CITRUS TRISTEZA VIRUS INFECTION ON PLANTS OF TAROCCO O.L. GRAFTED ON SOUR ORANGE: EVALUATION OF THE EFFECT ON SOME PRODUCTIVE AND PHYSIOLOGICAL PARAMETERS, BY SIMPLE VARIANCE AND DISCRIMINANT ANALYSIS.

In this paper the effect of Citrus tristeza virus (CTV) on yield, fruit quality and some plant physiological index are evaluated. The observations were carried out on a plot located in Catania province constituted by 500 plants 30-years-old of Tarocco O.L. grafted on sour orange, combination susceptible to CTV. The citrus grove, upon screening by immunoenzymatic test, was infected by CTV. The virus characterization revealed the presence of CTV-DS2, virulent and easily transmitted by aphid populations. The percentage of infection was 32% and showed different decline levels. The sampling was carried out on four groups of 30 trees each: group 1, CTV infected showing severe decline; group 2, infected showing initial symptoms of decline; group 3, infected with good vegetative growth; group 4 CTV-free. On each plant we determined the mean yield, and analyzed fruit quality (average fruit weight, total soluble solids, percentage, total acidity and ripening ratio, peel, flesh and juice colour). Plant physiological index as chlorophyll contents in leaves were measured by SPAD 502plus Konica Minolta. The obtained data were elaborated through simple variance analysis and discriminant analysis. The results have underlined that all the considered parameters are influenced by the level of infection. Among all the mean yield, the weight of the fruits and the index of green (SPAD) determination showed the most meaningful values to the statistic and discriminating analysis; particularly interesting are the differences of these last values between the healthy plants and the CTV infected plants with good vegetative growth and without symptoms. [ABSTRACT FROM AUTHOR]