Dozens of cultivars have contributed to California's almond production, but the Nonpareil cultivar, selected in 1879, has consistently dominated California almond tonnage as a result of its excellent kernel characteristics and horticultural qualities. Currently, ‘Nonpareil’ occupies 37% of California almond acreage (Anon., 2009) and is marketed in an exclusive category that accounted for over 276 million kilograms of the total 732 million kilogram harvest during 2008 (Anon., 2009).
Although California's almond marketing categories (Nonpareil, Carmel, California, Mission, NePlus Ultra, and In-shell) group cultivars having similar kernel shape and appearance to facilitate their sale and use, no objective varietal standards exist to assign cultivars to a given category. Handlers, responsible for marketing almonds, have leeway in cultivar placement within specific marketing categories (Asaii et al., 1996). Consequently, cultivars other than ‘Nonpareil’ (e.g., ‘Jeffries’, ‘Kapareil’, and ‘Milow’) have at times been included within the Nonpareil marketing category. Public and private breeding efforts are now providing new cultivars for California orchards with their future marketing category still uncertain. Objective varietal standards for the specific marketing categories would benefit nurseries and almond producers in providing information on new cultivars during the decision-making process before orchard establishment.
Almonds in the Nonpareil category are a preferred choice in applications where the kernel is prominently visible and have historically received premium prices compared with other marketing categories (Wood, 1937). The Nonpareil cultivar has been categorized based on its free amino acid composition and fatty acid profile (García-López et al., 1996; Martín-Carratalá et al., 2002). Similarly, genetic markers have been developed to distinguish ‘Nonpareil’ from other cultivars (Dangl et al., 2009). However, marketing categories separate almond cultivars on the basis of kernel shape and appearance, and no standards to distinguish ‘Nonpareil’ kernels from those of other cultivars currently exist.
Interannual variability of phenological and carpological traits has been studied previously in a breeding population of almond (Sánchez-Pérez et al., 2007), and population mean values of several carpological traits (nut weight, kernel weight, kernel thickness) were found to vary significantly among the 4 harvest years. To our knowledge, studies have not yet been conducted to document the extent of interannual variability of carpological characters of the important ‘Nonpareil’ almond. Because ‘Nonpareil’ buyers pay a premium for its specific kernel characteristics, a more precise characterization of how ‘Nonpareil’ kernels vary between harvest years would benefit the industry. Hence, our objective in the current study is to document the variability in appearance, shape, and carpological characteristics of ‘Nonpareil’ almond kernels during seven consecutive growing seasons.
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