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  • Author or Editor: Howard F. Harrison x
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Abstract

Hoeing and glyphosate (N-(phosphomomethyl)glycine) application with a hand-held wiper were compared for weed control in mixed vegetable plantings. Weed control with wiper-applied glyphosate required significantly less labor and expense than hoeing. Vegetable yields were similar in hoed and wiper-weeded plots and both methods increased the yields of some vegetable species over yields from unweeded plots. Yellow nutsedge (Cyperus esculentus L.) shoot populations were reduced significantly by wiper weeding but not by hoeing.

Open Access

The discovery that broccoli (Brassicaoleracea L., Italica Group) sprouts contain high levels of sulforaphane, a constituent that may provide chemoprotection against certain carcinogens, has stimulated much interest in seed production of this crop. Studies were undertaken to determine the potential for producing broccoli seed using self-compatible selections from open-pollinated (OP) populations or doubled-haploid (DH) programs. In all outdoor and greenhouse trials, three OP selections and seven DH lines produced selfed seed, but seed weight per plant and number per plant varied significantly among the entries. In all environments there were individuals with relatively high (i.e., >3 g/plant) production that were significantly different from low (i.e., <2 g/plant) producers. The relative productivity of some lines varied greatly between experiments, which indicates that seed production of particular genotypes is affected differently by environmental conditions. This indicates the importance of identifying lines that are high producers of selfed seed across different environments. Two OP cultivar-derived lines (USVL102 and USVL104) and two DH lines (USVL062 and USVL093) were identified that consistently produced relatively high yields in greenhouse and screen cage trials. These lines are good candidates for evaluating seed production in field tests and as possible sources of seed for sprouting.

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Clomazone herbicide is registered for cabbage (Brassica oleracea Capitata group) in the United States but not for other crop groups within the species. Greenhouse and field experiments were designed to compare the tolerance of broccoli (B. oleracea Italica group) and cabbage cultivars to clomazone to assess its potential for weed management in broccoli. Four broccoli cultivars (Captain, Green Magic, Legacy, and Patron) and four cabbage cultivars (Bravo, SC 100, Stone Head, and Vantage Point) were evaluated in all experiments. In a greenhouse experiment where seedlings were transplanted into potting medium containing clomazone at 0, 1.0, 2.0, and 4.0 parts per million (ppm), ‘Bravo’ cabbage was most susceptible. Its injury ratings and shoot weight reduction at 1.0 ppm were similar to ratings and shoot weight reduction for the other cabbage cultivars at 4.0 ppm. Among the broccoli cultivars, Patron was highly susceptible, exhibiting injury and shoot weight reduction similar to Bravo. Green Magic was the most tolerant broccoli cultivar, and it exhibited injury and growth reduction similar to the tolerant cabbage cultivars. In a field experiment where clomazone was applied pretransplanting at 0.25, 0.5, and 1.0 lb/acre, 0.25 lb/acre caused moderate chlorosis to the susceptible cultivars, Bravo and Patron. At 0.50 and 1.0 lb/acre, most cultivars exhibited chlorosis at 2 weeks after transplanting (WAT); however, tolerant cultivars recovered and injury was often not observed at 6 WAT. At 1.0 lb/acre, chlorosis persisted until maturity on ‘Bravo’ and ‘Patron’ foliage. Clomazone did not reduce mean broccoli head weight or the percentage of plants producing market-size heads. Mean cabbage head weight for ‘Bravo’ was reduced by clomazone at 1.0 lb/acre. This study indicates that the variability in clomazone tolerance among broccoli cultivars may be similar to that among cabbage cultivars and suggests that the herbicide can be used safely on tolerant broccoli cultivars at rates that are recommended for cabbage.

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Experiments were developed to study the inheritance of the high level of tolerance to the herbicide bentazon exhibited by the pepper (Capsicum annuum L.) cultivar Santaka. Parental, F1, F2, and backcross populations of the cross `Santaka' × `Keystone Resistant Giant' were evaluated for injury in a greenhouse test using bentazon at a rate of 4.5 kg·ha-1 (1.1 kg×ha-1 is the rate recommended for most applications). Additionally, parental and F1 populations were evaluated for injury under field conditions using sequential bentazon applications of 4.5, 4.5, 6.75, and 9.0 kg·ha-1. A single, dominant gene determined tolerance. F1 hybrid plants (heterozygous at the locus conditioning tolerance) exhibited a high level of tolerance under field conditions. Results of the greenhouse test suggested a possible cytoplasmic involvement in the expression of the tolerance gene, but the results of the field test provided strong evidence that cytoplasm does not play a significant role. We propose that this gene be designated Bentazon tolerance and symbolized Bzt. Chemical name used: 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (bentazon).

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Four sweetpotato [Ipomoea batatas (L.) Lam.] clones were evaluated for metribuzin tolerance in greenhouse and field experiments. W-262 exhibited metribuzin response similar to the highly tolerant clone Tinian (U.S.P.I. 153655). SC 1149-19 was highly sensitive to metribuzin, and the commercial cultivar Jewel was intermediate in tolerance. Due to its more desirable horticultural characteristics and higher yields, W-262 is superior to Tinian as a source of metribuzin tolerance in sweetpotato breeding. Chemical name used: 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one (metribuzin).

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Greenhouse and field studies were conducted to determine the genetic relationship between bentazon tolerance exhibited by the pepper (Capsicum annuum L.) cultivars Bohemian Chili and Santaka, and to evaluate the importance of cytoplasmic factors in expression of the tolerance in `Bohemian Chili.' Greenhouse evaluation of parental and F2 populations of the cross `Santaka' × `Bohemian Chili' indicated that the major dominant gene conditioning bentazon tolerance in `Bohemian Chili' is probably the Bzt gene that conditions bentazon tolerance in `Santaka' or a gene closely linked to the Bzt locus. Field evaluation of F1 and F2 progeny populations of the cross `Bohemian Chili' × `Sweet Banana' in both `Bohemian Chili' and `Sweet Banana' cytoplasms demonstrated that cytoplasmic factors do not affect the expression of the bentazon tolerance gene in `Bohemian Chili.' We conclude that `Santaka' and `Bohemian Chili' are equally satisfactory sources of a bentazon tolerance gene for use in pepper breeding programs. Chemical name used: 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (bentazon).

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Bioasssay-guided investigation of constituents possibly contributing to the allelopathic potential of sweetpotato led to the isolation of a nonpolar seed germination inhibitor in sweetpotato (Ipomoea batatas L.) roots. Mass spectral data supported by HPLC s pectroscopic analyses and data obtained from hydrolysis products revealed the presence of three monogalactosyl-diglycerides (MGDGs) (galactosyl-di-linoleneoyl glyceride, galactosyl-linoleneoyl-linoleoyl glyceride, and galactosyl-di-linoleoyl glyceride) in storage roots. The compounds inhibited proso millet germination, and at 100 ppm inhibition was about 90%. MGDG with fully saturated fatty acids (galactosyl-distearoyl glyceride) was not inhibitory in the bioassay. An efficient method for quantitation of individual MGDGs was developed, and the contents of each compound in the storage root tissues of 12 genetically diverse cultivars and breeding lines were determined. On a dry weight basis, total MGDG contents ranged between 107 and 452 μg/g in the periderm, 298 and 807 μg/g in the cortex, and 296 and 755 μg/g in the stele. Also, large differences in the ratios of the three compounds between clones and between tissues within a clone were noted. The differences between clones indicate that manipulating total content and ratios of MGDGs through plant breeding is feasible.

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Field experiments were conducted to assess how sweetpotato [Ipomoea batatas (L.) Lam.] clones interfere with weeds and how clones tolerate weed interference. Eleven clones with architecturally different canopies were evaluated for yield, canopy surface area and dry mass, weed dry mass, and light interception at ground level. A 2-fold difference in ground area covered by canopy surface area was observed among the eleven clones 42 days after planting, and a 3-fold difference in canopy dry mass at harvest. Yields were reduced from 14% to 68% by weed interference. The yields of high-yielding clones, `Beauregard', `Excel', L87-125, `Regal', `Centennial', and W-274, were reduced to a significantly greater extent by weeds than were yields of the other five clones. No differences were observed between clones for weed suppression as measured by weed dry mass at harvest and ground light interception. Short-internode and long-internode clones had similar competitive abilities. Yield of high-yielding clones was impacted more by weed interference than was that of low-yielding clones.

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After removal of the periderm, cortex tissue of the sweetpotato cultivar Regal was collected. Polar extracts of this tissue strongly inhibited germination of proso-millet seed. C18 preparative, step-gradient chromatography (H2O → 100% methanol) gave some 50+ fractions, all of which were assayed for inhibitory properties. Analytical HPLC, using diode array detection and signal processing, showed the presence of chlorogenic, p-coumaric and caffeic acid, scopolin and some unknown phenolic acids. Most fractions were inhibitory to some degree; however, the least polar ones (in 90% and 100% methanol), containing unknown compounds, were most inhibitory. Semi-prep HPLC of these fractions produced eight major peaks (λmax at 210–213 nm, λ2 at 281–284 nm). In our bioassays, the compounds produced 50% inhibition of proso-millet seed germination at ≈60 ppm. It is likely that these compounds contribute significantly to the allelopathic properties of sweetpotato.

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