Morphological and molecular identification of fungi associated with South African apple core rot

Abstract

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.

Natural Trichothecene Mycotoxins from a Rotten Moldy Apple Core-Derived Trichothecium roseum: Occurrence, Identification, and Potential Transfer to Commercial Apple Juice

“…Trichothecinol A (2) was found to be the most cytotoxic compound, with its smallest IC 50 value being 33 nM. This suggests that the αhydroxyl substituent at C-3 is a key factor contributing to its higher activity compared to that of trichothecin (4). Previous studies on the mechanisms of trichothecenes toxicity have indicated that highly complex functions might contribute to the cytotoxicity of compounds 1−7, including inhibition effect on protein synthesis, oxidative stress-mediated DNA damage, induction of cell-cycle arrest, and disruption of cell membrane integrity.…”

“…In addition, moldy apple core is classified based on three morphological symptoms: core browning, typical MC, and core rot . Phylogenetic analyses of apple MC have revealed a diverse pathogen composition, with Alternaria, Penicillium, Fusarium, and Trichothecium being the most frequent pathogenic fungi. − These diverse pathogens colonize the apple core, leading to excessive preharvest fruit-drop. These inferior apples with MC often go undetected on the fruit surface, raising food safety concerns due to the mycotoxins produced by pathogens.…”

A Novel Hyperspectral Method to Detect Moldy Core in Apple Fruits

“…The NIR light source spectral range start from 770 nm to 920 nm. Spectral data were collected by an Ocean Optics USB2000 spectrometer (Ocean Insight, Rochester, NY, USA) with a spectral sampling interval ranging from 350 to 1000 nm and a 0.2 nm spectral resolution, and internally based on a Sony ILX511 linear silicon CCD array (11,12). The apparatus was controlled by an industrial PC and data were collected by Ocean View software (Ocean Insight, Rochester, NY, USA) (13).…”

“…The damage by MC is an internal injury, with dry-brown areas developed in the inner part of the fruit. The fruit does not present any external sign of damage, making MC detection with classical non-invasive methods very challenging or practically impossible [11].…”

Morphological and Molecular Identification of Fungi Isolated From Spoilt Apples in OTA Metropolis

“…was found to be a frequent fungus found in stored apples, and Penicillium, Acremonium, Aspergillus, Aureobasidium, Cryptococcus, Sporobolomyces and Alternaria spp. (Robiglio and Lopez 1995;Watanabe 2008;Basson et al 2019).…”