Spray applications of naphthaleneacetic acid (NAA) at concentrations of 0.25 to 1.5% delayed bud break of sweet orange (Citrus sinensis (L.) Osbeck) seedlings for up to 177 days. Untreated buds on the same plants exhibited delayed growth initiation of up to 150 days due to translocated NAA. Length of time of bud break inhibition was dependent on NAA concentration, and the Na salt of NAA produced a more pronounced inhibitory effect than the ethyl ester formulation.
This study tested the effects of cutting length and auxin (NAA) concentration on adventitious root formation in softwood stem cuttings from mature eastern hemlock, Tsuga canadensis (L.) Carr., and carolina hemlock, T. caroliniana Engelm. Overall rooting percentage (41%) and percent mortality (22%) were higher for eastern hemlock compared with carolina hemlock (10% rooting and 13% mortality). Rooting percentage of each species responded differently to varying auxin concentrations (0, 1, 2, 4, 8 mm NAA). Maximum rooting (56%) for eastern hemlock occurred at 0 mm NAA; then decreased with increasing auxin concentration. Carolina hemlock rooting percentage increased from the control to a maximum (16%) at 1 mm NAA; then decreased with increasing auxin concentration. For both species, the lowest mortality occurred at the same auxin concentration as maximum rooting. The highest rates of mortality coincided with the same concentrations as the lowest rooting percentages. At all auxin concentrations, eastern hemlock had a higher number of roots and greater total root length relative to carolina hemlock. Mortality among 6-cm stem cuttings was twice that observed for 3-cm cuttings of both species. However, 6-cm cuttings of eastern hemlock that did form adventitious roots had more roots and longer total root length compared with 3-cm cuttings. Chemical name used: 1-naphthalenacetic acid.
Benzyladenine (BA), reported to increase fruit growth in apples, was evaluated with NAA to overcome NAA-induced inhibition of fruit growth. High volume sprays of NAA (15 mg·liter-1), BA (25 to 100 mg·liter-1) and combinations were applied to Redchief `Delicious' (king fruit = 10 mm). Yield was not significantly reduced. The combinations (NAA + BA 25, 50 or 100 mg·liter-1) resulted in the highest percentage of small fruit (39% < 70 mm) and the lowest percentage of large fruit (35% > 77 mm) compared to NAA, BA and hand thinned control. There was no significant effect of NAA or BA on size of king fruit in absence of lateral fruit competition on a given spur, while the combinations decreased (P = 0.01) king fruit size. NAA, but not BA, reduced growth of lateral fruit, with or without competition. However, the combinations caused marked suppression of lateral fruit growth and reduced seed content. With `Empire', both NAA (10 mg·liter-1) and BA (25 to 150 mg·liter-1) effectively thinned. Fruit size was greater with BA than NAA. The combinations (NAA, 10 mg·liter-1 + BA, 25 or 50 mg·liter-1) over-thinned and did not increase the amount of small fruit as in `Delicious'.
The plant cuticle is the prime barrier to penetration of foliar-applied plant growth regulators (PGR). Spray additives of various chemistries are frequently included in a tank mix to increase performance of PGRs. We have reported that urea and ammonium nitrate (AN) enhance transcuticular penetration of 14C-labeled NAA (pKa 4.2) from aqueous droplets (pH 5.2) and their subsequent deposits through enzymatically isolated tomato fruit cuticular membranes (CM). Studies on effects of Triton × surfactants on AN-enhanced NAA penetration showed an additional 25% increase in NAA penetration and the AN:surfactant interaction was significant. Also, some alkylamine hydrochlorides increased NAA penetration. Studies comparing NAA penetration through tomato and pepper fruit and Citrus leaf CM in the presence of 8 mM AN or 8 mM ethylamine HCl showed that all three species exhibited the same trend for penetration at 120 h: ethylamine HCl > AN > NAA only. Comparative NAA penetration for CM of the three species was pepper > Citrus > tomato, with significant differences (P > 0.006) in NAA penetration, as indexed by initial slope and penetration after 120 h. On addition of AN, NAA penetration was greater (range 3% to 40%) for Citrus and pepper CM than tomato CM. When ethylamine HCl was added, NAA penetration through Citrus and pepper CM was less (–37 and –27%, respectively) than tomato CM as measured by the initial slope, but 6% and 11%, respectively, more than tomato CM for penetration after 120 h. The differences in NAA penetration among the three species cannot be explained by cuticle thickness, since pepper and tomato CM are 2.5- to 3.5-fold thicker than Citrus CM. We have suggested that the enhanced NAA penetration mediated by AN and ethylamine HCl (and other alkylamine HCl examined) may be related to their hygroscopic properties leading to greater deposit hydration. The significance of the differences among the species CM and surfactant-enhanced NAA penetration will be discussed, in relation to diffusion in the non-living, non-metabolic plant cuticle.
The effects of naphthaleneacetic acid (NAA) and indolebutyric acid (IBA) on rooting, root quality, and budbreak of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stem cuttings were studied. Between 1 and 100 him, NAA was more effective than IBA in stimulating rooting. Regression analysis indicated that the highest rooting response to NAA was centered on 7.4 mM, whereas 100 mM IBA, the highest concentration tested, was the most effective. NAA concentration significantly affected budbreak percentage. Root quality was weak, but not significantly affected by auxin concentration.
For 2 years, 'Redchief Delicious' apple (Malus ×domestica Borkh.) trees were treated with combinations of NAA and oxamyl and 'Smoothee Golden Delicious' trees were treated with combinations of NAA and carbaryl. Oxamyl, at concentrations of 250 to 750 mg·L-1, but not NAA at concentrations of 1 to 6 mg·L-1, reduced fruit set, yield and crop value. NAA did not consistently affect average fruit weight or the percentage of small fruits on 'Redchief Delicious' trees. Carbaryl reduced fruit set and yield on 'Smoothee Golden Delicious' trees one of the two years. Fruit set and yield were negatively related to NAA concentration both years. In one of the two years the combination of NAA plus carbaryl was more effective than NAA alone. Treatments that provided adequate thinning tended to reduce crop value because the increase in fruit size did not compensate for the reduced yields. Chemical names used: 1-naphthyl-N-methylcarbamate (carbaryl); methyl N′,N′-demethyl-N [(methylcarbomoyl)oxy]-1-thiooxamimidate (oxamyl); 1-naphthaleneacetic acid (NAA).
Ethidium bromide (EB), at 10-5 to 10-4 M, progressively inhibits NAA-induced rooting of mung bean cuttings. Cycloheximide (CH), 6-methylpurine (6-MP) and kinetin (KIN) also inhibited rooting at the same concentrations, although CH and 6-MP were more effective.
At 70 and up to 130 hours of incubation, after cuttings received a 1-ml pulse of NAA (10-4 M), they exhibited a progressive increase in the number of observed adventitious roots. The addition of one of the inhibitors, 6-MP, EB or KIN to cuttings, pulsed 48 hours earlier with NAA, showed an initial slight inhibition with increased inhibition over time. CH, however, inhibited rooting immediately after addition. From these and other similar kinetic studies, it appears that 6-MP, EB and KIN operate at the transcriptional level and that CH inhibits translation.
Lineweaver-Burk plot analysis of NAA-induced rooting inhibition showed that EB may act as a competitive inhibitor of NAA. Since EB is a known intercalating agent and competitively inhibits NAA-induced rooting, NAA may influence gene expression by ultimately binding to DNA. Studies with space-filling and computer-generated models show that both NAA and EB can bind to certain dinucleotides by an intercalation mechanism.
NAA and Accel are used for fruit thinning of apples. However, when combined, many small (<65 mm) fruit were produced in `Delicious'. We extended our studies using Redchief `Delicious' and `Empire', and, since BA is common to both Accel and Promalin, to study the effect of NAA-thinning sprays on Promalin-treated Redchief trees. NAA (10–15 mg·liter–1) and Accel (25–100 mg·liter–1) were applied to Redchief and `Empire' at 100-mm king fruit diameter (KFD). NAA interaction with Promalin was studied using Redchief. Promalin (1.5 pt/A) was applied as a single spray (80% king bloom, KB) and as a split application (0.75 pt/A, 80% KB and repeated at 10-mm KFD) with NAA (15 mg·liter–1) at 10-mm KFD. In `Delicious', 2% to 9% of the fruit from Accel-treated trees was <65 mm in diameter, compared to 11% for NAA alone. However, when NAA was applied with Accel, 22% to 30% of the fruit was <65 mm and percentage of large fruit (75 mm+) was reduced by 24% to 36%. There was no strong interaction for fruit size in `Empire', but the combination decreased yield. NAA applied to Promalin-treated `Delicious' increased percentage of small fruit dramatically (14% to 25%). No increase in small fruit was observed with Accel of Sevin.
Naphthaleneacetic acid (NAA) sprayed as a 1% ethyl ester or sodium salt formulation below the grafts effectively controlled trunk and limb sprouts on topworked fig trees (Ficus carica L.). Reduction of scion growth and numbers of sprouts on unsprayed portions of grafted limbs indicated translocation of NAA for a distance of at least 10 cm.
Basal sucker shoots between 15 and 30 cm tall on multi-branched, tree-form crape myrtles (Lagerstroemia indica) were sprayed to run-off with NAA solutions of 0, 0.5, 1.0, and 1.5% in June. Five weeks later, sucker growth was assigned a visual rating from 0 to 4 denoting 0 to 100% control. Heights of three basal shoots were measured for each plant as another indicator of control. Visual ratings increased linearly from 1 to 3.6 as NAA increased from 0 to 1.5%. Basal shoot height decreased quadratically with increasing NAA concentration with the 1.0 and 1.5% NAA treatments resulting in a 53% reduction when compared to the control. Further work is needed to assess the effect of NAA on flowering and to determine if spring applications will result in season long control.
