The investigation showed that stem-pitting Citrus tristeza virus(CTV)occurred commonly in citrus production areas in several varieties of Hunan Province.Accurate detection of CTV strains was performed by p23/PCR method,PCR and the results indicated that the most samples were infected with several CTV isolates.Three mild strains were isolated and their pathogenicity was identified by biological identification,it indicated that p23/PCR groups had uniformity with the pathogenicity of CTV isolates.Furthermore,three mild isolates were tested in the cross protection by analysis of biological symptoms and composition of p23 gene.Different protecting effects were observed among these strains and W17 mild isolate was effective.
