Genomic structure and population genetic analysis of leaf spot disease, Ulocladium atrum‑potato pathotype isolates

M. Nasr-Esfahani, R. Gholamaliyan, A. Esmaiili, S. Mardani
Potato (Solanum tuberosum L.) is a globally important crop producing high yield of nutritionally valuable food in the form of tubers. The potato plant is susceptible to at least 80 diseases and non-parasitic disorders, many of which consistently cause yield losses in potato production areas. Among them, potato early blight disease is of global importance, caused mainly by Alternaria alternata, and A. solani. In addition there are also major concerns in potato, tomato and eggplant production for leaf spot caused by Ulocladium atrum (Pleosporaceae) isolated along with early blight disease. A leaf spot was observed on potatoes (Solanum tuberosum L.), affecting 18.6% of potato plants growing in the fields in Iran. Symptomatic leaf samples were collected from infected potato plants from the main potato-growing regions of Iran, including Hamadan, Fars and Isfahan provinces and isolations were made on a PDA medium. Single-spore isolates were identified as Ulocladium atrum on the basis of morphological characteristics. Morphological identification was confirmed by sequence analyses of the ITS, gpd and Alt a1 regions. Pathogenicity tests indicated that U. atrum causes leaf spots on potatoes. A total of 30 isolates were genetically analyzed using random amplified polymorphic DNA inter-simple sequence repeats (ISSR) markers and (RAPD). Cluster analysis using the un-weighted pair group method with the arithmetic average (UPGMA) method for RAPD marker revealed no clear grouping of the isolates obtained from different geographical regions. The groupings, based on morphological characteristics, virulence variability and RAPD analysis, were not correlated. Cluster analysis using Jaccard's coefficient for ISSR divided the U. atrum isolates into four main groups, in which there was no significant correlation between the isolate groupings regarding their geographic location and pathogenicity. Using molecular techniques, genetic variability was detected among the accessions, with cophenetic correlation coefficients (CCC) of 0.80 for RAPDs and 0.89 for ISSRs. The RAPD and ISSR marker results corresponded well, with a correlation of 0.55.To our knowledge, this is the first report of leaf spot caused by U. atrum outbreaks as a serious disease on potatoes in Iran.
Nasr-Esfahani, M., Gholamaliyan, R., Esmaiili, A. and Mardani, S. (2021). Genomic structure and population genetic analysis of leaf spot disease, Ulocladium atrum‑potato pathotype isolates. Acta Hortic. 1326, 255-264
DOI: 10.17660/ActaHortic.2021.1326.34
ITS, gpd and Alt a1 regions, ISSR, morphology, RAPD, pathogenicity, Solanum tuberosum

Acta Horticulturae