Genetic variability among populations of Fusicladium species from different host trees and geographic locations in the USA

Peach and almond scab caused by Venturia carpophila and pecan scab caused by Fusicladium effusum result in yield loss, downgrading of fruit, defoliation and subsequent decline of an orchard. To understand the levels of genetic diversity and divergence of pathogens from different hosts and locations 51 isolates were genotyped and analyzed using 10 RAPD and 5 UP-PCR markers, including 18 isolates of V. carpophila from peach trees in the southeastern United States, 12 isolates of V. carpophila from almond trees in California, and 21 isolates of F. effusum (a related species) from pecan trees in the southeastern United States. The combined marker results showed a low incidence of polymorphisms among the peach isolates (4.2 % of markers), but a higher incidence of polymorphisms among the almond isolates (42.0 %) and the pecan isolates (61.0 %). The Dice coefficient of similarity ranged from 0.932 to 1.000 for the peach V. carpophila isolates, 0.214 to 0.976 for the almond V. carpophila isolates, and 0.528 to 0.920 for the pecan F. effusum isolates. UPGMA bootstrap values indicated that UP-PCR data were slightly more robust and, based on the combined data, the UPGMA bootstrap analysis (1,000 runs) gave a high node value (100 %) differentiating all the isolates of V. carpophila from F. effusum and a moderate node value differentiating the peach and almond isolates of V. carpophila (68 %). The results suggest some divergence between the V. carpophila populations of almond trees in California and peach tree populations in the southeastern United States, and different levels of genetic diversity within the two populations.