Meiotic behavior in interspecific hybrids between Brachiaria ruziziensis and Brachiaria brizantha (Poaceae)

The meiotic behavior of two half-sib interspecific tetraploid (2n = 4x = 36) promising hybrids, a sexual and an apomictic one, from crosses B. ruziziensis and B. brizantha, was evaluated. Although chromosome paired predominantly as bivalents, a few tri- and quadrivalents were recorded. Results suggest that B. brizantha and B. ruziziensis are closely related and genetic recombination is expected in hybrids. Introgression of specific target genes from B. ruziziensis into B. brizantha and vice-versa may be foreseen. However, abnormalities such as irregular chromosome segregation, chromosome stickiness and abnormal cytokinesis reported in these hybrids affect pollen fertility. More than 65% of pollen grains are sterile. Since the distinctive cytological feature of these hybrids is abnormal cytokinesis, this fact suggests that both parental genomes are unable to coordinate their activities with regard to this cytological phenomenon. Deployment of such hybrids in the process of developing varieties is discussed.     

Studies of pollen grain germination,pollen tube growth,micropylar penetration and seed set in intraspecific and intergeneric crosses within three Cruciferae species

Summary Pollen grain germination, pollen tube growth and micropylar penetration were investigated in intraspecific and intergeneric crosses involving Brassica napus L. ssp. oleifera (Metzg.) Sinsk. (oil-seed rape or fodder rape), xBrassicoraphanus Sageret (Raparadish) and diploid (2x) and tetraploid (4x) accessions of Sinapis alba L.(white mustard). For the reciprocal intergeneric crosses between B. napus and xBrassicoraphanus no effective barriers to pollen tube growth on stigmata or in styles were observed. The resulting low frequency of hybrid plants was mainly associated with a low rate of ovules with micropylar penetration per siliqua or with embryo abortion. Hybrid plants could be obtained without use of embryo rescue. In reciprocal crosses between B. napus and S. alba 2x or 4x incongruity barriers were observed on the stigma, in the style, and in the ovary resulting in a low frequency of ovules with micropylar penetration per siliqua. Open flower-pollination compared to bud-pollination generally was the more favourable procedure for pollen grain germination and pollen tube growth in crosses involving S. alba, but for micropylar penetration and seed set no differences were observed. Crosses between S. alba 2x () and B.napus () were found to result in a higher frequency of ovules with micropylar penetration as compared to reciprocal crosses or crosses with S. alba 4x. All reciprocal crosses between B. napus and S. alba 2x or 4x were unsuccessful when no embryo rescue was applied. Embryo rescue shortly after pollination, i.e. 2 to 5 days, however, resulted in hybrid seeds and plants, but only when applied to crosses between S. alba 2x () and B. napus (). The possible effects of the genome constitution, taxonomic distance and the parthenogenetic and parthenogenesis inducing ability of the parental genotypes on the observed malfunctions at the pre-and/or post-zygotic stage of the pollen grain-pistil interactions are discussed.Abbreviations DAP Days After Pollination - IAA Indole-3-Acetic Acid - kin Kinetin     

Analysis of meiotic behavior in selecting potential genitors among diploid and artificially induced tetraploid accessions of Brachiaria ruziziensis (Poaceae)

Sexuality is correlated with diploidy and apomixis with polyploidy in the Brachiaria genus. Brachiaria ruziziensis is a key species in Brachiaria breeding due to its obligate sexuality and intrinsic agronomic qualities. Interspecific crosses in the genus became feasible only when a few diploid accessions of B. ruziziensis were artificially tetraploidized and remained sexual. Hybridization has been done since, using natural tetraploid apomictic accessions of B. brizantha or B. decumbens as pollen donors. Twenty two accessions of B. ruziziensis from the Embrapa Beef Cattle germplasm collection (Campo Grande, MS, Brazil) were cytologically analyzed: 16 are natural diploids (2n = 2x = 18) and six are artificially induced tetraploids (2n = 4x = 36). The meiotic behavior in the 16 diploid accessions varied. The mean of meiotic abnormalities per accession ranged from zero to 24.46%. Meiotic behavior in the induced tetraploid accessions also varied with the mean of meiotic abnormalities ranging from 5.20% to 54.71%. The most common abnormalities observed in both the diploid and the tetraploid accessions, were those related to irregular chromosome segregation. In one tetraploid accession, with a high frequency of those, other irregularities involving chromosome orientation at metaphase plate and chromosome convergence to the poles, a meiotic mutation known as divergent spindle, were recorded. Meiotic behavior should be considered in selecting potential genitors for breeding.     

Inheritance of seed protein in two interspecific pigeonpea (Cajanus cajan) crosses

Pigeonpea is one of the primary sources of protein for most rural communities of south Asia and Africa. The enhancement of protein from the present level of 20–22% will help masses in their nutritional well-beings. Breeders have identified high-protein (28–30%) germplasm amongst the wild relatives of pigeonpea; and these can serve as donors in breeding high-yielding high-protein cultivars. To achieve this, information on the inheritance of seed protein will be useful in organizing interspecific matings, generation advancement, and selection schemes. In the present study, two interspecific crosses, involving two pigeonpea cultivars ('Pant A2' and 'ICP 6997') and a wild species (Cajanus albicans (W. & A.)), were made to study the inheritance of seed protein in F₁, F₂, and BC₁F₁ generations. The high-protein trait was found to be controlled by two independent dominant genes with complementary effects. These genes are tagged with symbols “HPt₁” and “HPt₂”. The authors believe that now opportunities exist for enhancing the protein levels in pigeonpea through breeding approaches.     

Association between groat protein percentage and certain plant and seed traits in interspecific oat crosses

Summary Ten interspecific crosses of Avena sativa L. x A. sterilis L. were used to study associations of groat protein percentage with selected seed and agronomic traits. Each cross was grown in a replicated experiment, and the genetic material consisted of parents and F₂-derived lines grown in the F₄ generation.No close associations were found between groat protein percentage and plant height, heading date, or 10-groat weight. Individual crosses did show significant correlations, but none of the 3 traits was sufficiently associated with groat protein generally so as to be beneficial or inhibitory to combining high groat-protein percentage with the maturity, plant height, and 10-groat weight appropriate for good agronomic cultivars of oats.High groat-protein percentage was closely associated with abscission spikelet separation and jointed awn, both of which are A. sterilis traits. Shattering and dark seed color (A. sterilis traits) were also associated with high groat protein percentage, but kernel pubescence was not. Only a few segregates within each cross were A. sativa type for all 5 of the seed traits, but when A. sativa types from all crosses were grouped together, there was a large range for groat-protein percentages.Journal Paper No J-6950 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 1752. In cooperation with the Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture. Carried out with a grant from the Quaker Oat Co., Chicago, Illinois, USA.     

Chromosome number and microsporogenesis in a pentaploid accession of Brachiaria brizantha (Gramineae)

Chromosome number, microsporogenesis and mode of reproduction are described for an accession of Brachiaria brizantha, a grass of African origin. Cytological analysis revealed that the accession BRA005886 is pentaploid (2n = 5x = 45), with a base number of x = 9. Multivalent chromosome associations, from tri‐ to pentavalents, were recorded in diakinesis, and the further meiotic behaviour was highly irregular as well. Most abnormalities were related to irregular chromosome segregation commonly found in polyploids. Micronuclei were observed following telophases I and II. Some micronuclei near the cell wall were released as microcytes, whereas others remained in the tetrad. Other meiotic abnormalities, such as cell fusion and the absence of cytokinesis causing the formation of dyads and triads were also recorded. Binucleate microspores and 2n microspores resulting from nucleus restitution were observed among the normal ones. Limitations of this accession for use in hybridization programmes are discussed.     

Gamma-irradiation of cacao (Theobroma cacao L.) pollen: Effect on pollen grain viability,germination and mitosis and on fruit set

Summary Theobroma cacao pollen fertilization capability was studied after 0, 50, 100, 200, 500 and 1000 Gy gamma-irradiation. For all irradiation doses, no alteration of pollen grain viability and in vitro germination was observed. In situ, for all doses, pollen tubes penetrated into the styles and reached the ovules 20 hours after pollination. In vitro observations of the pollen grain nuclei after 20 hours incubation showed that pollen irradiation causes inhibition of the division of the generative nucleus. Fruit survival rate 30 days after pollination decreased as irradiation doses increased from 0 to 100 Gy, and over 100 Gy no fruit set was obtained. The possibility of using irradiated pollen as a method for obtaining haploid cacao plantlets is discussed.     

珍汕97A自交结实与花粉组成分析

本文简述了珍汕97 A自交结实和花粉组成情况.珍汕97 A套自交鉴定袋后虽然发现有自交结实现象,其花粉镜检结果表明,在花粉组成中典败花粉达不到100%,含有少量的园败花粉和染败花粉,但珍汕97 A后代的育性都是较稳定的.     

The effect of temperature on seed set and embryo development in reciprocal crosses of wheat and barley

Summary The effect of temperature on seed set and embryo development in reciprocal crosses of barley and wheat was assessed in crosses involving two spring barley varieties (Betzes, Martonvásári 50) and one wheat variety (Chinese Spring). Detached tillers placed in nutrient solution were pollinated in controlled environments at constant day-night temperature regimes (12, 15, 18 and 21° C) with a light intensity of 30,000 lux and a relative humidity of 80%. When barley was used as the female, lower temperatures (12 and 15° C) produced the maximum seed set, whereas for the reciprocal cross, the highest temperature (21° C) produced the best seed set in the Chinese Spring × Betzes combination.Low temperature retarded the embryo development. The highest numbers of hybrid plants were produced at 18° C and 21° C in the barley × wheat cross and in the wheat × barley cross, respectively. Embryos of about 1.5 mm length in the barley × wheat cross, and of about 1.0 mm length in the wheat × barley cross germinated successfully. The smallest embryo giving rise to hybrid plants was 0.57 mm in the barley × wheat cross and 0.51 mm in the wheat × barley cross.     

Inheritance of straw-protein content and its association with other traits in interspecific oat crosses

Summary Ten interspecific crosses of Avena sativa L. x A. sterilis L. were used to study inheritance of protein content in oat straw and its associations with selected seed and agronomic traits. Each cross was grown in a replicated experiment, and the materials for each cross consisted of parents and F₂-derived lines in the F₄ generation. Straw-protein percentages were transformed to square roots to normalize the data before statistical analyses were carried out.Frequency distributions were reasonably symmetrical for square roots of straw-protein percentages (SP%) in eight crosses, suggesting that additive gene action conditioned this trait. There was a preponderance of low SP% lines in the remaining two crosses. SP% was not consistently correlated with plant height, 10-groat weight, or groat-protein percentage. SP% was positively and significantly correlated with heading date in all crosses, so the SP% variances were adjusted for heading date by covariance analyses. Whereas all crosses had significant variability among F₂-derived lines for SP% before covariance analysis, only two showed significant variability after adjustment for heading date.Mean per-plot and per-experiment heritabilities for SP% before adjustment for heading date were 56 and 69%, respectively, whereas after adjustment for heading date, they were 22 and 32%, respectively. Although the inheritance of SP% appears relatively simple, this trait is greatly influenced by date of maturity.Journal paper No J-7603 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, USA. Project 1752 Supported in part by a grant from the Quaker Oats Co., Chicago, Ill., USA.     

Unravelling the inheritance,QST and reproductive phenology attributes of the tetraploid tropical grass Brachiaria ruziziensis (Germain et Evrard)

The autotetraploid forage Congo signal grass (Brachiaria ruziziensis) is an important component in the Brachiaria breeding programme. As with other tropical forage grass species, the association between flowering and seed yield components, the mode of inheritance and the effects of population structure on phenotypic breeding are lacking. Seventeen characteristics evaluated in 59 half‐sib progeny of seven subpopulations were analysed using a mixed model methodology. According to the commonality analysis, the total seed yield (0.67) and number of days to flowering (0.22) had a greater influence on the filled‐seed yield. The flowering synchrony, total number of panicles, filled‐seed yield, green matter yield and dry matter yield presented statistically significant additive genetic variance between and within the subpopulations. The Q_ST estimates ranged from 0.09 for the flowering synchrony index to 0.31 for the filled‐seed yield. The effects of population structure and its use in breeding programmes are further discussed.     

Selection for seed set in crosses of Avena sativa L. × A. Abyssinica Hochst.

Summary Precoz oat line, discovered in a mass planting of wild oats in Colombia, is a tetraploid belonging to Avena abyssinica. It crossed easily with Kyto, but not with Bacata, both hexaploid oat cultivars. Pentaploid hybrid plants of Precoz × Kyto and Precoz × Bacata had 35 chromosomes, tended to have seven bivalents and 21 univalents at meiosis, and were completely sterile, Colchicine treatment of pentaploid F₁ plants produced decaploid tillers from which five amphiploid seeds were obtained. Selection for high percentage of seed set in the third and fourth amphiploid generations of Precoz × Kyto gave fifth generation plants with 80–100% fertility. The chromosome numbers of these plants approximated the octoploid level. Some derivatives from crosses of third generation amphiploids with hexaploid cultivars had the hexaploid chromosome number and good fertility.Pentaploid hybrid plants and amphiploid derivatives from them were as early in heading as Precoz when tested at either 12-or 15-hour photoperiods. This suggests that the photoperiod response from Precoz is dominant and has good penetrance.Journal Paper no J-7408, Project 1752.     

The effect of gibberellic acid on fruit and seed set in crosses of garden and winter hardy Rosa accessions

Summary The effect of gibberellic acid (GA₃) was studied on a wide range of crosses between various garden roses and two hardy breeding lines. Although there were fewer seeds per fruit, fruit set was higher in most crosses when GA₃ was applied to the stigma at the rate of 250 ppm ten days after pollination. However, higher fruit set did not result in more seeds per pollination for many crosses and seemed to be related to the degree of male parentage. Both parents used had a major effect on pollination success. Recently developed Rosa cultivars have a narrow genetic base and the use of distantly related cultivars as parents would possibly give a high seed set and greater numbers of progeny.Contribution No. 335/90.08.01R, Experimental Farm, L'Assomption; Contribution No. Ro 44, Research Program Service, Ottawa.     

Suppression of stripe rust and leaf rust resistances in interspecific crosses of wheat

Stripe rust and leaf rust caused by Puccinia striiformis (Ps) Westend. and P. triticina (Pt) Eriks., respectively, are important foliar diseases of wheat worldwide. Breeding resistant wheat cultivars is the preferred strategy to control these diseases. Genes for resistance when introgressed from alien species or wheats of lower ploidy are frequently diluted effectiveness in the hexaploid wheat background or are completely suppressed. The objective of this study was to examine the expression of wheat stripe rust and leaf rust resistances derived from wild emmer wheat and Aegilops tauschii when combined in synthetic hexaploid lines. Eight amphidiploid wheat lines, synthesized by crossing five tetraploid wheats (AABB), viz. Triticum carthlicum var. darginicum, T. carthlicum var. fuligioscum, T. dicoccoides var. fuligioscum, T. durum with five lines of Ae. tauschii (DD), were evaluated in the seedling stage for resistance to five pathotypes of stripe rust caused by Ps and four pathotypes of leaf rust caused by Pt. Resistance in one or both parents was frequently suppressed in synthetic hexaploid lines, indicating the presence of suppressor genes in both Ae. tauschii and T. carthlicum var. darginicum. Specific suppression of resistance genes in the parental genotypes and to pathotypes of Ps and Pt were also observed. The presence and specificity of the suppressors for rust resistance obtained in this study provides useful knowledge for developing cultivars resistant to both rusts utilizing such genetic stocks in wheat breeding programs.     

Statistical discrimination between pollen tube growth and seed set in establishing self incompatibility in Gaura lindheimeri 1

The University of Minnesota Gaura breeding program is developing USDA Z3-4 winter-hardy genotypes via interspecific hybridization of G. lindheimeri (Z5-6) and G. coccinea (Z2-4). Prior to commencing interspecific hybridization, the reproductive barriers operating in both parental species need to be characterized. The objective of this research was to determine the type and stability of reproductive barriers operating in G. lindheimeri by statistical comparisons between pollen tube growth and seed set in a full-sib diallel. Slowed or aborted pollen tube growth in the style indicated the presence of a gametophytic self incompatibility (SI) system. A statistical method, female (FCC) and male (MCC) coefficients of crossability, was used to verify that a stable SI system was operating and that other reproductive barriers were present. Several genotypes also expressed stage-specific inbreeding depression and incongruity. The simple linear regression equation for FCC/MCC, using pollen tube growth, was Y = 0.0124 + 0.974X, which was much closer to the expected Y = 0.0 + 1.0X (indicating a stable SI system) than the equation for seed set, Y = 0.012 + 0.910X. Using pollen tube length, both general combining ability (GCA) and specific combining ability (SCA) values were highly significant for G. lindheimeri (P ≤ 0.001). Histograms were used to delineate cut-offs to identify intra-incompatible/inter-compatible classes and S allele groups. Four possible classes were identified, but further research is needed to verify S allele genotypes.Scientific Research Paper No. 031210120 of the Department of Horticultural Science. This research was supported by a grant from the Perennial Plant Association and, in part, by the Minnesota Agricultural Experiment Station     

Glucosinolate content in interspecific crosses of Brassica carinata with B. juncea and B. napus

Brassica carinata A. Braun is a highly productive oilseed crop in the Ethiopian highlands, but the seed has a high 2-propenyl glucosinolate content, which is undesirable. The objective of this study was to introgress, through interspecific crosses, genes for low 2-propenyl glucosinolate content from the B genome of B. juncea and C genome of B. napus into the B. carinata B and C genomes and thus develop low glucosinolate B. carinata. The cross [(B. carinata×B. juncea) ×B. carinata] yielded plants that contained only ～ 20 μmoles of 2-propenyl glucosinolate, which was an 85% reduction compared with levels in B. carinata seed. Plants of the [(B. carinata×B. napus) ×B. carinata] cross had normal high concentrations of 2-propenyl glucosinolate. Backcross plants of both interspecific crosses also contained 3-butenyl and 2-hydroxy-3-butenyl glucosinolates. The results of these crosses suggested that genes for glucosinolate synthesis were located on B genome chromosomes of B. carinata because B. napus C genome introgressions did not result in reductions of total glucosinolate contents. The total alkenyl glucosinolate content of one F₃ family of the B. juncea backcross was similar to that of the B. juncea parent. It was concluded that through further selection in this family, B. carinata plants could be identified that would be basically free of 2-propenyl glucosinolate, and have a low total alkenyl glucosinolate content.     

Elucidating the behaviour of pollen tubes in intra-and interspecific pollinations of Phaseolus vulgaris L. and P. coccineus Lam.

Summary The behaviour of pollen tubes in intra-and interspecific pollinations of P. vulgaris and P. coccineus has been examined using a combination of phase-contrast, and UV fluorescence microscopy. The results indicate that P. coccineus is self-compatible in terms of pollen tube growth, and that pollen tube inhibition is not responsible for the reciprocal differences in seed set which have been observed in crosses between these species.     

Chromosome association and pollen fertility in some interspecific hybrids of Lilium

Summary Meiotic observations in PMCs were made in eight kinds of interspecific hybrids in Lilium. Three hybrids, 6134-S × L. cernuum. L. regale × L. leichtlinii maximowiczii and L. auratum platyphyllum × L. henryi showed respectively the mean chromosome association frequencies of 1.4_II, 0.8_II and 1.5_II per cell at MI which were the lowest values hitherto reported in Lilium hybrids. In L. longiflorum × L. henryi, 33.3° of the cells had 1 or 2 multivalents of three to five chromosomes in addition to uni- and bivalents. 12° bivalents and 12 univalents were invariably observed in the triploid hybrid L. longiflorum × L. cernuum. The hybrids between the species belonging to the different sections of the genus generally showed high pollen sterility, with some exceptions. A more or less remote genomic homology was found between the different sections in Lilium.     

Pollination systems, hybridization barriers and meiotic chromosome behaviour in Nemesia hybrids

The ability of 13 Nemesia species (six annual and seven perennial) to sexually hybridize was investigated. Six of the perennial Nemesia species investigated were inter-fertile with one another. Two of the annual species, N. macroceras and N. strumosa, were inter-fertile. Thirty three crosses were successful and resulted in viable seeds. The analysis of meiotic chromosome behaviour in interspecific hybrids indicated that Nemesia chromosomes in different parental species were homeologous. No evidence of chromosome inversions or chromosome translocations was observed during meiosis in interspecific hybrids between the six perennial Nemesia species. In the hybrids produced between N. macroceras and N. strumosa, a quadrivalent was observed during meiotic metaphase I, indicating that these two species differ by a reciprocal translocation. A successful hybridization was made between N. anisocarpa (annual) and N. foetans (perennial), producing two triploid hybrids. In the unsuccessful crosses, pollen tubes were observed entering ovaries and ovules, suggesting that post-fertilization barriers were preventing sexual hybridization. Many of these crosses produced nonviable, shrunken, empty seeds, suggesting that endosperm breakdown and embryo abortion prevent interspecific hybridization in unsuccessful crosses. The manipulation of ploidy levels in N. fruticans and N. strumosa and tissue culture of N. strumosa × N. fruticans ovules failed to overcome post-fertilization barriers between these species.