臺灣香蕉黃葉病菌遺傳多樣性及病原性分析

Abstract

Fusarium oxysporum f. sp. cubense (Foc) causes Panama disease (Fusarium wilt), which is one of the major disastrous diseases of banana and plantain. Among four races, Foc race 4 (Foc R4) strains cause diseases on Musa AAA Cavendish and the hosts attacked by race 1 (R1) and race 2 (R2). Since late 1960s with the emergence of Foc R4, Taiwan has been facing steep decline of banana production and its export. Although different control measures have been developed and practiced, none of them showed significant or effective results. Currently, development of resistant cultivars has been thought to be a promising way for disease management. However, deployments of resistant cultivars require thorough understandings of population structure and pathogenic variation of pathogens in the fields. In my studies, we aim to first characterize histological features of banana somaclone variants selected with different level of resistance, i.e. Tai-Chiao No. 5 and GCTCV-119, against Foc R4 infection. We also aim to characterize Foc population by genetic markers and determine their pathogenic variation in Taiwan. In order to monitor infection processes in different cultivars, eGFP transformed Foc R4 wild type strain was generated and showed same aggressiveness toward susceptible Pei-Chiao cultivar with the original wild type. While further infected moderately resistant or highly resistant cultivars with eGFP strain, in contrast to brown water-soaked discolored roots with heavily colonized hyphae in Pei-Chiao, GCTCV-119 and Tai-Chiao No. 5 showed less infection or colonization that distinguished them as good somaclone or derived cultivar against Panama disease for commercial purpose. For genetic population study of Foc, 162 field strains were isolated from six banana cultivars in main banana producing regions of Taiwan as well as 16 Foc (12 R1 and 4 R4) strains provided from Taiwan Banana Research Institute (TBRI). Among 162 collected isolates, all of them were diagnosed as Foc tropical R4 (TR4) by molecular technique except 15TDLY1X1 isolated from Taitung. Furthermore, 13 SSR markers were designed and screened 4 Foc isolates. Out of 13 SSR markers, 5 markers showing polymorphic results were further selected for population studies. The results showed that out of 178 Foc isolates, 122 field isolates in Taiwan were relatively less polymorphic among the Foc tropical R4. Principle of coordinate analyses (PCoA) defined genetic distance of 28 haplotypes in which H1 was major population, consisting of 32.78% of total population, and present in all collected fields except Nantou and Yunlin. H1 was abundantly found in the main banana production regions such as Pingtung County and Kaohsiung City. Interestingly, Nantou and Pingtung contained more diverse haplotypes composition than Kaohsuing area. Isolates selected from different haplotypes were further subjected to pathogenicity assay. H1, H4, H6, H11 and H15 isolates showed high virulence whereas H3, H7 ad H10 isolates showed moderate virulence when inoculating on three different cultivars or somaclone. In contrast, Foc R1 wild type and 15TDLY1X1 did not cause infection on these materials. In conclusion, our studies provide resistant feature of somaclone or cultivar selected from original somaclone developed by Taiwan Banana Research Institute and also reveal useful information of current Foc population in Taiwan. Keywords: Fusarium oxysporum f. sp. cubense, banana cultivar, somaclone, genetic diversity, pathogenicity, haplotypes, SSR markers