Merging new orchard designs with an efficient rootstock and high-coloring strain of an apple cultivar can result in production of higher yield with better fruit quality (Fallahi et al., 2011; Marini et al., 2008; Veberic et al., 2007). Consumer acceptance is determined by fruit color, size, eating quality, and texture (Crassweller and Hollender, 1989; Donati et al., 2003; Fisher and Ketchie, 1989; MacFie, 1995; Salveit, 1983). Nevertheless, poor color can drastically reduce the value of red-peeled apples even if they have acceptable fruit size (Baugher et al., 1990; Crassweller and Hollender, 1989; Iglesias and Alegre, 2006). Apple fruit color best in climates with clear bright days and cool nights during the preharvest period (Blankenship, 1987; Faragher, 1993; Westwood, 1993). Formation of red color in apple is also influenced by light (Arakawa, 1991; Saure, 1990), cultivar (Curry, 1997; Dickinson and White, 1986; Iglesias et al., 1999), strain (Fallahi et al., 2011; Greene and Autio, 1993), fruit bagging (Fallahi et al., 2001), evaporative cooling (Williams, 1993), and the use of reflective film to increase the intensity of light into the tree canopy (Ju et al., 1999). However, the high cost of many of these practices mandates planting high-coloring strains. Delaying harvest time can also improve color but this practice, in addition to the increased risk of freeze injury, can lead to higher respiration and endogenous ethylene production, lower firmness, and shorter storage life, particularly when trees are supplied with excess nitrogen (Fallahi et al., 1985).
Most of today’s red-peeled cultivars are developed by apple breeding programs (Sansavini et al., 2005), but the majority of highly colored strains are identified based on visual and/or physiological changes that occur on a limb of the original cultivar tree (limb mutations) such as ‘Gala’, ‘Delicious’, or ‘Fuji’. These mutants could show some reversions as a result of a lack of stability (Lacey and Campbell, 1987).
Differences in ‘Fuji’ strain quality attributes have been reported in Japan (Komatsu, 1998), Tasmania (Brown et al., 1998), and Spain (Iglesias et al., 2012). In each of these reports, a different set of strains has been compared for their quality attributes. Komatsu (1998) reported that color of different sports of ‘Fuji’ varied, depending on the location where they were grown and the year when they were observed. Some clones did well in cold but not hot climate areas and vice versa. Based on that report, the pattern of peel color (stripe or blush) was not always stable. Also, some striped strains reverted back to produce poor-colored apples like standard ‘Fuji’. The striped-type sports showed more tendencies to develop red color in sectors than did the solid-type sports. Poor eating quality was detected in some red sports, more often in solid type than in stripe type. However, some striped-type clones were comparable with standard ‘Fuji’ (Komatsu, 1998). Iglesias et al. (2012) measured fruit anthocyanin content and visual color of different strains and reported that the most colored strain was ‘Zhen Aztec Fuji’ (blushed) followed by ‘6629 Fuji’ (also blushed), ‘Kiku 8 Fuji’, and ‘Rubin Fuji’ (both striped). Differences in various quality attributes among ‘Fuji’ strains remained proportionally the same across different harvest times (Iglesias et al., 2012). Comparing four strains of ‘Fuji’ apples in Tasmania, ‘Naga Fu 2 Fuji’ produced the largest fruit with best red color but least firmness (Brown et al., 1998). In that study, Akafu strains maintained higher fruit firmness than Naga Fu strains. ‘Naga Fu 1 Fuji’ had lower soluble solids concentration (SSC) when compared with the other strains, whereas the ‘Aki Fu 1 Fuji’ fruit had a lower area of red peel. Veberic et al. (2007) compared fruit quality attributes of ‘Kiku 7 Fuji’, ‘Kiku 8 Fuji’, ‘Naga-fu 6 Fuji’, and ‘Standard Fuji’ over two seasons. In their study, ‘Kiku 8 Fuji’ fruit had the best red color and accumulated the largest amount of reducing sugars with the lowest quantity of phenols in both years and recommended this strain for planting in the areas with high variations in daily and nightly temperatures.
Although the Pacific Northwest, particularly Idaho, is a major area for production of ‘Fuji’, there have not been any comparative studies among different strains of ‘Fuji’ in the region. Thus, the objective of this long-term experiment was to study the yield and harvest time fruit quality differences among ‘Fuji’ strains in southwest Idaho, which has similar climate conditions as those of the Intermountain West region of the United States and many other regions worldwide.
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