台灣產芒果與草莓炭疽病菌對Strobilurin (QoI) 類及 Benzimidazole 類殺菌劑之抗感性

Abstract

Anthracnose caused by Colletotrichum spp., including mango and strawberry, is an important crops disease throughout the world. Anthracnose is one of factor to reduce economic worth and time of post-harvest of fruits. A total of 105 Colletotrichum isolates obtained from infected fruits and leaves of strawberry and mango in main production area. Based on morphological and molecular characteristics, three C. acutatum and 102 C. gloeosporioides isolates were identified. For compaSnng sensitivities to strobilurins (QoIs), all C. gloeosporioides isolates were examined sensitivities to four QoIs, kresoxim- methyl, azoxystrobin, trifloxystrobin and pyraclostrobin at 1, 10, 100 and 500 ppm (a.i.) by mycelial growth. Pyraclostrobin was highly efficacy to inhibit mycelial growth of all C. gloeosporioides isolates at 10 ppm (a.i.). Contrary to pyraclostrobin, kresoxim- methyl, azoxystrobin and trifloxystrobin only showed 45.0%, 44.6% and 46.1% mycelial growth inhibition rate at 500 ppm (a.i.), respectively. Previous studies indicated that the mutation at codon 143 in cytochrome b gene (cyt b) is the principal action of QoIs-resistant fungal pathogen. However, the QoIs-resistant isolates of C. gloeosporioides obtained from mango and strawberry did not be found the mutation at codon 143 of cyt b. The result indicated that the mutation at codon 143 of cyt b is not available character to increase the resistance of C. gloeosporioides isolates from mango and strawberry to QoIs in Taiwan. Moreover, the azoxystrobin did not raise the inhibiting efficacy of C. gloeosporioides isolates at salicylhydroxamic acid (SHAM) added PDA medium. Thus, alternative pathway respiration did not play an important role for C. gloeosporioides isolates enhanced resistance to QoIs. Interestingly, the nucleotide deletion of cyt b between codon 144 and 145 was detected among C. gloeosporioides isolates from mango, strawberry, orange, yam and sweet potato. The result suggests that the nucleotide deletion may change the protein structure of cyt b and enhance the resistance of C. gloeosporioides isolates to QoIs in Taiwan. In this study, thirty C. gloeosporioides isolates obtained from mango and strawberry were tested the sensitivities to benzimidazole fungicides, benomyl, thiabendazole and carbendazim. Results showed that mycelial growth of 18 C. gloeosporioides isolates were significantly inhibited at 1 ppm (a.i.) and 12 C. gloeosporioides isolates were resistant to those three benzimidazoles. Thus, the benzimidazoles-sensitive and -resistant C. gloeosporioides isolates were simultaneously existed in the field at Taiwan. Moreover, the positive cross-resistance among benzimidazoles on C. gloeosporioides isolates was existence, and the negative cross-resistance between benzimidazoles and QoIs were detected on some C. gloeosporioides isolates. For the benzimidazoles-resistant mechanism analysis, the resistant C. gloeosporioides isolates showed point mutation at codon 198 in β-tubulin gene and the amino acid was substituted glycine (Gly) to alanine (Ala). While, the codon 200, caused the moderately resistant to benzimidazoles, did not be detected among all C. gloeosporioides isolates. The results suggest that the mutation at codon 198 in β-tubulin gene is major mechanism of benzimidazoles-resistant C. gloeosporioides isolates in Taiwan. Consequently, the specific primers of TubGF1 and TubGR were designed to amplify partial β-tubulin gene, including codon 198, and used PCR-RFLP method to detect the benzimidazoles -resistant C. gloeosporioides isolates in field. According to the result, this method could be rapidly and precisely to diagnose benzimidazoles-resistant C. gloeosporioides isolates obtained from mango and strawberry in Taiwan.