高歧異度的番木瓜園內木瓜輪點病流行之探討

Abstract

木瓜輪點病(Papaya ringspot)蔓延於全世界重要番木瓜(Carica papaya L.)產區，造成嚴重危害。本試驗探討隔離田之木瓜輪點病毒(Papaya ringspot virus; PRSV)於自然感染番木瓜後的蔓延模式，並比較定植時間先後、不同品系(種)以及在罹病田補植健康植株對病害發展之影響，提供制定防治策略的依據。試驗材料使用六個耐(抗)病選系和對照品種‘台農二號’(Tainung No. 2; TN2)，分二次定植於相同地點，並在第二次定植後1週進行補植。第一次定植(I區)和第二次定植(II區)的A選系，根據植株的累計感染率(cumulative rate of infection)分別建立迴歸模式─I區：y1 = 100.4/{1+exp[-(x-203.3)/13.38]}, r2 = 0.9994；II區：y2 = 93.41/{1+exp[-(x-149) /17.61]}, r2 = 0.9860，推測兩區因距離感染源的遠近，影響植株感染病害速率；補植的A選系則因病害壓力較大，植株感染病害速率相對較快，建立之迴歸模式為：y3 = 100/{1+exp[-(x-91.77)/1.468]}, r2 = 1，其病徵亦較正常定植植株嚴重。根據建立的迴歸模式估算，定植於I區的‘TN2’和選系A、B、C，達到10 %累計感染率的時間分別約為定植後120、175、135和225天，而達到50 %累計感染率的時間分別約為定植後160、202、188和234天；定植於II區的D、G和H選系，則依序約為定植後205、179和178天達10 %累計感染率，而達到50 %累計感染率的時間分別約為定植後210、190和193天；顯示各選系依耐(抗)病性程度的不同，相對‘TN2’可延後植株大量發病時間約15-105天。病徵嚴重程度經病害發展曲線面積(area under disease progress curve; AUDPC)量化後，可區分不同品系(種)間之差異，A、B、C、D、G和H選系相對於‘TN2’的AUDPC (relative AUDPC; RAUDPC)依序為68 %、50 %、21 %、6 %、67 %和51 %，病徵皆較輕微且發展較緩。另外採取‘TN2’和B選系不同病徵嚴重程度的病株汁液，接種於‘TN2’、‘台農一號’ (Tainung No. 1; TN1)、‘紅妃’ (Red Lady; RL)和‘台大八號’ (National Taiwan University No. 8; NTU8)；接種不同病毒汁液的‘台大八號’，病徵皆相對較其餘品種輕微。田間採樣的病株汁液經RT-PCR檢測後，皆偵測到DF病毒系統。根據植株累計感染率建立的迴歸模式推測，若能將田間病株比例維持於10 %以下，可有效管控病害的發生和蔓延，而栽植耐(抗)病品種有助於田間病害壓力的降低，減緩病害的蔓延並減輕因病害造成之損失。

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.