Meng-Ying Lin, Cheng-Lin Wu, Yung-Yeh Su, Chien-Jui Huang, Wei-Lun Chang, and Bor-Shyang Sheu. Gut and Liver 2023;17:318-27. https://doi.org/10.5009/gnl220030

Papaya (Carica papaya), a tropical fruit, is an economically important crop in Taiwan that is mainly cultivated in southern Taiwan. Anthracnose fruit rot caused by Colletotrichum spp. is the main postharvest problem of papaya in many countries, including Taiwan. However, not much is known about this disease in Taiwan. Papaya fruits cv. Tainung No. 2 with anthracnose symptoms of dark brown sunken necrotic lesions were collected from local markets in Dounan, Yunlin County, Taiwan in 2017. To isolate the pathogen, diseased fruits were surface-sterilized with 1% NaOCl for 1 min, rinsed in sterile water, and air dried. Surface-sterilized pieces of fruit were placed on water agar and incubated at 25°C. While fungi grew out of the tissues, fungal hyphal tips were transferred on potato dextrose agar (PDA) plates and incubated at 25°C. A fungus was isolated from symptomatic fruit, and three representative isolates, PC1, PC2 and PC3, were obtained. The isolates formed grey to greyish black colonies with white aeria...

Distribution of copper resistance gene variants of Xanthomonas citri subsp. citri and Xanthomonas euvesicatoria pv. perforans | Yi-Ru Lai, Chih-Hung Lin, Chun-Pi Chang, Hui-Fang Ni, Wen-Shi Tsai, Chien-Jui Huang | Agricultural Journals

Feasible Management of Southern Corn Leaf Blight via Induction of Systemic Resistance by Bacillus cereus C1L in Combination with Reduced Use of Dithiocarbamate Fungicides Bacillus cereus;Cochliobolus heterostrophus;dithiocarbamate;induced systemic resistance; Dithiocarbamate fungicides such as maneb and mancozeb are widely used nonsystemic protectant fungicides to control various plant fungal diseases. Dithiocarbamate fungicides should be frequently applied to achieve optimal efficacy of disease control and avoid either decline in effectiveness or wash-off from leaf surface. Dithiocarbamates are of low resistance risk but have the potential to cause human neurological diseases. The objective of this study was to develop a strategy to effectively control plant disease with reduced use of dithiocarbamtes. Southern corn leaf blight was the model pathosystem for the investigation. When corn plants were drench-treated with Bacillus cereus C1L, a rhizobacterium able to induce systemic resistance in corn plants against southern leaf blight, frequency of spraying dithiocarbamate fungicides could be decreased. The treatment of B. cereus C1L was able to protect maize from southern leaf blight while residues of dithiocarbamates on leaf surface were too low to provide sufficient protection. On the other hand, frequent sprays of mancozeb slightly but significantly reduced growth of corn plants under natural conditions. In contrast, application of B. cereus C1L can significantly promote growth of corn plants whether sprayed with mancozeb or not. Our results provide the information that plant disease can be well controlled by rhizobacteria-mediated induced systemic resistance in combination with reduced but appropriate application of dithiocarbamate fungicides just before a heavy infection period. An appropriate use of rhizobacteria can enhance plant growth and help plants overcome negative effects caused by dithiocarbamates.

Background: Worldwide citrus production is severely threatened by Asiatic citrus canker which is caused by the proteobacterium Xanthomonas citri subsp. citri. Foliar sprays of copper-based bactericides are frequently used to control plant bacterial diseases. Despite the sequencing of many X. citri strains, the genome diversity and distribution of genes responsible for metal resistance in X. citri subsp. citri strains from orchards with different management practices in Taiwan are not well understood.Results: The genomes of three X. citri subsp. citri strains including one copper-resistant strain collected from farms with different management regimes in Taiwan were sequenced by Illumina and Nanopore sequencing and assembled into complete circular chromosomes and plasmids. CRISPR spoligotyping and phylogenomic analysis indicated that the three strains were located in the same phylogenetic lineages and shared ∼3,000 core-genes with published X. citri subsp. citri strains. These strains differed mainly in the CRISPR repeats and pathogenicity-related plasmid-borne transcription activator-like effector (TALE)-encoding pthA genes. The copper-resistant strain has a unique, large copper resistance plasmid due to an unusual ∼40 kbp inverted repeat. Each repeat contains a complete set of the gene cluster responsible for copper and heavy metal resistance. Conversely, the copper sensitive strains carry no metal resistance genes in the plasmid. Through comparative analysis, the origin and evolution of the metal resistance clusters was resolved.Conclusion: Chromosomes remained constant among three strains collected in Taiwan, but plasmids likely played an important role in maintaining pathogenicity and developing bacterial fitness in the field. The evolution of pathogenicity factors and horizontal gene transfer events were observed in the three strains. These data suggest that agricultural management practices could be a potential trigger for the evolution of citrus canker pathogens. The decrease in the number of CRISPR repeats and pthA genes might be the result of adaptation to a less stressful environment. The metal resistance genes in the copper resistant X. citri strain likely originated from the Mauritian strain not the local copper-resistant X. euvesicatoria strain. This study highlights the importance of plasmids as ‘vehicles’ for exchanging genetic elements between plant pathogenic bacteria and contributing to bacterial adaptation to the environment.