A recent non‐destructive technique allows estimation of leaf chlorophyll content using the portable SPAD‐502 chlorophyll meter. Measurements were taken on four species (winter wheat, maize, soyabean and tobacco) subjected to different nitrogen regimes or senescence status and the: non‐destructive readings were compared with analytical results obtained by solvent extraction. In general, the relationship between the SPAD measurement and the analytical result was not linear and species was a factor in three out of four crops. Linear, quadratic and exponential curve fitting are presented; only die interpolation with a polynomial exponential function adequately descries the whole data set. The presence of statistically non‐significant differences between the estimated values of wheat and maize on the one hand and significant: points of difference between those of tobacco and soyabean on the other suggests distinct behaviour patterns far monocots and cicots. This type of response maybe explained by differences, in the optical properties of pigments with differing sparial distributions (sieve effect) and therefore by in vivo and in vitro different procedures and the structural diversity of leaves belonging to the two subclasses.

Fertilizer N excesses may have negative effects on both crop and water quality. To reduce the risk of N excesses it is essential to accurately define fertilizer N rates. The estimate of the most suitable N rate is complicated by the fact that a certain amount of the N taken up by the crop during the growth season is supplied by the soil. The aim of this work was to estimate the amount of N that can become available for plant uptake during the crop growth season. The effects of five N rates (0, 20, 40, 60, and 80 kg N ha 21 ) on production traits of flue-cured tobacco (Nicotiana tabacum L.) cv. K326, and on selected items of an N balance applied to the soil-plant system were studied on a loam soil, in 1998 and 1999, at Bovolone (Verona, northern Italy). The fertilizer N rate positively and significantly influenced cured-leaf yields only in 1999, whereas the time to harvest increased linearly for increasing N rates, in both years (0.25 d on average for every further kg of fertilizer N). The N balance indicated a remarkable reduction of the soil organic N stock and an increase of the soil inorganic N levels throughout the crop growth period. As these changes were both proportional to the fertilizer N rate, the occurrence of a positive priming effect was hypothesized. The formulation of N fertilizer recommendations to farmers should take into account the existence of priming effect phenomena.

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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.

Tobacco has been reported to be infected by Rhizoctonia solani isolates belonging to anastomosis groups 1 through to 5. Ten pathogenic isolates of the fungus were collected from tobacco fields in Italy and France that anastomosed in high frequencies with AG BI tester isolates and in low frequencies with tester isolates of all described subgroups of AG2, although morphology and thiamine requirement of the isolates were similar to AG 2‐1. Biomolecular evaluations by means of electrophoresis of polygalacturonase isozymes and RFLPs of ribosomal DNA internal transcribed spacers were carried out. The isolates shared a common pectic zymogram, distinct from those of AG BI and AG 2‐subgroups, while RFLPs of rDNA‐ITS evidenced a limited genetic variation within the homogeneous group and a closer similarity to AG 2‐1. As far as priority is due to the anastomosis behaviour, the isolates should be ascribed to AG BI. However, tobacco isolates differ from tester strains of the known AG BI in their morphology, thiamine requirement, pathogenicity and biomolecular features. In addition they do not anastomose with both AG 3 and AG 6. Therefore they may represent a new subgroup.