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C.L.H. Finneseth, Desmond R. Layne, and R.L. Geneve

Clonal propagation of pawpaw is currently limited to budding and grafting. A tissue-culture system to rapidly produce clonal material would be valuable for both production and preservation of germplasm. Forced scion wood, shoots from root cuttings, and seedlings were explant sources for ontologically mature, intermediate, and juvenile ages, respectively. Preliminary data indicated that nodal explants had more rapid adventitious shoot formation than shoot tip explants. Disinfestation protocols were developed for each explant source. Nodal explants were cultured on MS medium supplemented with 10 μM BA and 0.1 μM TDZ. Within 3 weeks, 60% of the seedling explants had expanded axillary buds, while no bud expansion was observed for explants of either the intermediate or mature sources. By 6 weeks, seedling axillary shoots had elongated and were suitable for subculture. By 8 weeks, multiple adventitious buds and shoots had formed on all seedling explants. At this same time, axillary shoots began to elongate on intermediate source explants, but mature source explants appeared to be recalcitrant. Explant exudation caused medium darkening, but, by reducing the transfer interval from 4 to 2 weeks, discoloration was minimized. Mature source explants were maintained in culture and after ≈7 months, axillary bud expansion occurred in a small percentage of these explants.

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James E. Faust and Royal D. Heins

Axillary buds of African violet develop vegetative shoots or reproductive inflorescences. Vegetative axillary development results in a multiple-shoot plant and reduces plant quality. We determined the effect of temperature and plantlet size on axillary bud development. Plantlets were removed from leaf cuttings, graded according to stem diameter, directly stuck into pots 10 cm in diameter, and placed in greenhouses at 18, 22, or 26C. Vegetative development was related to temperature, plantlet size, and nodal position. The number of vegetative axillary shoots per plant decreased from 3.7 to 1.3; that of leaves per vegetative axillary shoot decreased from 10.3 to 4.8 as temperature increased from 18 to 26C. The eight to 10 basipetal nodes developed vegetative shoots or were devoid of axillary development. The percentage of leaf axils in which inflorescences developed increased from 14 on node eight to 100 on nodes 12 and higher. The larger plantlets at the time of transplant had 20% fewer vegetative axillary shoots, whereas reproductive inflorescence development was not affected by plantlet size.

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R.E. Byers and K.S. Yoder

In 1995, BAS-125W applied at 125 to 500 mg/liter 23 days after full bloom (AFB) to `Starkrimson Delicious'/MM 106 and MM111 reduced average shoot weight and length of the longest shoots in the top and scaffold limbs by 50% at the highest rate. The number of nodes on the lower 40 cm of each shoot was increased by 1.8 times by the growth retardant. The number of pruning cuts, pruning time, and pruning weight per tree was reduce by 30%, 20%, and 29%. Fruit diameter, color, soluble solids, starch, fruit weight, and fruit number per tree were not altered by BAS-125 W. Growth suppression appeared to be greater on trees with heavier crop loads. In 1996, BAS-125W applied at 250 mg/liter 8 days after full bloom was more effective than when applied 19 days AFB to `Starkrimson Delicious'/MM 106 and MM111. Multiple applications of two, three, and four sprays to the same trees at 3-week intervals further reduced shoot growth with each application. Four applications reduced shoot weight by 72%, shoot length by 60%, and basal shoot diameter by 25%, and the number of pruning cuts, pruning time, and pruning weight per tree was reduce by 75%, 55%, and 80%, respectively. Thinning activity of NAA, Sevin, or Accel was not affected by tank mixed sprays with BAS-125W when applied to Gala/M.27 trees 20 days AFB. Tank mixing BAS-125W with combinations of Vydate + Accel or Carbaryl + Accel + Oil did not alter fruit thinning of Fuji/M.27 (at 10 mm fruit diameter). In one experiment, BAS-125 may have potentiated thinning by ethephon and NAA 10 days AFB in another experiment. BAS-125 W sprays at petal fall + 1 and 2 weeks later significantly suppressed % infection by fireblight, Erwinia amylovora, in inoculated shoots. In addition, BAS-125W reduced canker length in the first-year growth in shoots inoculated 2 weeks after treatment.

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Y.L. Qian, M.C. Engelke, M.J.V. Foster, and S. Reynolds

Turfgrass is grown under extremely variable light intensities. This presents difficult management problems, and methods are needed to improve turf performance under variable shade conditions. Two experiments were conducted to determine the influence of trinexapac-ethyl (TE) on turf performance and physiological responses of `Diamond' zoysiagrass [Zoysia matrella (L.) Merr.] under several light intensities. In a polyethylene-roofed greenhouse, `Diamond' was sodded in 12 wooden boxes (1.2 × 1.2 × 0.16 m) (Expt. 1) and 18 fiber containers (55 × 38 × 12 cm) (Expt. 2). Treatments applied to boxes or containers included three levels of shade (40%, 75%, and 88%) with and without multiple TE applications at 48 g·ha-1 of active ingredient. Without TE treatment, vertical shoot growth increased linearly with increasing shade levels. Excessive shoot growth under 75% and 88% shade exacerbated energy depletion, as evidenced by the 45% and 67% lower rhizome mass and the 37% and 65% lower total nonstructural carbohydrate content (TNC), respectively, compared with turf under 40% shade. Trinexapac-ethyl reduced excessive vertical shoot growth and increased rhizome mass and TNC. Mean turf quality was increased by 0.7 and 1.4 units for turf receiving multiple TE applications under 75% and 88% shade, respectively. Trinexapac-ethyl did not increase turf quality or TNC under 40% shade. Canopy photosynthetic rate (Pn) was not affected 4 weeks after the initial TE treatment under any shade level. However, 34 weeks after the initial TE treatment a 50% higher Pn was observed for turf treated with TE under 88% shade, possibly because of higher tiller density. Repeated TE application increased turf quality and provided more favorable physiological responses (such as TNC and Pn) under 75% and 88% shade, where conditions favored vertical shoot growth. However, little or no improvement in turf quality was observed under 40% shade, where conditions favored slow vertical shoot growth. Chemical name used: 4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl).

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P. Prutpongse and P. Gavinlertvatana

Fifty-four out of 67 species of bamboo tested were successfully propagated in vitro. For nearly every species, multiple shoots were produced from axillary buds on stem node segments cultured on Murashige and Skoog medium containing BA. In a very few species plants could be regenerated adventitiously from callus. This method of propagation was not very efficient or reliable. Rooting occurred in media containing NAA at 2.7 to 5.4 μM. Several species could be stored in vitro on half-strength medium at room temperature > 15 months without transfer. Chemical names used: N6-benzylamino purine (BA); napthyleneacetic acid (NAA).

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Logan S. Logendra, Thomas J. Gianfagna, and Harry W. Janes

A mixture of C8/C10 fatty acid methyl esters (FAME) when applied directly and exclusively to leaf axils of greenhouse-grown tomato (Lycopersicon esculentum Mill.) significantly inhibited side shoot development. Plants grown in a single cluster production system in winter produced 8.9 side shoots/plant, whereas those treated with C8/C10 FAME 45 days after sowing, produced only 0.7 side shoots/plant. Total pruning weight of the side shoots was reduced from 40.2 g/plant to 1.3 g/plant. Fruit yield increased 14% with C8/C10 FAME treatment and there was an increase in the harvest index from 0.63 to 0.70. For a spring crop, in which average daily irradiance was more than twice that in winter, overall yield increased 70% when compared to the winter crop. As in winter, side shoot number and side shoot weight/plant were significantly reduced by C8/C10 FAME, but there was no difference in crop yield between C8/C10 FAME and untreated plants. In both winter and spring, untreated plants required hand pruning three times during the production period, whereas C8/C10 FAME-treated plants were pruned only once at the time of application. A C8/C10 free fatty acid (FA) mixture was also applied to one and two-cluster plants with similar results. In the multiple cluster system, application of the C8/C10 FA mixture instead of side shoot pruning reduced plant height and increased yield from 6.4 to 7.4 kg/plant. C8/C10 FA or C8/C10 FAME treatment could be a useful labor saving strategy in greenhouse tomato production and may increase crop yield under conditions in which assimilates may be limited by environmental factors, or as a result of a high level of competition from other fruits or shoots.

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Francisco A. Ferreira, Dae-Geun Oh, and Edward C. Tigchelaar

Six F1's involving 6 multiple genetic marker stocks and a common inbred parent (PU812) were cultured to study the genotypic effect on regeneration ability and frequency of somaclonal variation in R0 for the known heterozygous marker genes. Leaf discs 7 mm in diameter were excised from young fully expanded leaves of 6-7 week old plants, and cultured on MS medium supplemented with cytokinins (Kinetin, Benzyladenine) and IAA. With few exceptions, the parents and F1's responded similarly to different hormone combinations. The beat hormone combinations for shoot formation were 4 mg/l Kinetin + 0.5 mg/l IAA and 2.3 mg/l BA + 0-0.18 mg/l IAA.

Only 2 of the 6 multiple marker stocks and the common inbred parent (PU812) were successfully regenerated. Four of the six hybrids between PU812 and the multiple markers were readily regenerated, whereas 2 hybrids failed to regenerate with several different hormonal combinations. No mutations have been observed for the known heterozygous markers in 76 R0 tissue culture regenerants.

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Timothy Spann, Robert H. Beede, Steven A. Weinbaum, and Theodore M. DeJong

Rootstock significantly alters the pattern of shoot growth of pistachio (Pistacia vera) cv. Kerman. Trees grown on P. atlantica typically produce a single flush of spring growth, whereas trees on P. integerrima selection PGI and P. atlantica × P. integerrima selection UCB-1 can produce multiple flushes during the season. We have shown that the spring flush is entirely preformed in the dormant bud for all three rootstocks, but later flushes are neoformed, that is, nodes are initiated and extended during the same season. Shoots producing both preformed and neoformed growth have lower yield efficiency than those producing only preformed growth. Additionally, yield components of the crop from shoots with both preformed and neoformed growth was different than for shoots producing only preformed growth. However, these differences do not appear to be significant at the whole tree level. These data suggest that neoformed growth can both compete with fruit growth for available resources (lower yield efficiency) and act as an additional source (altered yield components), depending on the factor being measured. Controlling neoformed growth may potentially increase pistachio yield through a shift to the more efficient preformed shoots while at the same time lowering orchard maintenance costs by reducing required pruning. We have data to indicate that regulated deficit irrigation and new pruning techniques may be viable methods for controlling neoformed growth in pistachio without affecting yield.

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Hak-Tae Lim, Eun-Ae Lee, and Won-Bae Kim

This study was conducted to investigate the possibility of obtaining plantlets via somatic embryogenesis and organogenesis as means of in vitro mass propagation in Allium victorialis var. platyphyllum Makino, one of the most popular wild vegetable plants in Korea. Shoots formed directly when bulb explants of A. victorialis were cultured on MS medium containing 0.2 mg·L–1 NAA and 2.0 mg·L–1 zeatin under 16 hours (light)/8 hours (dark) illumination. The use of leaf and shoot tip explants was not successful, largely due to explant senescence in the present of plant growth regulators. Embryogenic calli were obtained from the bulb explants of A. victorialis on MS medium supplemented with 0.2 mg·L–1 NAA, 0.2 mg·L–1 BAP, and 1.0 mg·L–1 picloram after 4–5 weeks of culture in the dark at 27°C. Upon transfer to shoot-induced MS medium containing 0.2 mg·L–1 NAA and 2.0 mg·L–1 zeatin, embryogenic calli gave rise to numerous somatic embryos, which subsequently developed into multiple shoots after 3 months of culture under 16 hours(light)/8 hours (dark) illumination. For root induction, regenerated shoots were transferred to MS medium added with 1.0 mg·L–1 NAA. Regenerants with well-developed roots were potted in an artificial soil mixture of vermiculite (1) and perlite (1).

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Don Waneck, H. Mathews, J. Stamp, and R. Bestwick

Zygotic embryo explants of grape cultivar AXR#1 were isolated from maw-e seeds and cultured on medium supplemented with naphthoxy acetic acid beta-(NOA) and benzylaminopurine (BA). Embryo explants dedifferentiated to form embryogenic callus. Globular stage embryos were visible in 9-10 months. On transfer 10 a growth regulator free medium supplemented with charcoal these globular embryos underwent further stages of embryo development. In a period of 30-40 days embryogenic tissues turned into clumps of somatic embryos displaying different stages of development Cotyledonary stage embryos were separated and transferred to basal medium. These embryos developed into complete plants. Cold and desiccation treatment of somatic embryos significantly enhanced the rate of plant conversion. Hypocotyl segments of elongated somatic embryos were good source explant for induction of shoot organogenesis. The hypocotyl-length and the proximity to-shoot-apex were found to influence the rate of shoot induction from hypotyl segments. Multiple shoot complexes which formed on hypocotyl segments were separated and individual shoots were grown on a root induction medium resulting in complete plant development. The possibility of both embryogenic and organogenic modes of plant regeneration make somatic embryos a highly versatile explant source for experiments on genetic manipulation.