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.     

Factors affecting the degree of self-incompatibility in inbred lines of Brussels sprouts

Summary Experiments were made in which four different lines of Brussels sprout, each homozygous for S-allele 2, were tested for self-incompatibility at various stages of plant and flower development under different environmental conditions. The tests were made by counting the number of pollen tubes present in the style 24 hours after pollination, by means of the Ultra-violet Fluorescence technique.The results showed that the degree of self-compatibility varied widely, being greatest during the middle to late stages of the flowering period, at the highest temperature treatment applied. No mean differences could be detected between the effects of self- or sib-pollination; or between pollination of flowers of different ages.One of the inbred lines showed a greater response than all the others to the highest temperature at a late stage of flowering. Under these conditions this inbred line showed more than a tenfold increase in the number of tubes growing after self-pollination, as compared with the overall mean of the experiment. This result is interpreted as indicating a modifying effect of the genetic background on the expression of the major S-allele. On the basis of the results obtained, methods are suggested for more efficient selection of inbred lines of Brussels sprouts with strong and stable self-incompatibility behaviour.     

Variation of flowering time in inbred brussels sprouts and cabbage (Brassica oleracea L.)

Summary Differences in time of flowering between two parent lines of F₁ varieties of Brassica oleracea could significantly affect both the total seed yield and the proportion of sibs in the hybrid seed crop.The results for the time to flower of an incomplete diallel show that even in relatively inbred material of brussels sprouts there is potential to select for altered flowering time. Results obtained from a set of highly inbred cabbage lines which were given three temperature regimes in early spring show that between line variation is complicated by different responses of some of the lines to the environments.     

Embryo culture of brussels sprouts for breeding

Summary A technique for the in vitro culture of embryos of Brussels sprouts (Brassica oleracea L. var. gemmifera) is described. It has been possible to grow the material at all embryonic stages, ranging from the Pre-heart to Mature, into normal seedlings. Pre-heart and Heart-stage embryos require coconut milk for growth. After a short period of growth on a medium containing coconut milk, the embryos have to be transferred to a simpler medium.Growth substances as well as sucrose are needed for the growth of Torpedo and Walking-stick embryos. When the embryos have sufficiently advanced in differentiation (Mature I and older) to germinate (i.e. to form roots) they can grow on a simple inorganic medium. The uniformity of the plants grown from in vitro embryo cultures and the percentage of success are generally high. The usefulness of the technique for obtaining seedlings early in spring for breeding purposes is discussed.     

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.     

Heterosis in brussels sprouts,especially with reference to cold resistance

Summary Experiments on heterosis in Brussels sprouts are described. The plants obtained after inbreeding showed reduced vigour and gave sprouts of poor quality. The heterosis cross yielded sprouts of a better quality than the original varieties. After the severe winter 1953–1954, it was observed that a heterosis effect for cold resistance also exists. These results are discussed and interpreted according to Jones' dominance hypothesis.

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Samenvatting Proefnemingen over heterosis bij spruitkool zijn beschreven. De door inteelt verkregen planten hadden minder groeikracht en leverden spruiten van slechte kwaliteit. De heterosis-kruising gaf spruiten van betere kwaliteit dan de oorspronkelijke rassen.Na de strenge winter 1953–'54 kon worden vastgesteld, dat een heterosis-effect voor kouderesistentie bestaat. Deze resultaten worden besproken en verklaard met behulp van de dominantiekoppelingstheorie van Jones.

     

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.     

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.     

Inbreeding and the production of commercial F1 hybrid seed of brussels sprouts

Inbred lines, many of which have reached or passed the I₄ generation, have been produced by successive generations of self-pollination of material selected stringently for desirable characteristics. Of 99 parent plants originally selected from three different non-inbred varieties only eight were represented in the I₄ generation, by which time individual inbred lines were virtually true breeding for characters of commercial importance.An F₁ hybrid named Avoncross, produced by crossing unrelated selected inbred lines, has given consistently good yields of high quality sprouts in trials grown during several seasons. In most of these trials Avoncross gave the greatest marketable yield as compared with various control varieties and its superiority was significant at the 5% level of probability. A further F₁ hybrid, as yet un-named, has also given promising results in recent trials.Genetic male sterility was found in the material but did not provide an economic method for the production of F₁ hybrid seed. The method developed for the field production of F₁ hybrid seed relies on natural crossing between partially sib-compatible inbred lines. The partial sib-compatibility makes it possible to multiply the parent inbred lines by using natural sib-pollination in the field, but leads to the presence of sibs in the F₁ hybrid seed produced by natural crossing. The percentage of sibs in field crops of the F₁ hybrid established from such seed, however, was acceptably low because the majority of the sib-seedlings initially present could be rejected, on the basis of their smaller size, at the time of transplanting from the seedbed to the field.Experimental seed production, both of parent inbred lines and of the F₁ hybrid Avoncross, indicated that commercial production of F₁ hybrid seed in this manner was likely to be economically feasible.     

Selection of snap bean recombined inbred lines by using EGT and SSD

With the objective of selecting superior recombinant lines of snap bean, four segregating F₂ populations were selected by early generation testing and advanced by single seed descent. In a randomized complete block design with two replications within sets 120 F_6:7 lines were obtained and evaluated for seven traits of agronomic interest. The mean pod yield of the F_6:7 generation was 72% higher than in generation F₂, confirming the efficiency of early selection. There was genetic variability in the F_6:7 lines within the sets. The selection of superior genotypes was possible by the high estimates of narrow-sense heritability. Highest gains in simultaneous selection of traits were expressed by the indices proposed by Mulamba & Mock for the genetic standard deviation and by Williams, based on tentatively attributed arbitrary weights. Line 3 of the F_6:7 generation, with a yield of 8,050.0000 kg ha⁻¹ and pod fiber content of 0.3650% is highly promising to be release as new cultivar.     

Early evaluation of popcorn inbred lines for phosphorus use efficiency

Phosphorus use efficiency (PUE) evaluation based on shoot dry weight in the early stages of plant development can be a useful measure to identify genotypes that are superior in phosphorus (P) use. The objectives of this study were to (i) identify inbred lines that are efficient and inefficient in P use, (ii) assess the genetic diversity among the inbred lines based on traits related to PUE, (iii) investigate the relationship among traits related to PUE and its components and (iv) estimate the expected responses to selection for increasing PUE. Twenty‐three S₆ popcorn inbred lines were evaluated under high and low P, and several traits related to PUE and its components were measured. Efficient and inefficient inbred lines under each P level were identified, and the genetic diversity assessment grouped these inbred lines in opposite clusters. Phosphorus acquisition efficiency (PAE) was the most important component of PUE in the early stages of plant development, and the direct selection for PAE seems to be the best method for increasing PUE in these stages.     

Differences in reciprocal crosses of maize inbred lines diverse for protein content

Summary Forty-two crosses and their reciprocals in maize (Zea mays L.) involving inbred lines highly diverse for protein content were evaluated in four environments. Data were recorded on crude protein content of grain, protein yield, grain yield, 1000 kernel weight, dry matter content of ear at harves,, days to 50% slking, plant height, ear height, and early vigor. No significant variation due to reciprocal differences was observed for protein content and early vigor. For all other traits the variance component due to reciprocal x environment interactions was significant while the variance component due to reciprocal differences was significant only for kernel weight, dry matter content of ear, plant height, and ear height. The variance components due to nuclear differences and their interactions with environments were always highly significant and larger than the components due to reciprocal differences and reciprocal x environment interactions. The instability and low magnitude of reciprocal differences indicated that it might be difficult to exploit them commercially. However, seeing the presence of reciprocal differences for most of the traits studied, the evaluation of breeding materials for these differences seems to be important.The research work was supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 142.     

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.     

Diallel analysis of maize inbred lines for carotenoids and grain yield

Vitamin A deficiency causes xerophthalmia in preschool-aged children worldwide. The objective of this study was to estimate the genetic parameters that would be useful in selecting parent plants for developing productive hybrids with higher levels of provitamin A in the maize kernel. A complete 7 × 7 diallel mating scheme was used to generate 21 single-cross hybrids. The F₁ crosses and check hybrids were evaluated in complete block design across three different Brazilian environments, and carotenoid content was analyzed by high performance liquid chromatography. General combining ability effects were significant for all traits except α-carotene This result indicates that the contribution of the additive effect was more important for provitamin A and other carotenoids and, consequently that there is high chance of improving this trait through recurrent selection methods. Line 3 produced the highest level of kernel provitamin A among the inbred lines evaluated and also demonstrated the potential to contribute to the development of genetic materials with a good performance for provitamin A. Inbred lines 1, 6, and 7 showed a higher concentration of favorable alleles for grain yield, and inbred lines 3 and 6 exhibited a higher concentration of favorable alleles for β-carotene. Hybrid 1 × 3 performed well in terms of provitamin A and grain yield and combination 2 × 3 was the best performer in terms of lutein content.     

Selection efficiency of tunnel length and stalk breakage to obtain maize inbred lines resistant to stem borer attack

There is not any conclusive result about the most suitable trait for performing pedigree selection for improving maize performance against corn borer attack: tunnel length or stalk breakage. We have used simultaneously both selection traits in the same genetic backgrounds and the objective of the present work has been to compare the suitability of pedigree selection for tunnel length and stalk breakage in order to obtain inbred lines that per se and in hybrid combination show lower stem damage and good agronomic performance. Tunnel length is better as selection criteria for increasing resistance to corn borers, but, in some genetic backgrounds, genetic linkage between yield and stalk tunneling by stem borers could make that selection for reduced tunnel length resulted in significant yield reductions.     

Genetic diversity and path analysis for nitrogen use efficiency in popcorn inbred lines

Popcorn inbred lines with more efficient nitrogen use are better able to uptake nitrogen from the soil and convert it into higher grain yield, resulting in lower environmental and economic impacts caused by nitrogen fertilization. The objectives of this study were to (i) identify inbred lines superior in nitrogen use (ii) assess the genetic diversity between popcorn inbred lines under high and low N conditions and (iii) investigate the causal effects of several traits in nitrogen use efficiency (NUE). We evaluated 25 popcorn inbred lines under high and low N, and several traits related to NUE and its components were measured. Efficient and inefficient inbred lines under both N levels were identified and can be useful for generating a segregating population for quantitative trait loci mapping. The genetic diversity assessment based on phenotypic traits grouped the inbred lines into four clusters under both N levels, and the efficient inbred lines were grouped together, as were the inefficient lines. The most divergent inbred lines under high N were classified as efficient and intermediate and can be useful to generate a divergent breeding population with a high frequency of favorable genes for NUE. Nitrogen uptake efficiency (NUpE) was considered the most important trait for NUE. To improve the accuracy of selection for NUE, a selection index involving the total root length (TRL), daily growth and NUpE traits under both N levels is recommended, as these traits had high correlations with and direct effects on NUE.     

Estimation of the proportion of inbred seed in Brussels sprouts hybrid seed by acid phosphate isoenzyme analysis

Summary The acid phosphatase isoenzyme patterns of extracts of seeds from Brassica oleracea subspecies and Brussels sprouts cultivars have been analysed. In view of the inhomogeneity of most seed material, the extracts must be prepared from single seeds if the patterns are to be used for taxonomic classification.The acid phosphatase isoenzymes located in the 15–20 mm region of the electropherograms proved to be controlled by one locus, which consists of 4 alleles acting without dominance. As a result, the acid phosphatase patterns of seeds of pure inbred lines are characterized by a single band in this region. Crossing of inbred lines with a different allele constitution gives hybrid seed with the related double-band pattern. No polypeptide hybridization occurs.By analysis of the acid phosphatase patterns of sufficient individual seeds in a seed sample from a new Brussels sprouts hybrid, it was possible to determine the proportion of inbred seed in the sample. The results were in good agreement with those obtained from field observations.     

Leafy reduced-stature maize for short-season environments: morphological aspects of inbred lines

Development of maize (Zea mays L.) types that produce leaf area rapidly and finish vegetative development quickly would increase production of maize in mid- to short-season areas. The Leafy (Lfy1) and reduced-stature (rd1) traits each make contributions to this end. However, these two traits have not previously been combined. Our objective was to evaluate the morphological aspects of non-leafy normal-stature (NLNS), leafy reduced-stature (LRS), non-leafy reduced-stature (NLRS), and leafy normal-stature (LNS) maize inbreds. Two traits, Lfy1 and rd1, were incorporated into a series of inbreds, resulting in a range of canopy architectures. Twelve variables were recorded for each of 30 inbreds over three years. The 12 variables were: seed emergence, above-ear leaf number, below-ear leaf number, dead leaf number at tasselling, live leaf number at tasselling, total leaf number, above-ear leaf area, ear leaf length, ear leaf width, ear height, internode length, and plant height. Inbreds containing the Lfy1 trait had more above-ear leaf area, above-ear leaf number, dead leaf number at tasselling, total leaf number and number of live leaves at tasselling than non-leafy inbred lines. Below-ear leaf number was not different among LRS, LNS, and NLNS inbred lines. LRS and NLRS inbred lines were also not different for below-ear leaf number. Plant height, ear height, and ear leaf length and width were higher in normal-stature than reduced-stature plants. The proportion of the seeds which emerged was higher for LRS inbreds than the other trait groups. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optimal allocation of resources in evaluating current sunflower inbred lines for resistance to Sclerotinia

Sclerotinia sclerotiorum (Lib.) de Bary is a major limiting factor for sunflower (Helianthus annuus) production. This study was conducted to (1) evaluate a large number of current sunflower lines for their reaction to Sclerotinia, and (2) determine the optimum allocation of resources for their selection. A set of 85 inbred lines was screened under artificial leaf infection in three environments. The test revealed ample variation for all resistance traits in the current germplasm. A line selected from NDBLOS, an oilseed sunflower germplasm poo, and its derivatives were most resistant to Sclerotinia. Lines derived from interspecific crosses with the wild species Helianthus tuberosus and Helianthus argophyllus also showed satisfactory Sclerotinia resistance. The evaluation of five plants per plot in two replications and four environments appears to be a reasonable allocation of resources in order to optimize the selection response.