A mutation affecting curd colour in cauliflower (Brassica oleracea L. var. Botrytis DC)

Summary A single gene mutation in cauliflower resulted in the production of an orange coloured curd when heterozygous, and a stunted orange curd when homozygous. The orange heterozygote has commercial potential.     

Conformation of cauliflower curds

Cauliflower curds are composed of numerous small identical whorls. In the autumn cauliflower variety Meroni Ugo these form small pyramidal replicas of the whole curd while they are less pronounced in early summer and most other autumn cauliflower varieties. By halving the curd and its primary and secondary whorls it was possible to draw and measure the angle formed by the sides. There was good correlation between the angles of the primary and secondary whorls but less between these and the whole curd.Measurements were made of curd angles of parents and F₂ progenies from the cross Meroni Ugo × No. 35, the extremes for pyramidal and smooth curds respectively. The F₂ progenies showed a range of angles between those of the parent varieties with a slight excess of curds in the smoother or shallower angle type. It was considered that factors affecting curd conformation were polygenically inherited and that there was slight dominance of the polygenes giving smooth curds.     

Further studies on the propagation of cauliflower

Use of carefully lifted, decapitated cauliflower plants with 6 to 7 leaves per se, eliminated the need of the rooting of shoots and provided seeds in reduced time. Previously, shoots obtained from decapitated and de-leafed plants were rooted and allowed to produce seeds. This latter method did not assure that seed would be available in time for the following season's planting.     

Selection against the bracting defect of cauliflower

Summary The appearance of bracts through the surface of the cauliflower curd had a heritability estimate of 0.73 ± 0.10 based on the regression of progeny on parent when grown under field conditions. When curds were taken from field grown plants and aseptically cultured, their bracting characteristics were enhanced. It is advocated that a two-tier system of selection, firstly in the field and then in culture, would increase the likelihood of breeding bract free cauliflowers.Also, Department of Biological Sciences, The Polytechnic, Hatfield, Hertfordshire, UK.     

Evolution of cauliflower types grown in Great Britain as indicated by the isoenzyme composition of the cauliflower curds

Summary The curds of cauliflowers (Brassica oleracea var. botrytis L.) which are representative of the European biennials, European annuals and Australian types were used to extract 12 of the enzymes involved in carbohydrate and amino acid metabolism. Each enzyme was separated into their isoenzymes using polyacrylamide gel electrophoresis. Two enzymes, acid phosphatase EC 3.1.3.2. and aspartate aminotransferase EC 2.6.1.1. were shown to have different numbers of isoenzymes depending upon which of the three main groups of cauliflower cultivars were used. The enzymes examined showed evolutionary divergence of the cauliflower types during the selection for different times of development.     

The use of aseptic meristem culture in cauliflower breeding

Summary The upper surface of the cauliflower curd consists of a mass of apical meristems. These would normally develop into flowers, but if devernalised they revert to the vegetative phase and develop into leafy shoots. This property is being exploited by aseptically culturing portions of the curd in order to generate clones of selected material.     

Investigations into the breeding system of cauliflower

In experiments to study the effect of inbreeding, I₁ progenies of summer cauliflower showed a trend towards increase in plant weight over their non-inbred commercial parents. Curd quality, however, showed no significant improvement.As summer cauliflower varieties tended to behave as pure lines, studies were made on F₁'s from crosses between five commercial varieties. The main results of hybridisation were an increase in earliness, and a slight, though significant increase in curd size over the parental varieties. It is suggested that summer cauliflowers have attained a state of homozygous balance, which could be emulated in the autumm and winter types, by selection of self-compatible individuals.     

Propagation and flowering of cauliflower

Summary Production of seed from selected plants in the shortest possible time is an important factor in the improvement of cauliflower. A requirement of the propagation technique is that it should not diminish plant growth. A modification in technique, previously reported, which included a portion of the curd in decapitation of the selected plants made it possible to obtain flowering in approximately 65 days after moving the plants to the greenhouse.     

The inheritance of curding periods in early summer and autumn cauliflower

Two series of diallel crosses were made between (a) eight varieties of autumn cauliflowers and (b) six inbred lines from a single variety of early summer cauliflowers in order to study the inheritance of curding periods. F₁'s and parents from each diallel were grown in separate randomised block experiments and the analyses presented as conventional Wr Vr graphs.The array points from the diallel analysis of autumn cauliflowers were spread along a regression line of unit slope thus indicating that the gene system controlling curding periods was additive with no evidence of gene interaction in these crosses. Varieties of early/mid period maturity with the exception of Veitch's Autumn Giant possessed most dominant polygenes while late maturity was controlled by recessive polygenes. The diallel analysis of curding periods for the early summer cauliflower inbreds indicated the presence of some interaction which was due to the influence of two lines. On reanalysis without these lines the regression of Wr Vr agreed with a slope of 1, although there was a higher degree of dominance than was shown by the autumn cauliflowers. Analysis of the early summer cauliflower lines for numbers of leaves produced before curding indicated an association between low leaf numbers and early curding, and between high leaf numbers and late curding.None of the F₁ hybrids in either series of crosses curded earlier than the earlier curding parent.     

Vegetative maintenance and propagation of cauliflower

1. 1.
   During the past 7 years research has been carried out on different propagation methods for cauliflower. Propagation from root-shoot cuttings proved to be the most efficient method. It was developed at the Institute of Horticultural Plant Breeding, Wageningen. The results obtained with it are generally satisfactory.     
   
   

Curd grafting as an aid to cauliflower breeding

Euphytica - Genetic improvements of autumn cauliflower have been impeded by difficulties in seedling plants selected from the field. A technique for grafting cauliflower curd portions on to young...     

Methods to determine solidity and dry matter content of onions (Allium cepa L.)

Summary Different testing methods to measure solidity and dry matter content of onion bulbs were examined. The correlation coefficients between the characters determined were calculated. No strong correlations were found between the results of the different methods of measuring solidity. The refraction value of the press juice gives reliable information on the dry matter content of the onion bulb.     

Investigations on the inheritance and responses to selection of riceyness in early summer cauliflower

F₁'s grown from crosses between cauliflower plants with perfect and very ricey curds showed a continuous distribution in the degree of riceyness (classified into four grades) with slight dominance of the most ricey grades. The effect of environment upon the expression of riceyness was shown, by X² tests on F₁'s, F₂'s and selfed parents grown in more than one year, to be limited.Selections made consistently over three generations for grade 1 curds resulted in marked increases in the proportion of curds in that grade, but selection for grade 2 and 3 curds over two generations was less successful. When disruptive selection was practised, i.e., the selection of plants showing a different grade from that for which the parent was selected, the progenies of these plants generally showed an increase in the proportion of the newly selected grade.From these results it was concluded that the inheritance of riceyness appeared to be under polygenic control and that plants were still heterozygous for polygenes at the F₃ generation.     

Inheritance of downy mildew resistance in Indian cauliflower (group III)

Summary Inheritance of downy mildew (Peronospora parasitica) resistance in three resistant x susceptible crosses, one susceptible x susceptible and one resistant x resistant cross were studied in Indian cauliflower (Group III) over the two years (1990 and 1991). No significant difference was observed between the years for various estimates and hence pooled data are presented. Downy mildew resistance in crosses cc×HR 5-4 and 3-5-1-1×244 (R×S) is governed by single dominant gene PPA3 but in cross cc×244 (R×S), recessive epistasis was observed. The resistance level was not improved in both the cc×3-5-1-1 (R×R) and 244×267-6-9 (S×S) crosses. Exploitation of downy mildew resistance from cc and 3-5-1-1 in F₁ hybrid is explained in detail.     

Selection of hydroxyproline-resistant proline-accumulating mutants of cauliflower (brassica oleracea var. botrytis)

Summary A procedure is described by which hydroxyproline-resistant lines could be selected from regenerating curd tissue of cauliflower. Mutagenesis was by N-nitroso-N-ethylurea, supplied as a drop of 0.3 mM solution on each 3 mm diameter curd piece. The mutagen generated numerous morphological and pigment mutations without significantly affecting shoot regeneration from explants. Thirty one resistant shoots were recovered from more than six thousand explants mutagenised on regeneration medium supplemented with 3 mM hydroxyproline, while none was obtained from a similar number of non-mutagenised controls. Out of twenty-three resistant shoots which survived subculture, only one showed consistently elevated levels of endogenous proline. During early shoot culture passages, proline levels were 3.6–4.7 times higher than controls, but this was reduced to 1.6 times after 10–12 culture passages in the absence of hydroxyproline. Possible reasons for this decline are discussed. Leaf strip assays suggest resistant shoots may be chimeras and current efforts are directed towards regenerating solid mutants from resistant sectors. These will then be evaluated for any alteration in frost tolerance.Abbreviations IBA Indole-3-butyric-acid - NEU N-nitroso-N-ethylurea     

Genotypic differences for induction of bracting in cauliflower with 2-chloroethylphosphonic acid (ethephon)

Summary Bracting (i.e. bracts of the inflorescence growing through the surface of the curd) is a serious problem in commercial growing of cauliflower. Enhancement of bracts was most effective when ethephon was applied to plants that had just initiated a curd. When ethephon was applied 7 to 10 days later the effect diminished again. Ethephon effects were small when the chemical was applied after only a few curds had been initiated. Bracting increased continuously over the range (0 to 960 mg l^-1) of applied concentrations. There was an interaction with temperature during the early curd growth. Higher temperatures increased the effectiveness of ethephon.After an ethephon application significant differences between cultivars were observed in the extent of bracting. For screening cultivar differences in resistance against bracting, an ethephon application (240 mg l^-1) when nearly all plants had initiated a curd, was best.The experiments were carried out when the author was employed at the Research Station for Arable Farming and Production of Field Vegetables (PAGV) in Lelystad, The Netherlands.     

Inheritance of stalk rot resistance in cauliflower (Brassica oleracea var. Botrytis L.)

Summary The inheritance of resistance in cauliflower to stalk rot (Sclerotinia sclerotiorum (Lib.) de Bary) was investigated in population from six generations of six crosses. Disease incidence was recorded on 4 parents, 6 F^s ₁, 6 F^s ₂ and 12 back-crosses in a screenhouse under artificially created epiphytotic conditions. Resistance to stalk rot in this set of parents was found to be polygenic and under the control of recessive genes and due primarily to additive gene action. A breeding strategy emphasizing recurrent selection should lead to improvement in resistance.