Characterization of Colletotrichum Species Causing Bitter Rot of Apple in Kentucky Orchards

Abstract

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.

Comparison of Anthracnose Resistance with the Presence of Two SCAR Markers Associated with the Rca2 Gene in Strawberry

“…These five isolates were identified initially based on cultural morphology, but sequence analysis of the b-tubulin 2 (TUB2) gene further classified the two C. fragariae isolates as C. theobromicola. Glyceraldehyde-3-phosphate dehydrogenase sequences further classified the C. acutatum isolates as C. nymphaeae, and the C. gloeosporioides isolate as C. fructicola (Miller-Butler et al, 2018;Munir et al, 2016).…”

Evaluation of Detached Strawberry Leaves for Anthracnose Disease Severity Using Image Analysis and Visual Ratings

“…Two isolates of C. fragariae (= C. theobromicola), Cf63 and Cf75, and one isolate of C. gloeosporioides (= C. fructicola), Cg162, were used as inoculum (Chang and Smith, 2007;Miller-Butler et al, 2018;Munir et al, 2016;Smith and Black, 1990). Each isolate was initiated from silica gel cultures and grown in petri dishes on oatmeal agar:potato dextrose agar (1:1) (Miller-Butler et al, 2018) under fluorescent lights with a 12-h photoperiod at a temperature of 20 to 28°C.…”

Interplay of apple volatile organic compounds with Neofabraea vagabunda and other post‐harvest pathogens

“…Besides BER, grey mould, caused by Botrytis cinerea , and blue mould, caused by Penicillium expansum , are also common diseases in all countries producing apples (Errampalli, ; Romanazzi & Feliciani, ), while bitter rot, caused by species belonging to the Colletotrichum acutatum complex (i.e. C. fioriniae ), has been recently reported in many growing areas and could become an emerging problem (Mari et al , ; Munir et al , ).…”