Three experiments were conducted at two locations, two at Summerland, British Columbia, Canada and one at Corvallis, Ore., to evaluate synthetic auxins (MCPB-ethyl or NAA) and ethephon as blossom thinners for `Fuji' apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.]. These experiments also involved application of carbaryl at 1000 mg·L-1 in the postbloom period. All blossom thinners were sprayed at 85% full bloom while carbaryl was applied at 11-mm fruit diameter. Within these experiments, MCPB-ethyl at up to 20 mg·L-1 or NAA at up to 21 mg·L-1 increased whole flower cluster removal linearly with rate; however, with the Corvallis experiment MCPB-ethyl failed to result in any thinning. Neither auxin treatment consistently reduced fruit set on the remaining clusters, resulting in “clustering”. Bloom-time application of ethephon at 100 mg·L-1 with NAA further reduced crop load. Carbaryl reduced total crop load by increasing both whole cluster removal and number of sites with a single fruit. Return flowering was not improved by the auxin treatments except where there was very excessive crop reduction. Ethephon or carbaryl promoted return flowering with the carbaryl effect being more pronounced. However, this carbaryl effect was significantly countered by the bloom-time auxin whereas ethephon overcame the negative effects of the auxin treatments. The combined use of ethephon and carbaryl was effective in terms of both crop reduction and return flowering benefits. Chemical names used: 1-naphthyl N-methylcarbamate (carbaryl); 2-chloroethylphosphonic acid (ethephon); ethyl 4-(4-chloro-2-methylphenoxy) butanoate (MCPB-ethyl); and 2-(1-naphthyl) acetic acid (NAA).
Abstract
Summer pruning significantly restricted radial growth of trunks, shoot growth, and root growth of young trees of ‘Delicious’ apple (Malus domestica Borkh.) the year of treatment. Summer pruning early in the season was most devitalizing. Application of naphthaleneacetic acid (NAA) to the pruning cut after summer pruning had inconsistent effects on dry weight accumulation, but usually reduced regrowth. Growth of summer-pruned trees was generally similar to growth of comparably dormant-pruned trees the year following treatment.
`Empire' is a popular new apple with fruit growers in the northeastern United States, noted for producing small-sized fruit. To test the efficacy of chemical thinners and rootstocks for increasing fruit size of `Empire', three-tree plots containing trees on M.7 EMLA, MM. 111, and seedling rootstocks were chemically thinned at petal fall with 10 ppm NAA or 85 ppm 6 BA, applied as Accel. Both NAA and Accel reduced fruit set. Trees on M.7 EMLA had higher set than trees on seedling. Yield was highest on M.7 EMLA and lowest on seedling. Fruit diameter after final set in July was increased by both chemical thinners and was greater for both clonal rootstocks than for seedling. Fruit on seedling trees were delayed in maturity relative to the two clonal rootstocks. Accel increased the number of fruit 70 mm or greater in diameter, while NAA increased the number of fruit in the 64- to 69-mm-diameter class. Analysis of covariance with crop load suggested that the increase in fruit size associated with Accel was a direct effect rather than a secondary effect from thinning.
Abstract
Adventitious root initiation decreased in ‘Berken’ mung bean cuttings treated with ≥ 10−4 m (2-chloroethyl) phosphonic acid (ethephon). Ethephon at 10−3 but not 10−5 m reduced root length and caused a redistribution of roots along the hypocotyl. The application of ethephon in combination with indoleacetic acid (IAA), indolebutyric acid (IBA), naphthaleneacetic acid (NAA), and 2,4-dichlorophenoxyacetic acid (2,4-D) reduced root initiation. An initial treatment of ethephon followed by NAA, or NAA followed by ethephon, inhibited root initiation to the same degree. Ethephon—whether applied at the time of cutting preparation or up to 12 hours later—inhibited root initiation to the same extent.
Benzyladenine (BA), carbaryl (CB), daminozide (DM), and naphthaleneacetic acid (NAA) were applied postbloom as fruitlet thinning agents to mature `Empire' apple (Malus domestica Borkh.) trees. BA, NAA, and CB reduced fruit set and yield per tree, and increased fruit size, percent dry weight, soluble solidscontent and return bloom. Fruit size was reduced, return bloom, length: diameter ratio and flesh firmness were increased, and fruit set and yield unaltered by DM. Although fruit set and yield were similar for BA, NAA, and CB, BA treated fruit were larger, indicating that BA increased fruit size beyond the effect attributable to chemical thinning alone. BA increased the rate of cell layer formation in the fruit cortex, indicating that BA stimulated cortical cell division. NAA, CB and DM had no effect on cell division rate. Mean cortical cell diameter at harvest was increased by NAA and CB and reduced by DM. Cell diameter at harvest in BA-treated fruit was similar to the control. These data support the hypothesis that BA-induced fruit size increase in `Empire' apple results from greater numbers of cells in the fruit cortex, whereas the fruit size increase due to NAA or CB is a consequence of larger cell size. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; 1-napthaleneacetic acid (NM); 1-naphthalenyl methylcarbamate [carbaryl (CB)]; butanedioic acid mono (2,2dimethyl hydrazide) [daminozide (DM)].
`McIntosh' apples (Malus ×domestica Borkh.) display a rapid increase in ethylene production as they ripen, resulting in more preharvest drop and accelerated softening compared with other major cultivars. Economic considerations often dictate a choice between delaying harvest to achieve color development or harvesting earlier to avoid excessive fruit softening and drop. We have evaluated the effects of plant growth regulators (PGRs) and summer pruning on this balance. Treatments were applied to trees in the Mid-Hudson region in New York state in 1995 and 1996, and a subset of treatments was applied in the Champlain Valley region in 1996. NAA, applied at 10 mg·L-1 in 1995 and 20 mg·L-1 in 1996, reduced drop on only one sample date in only one of the three trials. Ethephon at 150 mg·L-1 plus 10 mg·L-1 NAA, accelerated ripening and permitted harvest before substantial drop occurred. However, earlier harvest resulted in smaller fruit size, and if ethephon-treated fruit were not picked within a narrow window, rapid drop ensued, and fruit developed a high senescent breakdown incidence during storage. ReTain, containing AVG, at 124 g·ha-1 a.i. delayed drop in all three trials, but its use resulted in firmer fruit after storage in only two of seven comparisons. Use of ethephon on AVG-treated trees enhanced red color but accelerated drop, although it was reduced less than when ethephon was used alone. Severe late summer pruning accelerated red color development, drop and ripening in both years of the study. AVG was more effective for management of `McIntosh' harvest in the cooler Champlain Valley region than in the Mid-Hudson Valley region. Chemical names used: naphthalene acetic acid (NAA); 2-chloroethylphosphonic acid (ethephon); aminoethoxyvinylglycine (AVG).
Abstract
Naphthaleneacetic acid (NAA) and 1-naphthyl N-methyl carbamate (carbaryl) applied separately in both dilute and concentrated sprays significantly increased fruit size; however, when butanedioic mono-2,2-dimethylhydrazide (daminozide) was added, fruit size remained about the same as on unsprayed check trees. Crop load was not significantly affected by any of these treatments. Dilute and concentrated sprays of carbaryl produced more return bloom than did NAA. The most effective treatments were combinations of NAA and carbaryl, either dilute or concentrated. Combining first-cover pesticides [azinphosmethyl (guthion) and cis-N-(trichloromethyl)thio)-4-cy-clonexane-l,2-dicarboximide (captan)] with NAA, and captan with carbaryl, produced satisfactory thinning.
NAA, a weak organic acid plant growth regulator (pKa 4.2), penetrates the plant cuticle preferentially as an undissociated molecule (<10% dissociated at pH 3.2). We have reported, using a finite dose diffusion system, that NH4NO3 (AN, 8 mM) at pH 5.2 (>90% dissociated) enhanced the penetration of 14C-NAA through isolated tomato fruit cuticular membranes (CM). AN appears to preferentially enhance penetration of the dissociated NAA molecule over the nondissociated form. A possible mode of action is that AN affects the cuticle matrix, allowing for greater NAA penetration. Acid treatment (4 N HCl) of the cuticle, which alters the cuticle's ionic characteristics, resulted in a 10% reduction in NAA penetration from droplets in the presence of AN. When AN (80 mM) was included in the receiver solution of the diffusion cell in an effort to infuse the cuticle matrix, NAA penetration was not increased compared to when AN was present in the applied droplet. AN (8 mM) also increased NAA penetration through dewaxed tomato cuticular membranes (DCM; +252% for DCM vs. +190% for CM in 120 h). Since AN only enhances NAA penetration when included with the NAA in the treatment droplet, the AN effect may be related to the role of the droplet/deposit (droplet residue) as a donor. This conclusion is further supported with sorption studies, where AN over a 100-fold concentration range (0.8–80 mM) did not increase NAA sorption by tomato fruit CM and where no deposit is present. The role of the physicochemical nature of the deposit, including the chemical/ionic characteristics of any additive (i.e., AN) and active ingredient will be discussed.
Several inhibitors of ethylene biosynthesis and action, as well as an atmospheric ethylene scrubber, were used to investigate the role of ethylene in adventitious root initiation in de-bladed petioles from the juvenile and mature phase of English ivy (Hedera helix L.). Induction of root primordia required NAA regardless of the inhibitor treatment. Difficult-to-root mature petioles have been shown to produce higher amounts of ethylene than easy-to-root juvenile petioles. However, mature petioles failed to root under any combination of NAA and inhibitor treatment, indicating that the continued evolution of ethylene in NAA-treated mature petioles was not responsible for the absence of a rooting response. Root initiation in juvenile petioles was not affected by treatment with the ethylene action inhibitors STS and NDE, nor by removal of atmospheric ethylene with KMnO. Inhibition of ethylene biosynthesis using AVG or AOA reduced root initiation in juvenile petioles, but this response was not well-correlated to the observed reduction in ethylene evolution. The inhibitory action of AVG could not be reversed by the addition of ethylene gas or ACC, which indicated that AVG could be acting through a mechanism other than the inhibition of ethylene biosynthesis. Chemical names used: 1-naphthalene acetic acid (NAA); l-aminocyclopropane-l-carboxylic acid (ACC); silver thiosulfate (STS); 2,5-norbornadiene (NDE); aminoethyoxyvinyl-glycine (AVG); aminooxyacetic acid (AOA).
`Saturn', `Mars', and `Reliance' were compared based on their different Vitis vinifera and V. labrusca compositions. Disks (10 mm) from young leaves were placed abaxial side down on a standard media containing NAA or 2,4-D at 0.0, 1.0, and 2.0 mg/L with BAP at 0.0, 0.1, and 0.2 mg/L. Each treatment was replicated in 10 culture tubes and incubated at 25 ± 1C under cool-white fluorescent light for 10h photoperiods. Calli were compared by size, color, and occurrence of morphogenesis. NAA generally produced a larger callus by cultivar than 2,4-D. A greater quantity of callus was generally produced with the increase of the V. labrusca component. Callus produced on 2,4-D medium was round, compact and light to dark green in color. However, callus produced on NAA medium was amorphous, friable, and ranged in colors. Rooting occurred on some calli produced on NAA media.