Effect Of Temperature, Rice Growth Stages And Developmental Stages Of Sogatella Furcifera(Horváth) On Transmission Of Southern Rice Black-streaked Dwarf Virus

Southern rice black-streaked dwarf disease(SRBSDD) is caused by a newly discovered virus, Southern rice black-streaked dwarf virus(SRBSDV). White-backed planthopper(WBPH), Sogatella furcifera, is the only vector to transmit the virus in a persistent, circulative and propagative manner. WBPH transmit the virus through dispersing and migrating behaviors to south China, Japan, and Korea annually, and the viral disease areas are enlarging each year, which pose a great threat to rice production. To elucidate the epidemiology of SRBSDV as well as the factors influencing on its transmission by WBPH, this thesis investigated the effects of temperature, rice growth stages and developmental stages of the vector on the virus transmission by WBPH. The results are as follows: 1. Influence of temperature, rice growth stages and vector nymphal statdium on virus acquisition rates of WBPH. A 3 × 3 × 2 factorial experiment was conducted to evaluate the effects of temperature(22, 27 and 32 °C), rice growth stages(tri-leaf stage, tillering stage and booting stage) and vector nymphal stadium(3rd and 5th) on virus acquisition efficiencies of WBPH. Temperature had a significant influence on virus acquisition. Virus acquisition rates by both 3rd and 5th instar nymphs of WBPH increased with increasing temperatures from 22 to 32 °C. Rice growth stages also showed an influence on virus acquisition. Planthoppers feeding on virus-infected rice seedlings at tillering stage had a higher acquisition rates than those on rice seedlings at tri-leaf stage or booting stage. Different nymphal stadium of WBPH had different virus acquisition rates. Third instar nymphs were more efficiency than 5th instar nymphs. However, no significant interaction effects between the factors were found on virus acquisition. 2. Influence of temperature, rice growth stages and adult status of WBPH on virus inoculation rates by WBPH. Like the tests described above, a 3 × 3 × 3 factorial experiment was performed to elucidate the effects of temperature(22, 27 and 32 °C), rice growth stages(tri-leaf stage, tillering stage and booting stage) and adult status of WBPH(6-d old males, mated females and unmated females) on virus inoculation rates by WBPH. Adult status of planthoppers had a significant influence on virus inoculation rates, being significantly higher by males than by mated females and no difference between the other adult statuses. Virus inoculation rates were also affected by a significant interaction between temperature and rice growth stages. Temperature, rice growth stages and the other interactions among the three factors had no significant effects on virus inoculation rate of the adults. 3. Low temperature storage of SRBSDV-infected rice seedlings cannot sustain subsequent virus transmission by WBPH. Because of low virus transmission efficiencies by planthoppers, researchers are frequently confronted with shortage of viruliferous vectors or infected rice seedlings, especially in winter and the following spring. To find new ways to maintain virus-infected materials, viral rice seedlings were stored at-80 °C for 45 or 140 d and evaluated as virus sources in virus transmission by the vector. RNA of SRBSDV was not degraded during low temperature storage at-80 °C. When planthopper nymphs were fed 48 h on the infected frozen plants, they survived at about 40% but failed to acquire the virus after the virus latent period, while the nymphs on fresh infected plants had a 50.4% acquisition rate. However, a further study showed that planthopper nymphs acquired SRBSDV after fed 48 h on the frozen infected rice plants. These results indicated that low temperature storage of SRBSDV-infected rice plants cannot sustain subsequent virus acquisition by white-backed planthopper.