Comparisons between genetic diversity, virulence and colony morphology of Monilinia fructicola and Monilinia laxa isolates

Monilinia fructicola and M. laxa, causing brown rot in stone fruit (Prunus species), were first described from Western Australia in 1997. Our previous work indicated that original invasive isolates of both species were each of a single genotype. This research aims to compare isolates from the region in the present day in terms of genetic diversity, colony morphology, and virulence on fruit. Genetic diversity of 68 M. laxa and 66 M. fructicola isolates collected in 2016-2017 from five populations was measured using ISSR markers. The genetic diversity within M. fructicola was greater than that of M. laxa, having Shannon’s diversity indices of 0.50 and 0.41, respectively. Most genetic variation was present within populations for both M. fructicola (77%) and M. laxa (76%), with the rest of the variation between geographically separated populations. Genotype did not correlate closely with virulence of isolates as measured by symptom severity index (SSI) on inoculated plum fruit and colony morphology on potato dextrose agar (PDA) medium. M. fructicola isolates with wide genetic variation exhibited closely similar SSIs and one morphotype on PDA, whereas M. laxa isolates exhibited a broad range of SSIs and four different morphotypes