First Report of Leaf Spot Caused by Cladosporium herbarum on Centaurea solstitialis in Greece

A, B.M. M, Sherpa DC, C A, Suresh A, Kammar S, M S, S S, B.N. G, Doss S G. Diversity of fungal pathogens in leaf spot disease of Indian mulberry and its management

Leaf spot disease in mulberry significantly affects silk production by reducing the nutritive quality of the leaves. This disease caused by various pathogens, regardless of the localities under the same climatic region. In the present investigation, an approximate incidence rate of 84 % was recorded in Karnataka based on surveys conducted in both farmer fields and germplasm locations. The causative agents have shown diversification, including new candidates such as Bipolaris sorokiniana, Curvularia lunata, Cladosporium sphaerospermum, and Epicoccum sorghinum. These findings mark the first report of these pathogens in Indian mulberry production. The investigation involved detailed pathogenicity assessments on the predominant mulberry silk production cultivar under controlled and field environments. Pathogens were identified using morpho-cultural, microscopic and phylogenetic analyses, including the internal transcribed spacer (ITS). Various concentrations of fungicides, both individually and in combinations, were evaluated to identify effective measures for mitigating yield losses. Among the fungicides tested against the new pathogens, Hexaconazole 5 % SC and Hexaconazole 5 % + Captan 70 % WP demonstrated high promise and cost-effectiveness. Consequently, these fungicides could serve as immediate solutions to prevent further yield reduction. However, it is essential to conduct comprehensive field investigations before recommending them as standard practices. Future research endeavors should focus on assessing the extent of crop loss caused by these newly identified pathogens in mulberry cultivation.

Morphological, molecular characterization, plant pathogenicity and biocontrol of Cladosporium complex groups associated with faba beans

Vicia faba (faba bean) is one of the most significant leguminous crops. The faba bean is specialized by maximum nutritional value, in energy and protein content, which leads it to be suitable for food and feed production. Diseases caused with fungi are amongst the biotic factors responsible for decreasing in faba bean yields. In this work, Cladosporium isolates were recorded in cultivated faba bean leaves and pods collected from markets in Qena, Upper Egypt; morphological features and molecular characterization based on actin gene were performed. The ability of the pathogens to cause disease in faba bean seedlings and the biocontrol method to avoid the pathogenic effect of Cladosporium were determined. Results showed that Cladosporium is the main genera isolated from faba beans, and the morphological criteria showed presence of three species complex groups of Cladosporium (C. cladosporioides, C. herbarum and C. sphaerospermum) and the confirmation with molecular characterization revealed the existence of four species in the three groups. All the 26 tested strains of Cladosporium were able to cause leaf lesions on Vicia faba seedlings with different levels. Chaetomium globosum is a biocontrol agent could inhibit the growth of the majority strains of Cladosporium.

A peptidogalactomannan isolated from Cladosporium herbarum induces defense-related genes in BY-2 tobacco cells

Cladosporium herbarum is a plant pathogen associated with passion fruit scab and mild diseases in pea and soybean. In this study, a peptidogalactomannan (pGM) of C. herbarum mycelium was isolated and structurally characterized, and its role in plant-fungus interactions was evaluated. C. herbarum pGM is composed of carbohydrates (76%) and contains mannose, galactose and glucose as its main monosaccharides (molar ratio, 52:36:12). Methylation and 13C-nuclear magnetic resonance (13C-NMR) spectroscopy analysis have shown the presence of a main chain containing (1 → 6)-linked α-D-Manp residues, and β-D-Galf residues are present as (1 → 5)-interlinked side chains. β-Galactofuranose containing similar structures were characterized by our group in A. fumigatus, A. versicolor, A. flavus and C. resinae. Tobacco BY-2 cells were used as a model system to address the question of the role of C. herbarum pGM in cell viability and induction of the expression of plant defense-related genes. Native and partially acid hydrolyzed pGMs (lacking galactofuranosyl side-chain residues) were incubated with BY-2 cell suspensions at different concentrations. Cell viability drastically decreased after exposure to more than 400 μg ml-1 pGM; however no cell viability effect was observed after exposure to a partially acid hydrolyzed pGM. BY-2 cell contact with pGM strongly induce the expression of plant defense-related genes, such as phenylalanine ammonia lyase (PAL) and lipoxygenase (LOX), as well as the pathogen-related PR-1a, PR-2 and PR-3 genes, suggesting that pGM activates defense responses in tobacco cells. Interestingly, contact with partially hydrolyzed pGM also induced defense-related gene expression at earlier times than native pGM. These results show that the side chains of the (1 → 5)-linked β-D-galactofuranosyl units from pGM play an important role in the first line fungus-plant interactions mediating plant responses against C. herbarum. In addition, it was observed that pGM and/or C. herbarum conidia are able to induced HR when in contact with tobacco leaves and in vitro plantlets roots, producing necrotic lesions and peroxidase and NO burst, respectively.