| Summary: | 博士 === 國立中興大學 === 植物病理學系所 === 103 === Abstract
Sweet potato [Ipomoea batatas L. (Lam)], the dicotyledonous plant of the family Convolvulaceae, is the seventh most important food crop in the world after wheat, rice, maize, potato, barley and cassava. Besides food supply, sweet potato has diverse uses in green source, ornamental, feed, starch and liquor manufacture, human consumption, biofuel and bioplastic production, etc. Many cultivars have been currently developed for different uses through the world. Among these cultivars, vegetable sweet potato (VSP) has been bred for edible leafy vegetable and can produce a lot of leaves, tender shoots and small/non tubers constantly throughout the growth period in whole year period, especially, summer and rainy season. The VSP is considered as an important green source in summer or rainy season in Taiwan, and similar cultivars of VSP have been bred and grew in Japan. A new disease, Bacterial wilt (BW) caused by Ralstonia solanacearum (RS) broke out during 2000’s and reduced 30 to 80% yield of VSP last decade in Taiwan. The R. solanacearum isolates obtained from diseased VSP were identified as Ralstonia solanacearum phylotype I race 1 biovar 4 (R1bv4) based on physical and molecular analyses. Moreover, these isolates also caused wilting in convolvulaceous, solanaceaous and cruciferous plants. Field investigation indicated that R1bv4 was generally distributed in soil of VSP fields with 1.3×102 to 9.5×105 cfu/g soil. Further detection showed R1bv4 could latently infect healthy VSP cuttings with 2 to 98% isolation frequency. The severity of BW was closely related to R1bv4-carried VSP cuttings (R=0.913); however, the severity of BW did not show significant correlation with the R1bv4 density in soil (R=0.086). Similar phenomenon was observed in greenhouse test. Thus, the cuttings carried R1bv4 were more important inocula source than the R1bv4 residing in soil. The distribution of R1bv4 in VSP indicated that the terminal shoots or erect stems had low R1bv4 containation perecentage (<31%) and creeping stem had high R1bv4 containation percentage (45 to 100%) 8 wks after the VSP planted in infested soil (106 cfu/g soil). Results demonstrated that R1bv4 did not consistently move to the part of erect stem cuttings. For confirming the efficacy of the erect stem cutting on control BW of VSP in the fields, the erect stem cuttings were collected from VSP field. The results revealed that the erect stem cuttings used as new plants could decrease the BW in field. Moreover, companied with early R1bv4 detection in erect stems could increase the control efficient of BW in VSP production area. In this study, a bacterial endophyte, Bacillus amyloliquefaciens SPX1 from healthy VSP in Dali, had good ability to inhibit the growth of R1bv4 on TTC medium. The further experiment showed that the SPX1 isolate could decrease the wilting development of VSP in greenhouse and field conditions by soaking treatment. In addition, a resistance line of VSP, VSPSL-1, showed high reistance to bacterial wilt in field. Thus, the VSPSL-1 line is a promising cultivar resistant to R1bv4 in the future.
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