Munir M, Amsden B, Dixon E, Vaillancourt L, Gauthier N A Ward
Department of Plant Pathology, University of Kentucky, Lexington 40546-0312.
Plant Dis. 2016 Nov;100(11):2194-2203. doi: 10.1094/PDIS-10-15-1144-RE. Epub 2016 Aug 30.
Multiple species of Colletotrichum can cause bitter rot disease of apple, but the identities and relative representation of the species causing the disease in Kentucky are unknown. In total, 475 Colletotrichum isolates were collected from diseased apple fruit in 25 counties and characterized both morphologically and by using various molecular approaches. Multigene sequence analyses revealed that sample isolates belonged to several newly erected species within the Colletotrichum acutatum and C. gloeosporioides species complexes. The isolates were identified as C. fioriniae and C. nymphaeae, which reside within the C. acutatum species complex, and C. siamense, C. theobromicola, and C. fructicola, which are placed within the C. gloeosporioides species complex. C. fioriniae was the most common species causing bitter rot in Kentucky, comprising more than 70% of the isolates. Infectivity tests on detached fruit showed that C. gloeosporioides species-complex isolates were more aggressive than isolates in the C. acutatum species complex. However, isolates within the C. acutatum species complex produced more spores on lesions compared with isolates within the C. gloeosporioides species complex. Aggressiveness varied among individual species within a species complex. C. siamense was the most aggressive species identified in this study. Within the C. acutatum species complex, C. fioriniae was more aggressive than C. nymphaeae, causing larger, deeper lesions. Apple cultivar did not have a significant effect on lesion development. However, Colletotrichum spp. produced more spores on 'Red Stayman Winesap' than on 'Golden Delicious'. Fungicide sensitivity tests revealed that the C. acutatum species complex was more tolerant to thiophanate-methyl, myclobutanil, trifloxystrobin, and captan compared with the C. gloeosporioides species complex. The study also revealed that mycelial growth of C. siamense was more sensitive to tested fungicides compared with C. fructicola and C. theobromicola. These research findings emphasize the importance of accurate identification of Colletotrichum spp. within each species complex, because they exhibit differences in pathogenicity and fungicide sensitivity.
多种炭疽菌可引发苹果苦腐病，但在肯塔基州导致该病的菌种及其相对占比尚不清楚。总共从25个县的患病苹果果实中采集了475株炭疽菌分离株，并对其进行了形态学和多种分子方法的鉴定。多基因序列分析表明，样本分离株属于炭疽菌和胶孢炭疽菌复合种内几个新建立的物种。这些分离株被鉴定为炭疽菌复合种内的佛罗里达炭疽菌和睡莲炭疽菌，以及胶孢炭疽菌复合种内的暹罗炭疽菌、可可炭疽菌和果生炭疽菌。佛罗里达炭疽菌是肯塔基州引起苦腐病最常见的菌种，占分离株的70%以上。对离体果实的侵染性试验表明，胶孢炭疽菌复合种的分离株比炭疽菌复合种的分离株更具侵染性。然而，与胶孢炭疽菌复合种的分离株相比，炭疽菌复合种的分离株在病斑上产生的孢子更多。种复合体内不同物种的侵染性各不相同。暹罗炭疽菌是本研究中鉴定出的最具侵染性的物种。在炭疽菌复合种内，佛罗里达炭疽菌比睡莲炭疽菌更具侵染性，导致的病斑更大、更深。苹果品种对病斑发展没有显著影响。然而，炭疽菌在“红斯蒂曼·温莎普”苹果上产生的孢子比在“金冠”苹果上更多。杀菌剂敏感性试验表明，与胶孢炭疽菌复合种相比，炭疽菌复合种对甲基托布津、腈菌唑、肟菌酯和克菌丹更具耐受性。该研究还表明，与可可炭疽菌和果生炭疽菌相比，暹罗炭疽菌的菌丝生长对测试杀菌剂更敏感。这些研究结果强调了准确鉴定每个种复合体内炭疽菌物种的重要性，因为它们在致病性和杀菌剂敏感性方面存在差异。
