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Apple (Malus domestica Borkh.) trees were propagated by budding from selected fully grown hybrids that ranged in height from 1.5 to 8 m. The growth and development of the selected budded trees after 7 years in the orchard was similar to that of the parent trees. Additional grafting studies showed that the dwarfism was not associated with the roots. Differences in photosynthetic activity and associated processes were not related to the size difference between tissue culture-propagated orchard-grown standard cv. Golden Delicious and dwarf hybrid trees. Applications of GA3 did not stimulate elongation of shoots of dwarf trees. Shoots of both standard and dwarf trees started to develop in mid-April when they contained nearly the same amounts of GA1, GA3 and GA8, but standard shoots contained higher concentrations of GA19, GA20 and GA29. On 2 June standard shoots were almost three times the length of dwarf shoots, but the number of leaves and area per leaf were nearly the same. The relative amounts of GAs on 12 May and 2 June for both plant types were similar to those on 20 April, except that GA19, GA20, GA1 and GA29 levels had declined. Gibberellin levels in standard shoots declined further between 2 and 22 June, after which there was no further shoot elongation or production of new leaves. Between 2 June and the end of the growing season, when summer temperatures were high, dwarf shoots continued to elongate slowly and to develop new leaves, which expanded little. During this time, the GA19 content of dwarf shoots nearly doubled, whereas the amounts of GA20, GA1, GA29 and GA8 declined. By the end of the season, standard shoots were 40 cm in length with 20 leaves and dwarf shoots were 28 cm in length, but with 36 leaves. High summer temperatures appear to induce loss of GA-responsiveness in orchard-grown dwarf trees and to cause a reduced rate of conversion of GA19 to GA20 in these genotypes. [ABSTRACT FROM AUTHOR]

Tissueculturepropagated own-rooted cv. Spartan apple trees (Malus domestica Borkh.) planted in 1979 were treated in 1983 and 1985 via a soilline trunk drench with the plant growth retardant paclobutrazol [(2RS, 3RS)1(4chlorophenyl)4,4dimethyl-2-(1,2, 4-triazol1yl) pentan-3-ol]. Seeds of immature fruits from untreated and treated trees were sampled in 1989 ca 75 days after full bloom. After seeds were freezedried, gibberellins (GAs) were extracted, purified and fractionated via C18 reversedphase highperformance liquid chromatography (HPLC). Gibberellins A1, A3, A4, A7, A8, A9, A15, A17, A19, A20, A24, A34, A35, A44, A51, A53, A54, A61, A62, A63 and A68 were identified by using C18 HPLC, gas chromatography-selected ion monitoring and Kovats retention indices. Eight of the Gas identified were also quantified by using deuterated internal standards. The paclobutrazol applications caused a 55% reduction of vegetative shoot elongation in 1989, but both treated and untreated trees had developed a biennial bearing pattern by that time (heavy bloom or "on year" in 1989). Levels of early 13hydroxylation pathway GAs, viz. GA53, GA19, GA20, GA1 and also GA3, were not altered by treatment. However, GA4, GA7 and GA9 were increased 13.4, 6.5 and 3.8 times, respectively, in seeds of fruit from treated compared to untreated trees [ABSTRACT FROM AUTHOR]

High temperature has been implicated as the major factor responsible for dwarfing of selected apple (Malus domestica Borkh.) trees of a hybrid population of cv. Goldspur Delicious × cv. Redspur Delicious. Dwarf plants grew only 2.2 cm in 63 days under a ramped temperature regime (night 15°C, day ramped up to 38°C, held for 2 h and ramped down to 15°C - 14 h daylength), whereas semi-dwarf plants grew 26.3 cm. At a constant 27°C (14 h daylength), both dwarf and semi-dwarf plants grew nearly 50 cm. The gibberellin biosynthesis inhibitor, paclobutrazol, retarded growth of semi-dwarf plants in both ramped and constant environments and dwarf plants in the constant 27°C environment. It did not further reduce the size of dwarf plants growing under the ramped regime. Gibberellin (GA3) treatment reversed the inhibition of growth caused by paclobutrazol for all plants except it did not restore growth of dwarf plants in the ramped environment. These data suggest that neither pacobutrazol-treated nor untreated dwarf plants growing in the ramped environment (or in the orchard during hot summer months) are able to respond to GA3. In constrast, GA3 was utilized by the paclobutrazol-inhibited dwarf plants growing at constant 27°C, enabling shoot elongation to take place. It appears that high temperature may have caused alterations in GA target tissues in dwarf plants so that they no longer had the capacity to respond to GA. [ABSTRACT FROM AUTHOR]

'York Imperial' apple seedlings (Malus domestica Borkh.) were continuously supplied via the roots with paclobutrazol [(2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl- 2-(1,2,4-triiazol-1-yI)pentan-3-oI)], a triazole GA biosynthesis inhibitor, at 0.68 μM in a nutrient solution. In comparison to controls, seedlings treated with paclobutrazol for 66 days showed a 91% reduction in shoot length, a 66% reduction in leaf area but only a 17% reduction in leaf number. This effect could be reversed by GA, applied to the foliage at 71.4 μM 0, 19 or 35 days after paclobutrazol was initially supplied and leaf area values for paclobutrazol-treated seedlings given both treatments did not differ significantly from controls. Plots of growth data indicate linearity of shoot longitudinal growth of GA3-treated seedlings. Leaf area increase was non-linear alter GA3 treatment up to approximately 30 days, when the rate dropped. On a per shoot basis, leaf weight closely followed leaf area but on a per unit area basis, paclobutrazol-treated leaves were heavier than controls; GA3 applications temporarily reversed this trend. [ABSTRACT FROM AUTHOR]

High temperature has been implicated as the major factor responsible for dwarfing of selected apple (Malus domestica Borkh.) trees of a hybrid population of cv. Goldspur Delicious × cv. Redspur Delicious. Dwarf plants grew only 2.2 cm in 63 days under a ramped temperature regime (night 15°C, day ramped up to 38°C, held for 2 h and ramped down to 15°C - 14 h daylength), whereas semi-dwarf plants grew 26.3 cm. At a constant 27°C (14 h daylength), both dwarf and semi-dwarf plants grew nearly 50 cm. The gibberellin biosynthesis inhibitor, paclobutrazol, retarded growth of semi-dwarf plants in both ramped and constant environments and dwarf plants in the constant 27°C environment. It did not further reduce the size of dwarf plants growing under the ramped regime. Gibberellin (GA3) treatment reversed the inhibition of growth caused by paclobutrazol for all plants except it did not restore growth of dwarf plants in the ramped environment. These data suggest that neither pacobutrazol-treated nor untreated dwarf plants growing in the ramped environment (or in the orchard during hot summer months) are able to respond to GA3. In constrast, GA3 was utilized by the paclobutrazol-inhibited dwarf plants growing at constant 27°C, enabling shoot elongation to take place. It appears that high temperature may have caused alterations in GA target tissues in dwarf plants so that they no longer had the capacity to respond to GA. [ABSTRACT FROM AUTHOR]

Some physiological and biochemical changes in apple seedlings (Malus domestica Borkh cv. `York imperial') caused by an inhibitor of gibberellin biosynthesis, paclobutrazol [(2RS. 3RS)-1-(4-chlorophenyl)-4.4-dimethyl-2-(1 ,2,4-triazol-1-yl) pentan- 3-ol], were determined. Paclobutrazol shifted assimilate partitioning from leaves to roots, increased carbohydrates in all parts of apple seedlings, increased chlorophyll content on a leaf area basis, increased soluble protein in leaves, increased mineral element concentration in leaf tissue and increased root respiration. Foliar application of gibbercllic acid (GA3) counteracted the effects induced by paclobutrazol. [ABSTRACT FROM AUTHOR]