Induced systemic resistances (ISR) response is related to several biochemical changes in plants. Gliocladium roseum is a powerful biological control agent (BCA) as first emerged in controlling Botrytis cinerea in strawberry and later on diseases of raspberry and tomato. Enzymatic activities were measured on leaves of tobacco plants inoculated on roots with an isolate of G. roseum. Leaf extracts were analysed for 1,3-b-glucanases, 1,4-b-glycosidases, chitinases, N-acetyl-b-dglucosaminidase and -b-d-N-N¢-diacetyl-chitobiosidase activities; peroxidase isozymes were examined by polyacrylamide gel electrophoresis. Plants inoculated with G. roseum showed: (i) an increased activity of 1,3-bglucanases, 1,4-b-glycosidases and chitinases; (ii) two new bands and a major expression of two other isoforms in peroxidase isozymes pattern. Bioassays were carried out making a challenge inoculation with Erysiphe orontii on leaves of plants previously treated with Gliocladium on roots. Leaves of these plants showed a reduced number of colonies and less severe symptoms of powdery mildew compared with the control ones. This is the first time that this effect has been demonstrated for G. roseum.U. S.

A disease characterized by the absence of sporulation on leaves and evident necrosis underneath the bark tissues affected adult tobacco plants during 2005 in south Italy. In the field, diagnosis was based mainly on recognition of symptoms, often non-specific, resulting in the application of the wrong control strategy. Two current diagnostic methods based on microscopic observations were compared with polymerase chain reaction (PCR) technique. DNA extraction protocol was modified by replacing sonication with a further lysis step at 60°C and PCR was performed using primers that amplified a specific DNA fragment (230 bp). Microscopy methods were able to detect the pathogen in 50% and 6% of cases, respectively, while PCR was able to detect Peronospora tabacina in all diseased plants. Elimination of sonication in DNA extraction rendered the method easier to perform and avoided the possibility of DNA fragmentation. The results demonstrated that PCR makes the diagnosis fast and reliable while microscopy gives discontinuous results, is time-consuming and not applicable for monitoring.

The N′ gene was shown to be present in the ‘Samsun NN’ line of Nicotiana tabacum by its differential response to tobacco mosaic (TMV) and tomato mosaic (ToMV) viruses in the segregating and test‐cross generations of the cross ‘Samsun NN’בSamsun nn’. The appearance of phenotypes reacting with local necrosis to ToMV and with systemic mosaic to TMV confirmed that the genes N and N′ are on distinct loci. An isogenic N′;N′ Samsun line was selected.