• Korean Journal of Organic Agriculture
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• v.23 no.3
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• pp.497-507
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• 2015

It is necessary to evaluate the resistance to disease among genetic resources for development of disease resistant grapes. This study was conducted to screen the resistance to crown gall in muscadine and Florida hybrid bunch grapes by pathogen inoculation. In order to compare the responses to infection with different pathogen strains, muscadine and Florida hybrid grapes were inoculated with 3 strains of Agrobacterium vitis. Although there were different levels crown gall formation among grape cultivars, there little variation in response to inoculated strains. Among 29 muscadine cultivars tested by inoculation of A. vitis 'C4612', most of them were shown to be susceptible, and 'Gold Isle' and 'Africa Queen' were highly susceptible, and two cultivars, 'Welder' and 'Jumbo' were found to be resistant to crown gall disease. Among Florida hybrid grapes, 'Daytona', 'Stover', and 'Swanee' were susceptible and 'Blanc du Bois' was moderately susceptible to crown gall. Because muscadine grapes have been actively utilized as useful genetic resources for development of new grape varieties by intersub-genus cross, this result from the screening of resistance among muscadine grapes can provide valuable information in breeding programs of grape resistant to crown gall.

• Food Science and Preservation
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• v.22 no.1
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• pp.12-18
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• 2015

The objective of this research was to investigate the antioxidant and antimicrobial activities of muscadine grape extracts. Three different cultivars of muscadine grapes including Higgings, Jumbo, and Noble were selected. The skin/pulp and seed parts of three selected muscadine grape cultivars were used for extraction. The total phenolic contents of muscadine grape extracts were expressed as gallic acid equivalents (GAE). The antioxidant activity of muscadine grape extracts were determined by scavenging activity of diphenylpicrylhydrazyl (DPPH) radical and expressed as effective concentration ($EC_{50}$), which represented the concentration of the extract exhibiting 50% DPPH radical scavenging. The antimicrobial activity against E. coli K12 was determined and expressed as the minimum inhibition concentration (MIC). The seed extracts exhibited greater total phenolic contents than the skin/pulp extracts, ranging from 231.24 to 294.81 mg/mL GAE. The seed extracts exhibited greater antioxidant activities than the skin/pulp extracts ($EC_{50}$ of Higgins seed extract=0.026 mg/mL). However, the skin/pulp extracts exhibited greater antimicrobial activities than the seed extracts, exhibiting the minimum inhibition concentration (MIC) in Higgins skin/pulp extract (MIC=4.0 mg/mL). This research indicated that the seed part and skin/pulp parts of the muscadine grapes possessed antioxidant activity and antimicrobial activity, respectively. Therefore, it was concluded that muscadine grapes possess the potential to be utilized as functional foods or nutraceuticals.

• Journal of Plant Biotechnology
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• v.44 no.4
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• pp.394-400
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• 2017

This study investigated whether culture filtrates produced by Xylella fastidiosa can be used to determine the varietal susceptibility to Pierce's disease in grapevines (Vitis spp.) as a substitute for pathogen inoculation or field screening. A bioassay of grape leaves with culture filtrates from the pathogen showed that their phytotoxicities were active and host-selective. Ethyl acetate extracts from them also showed toxicities and host selectivity in both bunches of grapes and muscadine grapes. The sensitive range of plants to the culture filtrates and their ethyl acetate extracts was consistent with the host range of the Pierce's disease pathogen. Susceptible cultivars are sensitive to even highly diluted culture filtrates, while resistant cultivars were not affected even at their original culture filtrates. Susceptible cultivars were more sensitive to the undiluted culture filtrate than were highly diluted culture filtrates, and the younger leaves were the most sensitive to the culture filtrates in grapes. Although some European grape cultivars showed moderately susceptibility in this study, the determination of varietal resistance to Pierce's disease by the treatment of culture filtrates of pathogens could provide valuable information for the preliminary selection of genetic resources and seedlings from hybridization in a disease resistant grape breeding program.