Molecular characterization of citrus tristeza virus (CTV) isolates and detection of fungi associated with Citrange root-stock in Sicilian symptomless Citrus growes.

The first monitoring on the CTV occurrence in central-western Sicily carried out during spring 2011 in asymptomatic citrus groves, has allowed to report CTV- free citrus-growing areas (province of Caltanissetta and Trapani), the first focus in province of Agrigento and two new others in province of Palermo. Molecular analysis (RT-PCR of p18, p20 and p23 genes, single strand conformation polymorphism and partial sequencing) showed that the obtained CTV isolates had a high homology (99%) with mild CTV strains (T 30 and T 385). Moreover, survey on the genetic flow and analysis of synonymous/nonsynonymous, by MEGA 5.0 and DNAsp 5.0 programs, demonstrated the provenience of the new “tristeza” foci near Palermo from the first one reported in 2006, probably due to aphid diffusion. Regarding the effect of artificial mycorrhization on fitness of citrange seedlings and micro-propagated plants, first findings suggest an improvement of some vegetative parameters. In addition, a collection of colonies of genera Fusarium and Trichoderma from roots and rhizosphere of citranges, using suitable selective substrates, was obtained. In vitro antagonism tests allowed to select a Trichoderma isolate, called 1TC, able to compete with the most of Fusaria. Appropriate mycorrhizal inocula and selected antagonists towards soil-borne pathogens, improving the vegetative performance of plants, both in the nursery and in the field, could improve the host tolerance to CTV.