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  • Author or Editor: Mark W. Farnham x
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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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Collard and kale (Brassica oleracea L. var. acephala) cultivars and several landraces obtained from southeastern growers were tested for potential winter production. Collard and kale entries were grown in four winter environments in South Carolina from 1993 to 1995. Transplants were set in the field during November or December, and leaf production and plant fresh weight were monitored through the winter. When plants reached a 22-leaf stage, a plot subsample was harvested and weighed. The date at which 50% of the plants per plot had bolted was also recorded. Essentially all entries survived the conditions of four winter environments. However, whether an entry reached harvest size depended on its date of bolting. Collard entries typically bolted earlier than kale entries, and most kale and several collard entries attained harvestable-size before bolting. The ranking of genotypes for days to 50% bolting was consistent among environments. `Blue Max' and a landrace of collard, and `Squire' and `Blue Knight' kale usually never reached 50% bolt.

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Resistance of a Brassica oleracea germplasm collection (broccoli, Italica Group; cauliflower, Botrytis Group; and collard and kale, Acephala Group) to silverleaf whitefly (SLW; Bemisia argentifolii Bellows and Perring) infestation was evaluated using several measures of insect infestation (including adult vs. nymph counts) taken at plant growth stages ranging from seedling to mature plant. An initial study was conducted in an outdoor screen cage artificially infested with the SLW adults; subsequent field trials relied on natural infestations. The glossy-leaved lines (`Broc3' broccoli, `Green Glaze' collard, and `SC Glaze' collard) had low SLW infestations in cage and field tests. SLW adult counts were less variable than similar comparisons using nymphal counts, although adult and nymph counts were positively and significantly correlated at late plant stages. Based on this study, comparing relative SLW adult populations would be a preferred criterion for identifying B. oleracea resistance to this insect.

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Wirestem, caused by Rhizoctonia solani, is a destructive disease of B. oleracea cole crops and is distributed worldwide. Effective means of wirestem control include soil fumigation and soil treatment with pentachloronitrobenzene, which are increasingly expensive and environmentally undesirable. As a consequence, alternative methods of wirestem control are needed. Thus, we conducted controlled-environment and field experiments to develop methodology to study host-plant resistance and possibly biocontrol agents as potential wirestem control alternatives. Seedlings of 12 cultivars (three each of cauliflower, broccoli, cabbage, and collard) at the four- to five-leaf stage were transplanted to trays in a growth room or into field plots and covered with soil infested with R. solani AG-4 sclerotia. Disease progression (percent of plants healthy, diseased, and dead) was observed every 3 days for 2 weeks in the controlled environments and for 3 weeks in field trials. At the end of two studies, plants were dug with roots intact and rated for disease using a 1 to 10 scale. In all trials, percent healthy plants stabilized at about 2 weeks after inoculation. Incidence of wirestem disease varied among experiments ranging from 70% to 100% diseased, dead plants in controlled environments, and from 51% to 88% and 33% 65% in the two respective field studies. Disease rating was always negatively and significantly correlated with percent healthy plants. Although a genotype × environment interaction was observed, some cultivars (i.e., `Snowcone' and `Snowcrown' cauliflowers) were always severely diseased, while others (i.e., `Viking' broccoli and `Blue Max' collard) were consistently among the least diseased.

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Over the last 3 decades, broccoli (Brassica oleracea L., Italica Group) hybrids made by crossing two inbred lines replaced open-pollinated populations to become the predominant type of cultivar. The change to hybrids evolved with little or no understanding of heterosis or hybrid vigor in this crop. Therefore, the purpose of the present study was to determine levels of heterosis expressed by a set of hybrids derived by crossing relatively elite, modern inbreds (n = 9). A total of 36 hybrids formed by crossing nine parents were evaluated for horticultural characters, including head weight, head stem diameter, plant height, plant width (in a row), and maturity (e.g., days from transplant to harvest) in four environments. When averaged across all four environments, roughly half of the hybrids exhibited high parent heterosis for head weight (1 to 30 g) and stem diameter (0.2 to 3.5 cm). Almost all hybrids showed high parent heterosis for plant height (1 to 10 cm) and width (2 to 13 cm). Unlike other traits, there was negative heterosis for maturity, indicating that heterosis for this character in hybrids is expressed as earliness. With modern broccoli inbreds, heterosis for head characteristics appears less important than for traits that measure plant vigor.

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Carotenoids are secondary plant metabolites in vegetables known to be essential in the human diet and reported to confer various positive health-promoting effects when consumed. Brassica oleracea L. vegetables like kale, cabbage, and broccoli are recognized as excellent sources of dietary carotenoids. Broccoli has emerged as the most important B. oleracea crop in the United States and it likely supplies more carotenoids to the U.S. diet than the other crops of this species. However, very little is known about the general carotenoid profile of this important vegetable or the levels of specific carotenoids and how they might vary among genotypes. Thus, the objectives of this study were to assess carotenoid profiles of different inbred broccoli heads; to assess chlorophyll concentrations measured simultaneously during carotenoid assays; to determine the relative effects of genotype versus environment in influencing head carotenoid levels; and to examine phenotypic correlations between carotenoid levels and other traits. Results show lutein to be the most abundant carotenoid in broccoli heads ranging from 65.3 to 139.6 μg·g−1 dry mass (DM) among nine inbreds tested in three environments. Genotype had a highly significant effect on lutein levels in broccoli heads and the ratio of σ2 g2 p for this carotenoid was 0.84. Violaxanthin also exhibited a significant genotype effect, but it was found at lower levels (17.9 to 35.4 μg·g−1 DM) than lutein. β-carotene and neoxanthin were detected at levels similar to violaxanthin, but genotypic differences were not detected when all environments were compared. This was also true for antheraxanthin, which was detectable in all genotypes at lower levels (mean of 13.3 μg·g−1 DM) than the other carotenoids. Significant genotypic differences were observed for both chlorophyll a and b among the studied inbreds; however, no environment or genotype-by-environment effects were observed with these compounds. Results indicated that most carotenoids measured were positively and significantly correlated with one another, indicating that higher levels of one carotenoid were typically associated with higher levels of others. This study emphasizes the relative importance of lutein in broccoli heads and the key role that genotype plays with this compound, ultimately indicating that breeding cultivars with increased levels of this particular carotenoid may be feasible.

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Breeding a vegetable crop for adaptation to a temperature regime that is higher than the recognized optimum for the species in question is an example of breeding for abiotic stress tolerance. Before embarking on a project to breed for such stress tolerance, we propose that several critical considerations or questions must be addressed. These considerations include the following: 1) What is the effect of the abiotic stress on the crop to be improved; 2) what will be the conditions of the selection environment; 3) what germplasm is available that contains the necessary genetic variation to initiate improvement; 4) what breeding scheme will be used to facilitate improvement; and 5) what will be the specific goals of the breeding effort? We use a case study with broccoli to breed for adaptation to high-temperature environments to provide examples of how each of these considerations might be addressed in developing an improvement effort. Based on documented success with this case study in which broccoli quality and performance under high-temperature summer environments has been improved, insights are provided that should be useful to future attempts to breed vegetables more tolerant of an abiotic stress.

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Broccoli (Brassica oleracea L. Italica Group) is a vegetable crop requiring relatively cool conditions (e.g., less than 23 °C) to induce and maintain vernalization and to allow normal floral and head development to proceed. In general, this requirement is a major limiting factor to production of broccoli in eastern states where growing seasons are often interrupted by high temperature spikes. The USDA, ARS, U.S. Vegetable Laboratory (USVL) is conducting a program to breed broccoli varieties adapted to summer conditions of the southeastern United States. The goal of the current study was to compare performance of three experimental broccoli hybrids from that program with some commonly raised commercial hybrids (‘Packman’, ‘Marathon’, ‘Arcadia’, ‘Greenbelt’, ‘Patron’, and ‘Gypsy’) by conducting trials in summer environments as well as in more conventional growing environments (e.g., in fall). All hybrids produced marketable heads with high quality ratings in fall field trials (2006, 2007, and 2008). Under the high temperatures that were characteristic of the summer (2007, 2008, and 2009) trials in South Carolina, the commercial hybrids ‘Marathon’, ‘Greenbelt’, ‘Arcadia’, and ‘Patron’ failed to produce broccoli heads at all. The remaining hybrids produced heads with similar mean head mass, stem diameter, and bead size in South Carolina summer trials. However, the three experimental hybrids produced marketable quality heads, but ‘Gypsy’ and ‘Packman’ did not. The primary flaws in ‘Gypsy’ and ‘Packman’ heads were increased yellow color, flattening of the dome, increased roughness, and non-uniformity of bead size. In New York trials, all tested hybrids developed heads, but ‘Packman’ and ‘Marathon’ produced relatively poor-quality heads when maturing in summer and better quality heads when maturing in the fall. The experimental hybrids exhibited more consistent quality across different maturity times in the New York tests. Results of this research indicate that broccoli response to summer conditions of the eastern United States is dependent on the cultivar grown. Many cultivars are not adapted to extreme summer conditions of the Southeast because they will not be effectively vernalized and will therefore not head. Others such as ‘Gypsy’ and ‘Packman’ will head, but non-uniform bud development results in a rough-appearing curd in which flower buds are at various stages of development. The experimental hybrids that are single crosses of inbreds selected for adaptation to southeastern summer conditions represent a unique class of broccoli hybrids that combine early maturity and the ability to produce heads under summer conditions of South Carolina. Additional tests of these latter hybrids in New York indicate that they may be generally adapted to summer environments of the eastern United States.

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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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Broccoli (Brassica oleracea L., Italica Group) has been recognized as a source of glucosinolates and their isothiocyanate metabolites that may be chemoprotective against human cancer. A predominant glucosinolate of broccoli is glucoraphanin and its cognate isothiocyanate is sulforaphane. Sulforaphane has been shown to be a potent inducer of mammalian detoxication (Phase 2) enzyme activity and to inhibit chemical-induced tumorigenesis in animal models. Little is known about phenotypic variation in broccoli germplasm for Phase 2 enzyme (e.g., quinone reductase) induction potential. Thus, this study was undertaken to evaluate: 1) quinone reductase induction potential (QRIP) diversity among a population of broccoli inbreds; 2) QRIP levels in selected lines; 3) correlation of QRIP with other horticultural characteristics; and 4) QRIP expression in a sample of synthesized hybrids. In 1996, 71 inbreds and five hybrid checks (all field-grown), ranged from a QRIP of nearly zero to 150,000 units/g fresh weight (FW) (mean of 34,020 units/g FW). These values were highly correlated with methylsulphinylalkyl glucosinolate (MSAG; primarily glucoraphanin) concentrations that ranged from 0.04 to 2.94 μmol.g-1 FW. A select subset of lines evaluated in 1996 were reevaluated in 1997. QRIP and MSAG values in this second year were similar to and correlated with those observed in 1996 (r = 0.73, P < 0.0001 and r = 0.79, P < 0.0001, respectively). In addition, both QRIP and MSAG concentration were highly correlated with days from transplant to harvest. Average F1 hybrid values for QRIP and MSAG in 1997 fell typically between their parental means, but were often closer to the mean of the low parent. Results of this study indicate that divergent QRIP expression can effectively be used to select enhanced inbred lines to use in development of value-added hybrids. Evidence is also provided that there is a significant genetic component to both QRIP and MSAG concentration, and that selection for either one may provide an effective means for developing broccoli hybrids with enhanced chemoprotective attributes. Chemical names used: 4-methylsulphinylbutyl glucosinolate (glucoraphanin) and 4-methylsulphinylbutyl isothiocyanate (sulforaphane).

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