GENETIC VARIABILITY IN GNOMONIA LEPTOSTYLA

Gnomonia leptostyla (Fr.) Ces. et de Not., the teleomorph of Marssonina juglandis (Lib.) Magn., is the causal agent of the walnut anthracnose, a wide spread disease in almost all the walnut growing areas and particularly severe in the Mediterranean basin. It has been recorded on numerous Juglans spp. however, its economical importance is mainly due to the damage caused to Persian (English) walnut (Juglans regia L.), the major orchard species.

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.