Distribution and population structure of Citrus tristeza virus in Poncirus trifoliata

Citrus tristeza virus (CTV) isolates were detected in Poncirus trifoliata, but few research focused on the distribution and population structure of CTV isolates in this resistant species. In this study, 9 P. trifoliata cv. 'Zaoyangxiaoye' seedlings were tested positive for CTV in the field. CTV was detected in petal, stamen, pistil and rootlet tissues from CTV-infected plants by real-time RT-PCR, but the incidence of CTV in young flush and old shoot tissues was 68.9% and 4.4%, respectively. The results also showed the highest relative amount of CTV was detected in pistils, followed by rootlets, stamens, petals and young flush. The lowest CTV accumulation was in old shoots, with a viral load two orders of magnitude lower than in pistils. Furthermore, CTV present at a concentration approximately 5 to 10 times higher in petals than in young shoots. These results indicated that the floral parts and rootlets of Zaoyangxiaoye trifoliate orange were more susceptible to CTV accumulation than shoots. Furthermore, T36, T30 and VT genotypes were detected in all of CTV-infected petal, stamen, pistil, rootlet and young flush tissues, but only VT genotype was found in old shoots. Further analysis by specific real-time RT-PCR suggested that the relative amount of VT genotype was most abundant in all of tissue samples, followed by the T30 and T36 genotypes.