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  • Author or Editor: Gregory C. Phillips x
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Abstract

The procedures for micropropagation and plant regeneration from callus were developed for Allium fistulosum L., A. altaicum Pall., A. galanthum Kar. & Kir., A. roylei Stearn, and selected progeny of interspecific crosses of A. cepa × fistulosum, A. cepa × galanthum and A. cepa × oschaninii O. Fedtsch. Each of the genotypes exhibited shoot multiplication in micropropagation systems, and most regenerated plants from callus. The results demonstrate the general applicability of the picloram-based tissue culture model for the genus Allium. Chemical names used: 4-amino-3,5,6-tri-chloro-2-pyridinecarboxylic acid (picloram).

Open Access

In vitro genetic transformation of chile pepper, Capsicum annuum var. New Mexico 6-4, was achieved. Seeds of `New Mexico 6-4' were grown aseptically on Murashige and Skoog medium. Seedlings 22 days old were wounded on the hypocotyl region using a sterile hypodermic needle. A. rhizogenes strain K 599 harboring the plasmid p35S GUS Intron was inoculated on the wound site. Three days later the seedlings were transferred onto MS media with antibiotics (Cefotaxime, Carbenicillin, Amoxicillin, Clavulanic acid, and Kanamycin). New roots were seen to initiate from the wound site 15 to 20 days after inoculation. The roots were morphologically identified as “hairy roots.” Glucuronidase (Gus) assay performed 40 days after inoculation on randomly chosen roots that had grown into the selection medium, showed that 6/25 (24%) of the inoculated seedlings had roots that showed intense blue coloration. Presence of an intron makes it impossible for the bacteria to express the reporter gene. The seedlings that had transformed roots had a different morphology with wrinkled leaves and short internodes. The pattern of expression of the introduced gene varied greatly. Some positive tissues had the root tips alone being blue; a few had the vascular tissues and the root tips blue; and others had the vascular tissues, the surrounding parenchyma cells, root tips, and the root hairs turn very dark blue. The transformed roots did not need to grow into the selection media to be Gus positive. Isolated roots cultured on MS media supplemented with 0.2 mg/L IAA were maintained for 120 days and continued to express the reporter gene. Currently, methods to regenerate transformed shoots from roots are being tested. The “hairy root” transformation system in pepper could have application in the testing of root-expressible constructs for transgene expression assays.

Free access

Abstract

Seedling shoot meristem-tip explants of ‘Yellow Grano’ and ‘Yellow Sweet Spanish’ onions (Allium cepa L.) were cultured in vitro on media varying in auxin and cytokinin composition. 4-Amino-3,5,6-trichloropicolinic acid (picloram) as an auxin source was superior to α-naphthaleneacetic acid (NAA) used as a control for shoot multiplication cultures maintained for 6 months or longer. A combination of 0.03 mg/liter picloram and 0.5 mg/liter 6-benzylamino purine (BA) was optimal. Picloram was comparable or superior to the 2,4-dichlorophenoxyacetic acid (2,4-D) control for induction, continued maintenance and friability of callus, and subsequent regeneration of plants. Somatic embryos developed at high frequency in some lines of both cultivars on media containing 0.75 mg/liter picloram and 1.5 to 2.0 mg/liter BA. The most promising scheme for plant regeneration from 6- to 12-month-old callus cultures involved transfer from somatic embryo induction media to modified shoot multiplication media. These techniques also were successful using mature bulb basal plate-scale explants.

Open Access

Abstract

Allium cepa L., A. fistulosum L., A. galanthum L., and A. cepa × A. fistulosum reciprocal interspecific hybrids were grown in vitro as calluses, shoots, and plantlets, and exposed to the filtrate of the pink root disease-causing fungus, Pyrenochaeta terrestris (Hansen) Gorenz, Walker, and Larson. Tissue culture reponses to the filtrate were assessed by visible damage ratings and fresh weights. Calluses exposed to the filtrate incorporated into the culture medium reflected the degree of whole plant susceptibility among the tester lines. However, in vitro shoot and plantlet culture responses did not reflect this correlation. Filtrate action appeared to be localized in meristematic cells. This in vitro approach may prove useful in screening or selection for onion pink root disease resistance.

Open Access

Callus cultures were established from intraspecific lines of Allium cepa L., interspecific F1 progeny of A. cepa crossed to A. fistulosum L. and to A. galanthum L., advanced generations of A. fistulosum x A. cepa backcrossed to A. cepa, and lines of A. fistulosum and A. galanthum. These genotypes had been identified as susceptible, resistant, or partially resistant tester lines based on prior seedling and field nursery screenings using the pink-root pathogen Pyrenochaeta terrestris (Hansen) Gorenz, Walker and Larson. Tester line calli were challenged in vitro with culture filtrates of the fungal pathogen and were assessed by visible damage ratings expressed as the percentage of pigmentation in response to the filtrate. The degrees of callus sensitivity to the filtrate observed in vitro corresponded well with the in vivo tester line classifications. These results eliminated the possible confounding influence of using various species of Allium for in vitro screening. Our results indicated the suitability of the in vitro screening approach for the possible identification of useful segregants or somaclonal variants possessing pink-root resistance. However, in vivo pathogenicity may involve mechanisms in addition to sensitivity to the putative toxins present in the filtrate.

Free access

Micropropagation of 11 rare or endangered cacti species belonging to the subtribe Cactinae was achieved by rooting of proliferated axillary shoots. Shoot tip explants were obtained from seedlings of Escobaria missouriensis D.R. Hunt, E. robbinsorum (Earle) D.R. Hunt, Sclerocactus spinosior (Engelm.) Woodruff & L. Benson, and Toumeya papyracantha (Engelm.) Br. & Rose, and from mature plants of Mammillaria wrightii Engelm., Pediocactus bradyi L. Benson, P. despainii Welsh & Goodrich, P. knowltonii L. Benson, P. paradinei B.W. Benson, P. winkleri Heil, and S. mesae-verdae (Boissevain) L. Benson. Three or four species were used in each of a series of experiments investigating the effects of basal media and auxin and cytokinin types and concentrations on axillary shoot proliferation. Low or no auxin but moderate to high cytokinin concentrations were required for axillary shoot production. All species rooted spontaneously on hormone-free media; however, several species rooted better on media containing auxin. All species were re-established in the greenhouse.

Free access

Selective weed control in ornamental plant production can be difficult as many herbicides can cause unacceptable injury. Research was conducted to evaluate the tolerance of several ornamental species to applications of p-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides for the control of problematic weeds in ornamental production. Mestotrione (0.09, 0.18, and 0.36 lb/acre), tembotrione (0.08, 0.16, and 0.32 lb/acre), and topramezone (0.016, 0.032, and 0.064 lb/acre) were applied alone postemergence (POST) in comparison with the photosystem II-inhibiting herbicide, bentazon (0.5 lb/acre). All herbicide treatments, with the exception of the two highest rates of tembotrione, caused less than 8% injury to ‘Noble Upright’ japanese holly (Ilex crenata) and ‘Compactus’ burning bush (Euonymus alatus). Similarly, no herbicide treatment caused greater than 12% injury to ‘Girard’s Rose’ azalea (Azalea). Conversely, all herbicides injured flowering dogwood (Cornus florida) 10% to 23%. Mesotrione- and tembotrione-injured ‘Radrazz’ rose (Rosa) 18% to 55%, compared with only 5% to 18% with topramezone. ‘Siloam June Bug’ daylily (Hemerocallis) injury with topramezone and tembotrione was less than 10%. Topramezone was the only herbicide evaluated that provided at least 93% control of redroot pigweed (Amaranthus retroflexus) with all application rates by 4 weeks after treatment (WAT). Redroot pigweed was controlled 67% to 100% with mesotrione and tembotrione by 4 WAT, but this activity was variable among application rates. Spotted spurge (Chamaesyce maculata) was only adequately controlled by mesotrione applications at 0.18 and 0.36 lb/acre, whereas chamberbitter (Phyllanthus urinaria) was not controlled sufficiently with any herbicide evaluated in these studies. Yellow nutsedge (Cyperus esculentus) was suppressed 72% to 87% with mesotrione applications at 0.18 lb/acre or higher and with bentazon at 0.5 lb/acre by 4 WAT. All other herbicide treatments provided less than 58% control of yellow nutsedge. In the second study, ‘Patriot’ hosta (Hosta), ‘Green Sheen’ pachysandra (Pachysandra terminalis), autumn fern (Dryopteris erythrosora), ‘Little Princess’ spirea (Spiraea japonica), ‘Green Giant’ arborvitae (Thuja plicata), and ‘Rosea’ weigela (Weigela florida) displayed no response to topramezone when applied at 0.024 and 0.095 lb/acre. Since 10 ornamental species in our studies exhibited less than 10% herbicidal response with all rates of at least one HPPD-inhibiting herbicide then it is possible that these herbicides may provide selective POST weed control in ornamental production systems.

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Field and greenhouse studies were conducted to determine if two indole-3-acetic acid herbicide mimics, aminopyralid and aminocyclopyrachlor-methyl, applied at 70, 140, and 280 g·ha−1 postemergence (POST) would control mugwort (Artemisia vulgaris) in an abandoned nursery. These were compared with the commercial standards picloram at 280 g·ha−1 a.i. and clopyralid at 280 g·ha−1. In the field study, picloram and clopyralid controlled mugwort 75% and 31% by 365 days after treatment (DAT), respectively. In contrast, aminopyralid and aminocyclopyrachlor-methyl applied at 140 g·ha−1 controlled mugwort over 90% by 365 DAT. In the greenhouse study, aminopyralid and aminocyclopyrachlor-methyl applied at 140 g·ha−1 controlled mugwort 92% and 96% respectively, although aminopyralid at 70 g·ha−1 provided better visual control (94%) in comparison with aminocyclopyrachlor-methyl (79%) at 70 g·ha−1. Regardless, following shoot growth removal at 30 DAT, mugwort failed to regrow by 60 DAT following exposures to all rates of both herbicides. On the basis of these studies, aminopyralid and aminocyclopyrachlor-methyl have potential to provide excellent control of mugwort compared with the current standards clopyralid and picloram.

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