CICYT, Project ALI98-1006, for a research contract to E. Aguayo and for financial support. Thanks are also due to CEBAS-CSIC (Murcia) and to FRUVEG Soc. Coop. (Torre Pacheco, Murcia) for providing facilities and kohlrabi, respectively.
Tissue culture techniques now are used to propagate species of brassica, many of which are used as vegetables, forage and fodder, and oilseed (2). Tissue culture has been especially beneficial in the maintenance of self-incompatible parent lines of Brassica oleracea and also in eliminating the reduction of vigor associated with continuous inbreeding of parent lines (4). Although many members of B. oleracea have been propagated by tissue culture techniques, the study of the in vitro growth of kohlrabi has been limited (1). In most cases where in vitro growth has been reported, either no plants were regenerated or the regeneration percentage was extremely low (3, 6, 7). We determined the optimum concentration of plant growth regulators needed to induce shoots and to promote their subsequent rooting.
Two-year field experiments were carried out to evaluate the suitability of crop water stress index (CWSI) as a basis for irrigation scheduling of kohlrabi (Brassica oleracea L. var. gongylodes) by comparison with irrigation scheduling based on total soil water content (SWC). In the first year, irrigation scheduling when CWSI exceeded 0.3 resulted in more frequent water applications, but the total amount of irrigation water given was lower compared to irrigation when SWC fell below 70%. Kohlrabi tuber fresh weight at harvest was similar in both scheduling treatments, leading to 25% higher irrigation water use efficiency in the CWSI-scheduled plots. In the second year, three threshold levels, i.e., 0.2 and 80%, 0.4 and 60%, and 0.6 and 40% of CWSI and SWC, respectively, were investigated. At the level of highest water supply (CWSI = 0.2 and SWC = 80%), the total amount of water supplied was less in the CWSI but the number of irrigations was higher than in the SWC plots. The CWSI-based approach may be a method for irrigation scheduling of vegetables under temperate conditions. The higher irrigation frequency required would make this method particularly suitable in combination with irrigation system that allow frequent applications, i.e., in drip irrigation. To improve the method, a coupling with a soil water balance model seems promising.
The relative resistance of 18 cultivars of Brassica oleracea L. to attack by the sweetpotato whitefly [Bemisia tabaci (Gennadius)] was studied in screen cage (spring), field (autumn), and laboratory tests. The B. oleracea entries consisted of six types, including 16 green and two red cultivars. Cabbage (Capitata Group) and broccoli (Boytrytis Group) were less infested than other crops in a screen cage test, with kale, collard (Acephala Group), and brussels sprouts (Germmiter Group) experiencing relatively high and kohlrabi (Gongtlodes Group) intermediate infestations. Relative ranking of crops was similar in an autumn field study, with the exception of brussels sprouts, which had an intermediate level of infestation. Differences in numbers of whiteflies among cultivars within crops were negligible or inconsistent, except that red cultivars of brussels sprouts (`Rubine') and cabbage (`Red Acre') were much less infested than green cultivars. In a laboratory test, differences of whitefly oviposition and nymphal survival and development were small, indicating that nonpreference factors, rather than antibiosis, are the best explanations for differences in the numbers of whiteflies among the B. oleracea cultivars that were tested,
Segregation for annual vs. biennial flowering habit was observed in F2 progenies from crosses of early and late-maturing broccoli (Brassica oleracea L. Italica Group) inbred lines with cabbage (B. oleracea L. Capitata Group), kohlrabi (B. oleracea L. Gongyloides Group), collards (B. oleracea L. Acephala Group), kale (B. oleracea L. Acephala Group), and brussels sprouts (B. oleracea L. Gemmifera Group). F, progenies were usually completely annual. F2 progenies from crosses involving late broccoli contained two to five times as many biennials as F2 progenies from early broccoli crosses. Maturity factors carried by the biennial parents also appeared to affect expression of flowering habit. Annual habit is dominant over biennial and is controlled by several major genes with a strong effect of modifiers from both the annual and biennial parent. Time of heading of annual plants in F2 progenies appeared to be controlled by quantitative, mainly additive, factors. Distribution of heading dates for the F1 and annual broccoli parents showed a large environmental or cultural effect. It appears that the biennial parents, especially brussels sprouts and collards, contributed strong factors for late maturity.
Methanethiol (MT) is a volatile compound responsible for the unpleasant odor evolved when fresh broccoli (Brassica oleracea L., Italica group) is held under anaerobic conditions. Inductive atmospheres can develop in storage, transportation containers, or modified atmosphere packages, resulting in reduced quality. To determine if related vegetables are capable of producing MT, 12 different vegetables from the genus Brassica were cut into ready-to-eat forms. Fifty-gram samples were sealed in 500-mL glass jars and flushed with N2. After 24 h in the dark at 20 °C, headspace samples from the jars were analyzed for MT and other volatiles. Headspace concentration of MT was greatest in broccoli florets, followed by pak choi (Brassica rapa L., Chinensis group) leaf blades, savoy cabbage (Brassica oleracea L., Capitata group), broccoflower (Brassica oleracea L., Botrytis group), and green and red cabbage (Brassica oleracea L., Capitata group). Broccoli stems, kale (Brassica oleracea L., Acephala group), Brussels sprouts (Brassica oleracea L., Gemmifera group), pak choi petioles, rutabaga (Brassica napus L., Napobrassica group) root, cauliflower (Brassica oleracea L., Botrytis group) florets, Chinese cabbage (Brassica rapa L., Pekinensis group), and kohlrabi (Brassica oleracea L., Gongylodes group) tubers produced <3% of the MT produced by broccoli florets. Green tissues appeared to have a greater capacity to produce MT than nongreen tissues. Anaerobic production of CO2 and ethanol did not relate to the vegetable's ability to produce MT. The production of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) were also induced by the anaerobic conditions. Green cabbage produced the greatest concentration of DMDS, followed by savoy cabbage and broccoli florets. Production of DMTS was similar to the pattern observed for MT, but DMDS production was not highly correlated with MT production.
Correlation coefficients based on relative concentrations of 13 glucosinolates in the edible parts of 30 cultivars were determined. Brussels sprouts (Brassica oleracea L. gemmifera group), cauliflower (B. oleracea L. botrytis group), and either marrow-stem or smooth-leafed kale (B. oleracea L. acephala group) had similar glucosinolate patterns based on significant correlations (P < 0.01). The glucosinolates of ‘Morris Heading’ collards [(B. oleracea L. acephala group (var. sabellica)] were highly correlated with those of curly kale [B. oleracea L. acephala group (var. selensia)]. Mustard greens [B. juncea (L.) Czern. & Coss. var. rugosa Bailey] and the corresponding seeds were the most highly correlated of the 17 cultivars for which the edible parts and seeds were compared. Seed analyses indicated relationships among the cultivars somewhat similar to those seen for the edible portions.
and provide 100 mg·L −1 Ca to assist in uniform germination. For each species, nine tray systems were established by sowing seeds evenly onto each hydrated pad in the amounts of 25 g for purple kohlrabi, 15 g for mizuna, and 15 g for mustard (cv
reduced hypocotyl elongation of kohlrabi ( B. oleracea var. gongylodes ‘Delicacy Purple’), tatsoi ( B . rapa var. rosularis ), and mustard ( B . juncea L. ‘Red Lion’), and increased percent DW of red pak choi ( B . rapa var. chinensis ‘Rubi F 1
evaluated included broccoli, cauliflower, brussels sprouts, cabbage, napa cabbage, pak choi, kohlrabi, turnip, and rutabaga. For each crop, a clubroot susceptible cultivar was planted as a comparison. In 2015, five on-farm trials were initiated in fields