Effects of NAA, TIBA, ethephon, and CMN-Pyrazole on fruit detachment force (FDF) of mature `Valencia' and `Hamlin' orange [Citrus sinensis (L.) Osb.] fruit were examined in 2000 and 2001. NAA effectively inhibited the reduction in FDF or fruit abscission caused by ethephon when applied to the abscission zone 24 hours before ethephon application, but had no significant effect when applied to the fruit without contacting the abscission zone, or to the peduncle ≈4 cm above the abscission zone. TIBA, an auxin transport inhibitor, decreased FDF of mature fruit and promoted fruit abscission when applied alone as a spray to the canopy or directly to the fruit peduncle. This response was dependent on TIBA concentration. TIBA was more effective when applied in combination with ethephon or CMN-Pyrazole than alone. These results are consistent with our previous data that endogenous auxin concentration in the abscission zone of mature `Valencia' orange fruit is one of the factors controlling the sensitivity and thus the responsiveness of the abscission zone of mature fruit to abscission chemicals. Chemical names used: 5-chloro-3-methyl-4-nitro-pyrazole (CMN-Pyrazole); 2-chloroethylphosphonic acid (ethephon); naphthalene acetic acid (NAA); 2,3,5-triiodobenzoic acid (TIBA).
`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.
Hydrogen cyanamide (Dormex, 50% a.i.) for blossom thinning `Early Spur Rome' and `Law Rome' apple (Malus×domestica Borkh.) and `Flavorcrest' peach (Prunus persica L.) was applied with air-blast sprayers on a commercial scale. Full-bloom applications of hydrogen cyanamide at 4 pts formulation per 200 gal/acre (1288 mg·L−1) and 5 pts formulation per 200 gal/acre (1610 mg·L−1) significantly reduced fruit set in apple and peach. In `Early Spur Rome', a postbloom application of carbaryl [Sevin XLR Plus, 4 lb a.i./gal (0.48 kg·L−1)] following a full-bloom spray of hydrogen cyanamide increased fruit thinning with a significant increase in fruit size compared to an application of hydrogen cyanamide alone. In `Law Rome', trees receiving a full-bloom application of hydrogen cyanamide followed by a postbloom application of 1-naphthyl-N-methylcarbamate (carbaryl) + naphthalene acetic acid (NAA) had significantly lower fruit set and larger fruit than those in the carbaryl + NAA treatment. Apples or peaches were not marked by hydrogen cyanamide.
AVG was applied as the ReTain formulation over three harvest seasons to determine the influence of time of application on drop control efficacy and its influence on fruit maturity of 'McIntosh' apples. Effective drop control was achieved through the commercial harvest season with application of AVG made from 1 to 6 weeks before the anticipated start of harvest for untreated fruit. Drop control extended beyond the normal harvest period when application was made either 2 weeks or 1 week before anticipated harvest. Application made between 6 and 4 weeks before anticipated harvest generally delayed parameters associated with ripening, such as softening, degradation of starch, and development of red color, more than applications made on later dates. While AVG consistently and effectively retarded abscission, the length of time it controlled drop varied from year to year, even when used on similar trees in the same block. Once applied, it required 10 to 14 days before AVG started to retard fruit abscission. AVG controlled drop linearly with increasing concentration. AVG was a superior drop control compound than NAA. Chemical names used: aminoethoxyvinylglycine (AVG), naphthaleneacetic acid (NAA).
A series of field and greenhouse experiments was conducted with three cultivars of bell pepper (Capsicum annuum L.) to determine the hormonal basis for flower bud and flower abscission as induced by low light intensity (LLI). Imposition of 80% shade for 6 days increased abscission of reproductive structures by 38% and resulted in an increase in bud ethylene production. Concomitantly, bud reducing sugars and sucrose decreased and these were negatively correlated with ethylene levels and those of its precursor, ACC. Infusion of ACC into the pedicel resulted in flower bud abscission within 48 hr. The results indicate that ethylene is the primary causal agent of pepper flower bud abscission. Production of auxin by the bud plays a role in prevention of abscission. The abscission of disbudded pedicels was prevented by infusion of NAA. Although the three cultivars had similar responses to ACC, they differed in the amount of abscission under stress, bud sugar levels, and the time of onset of ACC and ethylene production. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); α-napthaleneacetic acid (NAA); (2-chloro-ethyl)phosphonic acid (ethephon).
Ethylene liberated from control and auxin-treated cuttings of Vigna radiata (L.) R. Wilcz cv. Berken was monitored for 14 hours. For root initiation, naphthaleneacetic acid (NAA) and indolebutyric acid (IBA) were the most effective with indoleacetic acid (IAA) intermediate and 2,4-dichlorophenoxyacetic (2,4-D) the least effective. No correlation was observed between the quantity of auxin-induced ethylene evolved and the number of roots formed. Decreasing the NAA solution pH from 7.0 to 3.0 reduced the evolution of ethylene but did not alter the rooting response of the cuttings. It was concluded that stimulation of adventitious root initiation by auxin is not mediated by ethylene.
A protocol was developed for efficient plant regeneration of Iris germanica L. `Skating Party' from suspension cultures. Suspension cultures were maintained in Murashige and Skoog (MS) basal medium (pH 5.9) supplemented with 290 mg·L–1 proline, 50 g·L–1 sucrose, 5.0 μm 2,4-D, and 0.5 μm Kin. Suspension-cultured cells were transferred to a shoot induction medium (MS basal medium supplemented with 10 mg·L–1 pantothenic acid, 4.5 mg·L–1 nicotinic acid, 1.9 mg·L–1 thiamine, 250 mg·L–1 casein hydrolysate, 250 mg·L–1 proline, 50 g·L–1 sucrose, 2.0 g·L–1 Phytagel, 0.5 μm NAA, and 12.5 μm Kin). Cell clusters that proliferated on this medium differentiated and developed shoots and plantlets in about 5 weeks. Regeneration apparently occurred via both somatic embryogenesis and shoot organogenesis. A series of experiments was conducted to optimize conditions during suspension culture to maximize subsequent plant regeneration. Parameters included 2,4-D and Kin concentrations, the subculture interval, and the size of cell clusters. The highest regeneration rate was achieved with cell clusters ≤280 μm in diameter, derived from suspension cultures grown for 6 weeks without subculturing in liquid medium containing 5 μm 2,4-D and 0.5 μm Kin. Up to 4000 plantlets with normal vegetative growth and morphology could be generated from 1 g of suspension-cultured cells in about 3–4 months. Chemical names used: 2,4-dichlorophenoxyacetic acid (2,4-D); kinetin (Kin); 1-naphthaleneacetic acid (NAA).
Five chemical thinning trials, conducted over 4 years, indicated that BA is an effective thinner for ‘McIntosh’ apples (Malus domestica Borkh.). Although it can thin at concentrations as low as 25 mg·liter−1, in most years a higher concentration was required to thin adequately. It appeared that 14 to 18 days after full bloom, when fruit size was about 10 mm, may be the period when maximum thinning was achieved. Greater thinning occurred when BA and carbaryl were combined than when they were used individually. BA increased fruit weight, flesh firmness, and soluble solids content at harvest relative to no thinning. The storage life of fruit treated with BA was less than that of fruit from nonthinned trees, but this effect may have been an indirect response related to the larger fruit size rather than a direct response to the chemical. BA caused thinning and induced lateral branching simultaneously on young ‘Macspur McIntosh’ trees. Therefore, crop load on trees just coming into production may be significantly reduced when BA is used to induce lateral branching. Chemical names used: N-(phenylmethyl)-IH-purine-6-amine [benzyladenine (BA)], 1-napthaleneacetic acid [NAA], 1-naphthalenyl methylcarbamate [carbaryl].
Postbloom applications of benzyladenine (BA) thinned young fruitlets of mature `Empire' apple trees (Malus domestica Borkh.) as well as or better than NAA or carbaryl (CB). BA increased fruit weight more effectively than either NAA or CB. Promalin (PR) was less effective than BA for both thinning and fruit-weight increase. In 1990, both BA and PR reduced fruit set up to 29 days after full bloom, but PR showed less thinning activity. BA and NAA produced independent and additive thinning responses when tank-mixed. Effects of all thinners on foliar mineral-nutrient concentrations were associated with changes in fruit load. BA increased return bloom as much or more than NAA or CB. PR did not affect return bloom. Chemical names used: N -(phenylmethyl)-1 H -purine-6-amine [benzyladenine (BA)]; BA plus gibberellins A, and A, [Promalin (PR)]; 1-naphthaleneacetic acid (NAA); 1-naphthalenyl methylcarbamate [carbaryl (CB)].
The propagation method and vegetative condition of ‘Northblue’ blueberry (Vaccinium corymbosum L.) stock plants influenced microshoot production in vitro and root formation on leaf-bud cuttings. In tissue culture (TC), explants from TC-derived stock plants produced longer shoots than explants from leaf-bud, standard- (ST-) derived stock on either Zimmerman’s (Zimm) medium at pH 4.8, Lloyd and McCown’s woody plant medium (WPM) at pH 4.8 or pH 5.2. Microshoots from explants of TC-stock plants also rooted more readily. Microshoot rootability decreased after 18 weeks on medium containing 68.6 μmol (12 mg/liter) 2iP. Microshoot production and rootability increased after 3 additional weeks on Zimm medium without 2iP present. Leaf-bud cuttings of ‘Northblue’ TC-stock plants treated with 5% and 10% concentrations of a commercial rooting compound (Dip-n-Grow) had a slightly higher rooting percentage and root rating than nontreated cuttings from ST-stock plants. However, cuttings from ST-stock plants of the same age showed larger increases in root formation and percentage of rooting in response to the same rooting compound treatments. Leaf-bud cuttings from vegetative TC-stock plants that developed shoots had more basal branches than those from floral ST-stock plants. Branch elongation was greatest and basal branches fewest on cuttings from floral ST stock plants. Successful propagation with cuttings and in vitro explants may be related to the condition of the stock plants, which have been altered by their own propagation methods and the plant growth regulators applied. Chemical names used: 1H-indole-3-acetic acid (IAA); 1H-indole-3-butanoic acid (IBA); 1-naphthaleneacetic acid (NAA); N-(3-methyl-2-butenyl)-2H-purin-6-amine (2iP).