Investigation of papaya ringspot viral disease spread in the diverse papaya populations
Date Issued
2012
Date
2012
Author(s)
Huang, Han-Chun
Abstract
Papaya ringspot virus (PRSV) is a limiting factor for papaya (Carica papaya L.) production worldwide. The objective of this study was to investigate the viral epidemiology after papaya naturally infected PRSV and to compare different transplanting times, papaya genotypes and replanting effects on the viral disease severity and infection rate in the isolated field of the pandemic areas. Diverse papaya lines with different degree tolerance to PRSV and ‘Tainung No. 2’ (TN2) as a control were used and completely randomized design was practiced. The regression models on the cumulative infection rate of A line were y1 = 100.4/{1+exp[-(x-203.3)/13.38]}; y2 = 93.41/{1+exp[-(x-149)/17.61]}; and y3 = 100/{1+exp[-(x-91.77)/1.468]} for the zone I, zone II and replanting at zone I, respectively. The coefficient of determination of the three models were r2 = 0.9994, r2 = 0.9860, and r2 = 1.0, respectively. There were very significant. The comparison on different models for PRSV infection rate was discussed in the text. Estimating the 10 % cumulative rate of infection were 120, 175, 135 and 225 days after planting on ‘TN2’ and A, B, C lines at zone I. There were quite different cumulative infection rate on different genotypes. The cumulative infection rate of the susceptible TN2 had the shortest period compared to that of the others in zone I. Estimating the 10 % cumulative rate of infection were 205, 179 and 178 days after planting on D, G, H lines at zone II. In comparison with ‘TN2’, different papaya lines could delay the time of disease spread about 15-105 days depending on their resistance degrees. If the cumulative rate of infection was under 10 %, it appeared to effectively minimize the PRSV spreading according to the regression models. The disease severity was quantified by area under disease progress curve (AUDPC) which was capable of distinguishing the different papaya lines. The RAUDPC of A, B, C, D, G and H lines compared the control ‘TN2’ were 68 %, 50 %, 21 %, 6 %, 67 % and 51 %, respectively. The viral symptom of the A, B, C, D, G and H genotypes was milder and the disease development was slower compared to the control. The leaf extracts of ‘TN2’ and B line with different viral severity were inoculated with ‘TN2’, ‘Tainung No. 1’ (TN1), ‘Red Lady’ (RL) and ‘National Taiwan University No. 8’ (NTU8) to investigate the isolate aggressiveness. The deformed symptom was developed on different cultivars but the severity was different and its significant dependent upon the cultivars. ‘NTU8’ was milder than the others. The RT-PCR was used and PRSV-DF strain was verified among viral isolates of different papaya genotypes in the field. The strategies of viral disease management including the control of vectors, using PRSV resistant papaya genotypes and rouging of infected plants to maintain the infection rate under 10 % could effectively mitigate the loss caused by the PRSV disease.
Subjects
Papaya ringspot virus
cumulative rate of infection
area under disease progress curve
regression model
viral disease management
resistant papaya genotype
Type
thesis
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