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L. Chen, S.O. Park, S. Dhir and A.S. Bhagsari

Several experiments were conducted to evaluate the influence of explant type, sucrose level, and callus development time on sweetpotato [Ipomoea batatas (L.) Lam] in vitro culture. Shoot tip, petiole, and leaf of Selection 75-96-1 was used as explants in Murashige and Skoog (MS) media with different plant growth regulators. Calli derived from shoot tip and petiole produced 42.1% and 10.3% somatic embryos, respectively, but the leaf failed to produce somatic embryos. The effect of sucrose level was determined using shoot tip as explants. Compared with 3% sucrose in the same plant growth regulators level medium during callus initiation and callus proliferation periods, 5% sucrose level suppressed root growth and improved shoot regeneration. The callus development time was measured by using shoot tips on callus initiation medium containing 1.5 mg/L alpha-Naphthaleneacetic acid (NAA) and 0.25 mg/L Kinetin (KIN) plus 5% sucrose. When explants were cultured for less than 6 weeks during callus initiation, then transferred onto plant regeneration medium, plant regeneration via organogenesis occurred; whereas, maintaining cultures for more than 12 weeks on the same callus initiation/proliferation medium, plant regeneration was favored via embryogenesis. Explant type and other factors affecting plant regeneration noted here could be applied to protoplast culture, somatic hybridization, and transformation in sweetpotato.

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T. Kostman, J. S. Cameron, C. Chen and S. F. Klauer

The red raspberry industry of the Pacific Northwest depends upon chemical primocane suppression to temporarily reduce competing vegetation during fruit development. This practice increases yield and harvest efficiency, but can reduce cane vigor, number and diameter over time. Few chemicals are available for this purpose and thus the potential of nonchemical alternatives is being explored. The purpose of this project was to evaluate the potential of blown air as a thigmic stress to temporarily suppress primocane growth.

Blown air treatments were applied once (12 PM) or twice (12\4pm) per day, five days per week using a portable leaf blower generating winds of 273 km per hr. Treatments also included several rates of three experimental herbicides and an untreated control. All treatments were applied when primocanes were 10-15 cm in length and blown air treatments continued through fruit development. Primocane development was monitored over the course of the season.

Blown air reduced primocane length by 15-30% prior to harvest giving control equivalent to current chemical methods. Blown air increased cane diameter but reduced yield by reducing fruit numbers. Reductions in fruit numbers are likely due to flowering\fruiting points removed by blown air.

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S.O. Park, L.H. Chen, S.K. Dhir and A.S. Bhagsari

The objective was to determine optimum conditions for embryogenic callus, embryo, organogenesis, and embryogenesis developed from leaf, petiole, stem, and tip tissues of the sweetpotato `Jewel' cultivar and from subcultured callus. Embryogenic callus was developed from stem and tip tissues on MS medium containing combinations of BA and NAA only under light conditions. Plant regeneration via organogenesis was developed from stem and tip tissues on medium including 1, 3 and 4 mg/L BA under dark and light conditions, while no plant regeneration via organogenesis was developed from leaf and petiole tissues. Frequencies for plant regeneration via organogenesis from the tissues were very low. No plant regeneration via embryogenesis was developed from the four tissues on medium having any combinations of BA+NAA and of kinetin+NAA. Embryogenic callus was observed in the subculture of callus developed from petiole and tip tissues on medium containing 0.2 and 2 mg/L 2,4-D only under dark conditions. Embryo was found in the subculture of callus from the tissues on medium containing 0.2 mg/L 2,4-D only under both conditions. Plant regeneration via embryogenesis was obtained in the subculture of callus from the tissues. Plant hormones and other factors affecting plant regeneration from the four tissues of the `Jewel' cultivar and other elite cultivars are currently being investigated at our lab for its application in transformation.

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J. S. Seron, S. L. Knight, L. A. Spomer and G. S. Chen

Proponents of global climate models predict a doubling of world CO2 concentration from 350 to 600 ppm by the year 2030, concurrent with a 2-5°C temperature increase. Consequences of this “greenhouse effect” on Oryza sativa L. were determined using four rice lines selected for their widespread use in cultivation and research. A 2×2 factorial design was used with CO2 at 350 and 600 ppm and day/night temperature regimes of 31/27°C and 37/33°C. Combined effects of CO2/temperature were determined during 5 harvests from seeding to reproductive maturity. Elevated CO2 enhanced dry weight and photosynthetic capacity over both temperature regimes relative to plants grown at ambient CO2. The 37/33°C day/night temperature regime increased sterility in rice by decreasing pollen shed.

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G. Jelenkovic, S. Billings, Q. Chen, J. Lashomb and G. Ghidiu

A chimeric construct, containing the synthetic cryIIIA (Btt) gene, the NPTII selectable marker and the uidA reporter gene, was incorporated via Agrobacterium tumefaciens into eggplant, variety Hibush. The synthetic cryIIIA gene, altered at the nucleotide level without changing the amino acids of the toxic protein by J. Kemp of New Mexico State Univ., Las Cruces, is adapted for high expression in plant cells. To verify the transgenic status, GUS assays were performed on over 300 plants, from which 185 were confirmed to be transgenic. Physical incorporation of the chimeric construct was further confirmed by Southern analysis of about 30 transgenic plants; both single and multiple site incorporation of the Btt gene were found. Resistance to Colorado potato beetle (CPB) was assessed by: a) placing egg masses of CPB on leaves of plants grown in the growth chamber; b) placing first-instar larvae on detached leaves; c) observing 173 transgenic plants under field conditions. About 60% of the transgenic plants displayed a very high level of resistance to CPB. No larvae survived on the resistant plants longer than 50–60 hours after hatching. Upon selfing, the transgenic plants with a single construct segregate in the S1 generation in a Mendelian fashion.

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C. Chen, R.J. Roseberg, D. Sugar and J.S. Selker

A study was undertaken to determine if microsprinkler irrigation (MI) can provide sufficient water and produce similar yield and quality of pear (Pyrus communis L.) fruit as flood irrigation (FI) in a cracking (shrinking-swelling) clay soil. Soil water content and fruit quality attributes were measured under MI and FI in 2 years. Water potential of the upper 120 cm (47 inches) of soil was maintained at 0.1 to 0.3 MPa (14.5 to 43.5 lb/inch2) through most of the growing season in both MI and FI treatments. MI and FI treatments did not differ in their effect on fruit size, yield, or firmness decline during cold storage. No consistent effect on fruit susceptibility postharvest fungal decay related to irrigation treatment was observed. MI has the potential to reduce chemical and water movement to groundwater, while providing sufficient water to produce satisfactory yield and fruit quality in a cracking clay soil.

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Chen-Yi Hung, Cindy B.S. Tong and John R. Murray

The color of red potatoes is due to an accumulation of anthocyanins in periderm tissues. The objective of this study was to examine the effect of several factors on tuber redness. Using the red tuber-producing S. tuberosum ssp. tuberosum cultivar Norland, we observed that chroma (intensity of redness) and anthocyanin content of greenhouse-grown tubers decreased as tuber weight increased. There was a slight or no increase in hue (tint). We used HPLC to determine that pelargonidin and peonidin are the major anthocyanidins (aglycones of anthocyanins) in tuber periderm. The ratio of pelargonidin to peonidin increased as tuber weight increased up to 25 g fresh weight. The decrease in chroma was not due to an increase in cell sap pH; we observed a decrease in cellular pH as tuber weight increased. Controlled-atmosphere storage had no effect on tuber chroma or anthocyanin content compared to air storage. Methyl jasmonate, sucrose, or light treatment did not increase anthocyanin accumulation. Tubers exposed to light had less anthocyanin than those kept in the dark. We are examining the developmental expression of anthocyanin biosynthetic genes, as well as the effect of maize transcription factors on anthocyanin synthesis, in tuber periderm.

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S.J. Li, T.J. Facteau and P. Chen

Several characteristics of amylases involved in starch degradation were studied in extracts from immature (30 days before harvest) `d'Anjou' pears (Pyrus communis L.). Enzyme activity was not detected until after at least 60 minutes of incubation in frozen or lyophilized tissues. Activity increased significantly after 90 minutes and increased linearly after 2 to 12 hours of incubation. Activity was greater, however, in frozen than in lyophilized tissues. Three buffers (acetate, tris-HCl, and imidazole-HCl) were used at a range of pH levels (4.6-8.2) to ascertain the optimum assay system. Highest specific activity was recorded with acetate buffer at pH 5.6. The Km value in this system was 1.43 × 10-3g·ml-1. Specific activity increased as Ca concentration in the reaction mixture increased from 1 to 15 mm CaCl2 but did not change as Ca concentration increased from 15 to 25 mm CaCl2. The `d'Anjou' pear amylases were purified 5.7-fold using ammonium sulfate fractionation.

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Lianghong Chen, Ajmer S. Bhagsari, Soon O. Park and Sarwan Dhir

This study was carried out to optimize conditions for plant regeneration of sweetpotato [Ipomoea batatas (L.) Lam] using shoot tips, petioles, and leaves of Selection 75-96-1 as explants in Murashige and Skoog (MS) with several growth regulators at different levels. Callus initiation and callus proliferation media were 9.0 μm 2,4-dichlorophenoxyacetic acid (2,4-D) and 9.0 μm 2,4-D + 1.1 μm N 6-benzyladenine (6-BA) in protocol I; 8.1 μm α-naphthaleneacetic acid (NAA) + 1.2 μm kinetin (KIN) and 5.4 μm NAA + 4.6 μm KIN in protocol II; 0.9 μm 2,4-D, and 0.9 μm 2,4-D + 1.2 μm N-isopenylamino purine (2iP) in protocol III; NAA (8.1 μm) + KIN (1.2 μm) and 2,4-D (0.9 μm) + 2ip (1.2 μm) in protocol IV, respectively. In protocol I and II, shoot tip, petiole, and leaf were used, but only petiole and leaf in protocol III and IV. In the protocol I and II, somatic embryos were obtained only from shoot tip explants; in protocol III and IV, only from petioles. The frequencies of somatic embryo development were 33.3% in protocol I, 42.1% in protocol II, 21.2% in protocol III, and 10.3% in protocol IV, respectively. The leaf explants failed to produce somatic embryos in all the experiments. In protocol I, somatic embryogenesis occurred through the well-known sequence of globular-, heart-shaped-, torpedo-, and cotyledon-type embryos. However, in protocol II, the structures resembling plumule and radicle were observed before the emergence of torpedo/cotyledon type embryo clusters. The somatic embryogenesis in protocol III and IV was similar to that in protocol I. Growth regulators influenced somatic embryo development. Further, this study showed that explant resource and growth regulators affected the frequency of plant regeneration in sweetpotato.

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W.C. Lin, G.S. Block, S. Chen and D.L. Ehret

In commercial production of greenhouse cucumber, moderate water stress is often undetectable until plants show severe wilting. The purpose of this study was to establish a noncontact, early detection method for such moderate stress before visual wilting takes place. An infrared imaging system including an infrared camera, a personal computer, and necessary image processing software was placed in a greenhouse with the camera elevated and viewing the plant canopy. Selected plants, each in a bag of sawdust growing medium, were subjected to water stress by removing irrigation tubes from the growing medium. The infrared images obtained from a crop canopy displayed an increase in foliar temperature of stressed plants, which were located among normally watered (control) plants in the same greenhouse. Increased foliar temperatures of stressed plants occurred 1 to 3 days before wilting was observed. When visual wilting occurred, the stress treatment was stopped and irrigation was resumed within the same day. Cucumber plants showed no crop loss after one cycle of moderate stress. Repeated moderate stress caused yield loss. The potential applications of this nondestructive, noncontact detection method in plant science research and in commercial greenhouse production will be discussed.