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The maximum level of ethylene production is closely related to fruit ripening and storage potential in Asian pears. In a previous study, we identified two markers (A and B) linked to high and moderate ethylene production during fruit ripening, respectively, by restriction fragment-length polymorphism analysis of two 1-aminocyclopropane-1-carboxylate (ACC) synthase genes (PPACS1 and PPACS2). In this study, a total of 152 cultivars were categorized into four marker types (AB, Ab, aB, and ab); types AB and Ab show high levels, aB a moderate level, and ab a low level of ethylene production during fruit ripening. A large number of ab and aB cultivars but few AB and Ab cultivars were observed. It suggests that there has been a decrease in high ethylene producers by artificial selection because of short shelf life. The ab cultivars are a good genetic resource for production of new cultivars with a long shelf life. Such information on marker types is useful for breeding strategies aimed at improving storage ability in Asian pears.
Black spot disease is one of the most serious diseases in Asian pear cultivation, with the commercial cultivar Nijisseiki being susceptible. Ethylene is known to play major roles in regulating plant defense responses against various pathogens. We investigated the relationship between ethylene synthesis and black spot disease in ‘Nijisseiki’ pear leaves by treatment with an analog of ethylene and 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action. Interestingly, both treatments enhanced black spot disease symptoms. Both treatments also increased ethylene production in accordance with disease symptoms through altered gene expression of ethylene biosynthetic enzymes, especially 1-aminocyclopropane-1-carboxylate (ACC) synthase genes (PpACS3 and 4). Chemical names used: 1-methylcyclopropene (1-MCP), 1-aminocyclopropane-1-carboxylate (ACC).