Abstract
Japanese plums are classified as climacteric; however, some economically important cultivars selected in California produce very little ethylene and require long ripening both “on” and “off” the tree to reach eating-ripe firmness. To unravel the ripening behavior of different Japanese plum cultivars, ripening was examined in the absence (air) or in the presence of ethylene or propylene (an ethylene analog) following a treatment or not with 1-methylcyclopropene (1-MCP, an ethylene action inhibitor). Detailed physiological studies revealed for the first time three distinct ripening types in plum fruit: climacteric, suppressed-climacteric, and non-climacteric. Responding to exogenous ethylene or propylene, the slow-softening supressed-climacteric cultivars produced detectable amounts of ethylene, in contrast to the novel non-climacteric cultivar that produced no ethylene and softened extremely slowly. Genetic analysis using microsatellite markers produced identical DNA profiles for the climacteric cultivars “Santa Rosa” and “July Santa Rosa,” the suppressed-climacteric cultivars “Late Santa Rosa,” “Casselman,” and “Roysum” and the novel non-climacteric “Sweet Miriam,” as expected since historic records present most of these cultivars as bud-sport mutations derived initially from “Santa Rosa.” This present study provides a novel fruit system to address the molecular basis of ripening and to develop markers that assist breeders in providing high-quality stone fruit cultivars that can remain “on-tree,” increasing fruit flavor, saving harvesting costs, and potentially reducing the need for low-temperature storage during postharvest handling.
Highlights
Fleshy fruit ripening is a genetically regulated process that coincides with seed maturation, advancing many physicochemical changes that transform a fertilized ovary into a tasty, nutritious, and appealing fruit that attracts animals and promotes dispersal of mature seedsNon-climacteric mutation of a climacteric plum cultivar (Giovannoni, 2004)
Fruit Quality Traits Flesh firmness, solids concentration (SSC), and titratable acidity (TA) ranged within commercial standards among “Santa Rosa,” “Eldorado,” “Ambra,” “Friar,” “Durado,” “July Santa Rosa,” “Laroda,” “Joanna Red,” “Angeleno,” “Casselman,” “Roysum,” “Late Santa Rosa,” and “Sweet Miriam” plum fruits
The fast softening rate of 2.1–3.7 N firmness loss per day (Table 1), measured in “Ambra,” “Friar,” “Durado,” “Joanna Red,” “July Santa Rosa,” “Santa Rosa,” and “Eldorado,” is similar to that observed in most commercial climacteric Japanese plum cultivars (Martinez-Romero et al, 2003; Crisosto and Day, 2011)
Summary
Fleshy fruit ripening is a genetically regulated process that coincides with seed maturation, advancing many physicochemical changes that transform a fertilized ovary into a tasty, nutritious, and appealing fruit that attracts animals and promotes dispersal of mature seedsNon-climacteric mutation of a climacteric plum cultivar (Giovannoni, 2004). Fruits are classified as climacteric or non-climacteric according to their ripening behavior (Burg and Burg, 1965; Giovannoni, 2001). Physiologically mature climacteric fruits exhibit a logarithmic (autocatalytic) increase in endogenous ethylene biosynthesis (system II) and respiration (Lelievre et al, 1997; Giovannoni, 2004). It is generally accepted that climacteric fruit cell wall remodeling and softening is triggered by endogenous or exogenous ethylene, which mediates expression of specific genes and transcription factors involved in primary (soluble sugars, organic acids) and secondary (aroma volatiles and anthocyanin biosynthesis) metabolism and defines fruit quality development (Osorio et al, 2013; Tohge et al, 2014). Exposure of fruit to exogenous propylene (an analog of ethylene) can induce autocatalytic endogenous ethylene production in climacteric fruit only and serves as a second criterion to distinguish climacteric and non-climacteric fruits (Burg and Burg, 1965)
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