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 … Show more
“…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).…”
Strawberry anthracnose diseases are caused primarily by three Colletotrichum species: C. acutatum J.H. Simmonds, C. fragariae A.N. Brooks, and C. gloeosporioides (Penz.) Penz. & Sacc. Molecular markers are being used in breeding programs to identify alleles linked to disease resistance and other positive agronomic traits. In our study, strawberry cultivars and breeding germplasm with known anthracnose susceptibility or resistance to the three anthracnose-causing Colletotrichum species were screened for two sequence characterized amplified region (SCAR) markers linked to the Rca2 gene. The Rca2 resistant allele SCAR markers were associated with varying degrees of significance for a strawberry plant’s anthracnose resistance to C. fragariae but not to C. acutatum or C. gloeosporioides. Although the presence or absence of the markers associated with the Rca2 resistance gene is an imperfect indicator of anthracnose resistance, it may serve as a useful starting point in selecting germplasm for breeding programs.
“…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).…”
Strawberry anthracnose diseases are caused primarily by three Colletotrichum species: C. acutatum J.H. Simmonds, C. fragariae A.N. Brooks, and C. gloeosporioides (Penz.) Penz. & Sacc. Molecular markers are being used in breeding programs to identify alleles linked to disease resistance and other positive agronomic traits. In our study, strawberry cultivars and breeding germplasm with known anthracnose susceptibility or resistance to the three anthracnose-causing Colletotrichum species were screened for two sequence characterized amplified region (SCAR) markers linked to the Rca2 gene. The Rca2 resistant allele SCAR markers were associated with varying degrees of significance for a strawberry plant’s anthracnose resistance to C. fragariae but not to C. acutatum or C. gloeosporioides. Although the presence or absence of the markers associated with the Rca2 resistance gene is an imperfect indicator of anthracnose resistance, it may serve as a useful starting point in selecting germplasm for breeding programs.
“…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.…”
Inoculation of detached strawberry leaves with Colletotrichum species may provide an accurate, rapid, nondestructive method of identifying anthracnose-resistant germplasm. The purpose of this study was to statistically compare two methods (visual and image analysis) of evaluating disease severity of strawberry germplasm screened for anthracnose resistance. Detached leaves of 77 susceptible and resistant strawberry clones were inoculated with one Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. and two C. fragariae A. N. Brooks isolates. Anthracnose disease symptoms on each leaf were assessed quantitatively via computer-based image analysis to determine percentage lesion area and qualitatively by two independent raters using a visual disease severity rating scale (0 = no symptoms to 5 = entire leaf dead). The two visual raters’ average disease severity ratings (n = 3413) were in substantial agreement with a weighted Cohen’s kappa coefficient (k) of 0.80 [95% confidence interval (CI) 0.79–0.82]. There was a strong positive correlation between percent lesion area determined by image analysis and the visual disease scores of the two raters (rp= 0.79). Image analysis provided a precise measurement of percent lesion area of infected leaves while visual assessment provided more rapid results. Our results indicate that detached leaf inoculations can be used as a rapid preliminary screen to separate anthracnose-susceptible from -resistant germplasm in large populations within breeding programs. It also may be used for assessing the resistance/susceptibility of parental breeding lines to various Colletotrichum species and isolates, for mapping germplasm for resistance genes, and in pesticide development studies.
“…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 , ).…”
Neofabraea vagabunda, causing bull’s eye rot, produces notable loss during cold storage of apples growing in cool humid regions. The infection initiates in the orchard, but the pathogen lives quiescently in fruit for some months before causing the symptoms of the disease. In vivo and in vitro assays were carried out to gain knowledge on the influence of fruit volatile organic compounds (VOCs) in N. vagabunda development and define volatile markers for pathogen detection, using SPME/GC‐MS, PTR‐ToF‐MS analysis and light microscopic observations. This study reports that: (i) the main VOCs of Cripps Pink apple (highly susceptible to bull’s eye rot) are degraded during the conidial germination of N. vagabunda, stimulating pathogen hyphal growth towards the host; (ii) first disease symptoms appear when fruit releases VOCs related to senescence, which also stimulate pathogen hyphal growth; (iii) VOCs typical of ripe‐senescent fruit are also emitted by infected fruit during N. vagabunda quiescence, and methanol and ethanol are the earliest markers of bull’s eye rot; and (iv) the in vitro volatile metabolism of Botrytis cinerea, Penicillium expansum and Colletotrichum fioriniae has similarities with that of N. vagabunda, but the volatile profile of each pathogen is distinguishable. Overall, this study provides novel knowledge on fruit–fungus interaction and insights for the development of tools for early disease detection in packing houses.
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