Study of distribution, migration and propagation of apaya Ringspot Virus in papaya hosts with Real-Time T-PCR techniques
Date Issued
2009
Date
2009
Author(s)
Liang, Hsin-Yueh
Abstract
Papaya ringspot , caused by the Papaya ringspot virus (PRSV), is one of the most important diseases in papaya. PRSV is divided into three major strains distinguished by the symptoms on leaves: severe mottling (SM), deformation (DF), and severe mottling with necrosis (SMN). In this study, three papaya cultivars (lines) were inoculated with PRSV (DF and SMN strain), then the Real-Time RT-PCR assay was used to perform quantitative detection to track the distribution, migration, and propagation of each PRSV in papaya hosts. Three papaya cultivars (lines) were used including Tainung No.2 (TN2), Red Lady (RL), and National Taiwan University Hybrid No.8. (NTU8). After inoculation with the DF strain of PRSV (PRSV/DF), viruses could be detected in roots, stems and leaves of NTU8 within 2 days, which is earliest among the three cultivars. Viruses were found in NTU8 leaves within 4 days post-inoculation, indicating that the viruses moved very fast in NTU8, although they did not replicate well and remained at low quantity (103 copies). PRSV/DF was monitored in roots, stems and leaves of TN2 4, 8 and 10 days after inoculation respectively; the virus quantities in leaves of TN2 reached to a peak (107~8 copies) 24 days later, which is the highest compared to RL and NTU8 . For the RL cultivar, viruses were detected in roots, stems and leaves at 7, 8, and 8 days post-inoculation respectively, and the peak quantity in leaves 24 days after inoculation reached 104 copies. In the inoculation tests with the SMN strain of PRSV (PRSV/SMN), NTU8 exhibited detectable virus levels in roots, stems and leaves 2, 2 and 7 days after inoculation respectively, and the virus quantity remained (103~4 copies) at 24 days later. PRSV/SMN in TN2 was detected in roots and stem after 8 and 4 days respectively, and reached into leaves 10 days after inoculation, where quantity could reach as high as 106 copies after 30 days. The roots, stems and leaves of RL showed detectable virus at 8, 8 and 4 days after inoculation, with quantities at about 104 copies in the leaves 24 days later. In roots usually accumulate more or the same amounts than in leaves, and stems gave rise to slightly lower quantity of viruses than in roots as a results of comparative quantitative detection among roots, stems and leaves no matter what cultivar of papaya was used. It seems that roots are very important for PRSV to propagate. The new bred papaya cultivar tolerant to PRSV, NTU8, constantly showed a good replication of PRSV/DF at 106 copies in roots, but a lower amount of 103 copies in the leaves. TN2, the susceptible cultivar to PRSV, showed more viruses in the leaves approximately 104~5 times than NTU8. This is probably one of the factors resulting in the tolerance of NTU8. When NTU8 was inoculated with PRSV/SMN, it had the virus quantity of 107~8 copies in roots, but only 103~4 copies in leaves; which is similar to the case of PRSV/DF. However, NTU8 seems to have slightly lower tolerance to PRSV/SMN. In this thesis, in addition, the Real-Time RT-PCR method performed its better sensitivity and could detect these viruses at the same time or earlier than the conventional RT-PCR method. Furthermore, this method also provides a precise relative quantification for PRSV and it is helpful to understand how the virus propagates in the host, and will be valuable for future ecological study and control of PRSV.
Subjects
papaya,
Papaya ringspot virus
Real-Time RT-PCR
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