Pathological variation and interaction between two Papaya ringspot virus (PRSV) strains in different papaya cultivars
Date Issued
2012
Date
2012
Author(s)
Chiu, Hsien-Kuang
Abstract
Papaya ringspot virus (PRSV) is one of the limiting factors in the papaya industry. The infected papayas produce several symptom such as mosaic, yellowing, ringspot in fruit, which causes tremendous economic losses and poor quality of fruits. According to the symptoms developed on leaves, PRSV was categorized into three strains: SM(severe mottling), DF(deformation),and SMN(severe mottling with necrosis)strains. The DF strain is predominated in the field at present time, and the SMN strain induce most destructive symptom in papayas. This study we dedicated to investigate the correlation between the severity of symptom and replication of virus, and develop a evaluation method to evaluate the resistance or tolerance of new papaya cultivars. The RT-PCR and real-time RT-PCR assays were used in this study to monitor the fluctuation dynamic of virus replication for comparative study of tolerance between new developed papaya lines and commercial cultivars. In addition, the simultaneously or asynchronously inoculation experiment test with the DF and SMN strains to were also conducted to investigate the interaction between these 2 strains in either new line or commercial cultivars of papaya based on the real-time RT-PCR assays with train-specific primers. The result might be able to know the co-infection effect of the DF and SMN strains in various papaya cultivars(lines). The inoculation tests showed that all of 3 newly bred papaya lines(10A, 10B, and 10F) were tolerant to the DF strain without appearing apparent symptoms. However, only the 10A line is tolerant to the SMN strain. The real-time RT-PCR assays demonstrated the amounts of replicated virus in newly bred lines was 10 times higher than those in commercial cultivars. It means revealed that these newly bred papaya lines are actually better host for PRSV-replication though they do not produce symptoms showing their tolerance. The data also indicated that the SMN strain replicated very well in either Tainung 2 (TN 2) and Red-Lady (RL) cultivars, which means TN 2 and RL probably provide better conditions for survival of PRSV-SMN. In the asynchronously inoculation tests with both DF and SMN strains, all of infected papayas by PRSV-DF before PRSV-SMN (2-week interval) developed the symptoms similar to those induced by PRSV-DF whereas all of infected papayas by PRSV-SMN before PRSV-DF developed the symptoms similar to those induced by PRSV-SMN. It presented that the earlier invading virus strain determines the symptom-type. The DF-induced symptoms could be visualized when the papaya hosts were co-infected by the DF and SMN simultaneously. In the inoculation tests of the NTU8 papaya, the real-time RT-PCR assays demonstrated that the later invading PRSV-DF could replicate well and reach or exceed the amount of earlier infecting PRSV-SMN whereas the later invading PRSV-SMN could not reach the amount of earlier infecting PRSV-DF. These two strains competed each other when they simultaneously co-infected a papaya host, and the DF strain gradually became prevailing. This study reveals that the DF trains seemed to be more predominant than the SMN strain in the field, and we should pay more attention to the evolution of various PRSV strains. The investigation of symptomatology and quantitative detections of PRSV based on real-time RT-PCR assays provided important data to evaluate the resistance or tolerance against PRSV for newly bred papaya lines. The newly developed papaya cultivar tolerant to PRSV, NTU 8, showed its stable tolerance in the co-infection trials with both DF and SMN strains. However, the continuous breeding of papaya should be conducted to cope with the evolution of various strains of PRSV.
Subjects
Papaya ringspot virus
real-time RT-PCR
virus strain
tolerance
Type
thesis
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