engleski

Genetic variability of Croatian Citrus tristeza virus isolates

About 30 citrus field samples (Satsuma mandarins, oranges, lemons) were collected from different orchards in the Croatian coastal region (Dalmatia), including one remote island. The majority of these trees was grafted on Poncirus trifoliata and displayed no symptoms of Citrus tristeza virus (CTV) infection. However, about 50% of tested trees were found CTV infected. The genetic variability and population structure of CTV from these samples were studied by single-strand conformation polymorphism (SSCP) and sequence analysis of the cloned coat protein (p25) and RNA-binding protein (p23) genes. In the majority of isolates, CTV populations consisted of a swarm of genomic variants with the one being predominant. Surprisingly, the results of phylogenetic analysis, corroborated by a biological characterization, showed that both CP and p23 sequences clustered into five out of seven phylogenetic groups defined by Zemzami et al. (Proc. 15th IOCV, 8-12, 2002). Three of these phylogenetic groups harbor sequences of severe quick decline, seedling yellows and stem pitting isolates. It has been generally believed that some of these strains do not exist in the Mediterranean region, or if found, they are immediately eradicated. It is possible that these CTV strains were introduced into the country with the infected Satsuma material 40-20 years ago and has been continuously spreading by grafting. We also found evidence of mixed infections and recombination events in our isolates. High genetic diversity of Croatian CTV isolates and their potential for further diversification should not be overlooked in the CTV epidemiological studies of the Mediterranean basin.

CTV; SSCP; genes p23 and p25; sequencing; phylogenetic groups

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