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Abstract
Field observations indicate that conjunctive use of ethephon (Ethrel) and NAA (Fruitone-N) can induce early pecan [Carya illinoensis (Wangenh.) C. Koch] shuck (involucre) dehiscence, while greatly reducing undesirable leaflet abscission. Comparisons of the efficacy of 2,4-D and NAA in preventing undesirable leaflet abscission revealed that the comparative molar protective activity of 2,4-D greatly exceeds that of NAA, providing leaflets absolute protection against ethephon-induced abscission, but it was functionally inferior to NAA due to the induction of leaflet necrosis. Single ethephon treatments accelerated shuck dehiscence 3 to 6 weeks for several cultivars. Treatment of ‘Stuart’ and ‘Moneymaker’ pecan fruit and foliage, several weeks prior to the completion of natural shuck dehiscence, with a NAA-ethephon mixture accelerated shuck dehiscence by 5 and 3 weeks, respectively, without severe leaflet abscission or loss of nut quality. These data indicate possible development of harvest-aid technology for early harvesting of pecan without severe leaflet abscission. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon); (2,4-dichlorophenoxy)acetic acid (2,4-D); and 1-naphthaleneacetic acid (NAA).
the gift of Accel, Der-I Wang, AMVAC Chemical Corp. for the gift of NAA, and James Flore for loan of his instrumentation and valuable discussion. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal
Abstract
Effects of the surfactants Pace, Regulaid and Tween 20 were determined on foliar penetration of NAA and on NAA-induced ethylene production by cowpea [Vigna unguiculata (L.) Walp. subsp. unguiculata cv. Dixielee]. All three surfactants decreased surface tension of NAA solutions, causing a marked increase in wetting and in droplet : leaf interface area. The greatest increase in NAA penetration was obtained with Regulaid followed by Pace and Tween 20. The surfactant effect was most pronounced during the droplet drying phase, but penetration continued to take place from the deposit after drying. The mode of action of surfactants in enhancing NAA penetration is complex. Regulaid-enhanced penetration closely paralleled the increase in interface area, but similar relationships were not found for Pace or Tween 20, particularly at concentrations above the critical micelle concentration. Surfactant-enhanced NAA penetration caused an increase in NAA-induced ethylene production. There was a strong correlation (r = 0.82) between NAA penetration and ethylene production for doses of 0.5 to 2.5 μg/disk. Above 2.5 μg/disk, ethylene production increased at a decreasing rate. The potential for using auxin-induced ethylene production as an index for quantifying auxin penetration is discussed. Chemical names used: l-naphthaleneacetic acid (NAA), polyoxyethylene polypropoxypropanol dihydroxypropane (Regulaid), polyoxyethylene (20) sorbitan monolaurate (Tween 20), surfactant blend in paraffin base petroleum oil (Pace).
Abstract
In an attempt to solve the problems of nonuniform and delayed shuck dehiscense of pecan [Carya illinoensis (Wangenh.) C. Koch], ethephon and NAA were evaluated for their efficacy as harvest-aid treatments. A 3-year study under commercial-like orchard conditions using 75-year-old ‘Stuart’ trees resulted in a spray mixture of 9 mm ethephon and 1.5 or 3.0 mm NAA, or just 9 mm ethephon alone, accelerating shuck dehiscence by 1 to 2 weeks relative to that of the nontreated control. While all three treatments induced some degree of leaflet abscission, the two treatments employing the NAA and ethephon combination induced only about one-fourth (21% vs. 75%) as much leaflet abscission as when ethephon was used alone. However, this level of leaflet abscission (21%), plus an associated 50% drop in net photosynthesis for several days post-treatment, was sufficient to reduce in-shell nut yields in subsequent years. This appears to preclude commercial acceptability of such treatments for pecan. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon), 1-napthaleneacetic acid (NAA).
The effect of temperature on uptake of C-labeled NAA was determined using detached apple leaves. Uptake by both adaxial and abaxial surfaces was measured at 15 and 35C over a 24-hotm period. Foliar absorption of NAA by the abaxial surface was greater than that by the adaxial surface. Absorption by the abaxial surface increased linearly (P < 0.001) with temperature over the range of 15 to 35C. These results are discussed in relation to fruit thinning. Chemical name used: 2-(1-naphthyl)acetic acid (NAA).
These studies with apple (Malus domestica Borkh.) spur tissues were conducted to investigate the mechanism whereby NAA may stimulate fruit abscission in the spring but acts to prevent fruit drop in the fall. NAA-induced ethylene evolution from `Delicious' spurs in vivo was similar to that evolved from excised leaf and fruit tissues that later were treated in the laboratory and incubated in darkness at 20C. The peak in ethylene production occurred 24 hours after treatment at 30C, 48 hours after treatment at 20C, and production was still increasing 72 hours after treatment at 10C. Leaf tissue showed the greatest induction of ethylene from NAA followed by fruit and petiolar tissues. Induction was greatest early in the season and declined steadily until about “June drop.” After this time, none of the tissues showed significant capacity for ethylene induction. Chemical names used: 2-(1 -naphthyl) acetic acid (NAA).
Exogenous ethylene could not substitute for NAA to induce adventitious root initiation in juvenile petiole explants of English ivy (Hedera helix L.), indicating that the action of auxin-stimulated root initiation was not directly mediated through ethylene production. Mature petioles did not initiate roots under any auxin or ethylene treatment combination. Ethephon or ACC supplied at 50 or 100 μm was inhibitory to NAA-induced root initiation in juvenile petioles. The pattern of ethylene production stimulated by NAA application was significantly different in juvenile and mature petioles. Ethylene evolution by juvenile petioles declined to near control levels during from 6 to 12 days after NAA application. Reduction in ethylene production was due to reduced availability of ACC in juvenile petioles. Mature petioles continued to produce ethylene at elevated levels throughout the course of the experiment. Ethylene does not appear to play a significant role in the differential root initiation response of juvenile and mature petioles treated with NAA. However, ethylene appeared to have an inhibitory effect during root elongation stages of adventitious root development in juvenile petioles. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); 1-napthaleneacetic acid (NAA); 2-chloroethylphosphonic acid (ethephon).
A series of greenhouse experiments was conducted with `Shamrock' bell pepper (Capsicum annuum L.) to gain insight into the flower abscission mechanism and to investigate methods to reduce reproductive structure abscission due to low light intensity. Foliar sprays of STS reduced stress-induced abscission. Application of the synthetic auxin NAA to the ovary substituted for pollination to effect fruit set under nonstress conditions, but did not improve fruit set compared to pollinated controls under low-light stress. Ovary treatment with GA3 and BA either alone or combined with NAA had similar results to NAA treatment alone. Foliar sprays of NAA or CPA also did not improve fruit set under low-light stress conditions. Application of NAA in an aqueous paste to the abscission zone prevented abscission but inhibited fruit growth. Taken together, the results indicate that stress-induced abscission is not prevented by auxin application to the ovary or foliage. The interaction of ethylene and auxin in reproductive structure abscission under stress conditions requires further investigation. Chemical names used: 6-benzylaminopurine (BA), p-chlorophenoxy acetic acid (CPA), gibberellic acid (GA,), silver thiosulfate (STS).
Abstract
Leaf explants from ‘Sugar Daddy’ and ‘Sugar Plum’ petunia (Petunia hybrida L.) were pretreated in solutions of 0, 200, 400, and 800 mg/liter 6-benzylamino purine (BA) and were placed in a cytokinin-free modified Murashige and Skoog (MS) medium, to which 0.05, 0.1, or 0.2 mg/liter naphthaleneacetic acid (NAA) were incorporated to test interaction. NAA at 0.05 or 0.1 mg/liter increased shoot number, fresh weight, and shoot quality rating for ‘Sugar Daddy’, while in ‘Sugar Plum’ addition of NAA increased shoot fresh weight and improved shoot quality rating without any effect on shoot number.
Abstract
Treatments with gibberellic acid (GA3), naphthaleneacetic acid (NAA), or their combination to Cyclamen persicum Mill. ‘Swan Lake’ plants resulted in separate, antagonistic, or cooperative effects on leaf lamina unfolding, days to flowering, number of leaves at first flower, and length of the first flower's peduncle. Generally, GA3 accelerated plant growth nonspeciflcally, resulting in plants which flowered earlier than untreated plants, but with a similar number of leaves at first bud flowering. The combination of GA3 plus NAA specifically accelerated flowering, but this effect diminished as the treatment frequency or quantity of the NAA application increased.