Browsing by Author "Lennox, Cheryl L."

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    In-vitro effects of garlic extracts on pathogenic fungi Botrytis cinerea, Penicillium expansum and Neofabraea alba
    (Academy of Science of South Africa, 2015) Daniel, Chanel K.; Lennox, Cheryl L.; Vries, Filicity A.
    The antifungal activity of garlic extracts applied directly and through volatile release was tested against the growth of postharvest pathogens Botrytis cinerea, Penicillium expansum and Neofabraea alba. Mycelial growth of B. cinerea and P. expansum was inhibited by aqueous and ethanol dilutions on garlic extract amended media (direct method) in a dose-response manner. The aqueous dilution was more effective than the ethanol dilution. Both dilutions inhibited mycelial growth of N. alba to a similar extent but no trend in data was noted across the concentration range. Calculated EC50 values indicated that 13.36% and 8.09% aqueous dilutions could be used to inhibit growth of B. cinerea and P. expansum, respectively; however, values generated for N. alba either bordered on or exceeded the concentration range. The volatile vapour application of garlic was able to inhibit mycelial growth and spore germination of all pathogens at concentrations as low as 20%. Gas chromatography–mass spectrometry analysis showed that 85.95% of compounds present in the garlic sample belonged to a sulphur or sulphur-derived group. Allicin, the active component of garlic, was not found; however, breakdown products of allicin were present in high amounts. Overall, the antifungal activity of garlic extracts for the control of B. cinerea and P. expansum was confirmed. Further investigations into the antifungal effect of garlic extracts on N. alba is required, although garlic volatiles seem to be effective. This report is the first of antifungal activity of garlic extracts against N. alba – the causal agent of bull’s eye rot, one of the major diseases of apples.
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    Morphological and molecular identification of fungi associated with South African apple core rot
    (Springer, 2018) Basson, Elaine; Meitz-Hopkins, Julia C.; Lennox, Cheryl L.
    Core rot is a major contributor to postharvest losses in apples worldwide. Pathogens most commonly associated with the disease are Alternaria spp. and Penicillium spp. Although both genera show specific morphological characteristics, they can be difficult to identify to species level. In this study, Alternaria spp. (49) and Penicillium spp. isolates (97), associated with pre- and post-harvest apple core rot-symptoms and isolates from potential inoculum sources were identified using molecular methods. Initially, dry core rot causing Alternaria spp. were identified morphologically in an average of 70% of infected fruit pre-harvest and 32% postharvest. Furthermore, 78% of mouldy core rot causing pathogens were identified as Alternaria spp. preharvest and 40% postharvest. Wet core rot was associated with Penicillium spp. in 64% of cases preharvest and 36% postharvest. Species identity of a selection of samples was confirmed using the endopolygalacturonase (endo-PG) gene, the ITS region, and the anonymous genomic regions (OPA1–3, 2–1), which resulted in the identification of A. alternata, A. arborescens, A. dumosa, A. eureka and A. tenuissima. Penicillium species were identified through ITS sequencing and partial beta-tubulin polymerase chain reaction – random fragment length polymorphisms (PCR-RFLP) for the samples collected from wet core rot symptoms. Phylogenetic analyses separated the Alternaria spp. into five clades, including three separate clades for A. alternata, A. tenuissima and A. arborescens, respectively. This is the first report of A. eureka and P. polonicum as potential core rot pathogens. Phylogenetic analysis identified Penicillium ramulosum and P. expansum as the most commonly occurring species associated with WCR symptoms.