Leaf Blight of Garlic Caused by Stemphylium sp. Subgroup C2

Abstract

During our routine disease surveys of garlic in Aomori Prefecture, Japan, leaf blight was frequently observed. An isolate was obtained from a diseased leaf in 2017. Conidiophores of the isolate were 15–145 μm long and 4.3–6.5 μm wide, with swellings at the distal ends. Conidia were 25–67×14–28 μm in size, with a length to breadth ratio of 1.20–3.04 (mean 2.30), and were constricted at 1–3 major transverse septa. The isolate also produced the perfect state, i.e., pseudothecia, asci, and ascospores. These morphological characteristics were similar to those of Stemphylium sp. Subgroup C2. We also conducted molecular phylogenetic analysis based on four loci (the rDNA-ITS region, EF-1α gene, GPD gene, and vmaA-vpsA gene). The isolate was classified into Subgroup C2 in the phylogenetic tree. Based on both morphology and phylogeny, the isolate was identified as Stemphylium sp. Subgroup C2. We confirmed the pathogenicity of the isolate toward garlic in an inoculation test. Leaf blight in garlic caused by Stemphylium sp. Subgroup C2 has not been reported in Japan; therefore, we propose to include it as one of the pathogens of the disease.