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  • Author or Editor: C. H. Thomas x
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Ligustrum japonicum, Rhododendron indica `Southern Charm' and Viburnum odoratissimum in 10-L containers were placed in a square grid pattern and overhead irrigated using impact sprinklers (30.3 L/min). Plants were irrigated with 12.5 mm with containers touching and, at 5 cm spacings, up to 50 cm between containers. Irrigation water reaching container surfaces (percent capture) increased for all species as container spacing increased. However, the increase in percent capture did not increase irrigation application efficiency because the percent of production area covered by the containers declined as spacing increased. Application efficiency declined with each increase in spacing to a low of 7%. The effects of intraand inter-canopy interference are discussed.

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Pyracantha coccinea `Lalandei' and `Kasan' were treated with a foliar application of 25, 50 or 100 mg/l uniconazole, 3000 mg/l chlormequat, a soil drench of 0.25, 0.50 or 1.00 mg/container of uniconazole, or 30 mg/container chlormequat. Heights of plants receiving foliar applications of uniconazole were significantly lower than untreated plants in both cultivars. Uniconazole soil drenches also reduced plant height in both cultivars, but differences were not apparent until 8 weeks after treatment. Chlormequat treatments had little effect on plant growth. At harvest, stem dry weight was significantly lower in both cultivars with uniconazole soil drenches and in `Lalandei' treated with 50 and 100 mg/1 and in `Kasan' treated with 100 mg/1 as a foliar application. There was also a tendency for leaf area to increase with uniconazole foliar applications.

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Pyracantha coccinea M.J. Roem. `Kasan' and `Lalandei' were treated with a soil drench of 30 mg a.i. chlormequat chloride per container or 0, 0.25, 0.50, or 1.00 mg a.i. uniconazole per container or with a foliar application of 3000 mg a.i. chlormequat chloride/liter or 0, 25, 50, or 100 mg a.i. uniconazole/liter. Chlormequat chloride applied as a drench did not affect growth of `Kasan' or `Lalandei' until 17 weeks after application, when `Kasan' was taller and `Lalandei' shorter than untreated plants. `Kasan' plants drenched with chlormequat chloride had more leaves with greater total leaf area and higher leaf and stem dry weights than untreated plants. However, area per leaf, root dry weight, and root: shoot ratio were not affected by the chlormequat chloride drench. In `Lalandei', the chlormequat chloride drench did not affect any of these criteria, except stem dry weight. Foliar applications of chlormequat chloride had little effect on either cultivar. Height of `Kasan' and `Lalandei' decreased with increasing uniconazole rates for both application methods. Area per leaf increased in `Kasan' but decreased in `Lalandei' receiving a drench applied to the medium. Foliar and drench applications of uniconazole both resulted in decreased stem dry weight of both cultivars. Chemical names used: 2-chloro-N,N,N-trimethylethanaminium chloride (chlormequat chloride); (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole).

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Rain drop momentum, based on the height from which it falls, is an important factor in drop penetration of plant canopy. This may explain why nursery operators report that substrates appear wetter from rain than from an equivalent amount of water applied with overhead irrigation. We investigated the influence of irrigation nozzle height on amount of water captured by Rhododendron sp. `Formosa' grown in 10-liter containers. A Wobbler® (#8, 7.6 liters·min–1) irrigation nozzle was positioned 1.2, 2.4, 3.6, 4.8, or 6.0 m above grade. Plants were placed in a circle 3.6 m from the riser base for the 1.2-m-high nozzle, 4.5 m from riser base for the 2.4-m-high nozzle, and 5.4 m from riser base for all other heights and irrigated for 3 hours. Preweighed disposable diapers were placed on substrate surface of each container with and without (control) plants. Diapers were weighed after irrigation and water captured was calculated and expressed as percentage of control containers. Capture increased from 144% at 1.2 m to 178% at 3.6 m then declined with increasing height. The decline was likely due to small drops with low momentum striking plants because plants remained 5.4 m from the riser base.

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Cultivars and seedlings of Rhipsalidopsis and Schlumbergera were subjected to isozyme analysis using seven enzyme systems [aspartate aminotransferase (AAT), aminopeptidase (AMP), glucose-6-phosphate isomerase (GPI), malate dehydrogenase (MDH), phosphoglucomutase (PGM), shikimate dehydrogenase (SKD), and triose phosphate isomerase (TPI)]. Isozymes were extracted from phylloclades and roots, and were separated by polyacrylamide gel electrophoresis (PAGE) using single percentage (5% to 10%) gels. Six enzymes exhibited polymorphism in Rhipsalidopsis, whereas all seven enzymes were polymorphic in Schlumbergera. Inheritance studies were performed on AAT, GPI, MDH, PGM, and TPI for Rhipsalidopsis and on AMP, PGM, and SKD for Schlumbergera. Significant segregation distortion was observed in some families. Polymorphic isozymes are potentially useful markers for cultivar identification and for genetic and breeding studies.

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Marketable size plants of sweet viburnum (Viburnum odoratissimum Ker-Gawl.), waxleaf ligustrum (Ligustrum japonicum Thunb.), and azalea (Rhododendron spp. L. `Southern Charm') grown in 11.4-L containers were irrigated with overhead impact sprinklers at container spacings ranging from 0 to 51 cm apart. Water reaching the substrate surface was quantified and the percentage of that applied calculated as percent capture (% capture). Percent capture is defined as the percentage of water falling above the plant within a projected vertical cylinder of a container that reaches the substrate surface. For all species, % capture increased linearly with the decline in adjacent canopy interaction, which results from canopies extending beyond the diameter of a container. Increases in total leaf area or leaf area outside the cylinder of a container, in conjunction with increasing distance between containers, were significantly (P < 0.05) correlated with increases in % capture for ligustrum and viburnum. Increases in % capture partially compensated for decreases in percentage of production area occupied by viburnum containers as distances between containers increased, but not for the other two species. Under commercial conditions, optimal irrigation efficiency would be achieved when plants are grown at the minimum spacing required for commercial quality. This spacing should not extend beyond the point where canopies become isolated.

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A germplasm collection of 59 Schlumbergera Lemaire clones was assayed for isozymes of aspartate aminotransferase, glucose-6-phosphate isomerase, leucine aminopeptidase, malate dehydrogenase, phosphoglucomutase, shikimate dehydrogenase, and triosephosphate isomerase. The collection included cultivars of holiday cactus [S. truncata (Haworth) Moran and S. ×buckleyi (T. Moore) Tjaden] plus accessions of S. kautskyi (Horobin & McMillan) N.P. Taylor, S. opuntioides (Löfgren & Dusén) D. Hunt, S. orssichiana Barthlott & McMillan, S. russelliana (Hooker) Britton & Rose, S. ×exotica Barthlott & Rauh, and S. ×reginae McMillan & Orssich. Twelve loci with 36 alleles were detected. Percent polymorphic loci, mean number of alleles per locus, and mean heterozygosity were 83, 3.00, and 0.24, respectively, for the entire collection. Forty-one clones (69%) could be distinguished solely on the basis of their isozyme profiles, but the remaining 18 clones shared profiles with one or two other clones. Isozymes proved useful for determining the parentage of some clones and verifying that some progeny were interspecific hybrids. About 28% of the genetic diversity within the entire collection is unique to four Schlumbergera species that have scarcely been exploited for breeding holiday cactus cultivars.

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Isozyme markers were used to identify cultivars and assess the genetic diversity within a germplasm collection of 49 Hatiora Britt. & Rose clones. The collection included accessions of Easter cactus [H. gaertneri (Regel) Barthlott, H. graeseri Barthlott ex D. Hunt, and H. rosea (Lagerheim) Barthlott] plus H. herminiae (Campos-Porto & Castellanos) Backeberg ex Barthlott and H. salcornioides (Haworth) Britton & Rose. Seven enzyme systems were analyzed: aspartate aminotransferase, glucose-6-phosphate isomerase, leucine aminopeptidase, malate dehydrogenase, phosphoglucomutase, shikimate dehydrogenase, and triosephosphate isomerase. Thirteen loci and 42 alleles were identified. Twenty-one clones (43%) displayed unique isozyme profiles, but the remaining 28 clones shared isozyme profiles with one to three other clones. Percent polymorphic loci, mean number of alleles per locus, and mean heterozygosity were 69, 3.23, and 0.30, respectively, for the entire collection. Isozymes also proved useful for verifying that some progeny were genuine F1 hybrids.

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Polyacrylamide gel electrophoresis was used to study inheritance and linkage of isozymes in Easter cactus (Hatiora species and interspecific hybrids). Five isozyme systems were analyzed: aspartate aminotransferase (AAT), glucose-6-phosphate isomerase (GPI), malate dehydrogenase (MDH), phosphoglucomutase (PGM), and triosephosphate isomerase (TPI). F1, F2, BC1, and S1 progeny were used for inheritance studies. Six polymorphic loci (Aat-1, Gpi-1, Mdh-1, Pgm-1, Pgm-2, and Tpi-2) were identified. Aat-1 and Pgm-1 were linked (recombination frequency = 26% ± 7%), but the other isozyme loci assorted independently. Aberrant segregation ratios were observed in at least one segregating family for all six isozyme loci. We hypothesize that segregation distortion was due to linkage between isozyme loci and other genes subject to pre- or postzygotic selection. The existence of five additional isozyme loci (Aat-2, Gpi-2, Mdh-2, Mdh-3, and Tpi-1) was inferred from segregation patterns and by comparison of isozyme profiles from phylloclades and pollen. These isozyme loci may prove useful for confirming hybridity in intra- and interspecific crosses, determining parentage of cultivars, and assessing genetic diversity in germplasm collections.

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The existence of self-incompatibility (SI) was demonstrated in `Britton' and `Rose' Easter cactus (Rhipsalidopsis). In a full diallel cross among five clones, 18 out of 20 outcrosses resulted in 68% to 100% fruit set, whereas reciprocal crosses between two of the clones and all five self-pollinations failed to set fruit. Pollen tube growth was greatly inhibited in styles of selfed pistils, but there was no evidence of pollen tube inhibition in compatibly crossed pistils. Easter cactus exhibited characteristics typically found in sporophytic SI systems (trinucleate pollen, papillate stigmas, and scant stigmatic exudate) together with those associated with gametophytic SI systems (stylar inhibition of pollen tube growth and absence of reciprocal differences in outcrosses). Additional experiments were performed to determine the effects of bud pollinations, growth regulators (BA, GA3, and NAAm), and high temperatures (0- to 48-h exposure at 40C) on the SI response. Heat treatments were more effective than either bud pollinations or growth regulators in overcoming SI, and yielded an average of 7.2 viable seeds per treated flower when plants were incubated for 12 h at 40C and selfed immediately after incubation. Isozyme analysis of the S0 parent and putative S1 progeny confirmed that selfing had occurred following heat treatments. Using S1 progeny in breeding programs may extend the flower color range and lead to a greater diversity in other plant characteristics than presently exists in cultivated germplasm. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine [benzyladenine (BA)], gibberellic acid (GA3), and α-naphthaleneacetamide (NAAm).

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