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Genetic Diversity and Fungicide Sensitivity of Colletotrichum spp. Isolated from Guava Fields in Southern Taiwan
(A) Symptoms of anthracnose caused by <i>Colletotrichum</i> sp. with irregular brown spots and dark brown sunken lesion at the center of cv. ‘Shui-jing Ba’ (red arrowed). Sometimes there are small brown sunken spots with red haloes on pericarp. (yellow arrowed). (B) Rounded to irregular lesion (red circle) of anthracnose on the fruit of cv. ‘Hong Zuan’. (C) Symptomless leaves of cv. ‘Zhen-chu Ba’. (D) Colonies of <i>Colletotrichum</i> sp. (red arrowed) isolated from symptomless leaves after strict disinfection.
(A) Symptoms of anthracnose caused by Colletotrichum sp. with irregular brown spots and dark brown sunken lesion at the center of cv. ‘Shui-jing Ba’ (red arrowed). Sometimes there are small brown sunken spots with red haloes on pericarp. (yellow arrowed). (B) Rounded to irregular lesion (red circle) of anthracnose on the fruit of cv. ‘Hong Zuan’. (C) Symptomless leaves of cv. ‘Zhen-chu Ba’. (D) Colonies of Colletotrichum sp. (red arrowed) isolated from symptomless leaves after strict disinfection.

Author:Shuen-Huang Tsai*, Kuan-Wen Chen, and Chien-Jui Huang

Abstract:

    Guava anthracnose is one of the important diseases of guava fruit from harvest to post-harvest. The aim of this study is to understand the main species of Colletotrichum that currently occur in guava orchards, and to investigate the sensitivity of these Colletotrichum spp. to the approved fungicides registered for anthracnose management. From 2019 to 2020, symptomless leaves and diseased fruits of guava anthracnose were collected from the main production areas in southern Taiwan. Fifteen isolates were obtained and inoculated on ‘Zhen-chu Ba’, respectively. The results showed that wounds are needed for most isolates to cause fruit rot symptoms, and the isolates obtained from diseased fruit is generally more virulent than the isolates obtained from symptomless leaves. To identify the species of collected Colletotrichum isolates, five genes including internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), β-tubulin 2 (TUB2), chitin synthase 1 (CHS-1) and calmodulin (CAL) were sequenced and a phylogenetic tree was constructed. The constructed phylogenetic tree indicated that guava anthracnose in Taiwan includes at least three species, namely, Colletotrichum siamense, Colletotrichum fructicola and Colletotrichum tropicale. The fungicide tests show that C. siamense and C. fructicola are generally insensitive to benzimidazoles and strobilurins, while C. tropicale is sensitive to benzimidazoles but it is not sensitive to strobilurins. Comparing with the other two Colletotrichum spp., C. tropicale has a different sensitivity to benzimidazoles. In addition, at concentration of 100 mg active ingredient per liter, iminoctadine and mancozeb can completely inhibit the mycelial growth of the three Colletotrichum spp. thiabendazole + oxine copper and dithianon can significantly inhibit the germination of the spores among three Colletotrichum spp. The above results can provide farmers a reference for integrated pest management of anthracnose in the field.

Key words:Guava (Psidium guajava L.), Colletotrichum spp., Phylogenetic analyses, Fungicides sensitivity test

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Journal of
Taiwan Agricultural Research
Vol. 73, No.1 (2024) ISSN: 2790-086X Vol. 73, No.1 (2024)
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