Cercospora diseases of Soybean and their diagnostics

In many soybean-growing regions of Russia cercosporosis remains among the most widespread diseases, typically caused by two phytopathogenic fungi: Cercospora sojina Hara and Cercospora kikuchii (Matsumoto & Tomoyasu) Gardner (a quarantine pest in the EAEU). The aim of this study was to assess the regional occurrence of cercosporosis in Russia and to refine the species composition of Cercosporaon soybean seeds and vegetative tissues. Our objectives were to synthesize two years of observations and to propose a practical, first-line diagnostic workflow based on cultural and morphological characters of the pathogens. The work was conducted in 2024–2025 at the All-Russian Plant Quarantine Center (FGBI “VNIIKR”). Over two years, 98 soybean samples were collected from seven regions of Russia (81 vegetative samples and 17 seed samples). In total 11 Cercospora isolates were obtained in pure culture (C. sojina – 5, C. kikuchii – 6). Within our dataset, C. kikuchii was detected only in territories already designated as quarantine phytosanitary zones, whereas C. sojina was more widespread. Molecular diagnostics employed PCR with universal primers ITS4/ITS5 followed by Sanger sequencing of the amplicons. Many samples presenting cercosporosis-like symptoms proved to be associated with other soybean pathogens (genera Diaporthe, Colletotrichum, Alternaria, Epicoccum, Fusarium, Botrytis, Sclerotinia, etc.), whose generic and species identities were confirmed by sequencing. In total, 446 fungal isolates obtained from soybean fields and seed lots were purified and deposited in the FGBI VNIIKR culture collection. The proposed morphological criteria (colony form and color, mycelial growth pattern, reverse pigmentation, and conidial shape and size) help streamline identification of cercosporosis agents on soybean and reduce the risk of false conclusions during monitoring.

соя, посевы, семена, церкоспороз, Cercospora sojina, Cercospora kikuchii, диагностика визуальная и культурально-морфологическая