Fusarium oxysporum f. sp. cubense is the causal agent of Panama disease of banana. A rapid and reliable diagnosis is the foundation of integrated disease management practices in commodity crops. For this diagnostic purpose, we have developed a reliable molecular method to detect Foc race 4 isolates in Taiwan. By PCR amplification, the primer set Foc-1/Foc-2 derived from the sequence of a random primer OP-A02 amplified fragment produced a 242 bp size DNA fragment which was specific to Foc race 4. With the optimized PCR parameters, the molecular method was sensitive and could detect small quantities of Foc DNA as low as 10 pg in 50 to 2,000 ng host genomic DNA with high efficiency. We also demonstrated that by using our PCR assay with Foc-1/Foc-2 primer set, Foc race 4 could be easily distinguished from other Foc races 1 and 2, and separated other formae speciales of F. oxysporum.
Fusarium oxysporum formae specialis cubense (Foc) is a soil-borne fungus that causes Fusarium wilt, which is considered to be the most destructive disease of bananas. The fungus is believed to have evolved with its host in the Indo-Malayan region, and from there it was spread to other banana-growing areas with infected planting material. The diversity and distribution of Foc in Asia was investigated. A total of 594 F. oxysporum isolates collected in ten Asian countries were identified by vegetative compatibility groups (VCGs) analysis. To simplify the identification process, the isolates were first divided into DNA lineages using PCR-RFLP analysis. Six lineages and 14 VCGs, representing three Foc races, were identified in this study. The VCG complex 0124/5 was most common in the Indian subcontinent, Vietnam and Cambodia; whereas the VCG complex 01213/16 dominated in the rest of Asia. Sixty-nine F. oxysporum isolates in this study did not match any of the known VCG tester strains. In this study, Foc VCG diversity in Bangladesh, Cambodia and Sri Lanka was determined for the first time and VCGs 01221 and 01222 were first reported from Cambodia and Vietnam. New associations of Foc VCGs and banana cultivars were recorded in all the countries where the fungus was collected. Information obtained in this study could help Asian countries to develop and implement regulatory measures to prevent the incursion of Foc into areas where it does not yet occur. It could also facilitate the deployment of disease resistant banana varieties in infested areas.
Unraveling the genetic diversity held in genebanks on a large scale is underway, due to advances in Next-generation sequence (NGS) based technologies that produce high-density genetic markers for a large number of samples at low cost. Genebank users should be in a position to identify and select germplasm from the global genepool based on a combination of passport, genotypic and phenotypic data. To facilitate this, a new generation of information systems is being designed to efficiently handle data and link it with other external resources such as genome or breeding databases. The Musa Germplasm Information System (MGIS), the database for global ex situ-held banana genetic resources, has been developed to address those needs in a user-friendly way. In developing MGIS, we selected a generic database schema (Chado), the robust content management system Drupal for the user interface, and Tripal, a set of Drupal modules which links the Chado schema to Drupal. MGIS allows germplasm collection examination, accession browsing, advanced search functions, and germplasm orders. Additionally, we developed unique graphical interfaces to compare accessions and to explore them based on their taxonomic information. Accession-based data has been enriched with publications, genotyping studies and associated genotyping datasets reporting on germplasm use. Finally, an interoperability layer has been implemented to facilitate the link with complementary databases like the Banana Genome Hub and the MusaBase breeding database. Database URL: https://www.crop-diversity.org/mgis/
Cavendish banana cv. Formosana is a high yielding commercial cultivar resistant to race 4 of Fusarium oxysporum f. sp. cubense. Mass micropropagation of this cultivar has a serious problem of high mortality due to lethal browning of plantlets. The mineral contents in leaves and corms of diseased and healthy plantlets were similar. Amendment of culture medium with anion exchange resins, cation exchange resins, polyvinylpyrrolidone or activated charcoal did not reduce the disease incidence. However, addition of ascorbic acid to the surface of culture medium not only prevented the development of lethal browning but also greatly increased the number of plantlets produced. Even at 0.005% ascorbic acid was able to reduce the disease incidence by more than 60% and caused over 8-fold increase in number of plantlets produced. When cultures raised from 12 different Formosana corms were tested, ascorbic acid was able to reduce disease incidence by an average of 83%, and increase the number of plantlets in each test. When diseased plantlets were transferred to culture medium with ascorbic acid, all of them recovered, and resumed normal growth and multiplication, while all control plantlets on culture medium without ascorbic acid died after one month
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