Increased atmospheric humidity post pollination: A possible aid to the production of inbred line seed from mature flowers in the Brussels sprout (Brassica oleracea var. Gemmifera)

Summary In two highly self incompatible inbred lines of Brussels sprouts the effect of increased atmospheric humidity post pollination was examined immediately following 1) hand pollination of green buds and open flowers, and 2) blowfly pollination of open flowers. Data were obtained for mean number of seeds set per pollination, mean number of fruits setting seed, and mean number of seeds produced per fruit which set for both varieties. Measured as number of seeds produced per minute spent pollinating, it was clear that open flower pollination followed by high humidity conditions was a much more efficient method of producing inbred line seed (46 seeds/minute) than green bud pollination (27 seeds/minute).     

The effect of alternating temperatures on the self-incompatibility of some clones of Brussels sprouts (Brassica oleracea L. var. Gemmifera (DC.) Schulz)

Summary The influence of temperature on self-incompatibility of six S-homozygous clones of Brussels sprouts was studied. The clones were treated with constant temperatures of 14°, 17° and 20°C and alternating day and night temperatures of 17/14°, 20/14°, 23/14° and 26/14°C. To determine the degree of incompatibility the mean number of pollen tubes per style after selfing was calculated.The clone with the weak S-allele S-5 was less self-incompatible in the 23/14° and 26/14°C treatments than in the other treatments. The other clones with the weak S-alleles S-15 and S-45 remained sufficiently self-incompatible during all treatments. The clone with the rather strong S-39 showed the highest level of self-incompatibility at 26/14°C.In the two weakly self-incompatible clones with S-5 and S-39 a clear difference in self-incompatibility was found between young and old flowers. The strongly SI clones with S-39 showed no difference and in the two clones with S-15 the differences were small and significant in one case only.     

Carbon dioxide treatment as an effective aid to the production of selfed seed in kale and Brussels sprouts

Summary The use of carbon dioxide to overcome the self-incompatibility mechanisms in marrow-stem kale and Brussels sprouts (Brassica oleracea L.) is discussed. Results are presented to show the effectiveness of the treatment, and a method is described of applying it as a routine procedure for the production of selfed seed in quantily.     

Chromosome doubling of mature haploid Brussels sprout plants by colchicine treatment

Summary The effect of colchicine concentration, and the mode and time of colchicine application in doubling the chromosomes of haploid Brussels sprout plants was assessed by scoring treated plants for the presence of diploid flowers and seed set after self-pollination.When colchicine treatments were applied after the plants had been vernalised, using 2 dose rates and 3 methods of application, only 38.1% became doubled and only 13.8% produced seed. Treatment with 0.1% colchicine with or without the addition of 2% dimethyl sulphoxide gave doubling rates similar to those reached with 0.05% colchicine, but resulted in more damage to the apices.When 0.05% colchicine solution was injected into the plants' apices at varying times during vernalisation, the rate of doubling was 71.2% on average and 50.7% of plants gave seed on selfing.Overall doubling rates of plants where the apex was easily accessible were 79.0%, while for plants with dense terminal heads they were 35.0% and for plants with visible buds 31.4%.     

Routine large-scale electrophoresis for plant breeding. An example with F1 seeds of Brussels sprouts (Brassica oleracea var.gemmifera)

Summary A routine method of large-scale electrophoresis is proposed for use in plant breeding. The method can be applied both with research and teaching and does not require sophisticated apparatus. A skilled laboratory technician can thus handle 768 samples a day. Within a series of electrophoretic investigations the individual electrophoresis can be stopped at any time, while the other investigations in the series continue.     

Inbred lines with dominant incompatibility alleles for use as parents of F1 hybrid brussels sprouts

Summary To improve the chances of obtaining highly self-incompatible inbred lines for use as parents of F₁ hybrid Brussels sprouts and to extend the range of mutually cross-compatible combinations available, new inbred lines are being produced from plants selected for the presence of dominant S-alleles. The material comprises 42 different inbred families representing 15 cultivars and contains 12 dominant S-alleles of uncommon occurrence in Brussels sprouts. Data on S-allele interactions in the material are presented.Tests showed that whilst many of the parent plants containing dominant S-alleles were highly self-incompatible, a few had only weak self-incompatibility. Although the chances of obtaining strongly self-incompatible inbreds may be increased by using material with dominant S-alleles, it remains necessary to test and select for strong self-incompatibility during the breeding programme.Production of such inbred lines requires the application of two independent selection procedures, one for agronomic type and one for S-allele constitution. Only a small proportion of the plants of a parent cultivar are acceptable on both counts. Thus large populations of the cultivar and large numbers of selections are necessary: this in turn involves much expensive S-allele screening. To alleviate this problem a wide-based panmix containing only dominant S-alleles is being produced. It is hoped that from this it will be possible to extract inbred lines which carry only dominant S-alleles, so avoiding the need to screen each parent plant for its S-allele content.     

The effects of bud self-pollination and open flower self-pollination on the field characteristics of broccoli (Brassica oleracea var. Italica)

Summary Broccoli (Brassica oleracea L. var. italica) progenies grown from seed obtained by greenhouse budpollination (BP), open-flower self-pollination (OS), open-flower self-pollination with ether treatment of the stigma (OSE), and cross.pollination (CP) were compared in the field. For plant height, plant weight, head diameter, and head weight, BP resulted in the lowest values, OS and OSE were intermediate, and CP gave highest values. BP was highest, OS and OSE intermediate, and CP lowest for days to head emergence and days to harvest. Differences between OS and OSE were slight and all were non-significant for the 7 lines with complete data, but were significant for plant weight and head diameter when 20 lines were analyzed by the unweighted means method. The comparison BP versus OS-OSE was non-significant for plant height in both analyses and for head weight in the 7-line analysis only. In a second experiment using only BP and OS, and omitting days to head emergence, trends were similar but only the effects on head diameter were statistically significant. In the greenhouse, BP produced much more seed than either OS or OSE, and CP produced more than BP. Treatment of the stigma of open flowers with ether to overcome self-incompatibility did not result in greater seed production. Weight/100 seeds was higher in CP but did not differ among the three self-pollination methods.Technical Paper 5089, Oregon Agricultural Expriment Station.     

The production of inbred lines of brussels sprouts with dominant S-alleles

Summary The best sources of Brussels sprout inbred lines with both good agronomic characters and high self-incompatibility are likely to be cultivars of reasonably good agronomic type which have not been too intensively selected. Comparison of three cultivars of different agronomic quality showed that the cultivars of poor and moderate quality had about 55% of plants with a dominant S-allele, but the most highly selected cultivar had only 25% of such plants. A programme of S-allele screening is suggested which incorporates the minimum number of tests required to determine whether or not a particular plant has a dominant S-allele. A survey of S-alleles present in commercial F₁ hybrids showed that the frequency of dominant S-alleles was only 19% in hybrids released prior to the end of 1971, but was 50% in hybrids released since 1971.     

Classification of S-alleles by their activity in S-heterozygotes of brussels sprouts (Brassica oleracea var. Gemmifera (DC.) Schultz)

Summary Over a period of many years, data on dominance relationships of S-alleles in Brussels sprouts were collected at URL and IVT. The level of activity of S-alleles in heterozygotes was assessed on the basis of the number of pollen tubes that penetrated into the stigma. 209 out of 210 possible combinations between 21 S-alleles were used for this investigation. The S-alleles were grouped separately for activity in pollen and style on the basis of their sensitivity to lose activity in S-heterozygotes. Besides S-allele interaction per se, activity was found to be influenced by environment and genetic background.Results suggest that in stigma, co-dominance is the normal pattern and that deviations are caused by factors other than S-allele interaction as such.In pollen, only three truly recessive alleles were found. Besides several combinations with mutual weakening in pollen, examples of independent weakening were found.     

The role of pollen and stigma in determining the level of partial self-compatibility in brussels sprouts

Summary Brussels sprouts inbred plants, homozygous for the same recessive S-allele, were intercrossed in all combinations and the number of pollen tubes penetrating the stigmas of such crosses measured. The results of five such experiments showed that pollen as well as stigma is significant in determining the number of pollen tubes counted. It was also found that the capacity of a plant's stigmas to permit pollen tube penetration was independent of the capacity of its pollen to penetrate other plants' stigmas. Variation in pollen tube production between pollens of the plants tested was often greater than that between their stigmas.     

‘Thermally aided pollination’: A new method of breaking self-incompatibility in Brassica oleracea L.

Summary Application of heat during self-pollination of open flowers by means of an electric mini soldering iron resulted in seed set in self-incompatible Brassica oleracea varieties. Temperatures of 60, 70 and 80°C were tested. Compared with bud-pollination, in some cases the so-called thermally aided pollination (TAP) method, gave a considerably higher seed yield at 70 and 80°C. In view of the ease and rapidity of TAP it should be ascertained how far this method can replace bud-pollination in maintaining inbred lines. The possible mechanism behind the TAP response is briefly discussed.     

The inheritance of partial self-compatibility in Brassica oleracea L.: Results from a half diallel homozygous for a moderately recessive S-allele

Summary In a study of partial self-compatibility in Brassica oleracea, flower number, seeded siliqua and seed production were recorded on self-and cross-pollinated inflorescences of the progenies of a half diallel between six in bred Brussels sprout plants homozygous for the same moderately recessive incompatibility allele S₄₅.On both self-and cross-pollinated inflorescences significant amounts of additively controlled genetic variation were found for seed set per flower. For cross-pollinated inflorescences this was also the case for the two components of seed set, seeded siliquae per flower and seeds per seeded siliquae, but for self-pollinated ones only seeded siliquae production showed significant additive variation. Considerable heterosis and gene interaction were always present and a simple additive dominance model did not explain the variation.Two of the parents transmitted lower levels of partial self-compatibility to their progenies and, in one of these, dominant genes appeared to be responsible. The most important feature determining the production of self seeds was found to be the number of flowering sites at which the incompatibility mechanism failed rather than the number of seeds produced at each site.     

Optimal pollination conditions for seed set after a self-pollination,an intraspecific cross and an interspecific cross of marrow-stem kale (Brassica oleracea var. acephala)

Summary The effects of different pollination techniques, with and without emasculation and delayed pollination, were investigated to find the conditions for maximum seed set after self-pollination and intraspecific and interspecific crosses of Brassica oleracea var. acephala. The results indicated that the pollination conditions achieving maximum seed set vary with the type of pollination. After controlled self-pollination, the best seed set occurs in bud 3 to bud 10. For the intraspecific cross, the youngest flower and the oldest bud produced the largest number of developed ovules but bud pollination was productive to bud 8. The yields from these two pollination types were best when the female parent was not emasculated. In the interspecific cross with B. campestris cv. Marco the best results came from the youngest flowers and the oldest buds subjected to the standard practice of pollinating directly after emasculation. Possible reasons for these effects are discussed.     

Genotype environment interactions and sib content in F1 hybrid —brussels sprouts

Summary Sib content of F₁ hybrid seed lots obtained from crossing four highly self incompatible brussels sprout lines was examined at two locations for four years. Parental combinations accounted for by far the greatest proportion of the total variation observed. Significant second and third order interactions terms suggest complex interactions between parental genotype, years, and locations. Attempts to interpret these data in terms of the regression model of Finlay & Wilkenson (1963), were unsuccessful.     

Identification of S-alleles in Brassica oleracea

Summary S-alleles of Brassica oleracea were identified using a method which is based on the amplification of S-sequences from genomic DNA, followed by digestion of the PCR products with selected restriction enzymes (PCR-RFLP). A study was made in which the same S-allele was present in the homozygous state in a range of different crop types. This showed that, with minor exceptions, characteristic restriction patterns were obtained, and therefore that it was possible to identify the S-allele. To test whether the method was also suitable for the identification of both the S-alleles present in heterozygotes, a number of S-heterozygotes together with an F₂ population were screened. The results showed that the standard method was not very reliable for the identification of both of the S-alleles. This is because firstly, one of the S-alleles may be amplified preferentially, and secondly, the restriction patterns are not unique to a particular combination of S-alleles. Finally, although it is not possible to identify unequivocally both S-alleles of heterozygotes using a standard technique, the procedure can be modified for particular combinations of alleles to enable the identification to be made.     

Effect of Ogura male-sterile cytoplasm on the performance of cabbage hybrid variety

Summary Cabbage hybrid seeds are commercially produced by means of self-incompatibility. This system may show some instability mainly under tropical conditions, where cytoplasmic male sterility can be an alternative approach for hybrid seeds production. However, cabbage hybrids holding Ogura male-sterile cytoplasm show some irregularities during development. By assessing some characteristics during the growing cycle of male-sterile cabbage hybrids and comparing them to genomic similar male-fertile ones and to the most common cabbage hybrid cultivated in Brazil, it was observed that the male-sterile hybrids had the same vigour, uniformity, number of leaves, resistance to Xanthomonas campestris pv. campestris, and earliness as their male-fertile counterparts and performed better than the commercial check hybrid for some of these characteristics. Although male-sterile hybrids showed yellowing of leaves, some parental combinations succeeded in overcoming or strongly reducing this cytoplasmic effect.Abbreviations dat days after transplanting - CMS Cytoplasmic Male Sterility - CNPH National Centre for Vegetable Crops Research     

The use of seed acid phosphatases in the determination of the purity of F1 hybrid brussels sprout seed

Summary Starch gel electrophoresis of single seeds of five different F₁ hybrids of Brussels sprouts showed that they possessed three cathodal acid phosphatases. By comparison with cathodal acid phosphatases present in their inbred parents these have been interpreted as the two parental types plus a hybrid enzyme. All of the parental material could be classified into two groups depending upon whether or not their cathodal acid phosphatase was fast or slow moving. It was shown that these acid phosphatases are suitable for the determination of sibs in F₁ hybrid sprout seed provided that one of the parents possesses the slow moving cathodal acid phosphatase and the other the fast moving one. A survey of 35 different F₁ hybrids showed that 18 could be analysed for sibs using this method, those which could not were assumed to have had parents who possessed cathodal acid phosphatases of the same mobilities.     

Overcoming self-incompatibility in Ipomoea cairica by IAA

Summary Ipomoea cairica Sweet (Convolvulaceae) exhibits sporophytic self-incompatibility. This has partially been overcome under in vitro conditions, by treating the pollen and/or stigma with 10^-5–10^-1M indole-3-acetic acid (IAA), the optimum being 10^-2M. The self-pollen. which otherwise does not even stick to stigma. germinates after self-pollination provided only one or both the partners are treated. The pollen tubes not only penetrate stigmatic papillae but also traverse the whole length of the style, at least in optimum experimental combinations.     

Cytogenetic and morphological characteristics of new types of diploids (2n=22, 24, 40) derived from consecutive selfing of aneuploids in brassica crops

Summary New types of diploids in Brassica crops were synthesized after three consecutive selfing of aneuploids derived from backcrossing of sesquidiploids (2n=29, AAC) with B. campestris (2n=20, AA). The cytogenetic and morphological characteristics of plants with 2n=22, 24 and 40 in the S₃ generation were analyzed in order to establish the extent in which these addition and polyploid lines were stabilized. A high frequency of 11_II (79.7%), 12_II (84.6%) and 20_II (100%), were observed at metaphase _I of pollen mother cells in 2n=22, 24 and 40 plants, respectively. The chromosome configuration at methaphase _II also indicates that a certain level of stability has been attained cytogenetically. Although pollen stainability was relatively high, the seed set percentage was still low. Variation in morphological characteristics indicate the incorporation of one or more chromosome pairs from the C genome of B. oleracea. Other diagnostic characters such as the formation of determinate inflorescence, branching from the base of the stem, and the shift from self-incompatibility to self-compatibility must have resulted from the interaction between A and C genomes. Thus plants with 2n=22, 24 and 40 have been stabilized to some extent and can be developed into new breeding lines of Brassica. It is suggested that limited pollination could be effective in increasing the seed fertility of these plants.     

A comparison of methods for hybrid seed production using self-incompatibility in swedes (Brassica napus ssp. napobrassica)

Procedures for producing seed of hybrid swedes using self-incompatibility were examined. Single-cross, double-cross and modified double-cross hybrids were compared in isolation plots using natural pollinators and in polythene tunnels using blow-flies. With good coincidence of flowering and the same flower colour, nearly 100% hybrid seed was produced by natural pollinators with the single-crosses, the double-cross and one of the two modified double-cross hybrids; the other modified double-cross hybrid produced 87%hybrid seed. With poor coincidence of flowering and different flower colours the proportion of hybrids dropped to 61%. Using different flower colours and blow-flies as pollinators in polythene tunnels, higher levels of outcrossing were produced than in isolation plots with natural pollinators; the opposite result was obtained when the same flower colour was used. This revised version was published online in July 2006 with corrections to the Cover Date.