萊豆（Phaseolus limensis）種子傳染菜豆普通嵌紋病毒（BCMV）與胡瓜嵌紋病毒（CMV）的特性

Lima bean (Phaseolus limensis) seedlings with symptoms of wrinkled and mosaic pattern on leaves were found on about 96% of tested grown-out seeds obtained from growers and market shops of various locations. The currently prevalent viruses of lima bean found in Taiwan are Bean common mosaic virus (BCMV) and Cucumber mosaic virus (CMV). The virus indexing methods of bioassay, enzyme-linked antibody immunoassay (ELISA), immuno-dot blotting, and reverse transcription-polymerase chain reaction (RT-PCR) were applied to compare their sensitivity on detecting BCMV and CMV from infected tissues and seeds of lima bean. We have found that BCMV could be effectively detected by all four aforementioned methods from crude sap preparations of infected lima bean leaves at a dilution end-point (DEP) of 10^(-3) while CMV could be detected at the DEP of 10^(-4) by biological, ELISA and immuno-dot blotting analyses and DEP of 10^(-6) by RT-PCR. Direct tissue blotting (DTB) was applied to detect the virus distribution in the diseased seed pod. Both BCMV and CMV could be detected at pod, funicle, and testa, but not at cotyledon. ELISA tests have confirmed the viruses distributed in internal tissues of the seed pods as the same as the results obtained by DTB. No symptoms and viruses have been observed on and detected in all tested seeds harvested from BCMV- or CMV- inoculated lima bean plants in growing-on tests. After a storage duration of one year, both BCMV and CMV were undetectable in the seeds of inoculated lima bean plants (1015 seeds in total) by ELISA. The ratios of seed-borne viruses in lima bean seeds were examined by ELISA. The results showed that there were 12.5% and 41.3% of grower’s seeds were infected by BCMV and CMV, respectively, while 3.8% and 4.8% of commercialized seeds were infected by BCMV and CMV, respectively. The incidences of seed-borne BCMV and CMV were both determined as 0.19% in a total of 540 seedlings derived from commercial seeds and indexed by grow-on tests. Accordingly, during the infection of BCMV or CMV to lima bean plants, viruses accumulate in the tissues of pod first, then invade seeds through the funicle. After maturation and dehydration of seeds, the BCMV and CMV exist only in the testa and their survival rates reduce as the storage duration extend. This, therefore, can be a possible explanation for the ratio of seed-transmission is lower than that of seed-borne of BCMV or CMV.