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Exposure of stratified apple (Malus domestics Borkh. cv. Golden Delicious) seeds to 30C induces secondary dormancy. To determine if an increase in abscisic acid (ABA) content was associated with the loss in germination capacity, stratified seeds (3,- 6, or 9 weeks at 5C) were held at 30C for 0, 3, or 6 days. Stratification at 5C either had no effect or increased ABA content in embryonic axes, cotyledons, and seed coats. Exposure to 30C after stratification either did not affect or decreased ABA content of embryonic axes and seed coats; in contrast, cotyledonary ABA was increased. Seed coats, cotyledons, and embryonic axes stratified for 3, 6, or 9 weeks at 20C contained the same or higher levels of ABA in comparison with nonstratified seeds or seeds stratified at SC. Changes in ABA levels were not consistently correlated with changes in germination capacity during stratification or after exposure to 30C. These data suggest that changes in ABA are not related to changes in dormancy. Chemical names used: abscisic acid (ABA); butylated hydroxy-toluene (BHT); n-(trichloromethyl) thio-4-cyclohexene-1,2-dicarboximide(Captan).
Saskatoon fruit are an emerging horticultural crop across the Canadian prairies. As fruit size varies greatly among cultivars, knowledge of fruit growth patterns and factors that affect fruit size can be used to establish breeding trials and develop orchard management strategies that could enhance the production of this crop. In this study, we 1) determined fruit and seed growth patterns among large-, medium-, and small-fruited cultivars of saskatoon using growing degree days to standardize time to crop development and 2) assessed the role of seed number on fruit size. Fruit growth patterns of four cultivars (Thiessen, Northline, Regent, and Smoky) were determined from weekly measurements of fresh and dry fruit mass during two consecutive seasons. These growth patterns exhibited three phases. The largest fruit at maturity were from `Thiessen', followed by `Northline', `Smoky', and `Regent', in descending order. Pedicel cross-sectional areas 1 week before maturity correlated linearly with increasing fresh and dry fruit mass and seed number per fruit. At maturity, seed number per fruit correlated linearly with fresh and dry fruit mass. `Thiessen' contained significantly more seeds per fruit (4.6) than `Northline' (3.7), `Smoky' (3.2), and `Regent' (3.2). The results of this research suggest potential areas for orchard management improvement and future research directions for saskatoon crop improvement.
Fruit growth in saskatoons (Amelanchier alnifolia Nutt.), an emerging horticultural crop across the Canadian prairies, results from development of the mesocarp and the endocarp-locular-ovular structure which includes the developing seeds. Contribution of these tissues to fruit size was assessed using transverse sections of ovaries sampled at six developmental stages among large- and small-fruited cultivars. Mesocarp development was similar among the larger-fruited cultivars (Thiessen, Northline, and Smoky); the number of cells increased rapidly through Stage I [162 to 293 growing degree days (GDDs)] of fruit growth, and cell number increase was minimal during Stages II (293 to 577 GDDs) and III (577 to 747 GDDs). In `Regent' fruit (a small-fruited cultivar), the maximal rate of cell division was delayed until Stage II and the mesocarp contained fewer cells than the larger-fruited cultivars at harvest maturity. Mesocarp cell enlargement was similar among all of the cultivars studied where cell expansion was maximal during Stage I and continued at a slower rate during Stages II and III. The area of the endocarp-locular-ovular structure was greatest for `Thiessen' and `Northline', midrange for `Smoky', and smallest for `Regent'. Data suggest that a minimum number of mesocarp cells early in fruit development is required to attain maximal mesocarp size, and that differences in cultivar fruit size are a function of both the mesocarp and the endocarp-locular-ovular structure.
Field experiments were conducted on two cultivars of saskatoon to test the effectiveness of ethephon in stimulating uniform fruit ripening without compromising fruit quality. Shrubs of cultivars Northline and Smoky were sprayed to runoff with ethephon (0, 250, 500, and 1000 mg·L-1 for `Northline'; 0, 500, and 1000 mg·L-1 for `Smoky') prior to fruit maturity. Fruit were harvested 4 to 8 days after treatment and sorted into ripeness categories by size, and the fully ripe fruit were evaluated for quality (surface color, firmness, mean fruit weight, soluble solids, and titratable acids). Ethephon significantly increased the percent ripe fruit per shrub (by up to 9.7%) in both cultivars, without a significant effect on fruit quality. At concentrations up to 1000 mg·L-1, ethephon may be an effective ripening agent for saskatoon fruit without reducing fruit quality. Although there were significant differences in yield from year to year for both cultivars because of their biennial-bearing habit, ethephon treatments did not significantly affect total yields.
Saskatoon fruits, an emerging horticultural crop across the Canadian prairies, vary greatly in size among cultivars. In this study, we compare fruit development patterns among large, medium, and small fruited cultivars of saskatoon, and assess the role of seed number and pedicel diameter on fruit size. Fruit growth patterns of four cultivars (Thiessen, Northline, Regent, and Smoky) were determined from weekly measurements of fruit diameters and fresh and dry flower/fruit weights during two consecutive growing seasons. The developmental patterns of fruit growth determined using the above criteria were similar among cultivars and between years. At maturity, the largest fruits (fresh weight) obtained were from cv. Thiessen, followed by `Northline', `Smoky', and `Regent', in descending order. Pedicel diameters (one week prior to maturity) correlated linearly with increasing fruit diameter and fresh weight. At maturity, seed number per fruit correlated linearly with increasing fruit weight. Thiessen contained significantly more seeds per fruit (4.6) than `Northline' (3.7), `Smoky' (3.2), and `Regent' (3.2).
Ethephon was applied in two consecutive years to saskatoon (Amelanchier alnifolia Nutt.) shrubs (`Northline' and `Smoky') to determine its effects on synchronizing fruit ripening. Ripeness can be visually assessed by color (green = immature; red = mature, not ripe; purple = mature, fully ripe). Ethephon (applied when fruit were ≈ 70% red) at 250, 500, and 1000 ppm increased the percentage of ripe fruit obtained from `Northline' by 2%, 4%, and 6%, respectively. Due to pronounced seasonal yield differences for `Smoky', ethephon had no effect on the percentage of ripe fruit obtained in 1994. However, in 1995, ethephon (applied at 70% red fruit stage) at 500 and 1000 ppm increased the percentage of ripe fruit obtained from `Smoky' by 4% and 2%, respectively. Fruit quality, evaluated with respect to surface color development, flesh firmness, fruit size, soluble solids concentration, titratable acidity, and the soluble solids: titratable acids ratio, was not significantly affected by ethephon treatments. This work was supported in part by AARI-FFF grant no. 940442.