GENETIC VARIABILITY IN GNOMONIA LEPTOSTYLA
During 1990 and for two consecutive years severe damage was observed in numerous walnut plantations in Italy stressing out the potential economic impact of the disease on walnut (Belisario, 1992). To obtain more information on the population dynamics of G. leptostyla specimens were sampled all over Italy by collecting freshly diseased material such as leaves and twigs with mature fruit bodies (acervuli). From the diseased material a total of 176 single spore cultures were obtained. The isolates were grouped in relation to their geographic origin and host variety. Molecular techniques were applied to investigate the genetic variability within the sampled population. Investigations were performed by polymerase chain reaction (PCR) and restriction fragment length polymorphism. DNA regions coding for the small-subunit ribosomal RNA (SrDNA-18S) and the internal transcribed spacer (ITS) were amplified and analyzed by restriction enzyme digestion.