Flower-bud formation in apple under various day and night temperature-regimes

Starting at full bloom, 4 temperature treatments were applied to 3-year-old ‘Golden Delicious’ and ‘Cox's Orange Pippin’ trees. Either 17 or 24° C were applied in 3 successive periods of 5–6 weeks each.In ‘Golden Delicious’, exposure to 24° C during the first 5 weeks after full bloom enhanced shoot growth and reduced flower-bud formation in spur buds. The difference in temperature-regime during the third period did not affect either growth or flowering. Almost all apical shoot buds became floral, irrespective of treatment.‘Cox's Orange Pippin’ trees maintained at 24° C throughout grew more vigorously than did those kept at 17° C continuously, but flowering-abundancy was the same. Lowering of the temperature in the last period before harvest did not influence shoot growth, but markedly reduced flowering of both spur buds and apical shoot buds.In a second experiment, a night temperature of either 20 or 10° C was applied in 2 successive periods to 3-year-old ‘Cox's Orange Pippin’ trees kept at a day temperature of 20° C throughout. Lowering of the night temperature in the middle of the season reduced flower-bud production, but there was no difference in growth vigour compared with 20° C continuously.It is postulated that temperature affects flowering in two opposite ways, whose relative importance determines the net result.     

Sind Pollenspritzungen oder Pollendispenser Alternativen zur herkömmlichen Bestäubung der Apfelbäume durch Bienen?

The efficacy of different methods of applying cv. ‘Golden Delicious‘ pollen to ‘Cox Orange‘ apple trees inside insect-proof cages was investigated: (1) spraying pollen suspended in water directly into the trees while they were in bloom (treatment A); (2) pollen transfer by honeybees (treatment B) or by bumblebees (treatment C), both of which had to pass through a dispenser loaded with cv. ‘Golden Delicious‘ pollen; (3) transfer by honeybees of pollen from cv ‘Golden Delicious‘ trees bearing compatible pollen and maintained in pots within the same cages (treatment D). Naturally pollinated cv. ‘Cox Orange‘ apple trees outside the cages in the orchard served as controls. For methods A–C normal commercially available ‘Golden Delicious‘ pollen was used for hand pollination, and its efficacy was assessed with reference to the amount of fruit that set. The fruit-set at the time of harvesting differed significantly (Nemenyi test) with the different methods of pollination: 1.0% (±2.0) of the blossoms ripened to yield marketable apples after treatment A, 6.1% (±5.2) after treatment B, 4.9% (±4.6) after treatment C, and 20.4% (±11.5) after treatment D, while the corresponding figure for the control trees was 7.3% (±2.8) and that for hand pollination, 41,9%. The low fruit-set after an aqueous suspension of cv. ‘Golden Delicious‘ pollen was sprayed on the test trees shows that this procedure did not result in adequate pollination. The density of pollen grains was determined on filter papers during spraying and was an average of 3 (±2.6, range 0.0–8.6) pollen grains/cm². When the pollen dispensers were used, the fruit-set was lower than on the hand-pollinated control trees. Despite the success of manual pollination with exogenous cv. ‘Golden Delicious‘ pollen, pollen spraying to enhance pollination, as specified in current instructions, cannot be recommended for commercial apple growing in Germany.     

Storage quality of ‘Cox's Orange Pippin’ apples grown on a range of rootstocks

This study involved storing samples of ‘Cox's Orange Pippin’ from the 1974 and 1975 crops from each of 2 rootstock trials. After 12 weeks cool storage, the samples were examined for bitter pit and internal breakdown.In the high-pit year 1974, ‘Cox's Orange’ on ‘M.16’ and ‘MM.115’ had significantly more pit and breakdown than when grown on ‘MM.106’, ‘MM.112’ and ‘MM.114’, with fruit from ‘MM.104’ in between the 2 groups. However, in the low-pit year 1975 there were no differences. In the second trial in 1974, ‘Cox's Orange’ on ‘M.16’ had significantly more pit and breakdown than when on ‘Northern Spy’, ‘MM.109’ and ‘M.7’. In the following year there were no differences in the incidence of pit, but fruit from ‘M.7’ and ‘M.2’ had more breakdown than from other rootstocks in this trial.     

The effect of soil temperature on lateral shoot formation and flower-bud formation in apple in the first year after budding

Under controlled environment conditions the influence of four soil temperatures (7°, 14°, 21°, and 28°C) on vegetative development and flower-bud formation of apple trees (cvs ‘Rode Boskoop’ and ‘Elstar’) were evaluated in the first year after budding. Relative air humidity was high, air temperature was 20°C. Broadly speaking, for both cultivars shoot growth clearly increased with increasing soil temperature. The effects on growth were mainly reflected in the number (not length) of the lateral shoots; the growth of the main shoot was little influenced by soil temperature. At 7°C the lateral shoots usually occurred higher along the main stem than at the higher temperatures. Flowering on the parent stem and on the lateral shoots was little affected by the soil temperatures tested. In general, flower-cluster quality was rather poor. If only clusters having more than four well-developed flowers are considered, flowering was favoured by higher soil temperatures; at 28°C, especially, cluster quality was much better than at the other soil temperatures. It is concluded that soil temperature is important in controlling the degree of lateral shoot-formation as well as the formation of well-developed flower clusters.     

Controlling growth of ‘Delicious’ apple trees with low- dosage applications of Uniconazole or BAS111

Foliar applications of 30, 60 or 120 mg I-1 uniconazole were made to ‘Delicious’ apple trees at full bloom or one, two or three weeks after full bloom. Application at full bloom reduced fruit weight and length/diameter ratio more than when applied two or more weeks after full bloom. In another experiment, a single application of uniconazole was applied to ‘Delicious’ trees three weeks after full bloom at 15, 30, 60, 120, 240 or 480 mg I-1. Posages of 240 or 480 mg I-1 controlled vegetative growth to about 50% of the control values at ten weeks after treatment. Thereafter, the rate of shoot elongation was similar to that of the controls. The lowest dosage to reduce vegetative growth was 15 mgl-1. In a third experiment, uniconazole was compared with BAS111 for controlling vegetative growth of ‘Delicious’ trees. Uniconazole or BAS111 applied six times at 350 mgl'1 reduced growth to 46% and 81% of that of the controls, respectively. Increasing the rate of surfactant from 0.1% to 1.0% reduced growth by an additional 8%. Growth reduction in the year of treatment was similar following uniconazole treatments of 350 mg l_l applied three times or 35 mg I-' applied six times.     

Use of 6-benzylamino purine and Promalin for improved canopy development in selected apple cultivars

Foliar sprays of Promalin (gibberellins A_{4 + 7} + 6-benzylamino purine) applied to 1-year-old apple (Malus domestica Borkh.) trees at the 3–5-cm growth stage significantly increased lateral branching in 5 of 9 cultivars tested. Branching response ranged from 0% (‘Winter Banana’) to 131% (‘Starkrimson Delicious’) of the untreated controls. Total shoot growth was not consistently increased by 6-benzylamino purine or Promalin in tests over 3 years on spur and non-spur 1- and 2-year-old apple trees. Sprays of 50–300 mg l⁻¹ Promalin were ineffective for increased branch development. Sprays of 300–500 mg l⁻¹ increased total shoot numbers and reduced average shoot length. Sprays applied prior to new terminal growth in spring were ineffective. Treatment during periods of active shoot growth were generally effective, but periods of stress may have reduced response. Sprays were more effective for inducing lateral shoot formation than dormant heading or delayed dormant heading (pruning) (10 days after full bloom) in ‘Criterion Golden Delicious’. No difference in branching response was observed between BA and Promalin. Addition of a spray adjuvant (Buffer-X) did not affect branching response. Repeat annual single sprays of Promalin applied to dormant pruned trees were generally less effective for stimulating lateral branching than a single application in a given year. Phytotoxicity was associated with Promalin sprays at 300–500 mg l⁻¹ on ‘Delicious’.     

Relations between the concentration of diffusable and extractable gibberellin-like substances and the alternate-bearing behaviour in apple as affected by chemical fruit thinning

The levels of diffusable and extractable gibberellin-like substances (GA_s) of apple fruits were investigated in the alternate-bearing ‘King of the Pippins’ and the regularly fruiting ‘Golden Delicious’, using the barley endosperm bioassay. During 1977 and 1978 there were marked differences between the two cultivars in both the chronological appearance and the absolute amounts of diffusable GA_s. The application of fruit-thinning chemicals (carbaryl, ethephon, NAAm) to ‘King of the Pippins’ suppressed the early increase of GA_s in diffusates, which normally occurs during the second week after full bloom. The following year, the thinned trees exhibited heavy flower- and fruit-set, while the untreated control trees showed a very poor bloom. The later appearance of the GA peak in diffusates from fruits of ‘Golden Delicious’ (5 weeks after full bloom), was not accompanied by a similar inhibitory effect on subsequent flowering.In contrast to their effect on the levels of diffusable GA_s, the thinning-treatments caused no real change in the amount of extractable GA_s, which was very similar in fruits from both cultivars.     

Varietal Reactions to Viruses Causing Star Crack and Russet Rings on Apple Fruits

English sources of viruses causing star crack and russet ring were grafted to nine apple varieties. Only Golden Delicious reacted to all virus sources. This variety differentiated most clearly between different sources of star crack inoculum. Cox’s Orange Pippin and Spartan reacted to all star crack sources; Belle de Boskoop, Weisser Winterglocken, Lord Lambourne, Laxton’s Fortune and Worcester Pearmain reacted when inoculated with some sources but not others, while Granny Smith reacted to none. Golden Delicious developed leaf and fruit symptoms when inoculated with russet ring viruses, but Cox’s Orange Pippin, Spartan, Belle de Boskoop, Weisser Winterglocken and Granny Smith did not. Mailing II rootstocks developed characteristic leaf symptoms when infected with russet ring viruses. One inoculation source caused leaf mottling and necrosis and russeted warts on the fruits of Golden Delicious and Cox’s Orange Pippin. A rough-skin condition of Belle de Boskoop was perpetuated by buds and grafts but not transmitted. Some of the English viruses caused symptoms, in certain varieties, indistinguishable from diseases reported from Germany, Switzerland, the Netherlands, and North America.     

Production variability in apple crops

The problem of year-to-year variation in English apple crops was studied for the cultivar ‘Cox's Orange Pippin’ by analyzing data collected from similarly-managed commercial blocks of trees. In the period 1971–1975 yields, in each block of trees, moved in the same direction each successive year. In low-average yield years the variation in yield tended to be as extensive as in high-average yield years. Over the period studied, no relationships between climatic factors during the blossoming-period and subsequent yield could be determined. The most important factor linked with low-average yield was found to be above-normal temperatures in the pre-blossom stage.It was postulated that in order for a tree to carry a crop to its full potential, a decisive vernal temperature impulse is needed. If this dormancy break does not occur, because of above-normal temperatures, a full crop cannot be carried, even though subsequent weather conditions are optimum. Yield failures are attributed to some hormonal or other physiological imbalance occurring due to the lack of the normal decisive vernal dormancy break.It was shown that the alternate-year bearing pattern evident in apple crops in the United Kingdom, The Netherlands and Belgium between the years 1971 and 1975 could be explained by this hypothesis.     

Effect of part-tree flower thinning on fruiting,vegetative growth and leaf photosynthesis in ‘Cox’s Orange Pippin’ apple

Flower clusters were removed at full bloom from ten year old ‘Cox’s Orange Pippin’ trees on M.9 rootstocks, over the whole tree, on alternate branches or on whole sides. Mean fruit weight per tree at harvest was linearly dependent on leaf area per fruit and on light interception per fruit, both relationships accounting for over 90% of the variance. These relationships did not differ between treatments, implying either a mobile pool of carbohydrate or photosynthetic adjustment within the tree to crop load. Measurements of leaf photosynthesis in July and September showed no statistically significant differences in photosynthetic rate of spur or extension shoot leaves on bearing or non-bearing branches. Although the treatments caused no overall effects on shoot growth or leaf area per tree, sides of trees without fruit had greater leaf area and shoot growth than did sides bearing fruit. Fruit mineral composition and percentage dry weight were not affected by treatment except where the treatments significantly altered fruit size. In the following spring, although the treatments did not affect the total number of flower buds produced, branches that were deflowered in the previous spring carried significantly more flower buds than did branches which had cropped.     

Hormonal regulation of physiological leaf spot and premature leaf abscission in ‘Golden Delicious’ apple trees

Exogenous growth substances (GA₄₊₇, IAA, PBA, and ABA) alone and in combination were applied as leaf dips to young ‘Golden Delicious’ apple trees in a growth room at 21 °C. All treatments containing GA₄₊₇ accelerated the incidence of physiological leaf spot over treatments without GA₄₊₇, ABA alone delayed the appearance of leaf spot. PBA, PBA + GA₄₊₇, and PBA + GA₄₊₇ + IAA retarded the abscission of spotted leaves.GA₄₊₇ and GA₄₊₇ + PBA also accelerated leaf spot development in bearing ‘Golden Delicious’ trees in the orchard.Fumigation of apple trees with ethylene at 2, 10, and 20 ppm had no influence on the occurrence of leaf spot or premature abscission.     

Apple rootstock studies: growth of trees on three clonal rootstocks planted with or without roots

Trees of Cox's Orange Pippin on M.IXa, M.26 and MM. 106 were planted either normally with roots or without roots to simplify the planting operation. Pruning treatments were superimposed, the trees being cut back at planting, left unpruned the first year and cut back the second year, or left entirely unpruned. All trees survived. After two growing seasons the trees were lifted and weighed. Removal of all roots before planting reduced shoot growth, trunk girth increment, final tree weight and incremental weight. However, on all rootstocks, trees planted without roots and left unpruned were similar in size when lifted to those planted with roots and cut back at planting in the orthodox manner.

In a complementary trial lasting one season Cox's Orange Pippin trees on M.26 were planted with or without roots. All trees were cut back at planting, and four times of planting were compared. The mid-April planting included trees that had been stored at 2.8 °C and trees that had been bedded-in outdoors. There were no tree losses attributable to removal of the roots before planting. Removing the roots at planting again reduced growth and weight of tree at lifting. Month of planting had no effect upon shoot growth or trunk girth increment.

The results are discussed, together with their practical implications in relation to mechanical tree planting for high density orchards.     

Promotion of floral initiation in ‘Fuerte’ avocado by low temperature and short daylength

Potted avocado (Persea americana Mill., cv. ‘Fuerte’) plants were maintained in growth cabinets for up to 32 weeks and new growth observed for flower formation. Flowers were formed if temperatures were 20°C or below, but with 25° or 30°, even if only for 1 hour per day, flower formation was inhibited. Time to flowering was accelerated, but number of flowers reduced, if daylength was shortened from 15 h to 9 h. With low temperature and short days, full bloom was about 4 months after starting experiments. Spring flowering of cv. ‘Fuerte’ in the field could follow flower induction about 4 months previously with the onset of winter temperatures and daylengths.     

Early forcing of narcissus: The effects of lifting date and stage of floral development at the start of cooling

Early Narcissus flowers may be obtained if bulbs are lifted early from the field, warm-stored (35°C) and then cool-stored (9°C) before forcing in a glasshouse. The earliest satisfactory forcing was investigated, in ‘Carlton’ and ‘Fortune’, by lifting weekly from 27 May to 22 June, and storing at 17°C for 0–7 weeks between warm- and cool-storage. Storage at 17°C is usually intercalated to allow the completion of flower differentiation prior to the start of cool storage.After warm-storage, the bulbs lifted on 27 May and 22 June had reached Stages Sp and A2 of flower differentiation, respectively; 5–7 weeks of 17°C-storage were then needed to reach complete flower differentiation (Stage Pc). Cool storage was therefore begun with bulbs ranging from Stage Sp to Stage Pc. The earliest cooled bulbs had progressed only to Stage A2, and all others to Stage Pc, after 14–16 weeks of cool storage. No floral defects (e.g., split paracorolla) were noted in any treatment, but in ‘Carlton’, about half the bulbs lifted on 27 May and stored for 0 or 1 week at 17°C did not yield a flower, due to failure of the scape to elongate and death of the flower bud within the spathe.Duration of the glasshouse period was reduced by later lifting and by longer 17°C-storage, but following lifting on 15 or 22 June and 2 or more weeks at 17°C, differences were trivial. For flowering within 30 days in the glasshouse, 5 or 6 weeks' 17°C-storage was needed with 27 May lifting, reducing to 1 week at 17°C after 22 June lifting. Flowering within 21 glasshouse days was achieved only after 15 or 22 June lifts followed by 4–5 weeks at 17°C. The earliest flowers in ‘Fortune’ (7 November) were produced following 3–5 weeks at 17°C after lifting on 27 May or 1 June, or following 1–2 weeks at 17°C after later lifting. In ‘Carlton’, the earliest flowers (23 November) followed 2–3 weeks at 17°C after lifting between 1 and 15 June, or 0–1 weeks at 17°C after the last lifting date (22 June). Following the use of 3 weeks' 17°C-storage, flowering date was about equal, irrespective of lifting date. However, further extension of 17°C-storage resulted in a delay in flowering date. Scape length increased irregularly with longer storage at 17°C; scapes were taller following later lifting (8–22 June) than following earlier lifting. Differences in flower diameter between treatments were relatively small.     

Short days and temperature effects on growth and flowering in strawberry (Fragaria × ananassa Duch.)

Summary

‘Korona’, ‘Elsanta’, ‘Bounty’ and ‘Senga Sengana’ strawberry (Fragaria × ananassa Duch.) plants, were placed at constant temperatures of 9, 15 or 21°C and daylengths of 8 h (short day) or 24 h (long day). The plants were given different numbers of short-day (SD) cycles, and flowering and growth were studied. ‘Korona’ and ‘Elsanta’ were responsive to both short-day treatment and temperature, with optimum flowering at 15°C and 24 SD. ‘Bounty’ was more responsive to temperature, inducing flowers independently of the number of SD cycles at 9°C and 15°C. In ‘Senga Sengana’ flowering was induced independently of temperature and the number of SD cycles, indicating that it had a stronger dependence on other environmental effects. The effect of the number of short-day cycles and the temperature on vegetative growth variâtes such as the number of stolons and daughter plants, the length of flower trusses and petiole length were also studied.     

Effect of temperature on growth and flowering of litchi (Litchi chinensis Sonn.) cultivars

Summary

Moderate day/night temperatures (20/15° v. 15/10°C) increased vegetative growth and reduced flowering in the seven litchi cvs Tai So, Bengal, Souey Tung, Kwai May Pink, Kwai May Red, Salathiel and Wai Chee. At higher temperatures (25/20° and 30/25°C), vegetative growth was promoted further and flowering eliminated. Temperature also influenced the type of inflorescence formed. More leaves were formed on the panicles of trees growing at 20/15° than at 15/10°C. All terminal shoots on all cultivars produced panicles at 15/10°C. The relative order for the amount of flowering at 20/15°C was: ‘Wai Chee’>‘Salathiel’>‘Kwai May Pink’>‘Tai So’>‘Bengal’>‘Souey Tung’>‘Kwai May Red’. Cultivars which were vigorous at high temperatures produced fewer panicles at 20/15°C and fewer leafless panicles at 15/10°C. Only small differences were observed in the leaf water potential and the nutrient status of the shoots at different temperatures. Vigour and flowering of the cultivars in the glasshouse generally reflected field performance in subtropical Australia (Lat. 27°S). Low vigour could be useful for selecting litchi cultivars for good fruiting in environments with warm autumns and winters.     

Long-day control of flowering in everbearing strawberries

Summary

Photoperiod and temperature control of flowering in a number of perpetual-flowering or everbearing strawberry cultivars of widely varying pedigree has been studied in controlled environments. Flower bud initiation in the cultivars ‘Flamenco’, ‘Ridder’, ‘Rita’ and ‘Rondo’ was significantly advanced by long-day (LD) conditions at temperatures of 15°C and 21ºC; while, at 27ºC, flowering took place under LD conditions only. Some plants of the seed-propagated F₁-hybrid ‘Elan’, raised at 21°C, also flowered under short-day (SD) conditions at 27°C, but reverted to the vegetative state after a few weeks when maintained under these conditions. When vegetative plants growing in SD at 27°C were transferred to LD conditions at the same temperature, they consistently initiated flower buds and started flowering after about 4 weeks. At such a high temperature, flowering could thus be turned on and off by switching between SD and LD conditions. This applied to all the cultivars studied. Also the cultivar ‘Everest’, which was tested only at 21°C, produced similar results. Night interruption for 2 h was effective in bringing about the LD response. At 9°C, flowering was substantially delayed, especially in ‘Flamenco’ and, at this temperature, flowering was unaffected by photoperiod. Runner formation was generally promoted by high temperature and SD conditions, but the photoperiodic effect varied between experiments. We conclude that everbearing strawberry cultivars, in general, whether of the older European-type or the modern Californian-type originating from crosses with selections of Fragaria virginiana ssp. glauca, are qualitative (obligatory) LD plants at high temperature (27°C), and quantitative LD plants at intermediate temperatures. Only at temperatures below 10°C are these cultivars day-neutral.     

Fruit set and June drop in Cox's Orange Pippin apple as affected by pollination and treatment with a mixture of gibberellins A4 and A7

Single spray applications of 100 ppm of a mixture of the gibberellins A₄ and A₇ (GA_{4 + 7}) were made on fruiting spurs of the apple cultivar Cox's Orange Pippin to investigate the effect on set, June drop and growth of fruits, as well as on shoot development and flower-bud formation on the bourses. Applications were made from 1 to 50 days after full bloom following partial hand-pollination of flowers, i.e. two stigmas per flower pollinated. In another experiment applications were made from 1 to 20 days after full bloom following complete (five stigmas per flower) or partial (two stigmas per flower) hand-pollination, after open pollination, or on emasculated flowers.GA_{4 + 7} only temporarily increased fruit set after open pollination or after effemination of flowers, and then only after application 1 day after full bloom. GA_{4 + 7} did not affect the very high fruit set after complete or partial hand-pollination. Both latter pollination treatments induced an equally high fruit set.GA_{4 + 7} reduced June drop significantly whenever fruits were left after first drop, except after early applications following open pollination. GA_{4 + 7} was effective in June-drop reduction up to 40 days after full bloom, i.e. until the onset of the June drop.Fruit size was not clearly affected by GA_{4 + 7}. The smaller fruits obtained in some cases after GA treatment could be explained by assuming that maturity was reached by fruits that would have abscised without an exogenous GA_{4 + 7} supply. GA_{4 + 7} also increased seed abortion. Fruit length was increased by GA_{4 + 7} only for applications made up to 20 days after full bloom.GA_{4 + 7} stimulated bourse-shoot development to some extent. Flower-bud formation on the bourses was not clearly affected by GA_{4 + 7}, but was markedly influenced by the presence of fruits.That GA_{4 + 7} reduced June drop so much in spite of a slight promotive effect on bourse-shoot growth and a slight abortive action on seeds suggests that these gibberellins may be specific stimuli for apple-fruit growth after actual fruit set is achieved.     

Prohexadione–Ca inhibits vegetative growth of ‘Smoothee Golden Delicious’ apple trees

Experiments to test the effectiveness of prohexadione–Ca as a growth inhibitor in apple trees have been carried out for 3 years in the Middle Ebro Valley (Spain). Also, effects on fruit quality and flower initiation were evaluated. The application of 100–400 mg l⁻¹ of prohexadione–Ca between 12 and 30 days after full bloom (DAFB) to ‘Smoothee Golden Delicious’/M9 apple trees resulted in the inhibition of shoot growth, the effect increasing with concentration, and a greater inhibition was obtained when the trees were first sprayed 12–20 DAFB. A second spray was usually needed to avoid a regrowth of the shoots. The effectiveness of the second application was related to the concentration applied and the date of the first spray. The relative increase in trunk-cross-sectional area was not affected by the growth inhibitor. No negative effects on yield and fruit quality were found except for a reduction of soluble solid content. Flower initiation in the following year was not affected. Concentrations of 100–200 mg l⁻¹ applied shortly after full bloom should be recommended, bearing in mind that a second application might be necessary 6–8 weeks later.