Objective To identify the pathogens of the severe defoliation and dieback diseases on Jianyang tangelos.
Method Leaf specimens were collected from the diseased tangelo plants in Jianyang city. Microbial strains were isolated for morphological observation, pathogenicity determination, and sequence analysis on internal transcribed spacer (ITS) of ribosomal DNA for taxonomic identification.
Result Separately, two strains were considered the pathogens for the diseases. The FJAT-32214 strain formed grayish brown colonies on a PSA medium and produced brown septate spores. Its rDNA-ITS sequences showed a 99% similarity with that of Alternaria alternata from NCBI. The other strain, FJAT-32151, formed on PSA gray-white, velvety, dense colonies with brick-red spore piles on the surface in late stage and produced columnar or rod-like, unicellular, colorless spores. The rDNA-ITS sequence of FJAT-32151 was 99% homologous with that of Colletotrichum gloeosporioides. Each of these isolated strains met Koch requirement with a challenge test by inoculation on healthy plants to show the typical morphological characteristics of the respective fungal disease.
Conclusion It was confirmed that A. alternata was the pathogen that caused the brown spots disease, and C. gloeosporioides the anthracnose disease on the tangelos.
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