Comparative study of Monilinia fructigena and Monilia polystroma on morphological features, RFLP analysis, pathogenicity and histopathology

In this study, we compared cultural, morphological, pathogenic and biological features of Serbian isolates of Monilia polystroma and Monilinia fructigena from apple fruit. Isolates of M. polystroma formed characteristic stromatal plates throughout the cultures unlike M. fructigena, while mycelial growth rates were not distinguishable features between species. Conidia of M. fructigena were larger than M. polystroma, and both species produced slightly larger conidia on apple fruit than on V8 medium. The existence and morphology of the microconidial state of M. polystroma was described for the first time using light and SEM microscopy. Microconidia were globose (2.19-3.44 mu m), similar to M. fructigena. Digestion of polymerase chain reaction (PCR) product of ribosomal ITS1-5.8S-ITS2 region with restriction enzyme HhaI provided a reliable method for specific detection of M. polystroma. In a pathogenicity test, both species produced larger lesions on cv. Golden Delicious, than on cvs. Idared and Granny Smith. On cv. Golden Delicious, the mean lesion size was not significatly different between species, while on cvs. Idared and Granny Smith M. fructigena tended to produce slightly larger lesions compared to M. polystroma. On artificially inoculated apple fruit after 1 and 4 months of incubation, M. polystroma, unlike M. fructigena, was capable of forming thicker and more compact stromata with complex morphology, which consisted of densely interwoven medullary hyphae covered with a discontinuous layer of melanized hyphal rind cells. The dynamics of stromata formation beneath the host's cuticle also showed differences between two species, where M. polystroma formed this layer after 1 month, while M. fructigena after 4 months of incubation.