Pathological and Molecular Characterization of Banana Streak Badnavirus Strains and Their Transmission Ecology

• Main Authors: RYU, IN-HEE, 柳仁喜
• Other Authors: Hong-Ji Su
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/79526856247176103136

博士 === 國立臺灣大學 === 植物病理學研究所 === 90 === Summary Detailed vectorship of comstocki mealybug (Pseudomonas comstocki), the new vector insect of banana streak badnavirus (BSV) found in Taiwan (Ryu, 1999) was investigated. Its acquisition-feeding period was confirmed to be 1 hour, and inoculation-feeding period was found to be 1 hour after 2 hours of inoculation period. The present virus was retained within the insect with retention period of at least 20 days or whole life, and also through transovarial passage. Using BSV / PCR analysis, BSV-DNA was detected in DNA extract from bunches of 5 banana aphid (Pentalonia nigronervosa Coq.) fed on BSV-infected banana leaf for 1 to 2 days, however the viruliferus aphides could not transmit the virus into banana plants. The natural transmission of BSV by the mealybugs occurred from diseased banana plants to the nearby healthy banana plants in outdoor test in the presence of vector mealybugs. Transmission of virus by vector was of short distance, but not long distance. The virus transmission rate was as highest as 23.3 ﹪within warm months of spring and summer, and 4.7 ﹪within another half year in cool months of autumn and winter. After the first discovery of the virus in banana germplasm collection farm of Taiwan Banana Research Institute in Chiuju of Pingtung prefecture in 1994, BSV infection was found in a few Pechiao Cavendish plants with streak mosaic symptoms resembling to mosaic caused by CMV (cucumber mosaic virus), grown in farmer’s orchards nearby the collection farm. In order to trace further spreading of the virus, BSV / PCR detection was made on samples of mosaic-diseased banana leaves collected in June 2002 from Pingtung banana-growing areas, and are showed negative. Only CMV was detected in the all samples with mosaic symptoms. Accordingly, it appeared to be no transmission and further spreading of BSV in the fields for a period up to years. About 51.9 ﹪(69 in 133 cultivars) of banana cultivars in germplasm depository of Chiayi Substation, TARI, were confirmed to be positive in BSV / PCR detection. The three symptom-expression types were differentiated including (1) BS-symptom expressing type on 9 ﹪banana cultivars (AA, AAA and AAB), (2) chlorotic type on 23.3 ﹪cultivars (ABB, AAB and AAA), and (3) symptomless type on 19.5 ﹪cultivars (in all genotype bananas). The studies on the pathological natures of the three strains of different symptom-types revealed that the BSV-symptom expression type strain showed vector transmissibility, positive virion detection by ISEM, and ELISA detection, while negative results of the above-mentioned natures were found on BSV-materials of the cultivars showing symptom expression of chlorotic and symptomless type. Such two strains of A and B types were isolated from BS-symptom expressing cultivars i. e. A strain isolated from BS-diseased Mysore (AAB) and Java (AAB) cultivars, caused typical BS-symptoms including typical chlorotic streaks and fine spindle-shaped spots, and B strain isolated from Java only, induced yellowish thick streaks with necrosis. The phylogenic identities among the present virus strains were investigated through the sequence homology by sequencing the DNA products (208 bp) of PCR amplification with the templates in DNA extracts from banana cultivars showing the three symptom expression types. The all DNA extract of banana plants A-type symptoms and vector fed on these plants, exhibited the same nucleotide sequence of 100 ﹪homology. The fact different sequence homology (98.1 ﹪) was found between strains A type and B type, revealed the both types were distinct strains. Different homologies were also examined among the sequences of PCR-products derived from the other strains of the chlorotic and symptomless types. Temperature, banana cultivars and different BSV strains affected symptom expression and virus replication. BSV-1A produced severe symptoms on Cavendish plants in any seasons, with the highest replication of virus at 28 ℃, follow by at 20 ℃ and lowest replication at 30 ℃. The virus strains in banana cultivars showing chlorotic and symptomless expressions, replicated lesser in warm months than in cool months. Such cultivars as Latundan (AAB), Awak (ABB) and Saba (ABB) showed cross-protection of mild strains against challenge inoculation with BSV-1A the most virulent strain. Heat-therapy of potted plants at 40 ℃ for 3 months followed by heat therapy of meristem culture at 40 ℃ for one month was found to be effective to eliminate BSV in Java(active strain) and Latundan (non-active strain) plants.