G. L. Steffens

Breaking bud dormancy in apple with a plant bioregulator, thidiazuron.

Abstract The effects of N-phenyl-N′-1,2,3,-thidiazol-5-ylurea (thidiazuron; Dropp; SN49537; TDZ) on metabolic changes in apple buds during dormancy break were determined. The data showed that thidiazuron has the capacity to release lateral buds from dormancy. Decreasing degree of bud break and bud growth with thidiazuron treatment occurred in a basipetal direction, suggesting a gradient of increasingly deep rest from shoot apex to base. The breaking of dormancy by thidiazuron is correlated with increase in DNA, RNA, protein, 1-aminocyclopropane-1-carboxylic acid (ACC), 1-(malonylamino) cyclopropane-1-carboxylic acid (MACC), S-adenosylmethionine (SAM) as well as with greater polyamine formation. Polyamine and ethylene biosynthesis did not seem to be competing for SAM, their common substrate, during bud break and bud development. The release of dormancy in apple bud by thidiazuron was inhibited by cordycepine, 5-fluorouracil, 6-methylpurine and cycloheximide. Inhibition of bud break and bud growth also resulted from treatment with α-difluoromethylarginine (DFMA) and α-difluoromethylornithine (DFMO). DFMO was more inhibitory than DFMA.

Effect of paclobutrazol on water stress-induced ethylene biosynthesis and polyamine accumulation in apple seedling leaves

Abstract Ethylene biosynthesis and polyamine content were determined in [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol] (paclobutrazol) pre-treated and non-treated water-stressed apple seedling leaves. Paclobutrazol reduced water loss, and decreased endogenous putrescine spermidine content. Gibberellic acid (GA) counteracted the inhibitory effect of paclobutrazol on polyamine content. Paclobutrazol also prevented accumulation of water stress-induced 1-aminocyclopropane-1-carboxylic acid (ACC), 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), ethylene production and polyamines in apple leaves. α-Difluoromethylarginine (DFMA), but not α-difluoromethylornithine (DFMO), inhibited the rise of putrescine and spermidine in stressed leaves. S-Adenosylmethionine (SAM) was maintained at a steady state level even when ethylene and the polyamines were actively synthesized in stressed apple seedling leaves. The conversion of ACC to ethylene did not appear to be affected by paclobutrazol treatment.

Gibberellin Content of Immature Apple Seeds from Paclobutrazol-Treated Trees over Three Seasons

Seeds from heavily fruiting (“on-year”), mature untreated, and paclobutrazol-treated apple trees (Malus domestica Borkh. cv. Spartan) were sampled in mid-June 1987, mid-July 1987, and mid-July 1990. After seeds were freeze-dried, gibberellins (GAs) were extracted, purified, and fractionated via C18 reversed-phase high-performance liquid chromatography (HPLC). Nine GAs (GA1, GA3, GA4, GA7, GA8, GA9, GA19, GA20, and GA53) were quantified by the use of deuterated GA internal standards. Paclobutrazol trunk drench treatments reduced vegetative shoot elongation in the seasons that seeds were sampled by 55% or more. Between June 17, 1987 and July 15, 1987, the dry weight of seeds from both untreated and treated trees increased about 2.5 times and there were reductions, on a per seed basis, of GA4 in seeds from both untreated and treated trees, of GA7 in seeds from treated trees, and of GA9 in seeds from untreated trees. However, GA9 increased in seeds from treated trees. Changes in levels of some of the early-13-hydroxylation pathway GAs (GA15 GA3, GA8, GA19, GA20, and GA53) also occurred during the month. For mid-July harvested seeds, the pattern, with some exceptions, was that 2 years after paclobutrazol treatment (1987), levels of early-13-hydroxylation pathway GAs in seeds from treated trees were lower compared to controls but after 5 years (1990) their levels tended to increase. For the non-13-hydroxylated GAs (GA4, GA7, and GA9), 2 years after paclobutrazol treatment, GA4 levels were equal in seeds from untreated and treated trees, GA7 decreased in seeds from treated trees compared with controls, but GA9 levels increased. Levels of these three GAs were higher in seeds from treated trees 5 years after treatment (1990) but levels of GA4, GA7, and GA9 dramatically increased in seeds from treated trees 4 years after treatment (1989), as we previously reported.

Size, flowering and fruiting of maturing own-rooted ‘Gala’ apple trees treated with paclobutrazol sprays and trunk drenches

Abstract Four-year-old, own-rooted, micropropagated cultivar ‘Gala’ apple ( Malus domestica Borkh.) trees were, (1) untreated, (2) treated with paclobutrazol (paclo) sprays (SP) at 500 or 1000 mg l −1 2, 4 and 6 weeks after full bloom or (3) treated with the 500 or 1000 mg l −1 paclo sprays plus a paclo trunk drench (TD) at 2.9 g per tree (SP + TD) in mid-May. Fruit load on trees of one treatment set was left intact (normal load) whereas 30–40% of the fruit was removed annually from the other set (reduced load) after ‘June drop’. Reducing fruit load in late May or early June over the 6-year period had little influence on vegetative growth, flower density, or fruit quality but fruit yields and the 6-year yield efficiency index were reduced. There were few differences between paclo 500 and paclo 1000 SP treatments. Compared with paclo SP + TD, paclo SP treatments caused fewer and less persistent changes. Over the 6-year period, paclo SP reduced trunk cross-sectional area (TCSA) 17% whereas paclo SP + TD reduced it by 49%. Flowering, fruit size and yield were minimally altered by paclo SP but paclo SP + TD reduced flower clusters over two seasons and reduced the 6-year average number of fruit per tree. Trees treated with paclo via sprays plus the trunk drench, especially paclo 1000 SP + TD, tended to develop biennial flowering patterns. Weight per fruit was reduced in two seasons by paclo SP + TD but it was greater in seasons when fruit numbers were reduced (low number of flowers). Fruit yields were reduced over four seasons by paclo SP + TD resulting in an overal yield reduction of 27% however, because TCSA was reduced by paclo SP + TD, the 6-year yield efficiency index (fruit yield per unit TCSA) was increased. Six-year average fruit length to width ratios were lower and russeting ratings were higher for fruit from trees receiving paclo SP + TD treatments compared with controls. Paclobutrazol did not alter net photosynthesis, stomatal conductance, leaf chlorophyll content or specific leaf weight the third season after treatment.

Influences of uniconazole on growth, fruiting, and photosynthetic activity of tissue culture-propagated own-rooted apple trees

Abstract Tissue culture-propagated (TC) own-rooted ‘Gala’ and ‘Triple Red Delicious’ apple trees grown at three planting densities were not treated (TC control) or were treated with annual uniconazole sprays or two trunk drenches starting with the third or fourth growing season. Budded (BUD) trees on M. 7a rootstock were also included as controls. After both the fifth and sixth growing seasons, the cultivars grown and the treatments applied had more influence on the attributes measured than did planting densities. Flowering and yield were greater on ‘Gala’ trees compared with ‘Triple Red’ for the fifth, but not the sixth season. The tree propagation method did not influence flower numbers and yield of ‘Gala’ trees in either the fifth or the sixth growing season but flower numbers were greater on BUD compared with TC trees of ‘Triple Red’ for both seasons. Flowering of TC ‘Triple Red’ trees tended to be increased by uniconazole treatment. Uniconazole applied by the trunk drench method markedly retarded vegetative growth of ‘Gala’ trees during the fifth season but flowering was reduced the following season. The trunk cross-sectional area of control TC trees for both cultivars increased more than for BUD trees but uniconazole treatment slowed trunk cross-sectional area increase so that treated TC trees were maintained at nearly the same size as BUD trees. Overall, ‘Triple Red’ leaves had higher chlorophyll concentrations than ‘Gala’ leaves, but there were no differences between BUD and TC leaves for net photosynthetic rate (Pn), stomatal conductance for water (g sw ), relative chlorophyll concentration, or specific leaf weight (SLW). Uniconazole treatment increased mean seasonal Pn, g sw , relative chlorophyll, and SLW compared with controls.

Long-term evaluation of micropropagated apple trees: vegetative growth, cropping, and photosynthesis

Abstract Micropropagated apple ( Malus domestica Borkh.) trees of 20 cultivars, of both standard and spur-type growth habits, were grown for up to 14 years and measurements taken annually of size (trunk cross-sectional area), flowering and yield. For three consecutive years (1988–1990), photosynthesis, stomatal conductance, chlorophyll content and specific leaf weight were measured on three trees of each of 16 of these cultivars on at least three dates per year. The data show differences among the cultivars in vegetative vigor, age at which flowering began, fruit yields, photosynthesis and stomatal conductance. Trees did not display intraclonal variation except for one spur type, ‘Redspur Delicious’, in which the spur characteristic was variable from tree to tree. The results document growth and yield data for micropropagated trees of a broad range of apple cultivars; no other data are available in the literature for most of these cultivars.

Effects of growth regulators on growth and fruiting of own-rooted ‘Golden Delicious’ apple trees

Abstract Established tissue-culture propagated own-rooted cultivar ‘Golden Delicious’ apple ( Malus domestica Borkh.) trees were treated with paclobutrazol at a dosage of 40 mg cm −2 of trunk cross-sectional area (average of 1.48 g per tree) via trunk drench at the end of the fifth growing season. They responded the second season after application. Treatment with the triazole GA biosynthesis inhibitor had more effect on vegetative growth than on flower cluster or fruit number. It reduced terminal shoot length and tended to reduce fruit yield and seasonal net photosynthesis on a leaf area basis. Weight per fruit was not changed but fruit length tended to be slightly reduced whereas russeting index was increased. Promalin (GA 4 + 7 + BA) applications to paclobutrazol-treated trees did not alter growth or fruiting. Despite the fact that paclobutrazol inhibited terminal shoot growth, treated trees went into biennial bearing as readily as untreated trees after a heavy fruit load season. Vegetative growth was vigorous the “off year” and terminal shoot growth was no longer inhibited by paclobutrazol. Applications of GA 4 + 7 to trees during the “off-year” did not affect vegetative growth that season or fruiting the following season. “On year” yield tended to be reduced from trees that had been treated with paclobutrazol 5 years earlier.

Plant growth inhibition by naphthoic acid esters

Abstract A series of alkyl esters of 1 - and 2-naphthoic acids and 1 - and 2-naphthaleneacetic acids were synthesized and tested for growth regulating activity