Identification Of Pathogen Causing Leaf Spot Disease On Ginger And Research On Mechanism Of Thiabendazole Fungicide Resistance

A novel disease infecting ginger (Zingiber officinale Rosc.) in Laiwu City, Shandong Province was observed and becoming more and more economically important. The pathogen causing leaf spot disease on Zingiber officinale Rosc. was isolated from diseased leaf in Shandong province. The morphological characteristics, pathogenicity test and the sequence of ribosomal DNA-ITS were studied. The results indicated that the colonies on PDA culture medium were white and later turned brown. Mycelium was achromatous or brown, branched and septate. Conidiophore was achromatous oval cell and there was one fat sphere apiece in each end. Conidiogenous cell was enteroblastic-phialidic (eb-ph). The sequence of ribosomal DNA-ITS showed homogeneity of tested pathogeny with Phoma was up to 95.6%. By analysing morphological character and pathogenicity, the fungus should be Phoma zingiberi(Hori)X. P. Zhu & Y. L. Liu.The biological study on the pathogen revealed that ginger extract was the best medium for mycelial growth. The optimum temperature and pH for mycelial growth were 25℃and 5 respectively; the fungus grew better in PD medium with cellobiose as carbon source and peptone as nitrogen source. For the conidial germination, the optimum temperature was 15~20℃, and the optimum pH was 5~8. Under RH 100%, the percentage of conidial germination was the highest.Carbendazim (MBC) is the main fungicide to prevent and cure leaf spot disease on ginger. 200 Phoma zingiberi strains were isolated from different plot in Laiwu City, two phenotypes were identified when tested for sensitivity to carbendazim: 138 isolates showed phenotype of carbendazim-sensitivity, and other 62 isolates showed phenotype of carbendazim-resistance.β-tubulin genes from 4 strains of carbendazim-resistance and 2 strains of carbendazim -sensitivity were cloned and compared the gene nucleotide sequences. Sequence comparison between carbendazim-sensitivity and resistance isolates revealed a single point mutation leading to change at amino acid position 198 from glutamic to alanine acid. This is the first time to report the mechanism on resistance of Phoma zingiberi to carbendazim. This paper used the molecular technique to detect the carbendazim-resistance isolates, and offered the information about how to use the chemical fungicide with reason.The reports in the world considered the pathogen causing leaf spot disease on ginger was Phyllosticta zingtiberi, this paper remends the status of the pathogen based on morphological characteristics and the sequence of ribosomal DNA-ITS. The study of biological characteristic offered the academic basis to investigate the disciplinarian of the pathogenic prevalence. Also it is the first time to elucidate the mechanism on resistance of Phoma zingiberi to carbendazim, cloned partialβ-tubulin gene sequence, and revealed a single point mutation leading to carbendazim-resistance.