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Esther E. McGinnis and Mary H. Meyer

Ontario and in the northern United States ( Crins and Ball, 1983 ). Achenes ripen and dehisce in June in Minnesota ( Table 1 ). Difficulties in achene germination limit the use of pennsylvania sedge for large horticultural and restoration projects. No

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Shahrokh Khanizadeh, Clément Vigneault, and Deborah Buszard

Development of strawberry fruit depends on the number of fertilized achenes on the surface. The achenes are distributed on the receptacle surface in a pattern of more or less regular rows, spirally arranged. The number of achenes is determined by 1) counting the number of achenes per square centimeter of surface on ripe berries; 2) weighing the achenes after separation from the receptacle; or 3) counting the number of achenes after pressing the fruit between two layers of glass. The above methods are laborious and time-consuming. We, therefore, described anew semi-automated method (Image Analysis System, IAS) as an alternative to the above procedures. The IAS is capable of grouping the achenes into two or more categories based on their size (sound or aborted), surface area, color, volume, etc. This will facilitate the study of the relationship between achene number and fruit weight in strawberry.

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Yoshiko Yambe and Kiyotoshi Takeno

The germination percentage of Rosa multiflora Thunb. achenes was greatly increased when they were treated with 1% Driselase, a macerating enzyme, for 36 hours. The seeds germinated more rapidly when the achenes were treated with the enzyme for a longer period. Treatment with Cellulase Onozuka improved seed germination at a lower concentration than did Driselase. Pure preparations of pectinase and cellulase had effects similar to treatment with the enzymes noted. Treatment with pectinase was more efficient than treatment with cellulase. These enzymes likely loosened the bond between cells along the suture of the pericarp and forced the pericarp to split.

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A. Raymond Miller and Craig K. Chandler

A protocol was developed for excising and culturing cotyledon explants from mature achenes of strawberry (Fragaria × ananassa Duch.). Cotyledon explants formed callus with multiple shoot buds on agar-solidified Murashige and Skoog media containing several combinations of hormones (1 μm 2,4-D; 10 μm 2,4-D; 1 μm BA + 1 μm 2,4-D; 1 μm BA + 10 μm 2,4-D; 5 μm BA; 5 μm BA + 1 μm 2,4-D; 5 μm BA + 10 μ m 2,4-D; 5 μ m BA + 5 μm NAA; 5 μ m BA + 15 μ m NAA). After three subcultures, only tissues maintained on the medium containing 5 μm BA + 5 μm NAA continued to form shoots. Tissues transferred to other media eventually died (1 μm 2,4-D; 1 μ m BA + 10 μ m 2,4-D; 5 μ m BA; 5 μ m BA + 1 μ m 2,4-D), became unorganized (1 μm BA + 1 μm 2,4-D; 5 μm BA + 10 μm 2,4-D; 5 μm BA + 15 μm NAA), or formed roots (10 μm 2,4-D). Whole plantlets were produced by transferring callus with buds to medium lacking hormones. The rapid regeneration of clonal plantlets from cotyledon explants may be useful for reducing variability in future developmental studies. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); (2,4-dichlorophenoxy) acetic acid (2,4-D); and 1-naphthaleneacetic acid (NAA).

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A. Raymond Miller, Joseph C. Scheereus, Patricia S. Erb, and Craig K. Chandler

A tissue culture protocol was developed that increased the germination percentage and decreased the lag time to germination for strawberry (Fragaria x ananassa Duch.) achenes. This technique involved cutting surface-sterilized achenes across the embryo axis then placing the shoot apex/radicle-containing sections on semisolid Murashige and Skoog medium lacking hormones. Cut achenes began germinating 5 days after culture and achieved maximum germination (97% to 100%) in less than 2 weeks, compared to whole achenes, which began to germinate 7 to 10 days after sowing and required more than 7 weeks for maximum germination (<50%). Enhanced germination of cut achenes was a general phenomenon since achenes from 231 hybrid crosses responded similarly. Following placement on culture medium, cut achenes could be stored up to 8 weeks at 4C then removed to 27C, where germination and seedling development occurred at percentages and rates comparable to freshly cut achenes. Achenes did not require stratification before cutting to exhibit increased germination. Nearly 100% of the achenes from freshly harvested red-ripe, pink and white strawberries germinated after cutting and culture, although cut achenes from white and pink berries germinated more slowly than those from red-ripe berries. Achenes from green berries, whether whole or cut, did not germinate. This method of “embryo rescue” could be used to generate more seedlings from poorly germinating hybrid crosses, would considerably decrease the time from sowing to seedling production compared to traditional means, and would produce seedlings of uniform age for subsequent field evaluation.

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Serge Gudin, Laurence Arene, André Chavagnat, and Camille Bulard

Rose achenes of different genetic origins, all belonging to the species Rosa hybrids L., subjected to radiography films, germination tests, in situ observations of embryo development, and different temperature conditions during maturation showed that achene germination is affected by endocarp thickness. Furthermore, a relation between embryo development rate and endocarp thickness is demonstrated.

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Guiwen W. Cheng and Patrick J. Breen

Fruit size, number of receptacle cells, and mean cell size were determined throughout development of secondary fruit of three day-neutral strawberry (Fragaria ×ananassa Duch.) cultivars grown in a greenhouse. Cells were counted after enzymatic separation of receptacle tissue, and mean cell volume was estimated from cell count and receptacle tissue volume. Size of mature fruit was small (3.8 g) in `Tillikum', medium (11.5 g) in `Tristar', and large (15.6 g) in `Selva'. Fruit size was correlated with the number of achenes per berry. Mature fruit of `Tillikum' had a lower fruit fresh weight per achene and lower achene population density (achenes per square centimeter) than the larger-fruited cultivars. The average number of cells per mature fruit was 0.72 × 106, 1.96 × 106, and 2.94 × 106 for `Tillikum', `Tristar', and `Selva', respectively. The relative difference among cultivars in the number of receptacle cells was established by the time of anthesis. In all cultivars, cell division was exponential for 10 days following anthesis and ceased by the 15th day. Mean cell volume increased slowly during active cell division, but rose rapidly and linearly for 10 days after cell division halted. Mean cell volume of all cultivars increased > 12-fold after anthesis and was ≈ 6 × 106 μm3 in mature fruit. The genotypic variation in the size of mature fruit was not the result of large differences in either duration of cell division after anthesis or mean cell volume, but rather was primarily due to differences in the number of receptacle cells established by anthesis.

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Shahrokh Khanizadeh, Clément Vigneault, and Deborah Buszard

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Fumiomi Takeda, Gary W. Lightner, and Bruce L. Upchurch