Genetic Diversity Assessment of the Diaporthe cinerascens Causal Agent of Fig Canker Using ISSR Markers

Diaporthe cinerascens is a significant plant pathogen that causes canker disease in fig trees. This pathogen is notably dominant in major fig-production areas in Iran, as well as in other fig-producing countries such as Bulgaria, USA (California), Canada, and Italy. In the present study, six Inter-Simple Sequence Repeats (ISSR) markers were used to investigate genetic diversity among representative D. cinerascens isolates, selected based on the variety of their host cultivars, aggressiveness, and morphological features. The discriminating power of each ISSR marker was assessed using 10 parameters including effective multiplex ratio, expected heterozygosis, observed heterozygosity, polymorphic information content, marker index, resolving power, Nei’s diversity, Shannon index, polymorphic percentage, and allele number. Among them, M1 primer was the best to detect the variability of the D. cinerascens isolates. The isolates exhibited a high degree of genetic similarity, as evidenced by Jaccard’s similarity coefficients, which ranged from 79% to 100%. Despite the high values of pairwise Jaccard’s similarity coefficient among the isolates (at least 79% similarity), they were grouped into four distinct genetic clusters, based on Principal Coordinate Analysis (PCoA) analysis. The observed grouping pattern was found to be partially influenced by their geographical origins and the specific fig cultivars from which the isolates were recovered. Based on ISSR fingerprinting, we provided genetic evidence regarding the clonal structure of D. cinerascens. These results could be critical to understanding Diaporthe canker epidemiology and adopting sustainable management practices for the disease.