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Abdoulaye Traore, Zizhuo Xing, Amy Bonser, and John Carlson

A successful tissue culture initiation step often begins with effective explant sterilization. To improve douglas fir bud culture initiation, five sterilization treatments (20% bleach, 100% bleach, 3 second flaming, 5 second flaming, and self-extinguishing flaming) were evaluated for their effectiveness on winter and spring bud sterilization. The 20% and 100% bleach treatments resulted in the highest percentage of healthy bud cultures (>90% for winter buds). Spring buds showed a higher level of contamination with 20% bleach sterilization (36%) than did winter buds (1%). Successful sterilization was also achieved by flaming, but bud injury was observed. Increased flaming time caused a decrease in the percentage of healthy actively growing buds. The percentage of healthy bud cultures after 3 second flaming, 5 second flaming and self-extinguishing-flaming (9 to 14 s) were 66%, 59%, and 10% respectively. In addition, sterilization by either approach required subsequent bud dissection to remove the outer scales; otherwise most buds were lost to contamination. When sterilization was followed by bud dissection, contamination rates for winter buds were <2% for all treatments. After successful sterilization and culture initiation, bud expansion was the highest (50% to 98%) in the presence of low concentrations of BA (0 to 0.045 μmol·L–1), while high concentrations of BA (0.448 to 4.527 μmol·L–1) reduced bud expansion (0% to 60%), but promoted bud multiplication.

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Fucheng Shan and Kevin Seaton

experiment. The SSTC method involved surface sterilization of immature single-node cuttings, root pulsing, root development, and acclimatization. Surface sterilization. The immature single-node cuttings were immersed in 0.1% Tween 80 (Rowe Scientific Pty. Ltd

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Brent Tisserat, Danny Jones, and Paul D. Galletta

Nutrient medium can be sterilized using a household-type microwave oven. The required microwave treatment time was influenced by the oven's microwave power intensity (70 to 700 W), vessel type, volume of medium employed, and the presence of energy sink water reservoirs (ESWR). Growth rates of strawberry (Fragaria vesca L.) shootlets, lemon [Citrus limon (L.) Burm. f.] fruit halves, or carrot (Daucus carota L.) callus cultured on either microwaved or autoclaved media were similar. Microwaving and autoclaving appeared to reduce GA3 activity compared with medium containing filter sterilized GA3. Chemical name used: gibberellic acid (GA3).

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Yu-Wei Liu and Chen-Kang Huang

soil-grown crops. However, whenever a plant is contaminated, pathogens can rapidly spread through the nutrient solution to neighboring plants. To prevent pathogen transmission in hydroponic systems, filters, heat, ozone, or/and ultraviolet sterilization

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Janet E.A. Seabrook and Gerald Farrell

Stock plants of `Shepody' and `Yukon Gold' potato (Solarium tuberosum L.) were grown in a greenhouse and irrigated with city water. Contamination rate of stem explant tissue cultures excised from these stock plants was 50% to 100%. A comparison of the microorganisms isolated from the contaminated cultures and from 0.22-μm filter disks through which 20 liters of city water had passed revealed the presence of similar bacterial floras. Five genera of bacteria (Listerium spp., Corynebacterium spp., Enterobacter spp., Pasteurella spp., and Actinobacillus spp.) were isolated from contaminated cultures and cultured filter disks. Watering greenhouse-grown stock plants with filtered city water decreased contamination of stem explant cultures 30% to 50%. Installing an ultraviolet light water-sterilizing unit at the greenhouse inlet point effectively reduced contamination.

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Peter L. Sholberg, Paul Randall, and Cheryl R. Hampson

Acetic acid (AA) fumigation of rootstocks and dormant shoots was explored as a method of eliminating plant pathogens from propagation material. Dormant shoots were tested in early winter to determine the rate of AA vapor that they could tolerate before being damaged. Apricot (Prunus armeniaca), apple (Malus ×domestica), and peach (Prunus persica) shoots collected from a single site in Dec. 1999 tolerated 30, 12, or 6 mg·L–1 AA, respectively. Vineland 3 (V3) and Malling-Merton 106 (MM.106) rootstock liners fumigated with 1 mg·L–1 AA were adequately surface-sterilized although the effect on growth was not recorded. A similar experiment with Malling 9 (M9) rootstocks showed that 12 mg·L–1 AA would eliminate most surface microorganisims from roots although it delayed shoot growth when the trees were planted. The higher 15 mg·L–1 rate delayed tree growth and appeared to kill some trees. The 12 mg·L–1 rate prevented growth of Erwinia amylovora and Pseudomonas syringae pv. syringae bacteria on shoots even when an enrichment technique was used to detect them. Finally, when 96 `Jonagold' apple shoots known to be infected by Podosphaera leucotricha were fumigated with AA in 2001, none developed powdery mildew, although 99% of the control shoots did. These promising results suggest that further research should be done toward adapting AA fumigation for use by commercial nurseries.

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Marianela Ramirez, Marek J. Krasowski, and Judy A. Loo

from each tree and, in sets of 10, surface sterilized for 5 min with 150 mL of 5.25% sodium hypochlorite containing three drops of antibacterial detergent followed by three rinses in sterile water. Bud scales were excised, and each bud was placed in a

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Bill Rhodes, Xingping Zhang, Tom Garrett, Tom Platt, and Chao Fang

A selection of Congo produced fruit that were not infected by blotch (pathogen Acidovorax avenae subsp. citrulli) in a replicated trial interplanted with infected seedlings. Ninety percent of Congo fruit not infected with the bacterial pathogen had a darker green background than those infected. PI 295843 and PI 299318 selections were also not infected. Infection rates in susceptible checks ranged from 22.5% to 47.6% and from 0 to 13.9% among triploids. Both ploidy level and genotype significantly affected infection rates. Infestation rates in triploid seeds were reduced but not eliminated by dry heat up to 75C. Heat treatment necessary to kill the pathogen was detrimental to germination.

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Randall P. Niedz

Controlling bacterial and fungal contamination in plant tissue cultures is a serious problem. Antibiotics are currently used but are not always effective, can alter plant growth, and are costly, and resistant strains can result with extensive use. Plant preservative mixture (PPM) contains a mixture of two isothiazolones—methylchloroisothiazolinone and methylisothiazolinone, which are a class of broad-spectrum, widely used industrial biocides. The isothiazolones used in PPM are reported by the manufacturer to be nonphytotoxic at concentrations suitable for the prophylactic control of microbial contaminants in plant tissue cultures. Our results indicate that PPM can be routinely added to tissue culture medium to control air- and waterborne bacterial and fungal contaminants effectively.

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M. I. Ragab and Kh. A. Okasha

The objective of thus work was to study the effect of soil fumigation with methyl bromide and different mulching types on growth and productivity of the strawberry cultivar Chandler. The experiment Included 8 Treatments which were the combination of 2 soil fumigation treatments × 4 mulching polyethylene types A split plot design with four replicates was adopted Soil fumigation treatments (fumigated and non fumigated) were assigned as main plots, whereas the four mulching polyethylene treatment (control, black, white and transparent) were distributed as subplots.

Results Indicated that in order to improve the vegetable growth and to increase the high yielding ability of strawberry cv. Chandler, it is recommended to fumigate soil with methyl bromide gas (50 gm/m2) and apply transparent polyethylene soil mulching

Moreover, in strawberry fields where weeds show serious problem. it is better to use the black polyethylene in controlling weeds of both the fumigated and non fumigated soils.