Variation in the impact of stem scar and cuticle on water loss in highbush blueberry fruit argue for the use of water permeance as a selection criterion in breeding
Introduction
Blueberries are highly perishable, with softening and dehydration as major factors that can limit their marketability (Ehlenfeldt and Martin, 2002, Vicente et al., 2007) or increase rejections at final markets (Prussia et al., 2006). Firmness is considered one of the most important attributes influencing acceptance of fresh blueberries with firmer fruit being preferred (NeSmith et al., 2002, Lobos et al., 2014). The rate of water loss varies substantially for blueberry cultivars and is a major contributor to softening during long-term refrigerated storage (Paniagua et al., 2013). Cultivar, cuticle characteristics, maturity stage, and the use of a moisture barrier are also important factors affecting moisture loss (Moggia et al., 2016).
Transpiration accounts for most of the weight loss in the majority of horticultural species (Burton, 1982). Gaseous exchange may take place from harvested produce to the atmosphere by four major routes: the stem scar region, stomata/lenticels, the calyx, and the cuticle (Ben-Yehoshua and Rodov, 2002, Díaz-Perez, 1998). Tomato (Solanum lycopersicum) fruit have a moderately thick waxy cuticle with no pores (Wilson and Sterling, 1976, Das and Barringer, 1999, Thompson, 2001) and sealing the stem scar significantly reduces gas exchange, reducing the ripening rate and prolonging storage life (Yang and Shewfelt, 1999). In eggplant (Solanum melonena) the fruit calyx is the main route for fruit water loss, accounting for at least 60% of fruit transpiration (Díaz-Perez, 1998).
Blueberries have a cuticle and wax-covered epidermis that, like tomato and eggplant, have no stomata (Gough, 1994). The cuticle, composed of a cutin polyester polymer with waxes and embedded with epicuticular waxes, is considered a major barrier against water loss (Lara et al., 2014, Lownds et al., 1993, Martin and Rose, 2014). In this context, the question arises as to the relative contributions of the stem scar (where the pedicel detaches) and the cuticle to fruit dehydration.
To our knowledge, selection for water loss rates has not been a priority in any blueberry breeding program. Nevertheless, moisture loss and shrivel are major quality concerns for blueberry industries (Paniagua et al., 2014 USDA, 1995). The blueberry industry in Chile permits no more than 5–7% weight loss in a commercial 3-week period at 0 °C (Paniagua et al., 2014). However, less than optimal temperatures can occur in real supply chains (Sargent et al., 2006). Given the potential value of blueberry germplasm with the quality characteristic of shrivel resistance, a good argument can be made for evaluating water loss physiology and assessing its potential for improvement through breeding.
The objective of this study was to evaluate morphometric fruit variables of stem scar size, fruit surface area, and the ratio between the two on fruit dehydration and softening using breeding lines from an active blueberry breeding program. Fruit exhibiting a wide range in stem scar size were selected from three half-sib families grown in Talca, Chile. Three lines were selected per family; one line had small-sized stem scars, a second had medium-sized stem scars and the third had large-sized stem scars. To determine the contribution of the stem scar to water loss, shrivel and firmness, half of the fruit had their stem scar sealed during storage at 20 °C and 0 °C.
Section snippets
Plant material
During 2015/2016 season, ripe fruit (100% blue) were collected from adult highbush blueberry plants grown at Panguilemo Experimental Station, University of Talca, Maule Region (35°22′15“S; 71°35′50“W). Plants were from a germplasm collection representing crosses made in a University of Talca blueberry-breeding program; the planting was established in 2009. For this study three families were selected, having the following female and male parents, respectively: Family 6 (F6; Legacy x Brigitta);
Initial condition
Scar area (mm2) for the three stem scar area categories (S, M, L) differed for each family, confirming the visual classification made at harvest (Table 1). Fruit from the germplasm lines with a large scar were bigger (greater in weight, length, and diameter) than those having medium or small scar for F6 and F40, but not for F16. The highest firmness values were found for the medium stem scar line from F6 (1.87 N mm−1) and the softest fruit were from the large stem scar line from F40 (1.50 N mm−1).
Discussion
Water loss through transpiration is an important cause of deterioration of horticultural crops, resulting not only in direct quantitative losses (less salable weight), but also in losses in appearance, texture, and nutritional quality (Kader, 2002). Blueberries have an outer epidermis with no stomata or lenticels (Gough, 1994), so moisture loss is strictly through the stem scar area and the cuticle. PH2O of whole tomato fruit (Shirazi and Cameron, 1993) was similar to that found for whole
Acknowledgements
In Chile, this work was supported by the National Commission for Scientific and Technological ResearchCONICYT (FONDECYT11130539) and the Universidad de Talca (research programs “Adaptation of Agriculture to Climate Change (A2C2)”, “Fondo Proyectos de Investigación” and “Núcleo Científico Multidisciplinario”). In the United States this work was partially supported by the “2015 Fulbright Specialist Program”, Project 6365. In Spain this work was partially supported by “Fundación Carolina” and
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