Search Results
Abstract
A procedure for the extraction and fractionation of nucleic acids from citrus tissues was developed. Typical elution profiles of nucleic acids extracted from leaves, root tips, flowers, and fruits at different stages of development showed the well-known peaks of s-RNA, DNA, lr-RNA, and hr-RNA. In flowers and, especially, in young fruits the additional X-RNA peak was also present following the hr-RNA peak. The level of nucleic acids decreased markedly in the young fruit on the dry matter basis during the first 3 months of growth, mostly due to decrease in hr-RNA. During maturation the RNA fractions in the albedo decreased, while it increased in the flavedo due to increase in hr-RNA content. The fast growth of the young fruit apparently is accompanied by intensive metabolization or turnover of nucleic acids, rather than by dilution.
Abstract
Morphological changes during development of cultured citrus explants (Citrus sinensis (L.) Osbeck cv. Shamouti) were observed with a scanning electron microscope (SEM). Prophylls of resting buds, covered with epidermal hairs, were closely appressed until the growth of a new shoot; they then expanded. The addition of 10-5 m 6-benzylaminopurine to the medium resulted in the formation of several adventitious buds, surrounded by multiple prophylls, in the axil of the petiole. Abscission of the petiole from the explant involved formation of a separation zone with no evidence of new dividing cells, or active cell division and formation of callus tissue in the abscission zone.
Abstract
Studies of pollen germination, stigmatic treatments and a field experiment were conducted in an attempt to decrease seed number of mandarin-type fruits (Citrus reticulata Blanco cv. Dancy and C. reticulata Blanco cv. Temple). Gibberellin (GA3) in the medium inhibited germination only above 250 ppm; cycloheximide inhibited it at 0.1 ppm. Treatments of the above and other compounds applied to stigmatic surfaces decreased either set or yield. Field treatments with 20 ppm GA at early- or mid-bloom or 150 ppm naphthaleneacetic acid (NAA) applied when fruitlets were 5 or 10 mm in diameter alone or in combinations, decreased seed number to 72% for ‘Dancy’ and 82% for ‘Temple’. Effects of NAA were greater than for GA. Neither treatment caused thinning. Instead, fruit number and yields increased, while fruit size decreased slightly. Bioassays of NAA-treated fruitlets showed residual active NAA 25 days after spraying as well as an increase in native gibberellin-like activity which was highest in NAA + GA-treated fruitlets.
Abstract
(2-Chloroethyl)phosphonic acid (ethephon), 200 ppm, and naphthaleneacetic acid (NAA), 350 ppm, sprayed on fruitlets 1 cm in diameter, caused satisfactory thinning of heavily loaded ‘Wilking’ mandarin trees (Citrus reticulata Blanco) without significant decrease of yield in kg per tree. Individual fruit size was increased 64% with ethephon and by 48% with NAA, increasing profit by about 30% in both cases as compared with hand thinned controls. A summer pruning treatment had similar effects but the increase in fruit size was smaller. Ethephon reduced alternation of bearing and resulted in satisfactory yields the following year on 57% of the treated trees.
Abstract
A previous report that girdling at the beginning of bloom increases yield of orange trees by increasing fruit number but not fruit size has been confirmed. Girdling caused the abortion of some flowers which were in the early differentiation stages at girdling time, and decreased the drop of ovaries during the first portion of the shedding season. Thus fewer flowers produced more fruits. Since it has been shown that girdling increases gibberellin activity in the aerial parts, the dual effect of gibberellin on flower formation and fruit setting may explain these influences of girdling.
Abstract
Excessive rough and thick peel, linked with large fruit sizes is found in ‘Shamouti’ oranges (Citrus sinensis (L.) Osbeck) grown under marginal soil and climatic conditions. This condition was overcome by early (April-May) sprays of succinic acid-2,2-dimethylhydrazide (SADH) and 2-chloroethyltrimethylammonium chloride (CCC, chlormequat), probably counteracting high endogenous promotors found in rough tissues. While SADH is too expensive to be profitable and it usually decreases fruit size, CCC can be used without this effect and is commercially rewarding.
Abstract
Attempts were made to identify the stage of flower differentiation of subterminal buds under water stress conditions. Anatomical and morphological studies established that flower differentiation occurs during the stress period and that the generative bud formed does not undergo flower development until water is supplied. Gibberellic acid applied under normal irrigation conditions inhibited summer flower formation even when supplied after the first stages of flower bud differentiation, and stimulated vegetative growth of either 1 or 2 dormant axillary meristems. In contrast, 2-chloroethyltrimethylammoniumchloride induced flower formation when applied by the end of August to irrigated trees. Treatments with gibberellic acid under water stress conditions prevented flower formation but were inactive when applied after the renewal of irrigation and beginning of anthesis.
Abstract
Paclobutrazol (PP333) [(2RS,3RS)-l-(4-chlorophenyl)-4, 4-dimethyl-2-(l,2,4-triazol-l-yl-)pentan-3-ol] sprays applied to ‘Minneola’ tangelo trees, at 500 or 1000 ppm, before the onset of summer flush, markedly reduced total growth, number of shoots, and internode length. Soil treatments (0.4 and 0.8 g per square meter) had only a small effect, probably because of the short time from application to flush inception. Sprays of Morphactin (an auxin transport inhibitor), at 250 and 500 ppm did not reduce growth, but rather enhanced it by increasing the number of emerging shoots. The spring flush of the same trees also showed effects of paclobutrazol soil treatments, whereas other treatments were not different from control. Paclobutrazol sprays on comparable ‘Minneola’ trees just before the spring flush also reduced this growth. Paclobutrazol may become a tool for the control of vegetative growth of mature citrus trees.
Abstract
Corky (silvery) spots of ‘Marsh’ grapefruit (Citrus paradisi Macf.) were substantially reduced by application of 16-22 ppm 2,4-dichlorophenoxy acetic isopropyl ester on developing fruitlets (May to July) or of 20 ppm gibberellin A3 in June. Success is probably due to enhanced growth potential of external fruit layers, preventing their splitting due to internal pressure.
Abstract
Conjugation of 14C-1-naphthaleneacetic acid (NAA) was followed in leaf discs of apple, apricot, grape, orange, peach and pear. NAA was metabolized by all crops studied. Free NAA and 2 metabolites that chromatographed with naphthylacety1-β-D-glucose (NAG) and naphthylacetylaspartic acid (NAAsp) constituted 90% of the radioactivity recovered, NAG was the major metabolite (45-90%) followed by NAAsp (5-30%) and NAA (2-22%). Conjugation was most complete in orange (98%), intermediate in apple, apricot, peach and pear and least in grape (68%).