Alternaria Species on Convolvulus arvensis Revealed as a Potential Inoculum Source for Solanaceous Crops in Serbia

Alternaria pathogens are a global agronomic challenge affecting the health of Solanaceae crops. Crop debris, seeds, and perennial weeds are potential inoculum reservoirs, but knowledge on their relative importance remains limited. Plants of Convolvulus arvensis showing early blight and brown leaf spot symptoms were collected from in and around potato and tomato fields in Serbia, grown both in open conditions and in tunnels, in the late season of 2021 to 2022. Morphological characterization and multilocus sequence analysis were performed on collected samples, using three genes (GPD, CAL, and RPB2) for large-spored species and six genes (Alt a1, ATP, HIS3, endoPG, TEF-1, and OPA10-2) for small-spored species of Alternaria. A total of 58 strains were identified: four large-spored species (A. grandis, A. solani, A. protenta, and A. linariae) and two small-spored species (A. alternata and A. arborescens). Phylogenetic analyses of concatenated loci and haplotype network for every investigated locus revealed that large-spored isolates from C. arvensis exhibit a low genetic variability, suggesting common haplotypes in a broad solanaceous host range. Meanwhile, small-spored Alternaria isolates displayed high genetic diversity in all examined gene regions, indicating potential geographical haplotype distribution per HIS3 locus. Pathogenicity tests confirmed the virulence of all isolates on original hosts, with crop plants of potato and tomato also showing high susceptibility. Notably, this research documents six Alternaria species on C. arvensis in Serbia for the first time, significantly broadening our understanding of the pathogen's diversity and suggesting new sources of inoculum in solanaceous crops.