ПЕРВОЕ СООБЩЕНИЕ О ЛИСТОВОЙ ПЯТНИСТОСТИ ТОМАТА, ВЫЗВАННОЙ ВИДОМ Cladosporium sphaerospermum

FIRST REPORT OF LEAF MOLD DISEASE OF TOMATO CAUSED BY Cladosporium sphaerospermum

Cladosporiosis or brown leaf mold of tomatoes is one of the most common and damaging diseases in greenhouses. Until recently, only one species, the hemibiotrophic fungus Cladosporium fulvum (Fulvia fulva) was considered the causative agent. However, in recent years, high tomato yield losses have increasingly been attributed to the underestimation of the role of fungi previously considered weakly or non-pathogenic to this crop, including other Cladosporium species. Thus, virulent isolates of the cosmopolitan species C. cladosporioides (Mexico), C. oxysporum (USA), and C. sphaerospermum, isolated from tomato plants in the post-harvest period, have been described in the literature over the years. In this study, a new species of the causative agent of leaf mold in protected soil in Russia — C. sphaerospermum was isolated and identified for the first time using a combination of phytopathological, molecular genetic (based on analysis of the ITS1 and ITS2 regions of the internal transcribed spacer), morphological, and immunological approaches. The goal of this study was to identify the Cladosporium species that causes tomato leaf mold in greenhouses of the Moscow Province, based on morphological and molecular characteristics. The experimental isolation, identification, and virulence study of C. sphaerospermum were conducted from 2023 to 2025 at the Federal Research Center for Vegetable Growing (FSBSI FSVC, VNIISSOK, Odintsovsky District, Moscow Province), the AllRussian Research Institute of Agricultural Biotechnology (Moscow), and the Peoples’ Friendship University of Russia (Moscow). Tomato plants at the cropping maturity stage with symptoms of leaf mold were collected in greenhouses (Moscow Province). For fungal isolation, at least five plants with initial leaf mold symptoms were collected from ten cultivars and breeding lines. Micro-and macromorphological characteristics were assessed by culturing the fungus on Czapek-Dox agar (HiMedia Laboratories, India), PDA, PDAnet (PDA supplemented with a decoction of stinging nettle Urtica dioica L. leaves), and PDAtom (PDA supplemented with a decoction of tomato Solánum lycopérsicum L. leaves). Total DNA was isolated from 7-to 12-day-old fungal mycelium using the K-Sorb kit (Synthol, Russia) according to the manufacturer’s protocol. For species identification, the nucleotide sequence of the internal transcribed spacer amplified with primers ITS5 (5'-GGA AGT AAA AGT CGT AAC AAG G-3') and ITS4 (5'-TCC TCC GCT TAT TGA TAT GC-3') was used. Pathogenic properties of C. sphaerospermum were studied on 10 tomato lines bred at the FSBSI FSVC. The tomato line VSIM-193-19 (L-15/25) for growing in greenhouses bred at the FSBSI FSVC was used as the standard of resistance (St R) to leaf mold, and the line VS-IM-15-19 (L-16/25) was used as the standard of susceptibility (St S). Leaf mold development on tomato leaves was assessed 14 and 21 days after inoculation. Based on the dynamic assessment, the average damage index (I), the degree of disease development (R, %), and the degree of disease spread (P, %) were calculated. In this study, a new species causing leaf mold of tomatoes, C. sphaerospermum, was isolated and identified for the first time in Russian greenhouses using phylogenetic analysis and morphological characteristics. The original and reisolated fungal isolates were identical in the ITS locus sequence and all morphological characteristics studied. Using the NCBI database, the species was determined to be C. sphaerospermum with 100 % homology, while homology to C. fulvum was less than 86 %. PDAtom medium was shown to be the most preferable for cultivating C. sphaerospermum, as the fungus demonstrated the highest linear mycelial growth rate (VR = 7.0 mm/day) on it. A high degree of agreement was found between the differentiation of tomato lines by resistance during field and laboratory assessments: from highly resistant (I = 0.3 points) to highly susceptible (I = 3.0 points), demonstrating the significant (p ≤ 0.05) high aggressiveness and broad virulence of C. sphaerospermum against tomato plants. The obtained data will have practical value for developing measures to combat the causative agent of tomato leaf mold. © 2025, Russian Academy of Agricultural Sciences. All rights reserved.