spore production was seven. The fungus grew and produced spores successfully on both PDA and PSA media. Additionally, the pathogen was efficiently inhibited using 450 g/L of prochloraz fungicide in vitro. To our knowledge, this is the first report of leaf spot disease on red clover caused by L. meliloti in China.