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Craig S. Charron and Carl E. Sams

The U.S. Clean Air Act bans the use of methyl bromide after 2005. Consequently, the development of alternative methods for control of soilborne pathogens is imperative. One alternative is to exploit the pesticidal properties of Brassica L. species. Macerated leaves (10 g) from `Premium Crop' broccoli [B. oleracea L. (Botrytis Group)], `Charmant' cabbage [B. oleracea L. (Capitata Group)], `Michihili Jade Pagoda' Chinese cabbage [B. rapa L. (Pekinensis Group)], `Blue Scotch Curled' kale [B. oleracea L. (Acephala Group)], Indian mustard [B. juncea (L.) Czerniak, unknown cultivar] or `Florida Broadleaf' mustard [B. juncea (L.) Czerniak] were placed in 500-mL glass jars. Petri dishes with either Pythium ultimum Trow or Rhizoctonia solani Kühn plugs on potato-dextrose agar were placed over the jar mouths. Radial growth of both fungi was suppressed most by Indian mustard. Volatiles were collected by solid-phase microextraction (SPME) and analyzed by gas chromatography-mass spectrometry. Allyl isothiocyanate (AITC) comprised >90% of the volatiles measured from `Florida Broadleaf' mustard and Indian mustard whereas (Z)-3-hexenyl acetate was the predominant compound emitted by the other species. Isothiocyanates were not detected by SPME from `Premium Crop' broccoli and `Blue Scotch Curled' kale although glucosinolates were found in freeze-dried leaves of all species. When exposed to AITC standard, P. ultimum growth was partially suppressed by 1.1 μmol·L-1 (μmol AITC/headspace volume) and completely suppressed by 2.2 μmol·L-1 R. solani was partially suppressed by 1.1, 2.2, and 3.3 μmol·L-1 AITC. Use of Brassica species for control of fungal pathogens is promising; the presence of AITC in both lines of B. juncea suppressed P. ultimum and R. solani but some Brassicas were inhibitory even when isothiocyanates were not detected.

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R.L. Parish and R.P. Bracy

Prior studies have demonstrated that a Gaspardo vacuum seeder provides less uniform seed spacing than a Stanhay belt seeder. It was hypothesized that the difference was primarily because of the greater seed drop height on the Gaspardo seeder. A Gaspardo metering unit was modified by adding a slide or an enclosed tube to guide the seeds from the release point (seed plate) to 1.0 inch (25 mm) above the bottom of the seed furrow. Seed uniformity tests were conducted with cabbage (Brassica oleracea), onion (Allium cepa), and mustard (Brassica juncea) seeds. The modified planter unit was compared with an unmodified unit. No improvement in seeding uniformity was noted with either the slide or the tube. In fact, seed placement uniformity was degraded with the addition of the slide and tube. Although it is probable that the seed spacing nonuniformity was caused by drop height, attempts to control the seed trajectory were unsuccessful.

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Owusu A. Bandele, Marion Javius, Byron Belvitt, and Oscar Udoh

Fall-planted cover crops of hairy vetch (Vicia villosa Roth), Austrian winter pea (Pisum sativum subsp. arvense L. Poir), and crimson clover (Trifolium incarnatum L.) were each followed by spring-planted 'Sundance' summer squash [Cucurbita pepo var. melopepo (L.) Alef.] and 'Dasher' cucumber (Cucumis sativus L.). Squash and cucumber crops were followed by fall 'Florida Broadleaf mustard green [Brassica juncea (L.) Czerniak] and 'Vates' collard (Brassica oleracea L. Acephala group), respectively. The same vegetable sequences were also planted without benefit of cover crop. Three nitrogen (N) rates were applied to each vegetable crop. Squash following winter pea and crimson clover produced greater yields than did squash planted without preceding cover crop. Cucumber following crimson clover produced the greatest yields. No cover crop effect was noted with mustard or collard. Elimination of N fertilizer resulted in reduced yields for all crops, but yields of crops with one-half the recommended N applied were generally comparable to those receiving the full recommended rate.

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David A. Bender, William P. Morrison, and Raymond E. Frisbie

A system of intercropping cabbage (Brassica oleracea var. capitata L.) with Indian mustard [Brassica juncea (L.) Czern.] to reduce pesticide applications was evaluated over three cropping seasons. Insects were monitored in nonintercropped cabbage, cabbage plots surrounded by Indian mustard, and the Indian mustard intercrop. Insecticide applications were made to individual plots based on specific treatment thresholds for lepidopterous insects and accepted pest management practices for other insects. Intercropping had no significant effect on the number of lepidopterous larvae in cabbage. Indian mustard did not appear to preferentially attract lepidopterous insects, but was highly attractive to hemipterans, especially harlequin bugs [Murgantia histrionica (Hahn)]. In one season with heavy harlequin bug pressure, intercropping with Indian mustard eliminated two insecticide applications to cabbage. Intercropping cabbage with Indian mustard does not appear to be an economical pest management practice under normal pest pressures in West Texas.

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Claudia Cunha, Muhammet Tonguç, and Phillip D. Griffiths

Chloroplast DNA (cpDNA) was used to identify polymorphisms between crucifer species using the polymerase chain reaction-random fragment-length polymorphism (PCR-RFLP) technique. Ten primer pairs based on cpDNA gene sequences were used to amplify cpDNA fragments in Brassica oleracea L., B. rapa L., B. nigra (L.) Koch, B. napus L., B. carinata Braun, B. juncea (L.) Czern, and Raphanus sativus L. accessions. Amplified DNA sequences were then digested using 11 restriction enzymes to identify polymorphisms between the 7 species. Of the 110 combinations, 38 generated polymorphisms that discriminated one or more of the species. Genotyping of these polymorphisms in 10 accessions of each of the diploid species (B. oleracea, B. nigra, B. rapa and R. sativus) did not reveal segregating polymorphisms among accessions within species, indicating that they can be used to help determine species identity. Ten accessions of each of the amphidiploids B. napus, B. carinata and B. juncea were genotyped to infer their maternal ancestry. The diploid source of cpDNA in B. carinata was B. nigra in all accessions tested and B. rapa for nine of ten B. juncea accessions tested. Two B. napus accessions amplified polymorphisms shared with B. rapa, and eight accessions produced unique polymorphisms from neither B. rapa, B. oleracea or B. nigra. The polymorphisms identified in this study can be used to help confirm identity of the diploid crucifer species for taxonomic and conservation studies.

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Richard L. Parish and Regina P. Bracy

Two studies were conducted on bed and row configurations. The first compared erosion effects on stand count with single and double drill plantings; the second evaluated bed heights. Vegetables are usually planted on raised beds in the Deep South. Both single and double drills per bed are common. The double drills offer higher yields in some cases, but may be difficult to maintain because of erosion on the bed sides after heavy rainfall. A series of plantings of cabbage (Brassica oleracea L. Capitata group) and broccoli (Brassica oleracea L. Italica group) was made over a period of nearly a year to compare stands from single and double drills. Heavy rainfall did not occur after any of the 18 plantings, so bed erosion did not occur. Differences in percent stand were few, although in a few cases the double drill planting resulted in higher stands. A field study was conducted to determine the optimum bed height for leafy greens crops grown on shaped beds. Bed heights of 5, 10, 15, and 20 cm (2, 4, 6, and 8 in) were evaluated with crops of mustard [Brassica juncea (L.) Czerniak.] and turnip (Brassica rapa L. Rapifera group) during three crop seasons. Few significant differences in stand count, yield, or product quality resulted from the different bed heights. A trend toward lower yields, quality, and reduced efficacy of precision cultivation was noted with the 5-cm (2-in) bed height.

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Regina P. Bracy and Richard L. Parish

Stands of brassica crops obtained with precision seeders are sometimes inadequate or nonuniform. Although several types of covering devices and presswheels are available from precision seeder manufacturers, the effects of covering devices and presswheels on plant emergence of direct-seeded Brassica crops have not been determined. In Spring and Fall 1996, six crops of mustard [Brassica juncea (L.) Czerniak] and four crops of cabbage (Brassica oleracea L. capitata group) were direct seeded with a precision belt seeder using four covering devices and four rear presswheels. All of the covering devices and presswheels evaluated were adequate for direct seeding mustard and cabbage under the soil moisture conditions and soil type (silt loam or fine sandy loam) found in these experiments. Although poor stands were obtained with all seed covering devices and presswheels when 7.8 inches (199 mm) of rain occurred within 3 days of planting, plant stand of cabbage was greater when the paired arm device was used than with drag-type or no covering devices.

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Federico L. Iñiguez-Luy, Michell E. Sass, Geunhwa Jung, Mitrick A. Johns, and James Nienhuis

Thomas Osborn of the Crucifer Genetics Cooperative for providing Brassica seed and for their vital input. The authors would also like to thank Daniel Gerhardt for his technical assistance. This research was funded by the National Science Foundation

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Xenia Y. Wolff and Robert R. Coltman

`Green Mignonette', `Salinas', `Parris Island Cos', and `Amaral 400' lettuce (Lactuca sativa L.); `WR-55 Days' Chinese cabbage (Brassica rapa L. Pekinensis Group); Waianae Strain' green mustard cabbage [Brassica juncea (L.) Czerniak]; `Tastie Hybrid' head cabbage (Brassica oleracea L. Capitata Group); and an unnamed local selection of green bunching onions (Allium fistulosum L.) were field-grown during Fall 1987 and Spring 1988 at Waimanalo, Oahu, Hawaii, in full-sun and with four artificially produced levels of shade (30%, 47%, 63%, and 73%). Yields of cos lettuce, green mustard cabbage, and green bunching onions were irresponsive to shade or negatively affected by shade in both seasons. Yield responses of the other crops to shade varied seasonally. Optimum shading of 30% to 47% increased `Green Mignonette', `Salinas', and `Amaral 400' lettuce yields by 36% and head cabbage and Chinese cabbage yields by 23% and 21%, respectively, compared to full-sun plots in one or both seasons. Leaf areas similar to unshaded controls were maintained as shade intensity increased, while leaf dry weight decreased in all crops except `Salinas' and `Parris Island Cos' lettuce. Maximum rates of net photosynthesis (Pn) were attained at 1500 umol·s-1·m-2, which was about two-thirds of full sunlight.

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Jianping Ren, James R. McFerson, Rugang Li, Stephen Kresovich, and Warren F. Lamboy

Fifty-two germplasm accessions of Chinese vegetable brassicas were analyzed using 112 random amplified polymorphic DNA (RAPD) markers. The array of material examined spanned a wide range of morphological, geographic, and genetic diversity, and included 30 accessions of Brassica rapa L. (Chinese cabbage, pakchoi, turnip, and broccoletto), 18 accessions of B. juncea (L.) Czern. (leaf, stem, and root mustards), and four accessions of B. oleracea L. ssp. alboglabra (Chinese kale). The RAPD markers unambiguously identified all 52 accessions. Nei-Li similarities were computed and used in unweighed pair group method using arithmetic means (UPGMA) cluster analyses. Accessions and subspecies were clustered into groups corresponding to the three species, but some accessions of some subspecies were most closely related to accessions belonging to other subspecies. Values for Nei-Li similarities suggest that Chinese cabbage is more likely to have been produced by hybridization of turnip and pakchoi than as a selection from either turnip or pakchoi alone. RAPD markers are a fast, efficient method for diversity assessment in Chinese vegetable brassicas that complements techniques currently in use in genetic resources collections.