Floral development was studied in buds of `Starkspur Supreme Delicious' apple trees growing on B.9, M.26 EMLA, M.7 EMLA, P.18, and seedling rootstocks. In each of 3 years, buds were sampled from the previous years growth at intervals throughout the growing season and dissected to determine whether the apex was domed, indicating the start of floral development. Number of bud scales and true leaves increased during the early part of the growing season, but remained fairly constant beyond 70 days after full bloom. The type of rootstock did not affect the number of bud scales or transition leaves, and effects on true leaf numbers were small and inconsistent. Final bract number per floral bud was similarly unaffected by rootstock. The proportion of buds in which flowers were formed was influenced by rootstock in only one year of the study, which was characterized by high temperatures and low rainfall over the period of flower formation. Bracts were observed only in floral buds, and became visible after doming of bud apices had occurred. Flowers were formed during the first 20 days in August, regardless of rootstock or year. The appendage number of vegetative buds was constant from 70 days after full bloom until the end of the growing season, but the number of appendages in floral buds increased due to the continued production of bracts. The critical bud appendage number for `Starkspur Supreme Delicious' before flower formation was 20, and was stable among rootstocks and years. Buds with diameters above 3.1 mm were generally floral, but on this basis only 65% of buds could be correctly classified. Spur leaf number, spur leaf area, and spur leaf dry weight were not good predictors of floral formation within the spur bud.
Peter M Hirst and David C Ferree
Michael Wisniewski, D. Michael Glenn, Lawrence Gusta, and Michael P. Fuller
to be as effective as extrinsic ice nucleating agents such as INA bacteria and frost crystals. Barriers appear to exist, however, that prevent ice propagation into lateral appendages such as buds or newly extended primary tissues ( Carter et al., 2001
Emily Hoover, S. McArtney, S. Tustin, M. White, and P. Hirst
Experiments were initiated to document the effect of cultivar, GA4+7, and number of fruit/spur on appendage number and flower bud initiation in apple. `Pacific Rose' is strongly biennial, `Braeburn' and `Fuji' are moderately biennial, and `Royal Gala' is not biennial. In the cultivar study, buds were sampled every 18 days starting at 50 days after full bloom and continuing through until leaf fall to determine the rate of appendage formation and appendage number in relation to doming. Because of the tendency for `Pacific Rose' to exhibit biennial bearing, the rate of appendage formation and the timing of doming were compared on nonfruiting trees, trees carrying a commercial crop, and trees sprayed with 300 PPM GA4+7 applied 14 days after full bloom. Number of appendages for the treatments were similar up to 100 days after full bloom. Presence of fruit on a spur has been demonstrated to inhibit flowering of apple. Spurs of `Pacific Rose', `Splendor', and `Royal Gala' were labeled with zero, one, two, and three fruit per spur and sampled three times during the season. As buds were harvested to count appendage number, the number of fruit per spur and the number of total seeds per spur were recorded. Correlation between number of seeds per spur and rate of appendage formation were done.
Joann M. McLaughlin and Duane W. Greene
Fruit-bearing limbs of five apple (Malus domestics Borkh.) cultivars varying in degree of biennial bearing were either unsprayed or received five repeat applications of BA at 50 mg·liter-1 with daminozide at 2000 mg·liter-1. BA and daminozide increased early appendage formation of potential flower buds, but this increase was sustained only on `Early McIntosh' and `Baldwin'. BA and daminozide increased return bloom on all treated limbs, with the exception of `Early McIntosh'. The annually bearing cultivars McIntosh and Delicious initiated 20 appendages before the formation of floral parts, while the biennially bearing cultivars Golden Delicious, Baldwin, and Early McIntosh initiated 19, 18, and 22 appendages, respectively. Flower removal before bloom increased appendage formation on the biennial cultivar Baldwin but not on the annual cultivar Delicious. Chemical names used: N -(phenylmethyl) -1 H-purine-6-arnine (BA); butanedioic acid mono(2,2-dimethyihydrazide) (daminozide).
Peter M. Hirst and Wendy M. Cashmore
Spurs were collected periodically throughout three growing seasons from the 1-year-old section of wood of `Royal Gala' trees growing in New Zealand. Three classes of spurs were sampled: purely vegetative spurs, those that flowered but did not carry fruit, and spurs on which a single fruit was borne. The bourse bud, in which flowers may form for the following year's crop, was dissected and bud appendages classified and counted. In addition, axillary buds from current-season shoots were sampled and dissected. Over the period 50–200 days after full bloom, the number of appendages in buds on vegetative spurs increased from ≈14 to 22, whereas the increase in buds on fruiting spurs was 14 to 20. In contrast, axillary bud appendage numbers increased from ≈11 to 14 over this period. By the end of the growing season, flowers were evident in a high proportion of buds of all classes. The critical appendage number at which the change from a vegetative to floral status became visible was ≈18 for spurs on 1-year-old wood, but 13 for axillary buds. The time at which flowers were able to form varied among years. The degree of flower differentiation that occurred prior to leaf fall was highest in vegetative buds and was reduced by flowering and fruiting, and was lowest in axillary buds.
Joann M. McLaughlin and Duane W. Greene
Combination postbloom sprays of BA at 50 mg·liter-1 and daminozide at 2000 mg·liter-1 were made to limbs of `Early McIntosh' apple (Malus domestics Borkh.) where all of the flowers were either removed before full bloom or allowed to remain. BA and fruit removal increased return bloom, whereas daminozide bad no effect. No treatment had a consistent effect on spur leaf area. Repeat sprays of GA4+7 to `Delicious' apple trees at full bloom (FB) +5, FB + 14, and FB +22 days reduced appendage development and flower bud formation on spurs. One spray of GAd+7 at 150 mg·liter-1 at FB +42 days reduced appendage formation and the percentage of flowering spurs but not as effectively as earlier repeat sprays of GA4+7 at 50 mg·liter-1 When BA at 150 mg·liter-1 was combined with the GA at FB +42 days, appendage formation was increased but the reduction in flowering was not reversed. One BA spray at 50 mg·liter-1 at FB +22 days to `McIntosh' trees increased the number of appendages formed in spurs, but return bloom was not influenced. Chemical names used: (N -phenylmethyl) -1 H -purine-6-amine (BA); butanedioic acid mono (2, 2-dimethylhydrazide) (daminozide); gibberellins A4 and A7 (GA4+7).
Christia M. Roberts
Lewisia tweedyi (A. Gray) Robinson is an endangered, herbaceous perennial native to the Cascade Mountains of northern Washington state and southern British Columbia. It is highly valued as an ornamental, but has a reputation for being challenging to grow and is only cultivated by alpine specialists. The better known Lewisia species, L. cotyledon, is a minor commercial crop in some areas of Europe and western North America. Lewisias are members of the Centrospermae; a linear peripheral embryo surrounds centrally located perisperm. Lewisia tweedyi seed is distinct from all other lewisias in having a fleshy appendage, or caruncle. Germination practices include stratification for an unspecified period in a garden cold frame. In addition to a long germination period, percent germination is characteristically low. A number of tests, including sowing under axenic conditions, and combinations of prechill periods and liquid N scarification were conducted. Seedcoat-imposed dormancy and germination requirements have been determined.
Audrey I. Gerber, Karen I. Theron, and Gerard Jacobs
Protea L. sp. can be assigned to groups according to similar times of flower initiation and harvest. The stages occurring during flower initiation and their synchrony relative to shoot growth were investigated for three cultivars when flower initiation occurred on the spring growth flush. For all three cultivars, the spring flush was preformed and enclosed in the apical bud before spring budbreak. During elongation of the spring flush, the apical meristem produced floral primordia which differentiated into involucral bracts. After completion of the spring flush, meristematic activity continued and produced floral bracts with florets in their axils. The different cultivars were characterized by differences or similarities in the time of budbreak, and the rates of shoot growth, appendage formation, and flower development. Insight into the time of flower initiation relative to vegetative growth could be useful in making management decisions, as well as forming a basis for manipulation of the flowering process.
Jose Lopez-Medina and James N. Moore
Root cuttings of A-1836, APF-13, and NC194 primocane-fruiting (PF) blackberry (Rubus subgenus Rubus) genotypes were dug from the field on 31 July 1997 and stored in plastic bags at 2 °C for 32 days. On 1 Sept. freshly dug root cuttings, along with the cold-treated ones, were planted in pots, which were kept in a lath house for 4 weeks and then moved to a heated greenhouse under natural daylength. Cold-treatment hastened emergence of all genotypes. Transition from vegetative to floral phase was first observed in cold-treated A-1836 and APF-13 at the fifth node, with floral appendages clearly evident in both genotypes at the seventh node 45 days after planting (DAP). Bloom started on 26 Nov. and 5 Dec. 1997 and the first fruits were picked on 10 and 25 Jan. 1998 in cold-treated APF-13 and A-1836, respectively. Plants of cold-treated NC194 and of all non-cold-treated genotypes remained stunted with rosetted leaves, showing no signs of floral initiation until 150 DAP. These findings show that exposure to chilling prior to shoot emergence greatly promotes flowering in PF blackberries, and may have application in greenhouse culture of blackberry.
Peter M. Hirst and David C. Ferree
In each of 3 years, vegetative spurs were sampled from l-year-old wood of `Starkspur Supreme Delicious' apple trees (Malus domestica Borkh.) growing on B.9, M.26 EMLA, M.7 EMLA, P.18, and seedling rootstocks. Mineral concentrations of spur leaves and bud apical meristems were determined, and related to spur bud development. The spur leaf P concentration decreased during the growing season each year, hut was unaffected by rootstock. Spur leaves of trees on B.9 rootstock had 30% higher Ca concentrations than trees on M.26 EMLA or seedling rootstocks. In each year, trees growing on M.26 EMLA rootstocks had the highest leaf Mg concentrations. Mineral concentrations were generally unrelated to spur leaf number, leaf area, leaf dry weight, or specific leaf weight. Phosphorus concentrations in spur bud apical meristems declined during two of the three growing seasons of the study and were unaffected by rootstock. Bud P concentration was weakly negatively related to bud diameter and bud appendage number in one year of the study. More vigorous spurs (as indicated by higher spur leaf number, leaf area, and leaf dry weight) had higher bud K levels during each year. No relationships between bud development and either spur leaf mineral concentration or bud apical meristem mineral levels were evident, suggesting that a direct role of mineral nutrition influenced by rootstock at the site of flower formation was unlikely.