Naphthaleneacetic acid (NAA) applied as a spray to apple trees on May 7 reduced fruit set, number of seed per fruit, percent and amount of reducing sugar in flesh of young fruits but did not affect protein level or fruit size. Fruit from trees sprayed with NAA on May 18 had more seed and less reducing sugar than the checks. The late NAA spray also reduced fruit size and set but did not affect the protein level of flesh or seed. Sprays of 1-naphthyl methylcarbamate (Sevin) applied on the same dates reduced fruit set but did not affect other factors measured. We propose that the reduced metabolite supply (reducing sugar) in the young fruit is the primary reason for reduced fruit set on trees sprayed with NAA and that effect on seed number is not related to this change in composition.
Leaves from succinic acid-2,2-dimethylhydrazide (daminozide)-treated seedlings of ‘McIntosh’ apple (Malus domestica Borkh) accumulated significantly more 45Ca than those from 1-napthaleneacetic acid (NAA)-treated seedlings. Stem sections from daminozide-treated seedlings accumulated significantly more 45Ca than stems from control seedlings. Total 45Ca content in daminozide-treated seedlings was significantly greater than in either controls or NAA-treated seedlings. The expected reduction in total shoot length by treatment with daminozide, NAA + daminozide and NAA was noted. The increases in 45Ca content in all treatments appear to be due in part to the concentration effect of reduced shoot growth and in part to an effect of daminozide on rate of uptake.
The cuticle is the prime barrier to penetration of foliar applied plant growth regulators, which must penetrate and be transported to a reaction site before a response can be induced. Urea has enhanced performance of Fe and Zn foliar sprays and a mixture of urea and ammonium nitrate (WAN) the performance of some herbicides. The mechanism of this enhancement is not clear. We find that urea and UAN increased 14C-NAA transport across enzymatically isolated tomato fruit cuticular membranes (CM) from simulated spray droplets using a finitedose diffusion system. The initial rate and total amount of NAA penetrated was significantly increased relative to NAA alone, the enhancement being greater for UAN than urea (total amount 101% vs. 78% at 120 hours) and for the NAA anion (pH 5.2, pKa 4.2) than for the nondissociated (pH 3.2) moiety. When evaluating the concentration effect of urea and NH4NO3 individually, the greatest enhancement with urea was at 62 mm and with NH4NO3 at 8 mm. Generally the effect of urea was significantly less than NH4NO3 (+24% vs. 296%). NAA penetration was greater with NH4NO3 than with KNO3 or Ca(NO3)2 or when the nitrate anion was replaced with sulfate or phosphate. Transcuticular penetration of NAA was enhanced greatly (190% in 120 hours) on removal of cuticular waxes; however, penetration was further increased (252% in 120 hours) by adding 8 mm NH4NO3. Methylamine hydrochloride (CH3NH2.HC1, 8 mm) also increased NAA diffusion, the initial slopes (>8 hours) were 23, 14, and 2 pmols·h–1 for methylamine, ammonium nitrate, and NAA alone, respectively, while the percent of applied that penetrated after 120 hours was 68.5, 67.6, and 21.4 for methylamine, ammonium nitrate, and NAA alone, respectively. The enhancement of NAA penetration by NH4NO3 equaled or exceeded that obtained with a group of surfactants of diverse chemistries. When the surfactant Triton X-100 was compared with NH4NO3, initial penetration was more rapid with ammonium nitrate (11.7 vs. 7.3 pmols·h–1) but percent penetrating after 120 hours was greater for Triton X-100 (80.5 vs. 66.8). The possible action of NH4NO3 on NAA uptake will be discussed.
Micelles of two nonionic surfactants (Triton X-114 and Neodol 91) were shown by gel filtration chromatography to solubilize nondissociated NAA molecules in aqueous solutions. Micelle solubilization of nonpolar active ingredients in aqueous spray systems alters the distribution of the chemical in the spray solution and may influence chemical deposit formation and penetration characteristics. Chemical names used: 2-(1-naphthyl)acetic acid (NAA), octylphenoxy polyethoxylate-7.5 POE (Triton X-114), linear alcohol (C9-11) polyethoxylate-6 POE (Neodol 91).
Generally, NAA is effective in inducing fruit thinning in `Delicious'. Although significant thinning may be induced, fruit size at harvest may not be closely related to crop load. Further, the magnitude of response to NAA may vary markedly between seasons. Herein, we present an analysis of response of `Redchief Delicious' over several years (tree age 11–14 years old) to high-volume sprays of NAA (15 mg·L–1), BA (25-50 mg·L–1), and CPPU (5 mg·L–1) at KFD of 8–12 mm. A single tree was used for each treatment replicated four to six times and response was measured by yield and fruit size distribution for each tree. In eight experiments over 4 years, NAA resulted in an average 22% reduction in yield, a 5.1% reduction in large fruit (70 mm+) and 2% reduction in small (<64 mm) fruit compared to NTC. There was a marked variation in response among years. Over 4 years, BA averaged a 5% decrease in yield, a 15% increase in large fruit and a 21% decrease in small fruit. In contrast, when NAA was combined with BA at 25-50 mg·L–1, yield decreased an average of 30%, large fruit decreased by 68%, and small fruit increased 8-fold (2.54 vs 20.6 kg/tree). CPPU alone (2-year study) had no significant effect on yield, but increased large fruit by 60% and significantly reduced production of small fruit. When CPPU was combined with NAA, yield was reduced in both years and the amount of large fruit was increased in 1995, but decreased in 1996. NAA had a very inhibitory effect on fruit size in 1996. One explanation may be that the crop was produced by lateral fruit (king flowers were lost to frost), and NAA has a greater inhibitory effect on lateral than king fruit. Results will be discussed in relation to studies with `Jonathan' and `Empire'.
The synthetic auxins NAA and 3,5,6-TPA were investigated for reducing abscission of mature citrus fruit in California (CA). NAA was investigated on navel orange trees in San Joaquin Valley and southern CA locations. Of the seven NAA experiments presented, five had substantial fruit drop. In these five experiments, a treatment of NAA reduced drop by 31% to 88% compared to the untreated control. Although NAA treatments as low as 25 mg·L-1 (acid equivalent) reduced drop, the greatest reductions in drop were obtained by spray concentrations in the 100 to 400 mg·L-1 range. 3,5,6-TPA was investigated for fruit drop control properties on navel orange and grapefruit grown in various CA locations. The untreated control in seven of the ten 3,5,6-TPA experiments had substantial fruit drop. In each of these cases, a treatment of 10, 15 or 20 mg·L-1 (acid equivalent) of 3,5,6-TPA reduced drop 69% to 96% compared to the untreated control. A strong linear response from 3,5,6-TPA in these seven experiments indicates maximum fruit drop reduction from the highest rate investigated. On an acid equivalent basis 3,5,6-TPA seems to be comparable to 2,4-D. Both NAA and 3,5,6-TPA were effective in controlling preharvest fruit drop in citrus under CA conditions. Both materials provided fruit holding late into the harvest season. NAA, and in particular 3,5,6-TPA, offer the potential to provide a substitute for 2,4-D which is commonly used for controlling fruit drop in many countries. Chemical names used: naphthaleneacetic acid (NAA); 3,5,6-trichloro-2-pyridinyloxyacetic acid (3,5,6-TPA, triclopyr); 2,4-dichlorophenoxyacetic acid (2,4-D).
Auxin induction of ethylene, and fruit growth rates were investigated as early indicators of NAA thinning response for Golden Delicious, Red Delicious, McIntosh, Empire, and Tydeman's Red over a four period. Abscission at the end of the drop period was correlated with ethylene evolution from leaves 24-48 hours after NAA application and with changes in fruit growth at 2-3 day intervals through 10-14 days after application. Variation in ethylene evolution and fruit growth were also associated with environmental conditions prior to and at the time of NAA application to determine which factors have the greatest influence on response. Ethylene was a better predictor of final fruit drop than changes in fruit size for all varieties tested. However both performed very well. The ethylene bioassay requires more equipment, but the response is more-immediate. Bourse, and spur leaves as well as fruit were capable of producing ethylene in response to NAA application. Thinning response was greatest when all leaves and fruit were treated with NAA, followed by the bourse and spur leaves. Little or no response was produced when the fruit alone were treated. Concentration experiments and radioisotope data indicate that ethylene response is directly related to the amount of NAA absorbed. Regression analysis indicates that approximately 60% of the variation in response can be predicted by ethylene evolution
Three levels of NAA (0, 10,000, and 20,000 ppm) and paclobutrazol (PP333; 0, 250, 500 ppm) were applied in latex paint to suckered vine trunks of ‘Okanagan Riesling’ (Vitis spp.). NAA reduced suckers/vine and percentage of sucker regrowth in each of three seasons. Cluster weight, berries/cluster, and berry weight were increased with NAA in each season, whereas vine size, °Brix, and total acidity (TA) showed a similar trend 1 year following application and thereafter. PP333 reduced sucker number and regrowth, but not as effectively as NAA, and its effects were shorter-lived. No yield components were influenced by PP333 except berry weight, which varied linearly in 1984 and 1986 and quadratically with concentration in 1985. PP333 increased °Brix and TA linearly 1 year following application. Both chemicals tended to reduce pH in 1984 and 1985, but NAA increased pH in 1986 relative to concentration. Chemical names used: 1-naphthaleneacetic acid (NAA); β-1[(4-chorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
NAA is commonly used for fruit thinning of apples. However, with spur-type `Delicious' fruit, size may be less than expected based on the remaining crop load. Attempts to enhance fruit size on NAA-thinned trees with benzyladenine (BA) resulted in an interaction causing an increase in small (≤64 mm) fruit. CPPU [N-(2-chloro-4-pyridinyl)-N'-phenylurea], a highly active cytokinin in promoting parthenocarpy and growth of a number of fruit, was evaluated alone and with NAA for its effects on cropping and fruit growth in Redchief `Delicious'. High-volume sprays of CPPU were applied at 0, 2.5, 5, and 10 mg·L–1 to 13-year-old trees at 7.26 mm king fruit diameter. NAA was applied at 15 mg·L–1 with and without CPPU at 5 mg·L–1. Each treatment consisted of a single tree replicated four times. Response was evaluated by determining yield per tree and fruit size distribution at harvest. CPPU increased the amount of large (≥70 mm) fruit produced without significantly reducing yield. The amount of large fruit produced was 35, 71, 91 and 85 kg/tree for the nonthinned control (NTC) and CPPU at 2.5, 5, and 10 mg·L–1, respectively. NAA (15 mg·L–1) reduced yield by 39 kg/tree and increased amount of large fruit by 44 kg/tree. When CPPU (5 mg·L–1) was oversprayed with NAA (15 mg·L–1), yield was reduced by 30 kg/tree, and amount of large fruit was increased by 56 kg/tree compared to the NTC. The interaction was not significant for yield but was significant (P = 0.01) for amount of large fruit produced. Seed content was significantly reduced by NAA and CPPU, the effect being greater for NAA and in small (51 to 56 and 57 to 63 mm) than in large (76 to 82 mm) fruit. These data showing no significant inhibition of fruit growth with a combination of NAA and CPPU in Redchief `Delicious' are in contrast with findings for a related cytokinin, BA, where fruit growth was depressed significantly when combined with NAA.
NAA (1-naphthaleneacetic acid) is widely used for thinning apples; however, its mechanism of action is not well understood. Postbloom application of NAA is cultivar-specific and may, in addition to causing fruit abscission, show unwanted side effects. The response of 5-year-old `Braeburn'/MM 111 apple (Malus domestica Borkh.) trees trained to palmette leader to NAA used alone or in combination with carbaryl (1-naphthyl-N-methylcarbamate) was evaluated in late thinning trials. The experiment was conducted at the Comahue National Univ. (lat. 38°56′S long 67°59′W), during the 1997-98 growing season. Treatments were 1) control, 2) NAA (13 ppm), and 3) NAA (6.5 ppm) + Carbaryl (600 ppm). Whole sprays were applied 17 Oct. at 22 days after full bloom (DAFB) to five trees per treatment. Fruit diameter (FD) was recorded twice weekly (n = 20 per date and treatment). At 169 DAFB, cropload and fruit fresh weight (FW) were determined. Fruit were then graded into size categories. Analysis of variance was used and mean separations were computed with Student's t test. Good thinning resulted from NAA applications; however, this did not reflect in increased mean FW. The number of fruit ≥70 mm was increased by 6.67%. Cropload was overthinned by NAA + carbaryl. Mean FW was slightly greater than control (185.15 and 172.45 g, respectively) and this treatment resulted in 90 % of the fruit ≥70 mm compared to 75 % from control. The following potential model best fitted the fruit growth pattern on non-thinned trees: FD =2.9077 DAFB0.6307 (R 2=0.98, P≤0.001). More work needs to be done to establish the most effective timing and concentration of spray for `Braeburn' to give the maximum crop of large fruit on a regular cropping basis.