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Corynespora cassiicola Causes Dieback on Basil
Symptoms of basil dieback disease caused by <em>Corynespora cassiicola</em> and its colony, conidia morphology. (A) symptom in the fi eld, (B) conidia and conidiophore of <em>C. cassiicola</em> on basil diseased shoot section, (C) colony of <em>C. cassiicola</em> grown on potato dextrose agar (PDA) at 25℃ for 14 d, (D) conidia developed in chain, (E) basil shoot symptom caused by <em>C. cassiicola</em> in pathogenicity tests, and (F) basil leaf symptom caused by <em>C. cassiicola</em> in pathogenicity tests. Bar = 50 μm.
Symptoms of basil dieback disease caused by Corynespora cassiicola and its colony, conidia morphology. (A) symptom in the fi eld, (B) conidia and conidiophore of C. cassiicola on basil diseased shoot section, (C) colony of C. cassiicola grown on potato dextrose agar (PDA) at 25℃ for 14 d, (D) conidia developed in chain, (E) basil shoot symptom caused by C. cassiicola in pathogenicity tests, and (F) basil leaf symptom caused by C. cassiicola in pathogenicity tests. Bar = 50 μm.

Author:Jia-Rong Tang*, Shu-Fen Tsai, Szu-Yu Chen, and I-Sheng Feng

Abstract:

    Basil (Ocimum basilicum L.) is a perennial herb belonging to the family lamiaceae, and is commonly cultivated as a condiment or spice in Taiwan. A symptom of dieback appeared on basil planted in the field and greenhouse at Wandan Township, Pingtung Country, and Luzhu Township, Kaohsiung City, Taiwan, during September 2019 to March 2020. The dark brown lesion initiated from the cutting ends made by the regular harvest, then extended progressively, and eventually resulted in the dieback of the branches and defoliation. Conidiophores and conidia characteristics of Corynespora cassiicola were observed from diseased tissues. Margin of lesion was excised and sterilized. Hyphae, once emerged from the plant tissue, were transferred from water agar, subcultured on potato dextrose agar (PDA) plates, and incubated at room temperature. The colonies on PDA were white to pale gray in color and dark olive green in the center area. After 25 days incubation, conidia characteristics of C. cassiicola were observed at middle of the colony. Genomic DNA was extracted from pure cultures. The internal transcribed spacer (ITS) DNA fragment was amplified by PCR with primer pairs: CoryITS-f1 and CoryITS-r1, and sequenced. ITS sequence was blasted with GenBank on National Center for Biotechnology Information (NCBI). Blast analysis showed that CC-2 and CC-3 had 100% identity to C. cassiicola. Necrosis or dieback appeared at seventh day on some inoculated basils, with disease severity being 75% at 25℃, while 16.67% at 20℃ and 30℃. C. cassiicola was reisolated from the lesions, thus fulfilling Koch’s postulate. The results suggested that the optimal condition for C. cassiicola to cause dieback of basil was at 25℃ in high humidity. Fungicides, which recommended on control of leaf spot caused by Alternaria alternata were tested and revealed that iprodione effectively inhibited mycelial growth of C. cassiicola.

Key words:Basil, Dieback, Corynespora cassiicola

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Journal of
Taiwan Agricultural Research
Vol. 72, No.3 (2023) ISSN: 2790-086X Vol. 72, No.3 (2023)
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