Factors affecting haploid production in wheat using the Hordeum bulbosum system. 3. Post-fertilization effects on embryo survival

Summary An investigation was made of factors affecting the frequency of development of fertilized ovules following wheat x Hordeum bulbosum hybridizations. Seed survival, a term used here to represent the relationship between seed set and fertilization, was shown to vary between the wheat genotypes tested, but was unrelated to the crossability genes present within the wheat genotype. A high seed survival was obtained in crosses involving the variety TH3929 and the single chromosome substitution line, Chinese Spring (Hope 5B). Chinese Spring showed a poor seed survival. Some influence of the H. bulbosum genotype on seed survival was detected. The two environmental factors studied, namely the post-pollination application of gibberellic acid and the ambient temperature, were both shown to affect seed survival. The application of gibberellic acid immediately after pollination or 1 and 2 days after pollination improved seed survival, although the extent of the response was dependent upon the number and timing of the application(s). A genotype-dependent response to the ambient temperature was observed, TH3929 showing a slight but insignificant reduction and Chinese Spring a significant improvement in seed survival with an increase in temperature from 20°C to 26°C. The physiological processes which may be influenced by GA and the ambient temperature and may thereby affect seed survival are discussed.     

Crossability and embryo rescue enhancement in wide crosses between wheat and three Agropyron species

Summary Soft winter wheat lines were crossed with Agropyron intermedium, A. elongatum and A. trichophorum using pollen from single plants of Agropyron spp. to pollinate wheat spikes. Not only species but also individual plants within varieties of Agropyron species differed in percent seed set with a wheat genotype. In two arrays of crosses between two phenotypically different plants of A. elongatum and nine wheat lines, one Agropyron plant gave higher seed set (overall=27.1%) than the other (overall=3.7%). The differences were significant in seven of the nine cross combinations. Results are consistent with the hypothesis that these two plants differ in their crossability as pollen parents with wheat, and suggest the possibility of occurrence of crossability genes in wheatgrasses. The success rate of hybrid embryo rescue was higher (87.5%) with cold treatment (4°C) than without cold treatment (75.0%) of excised embryos on culture media. Results underscore the significance of genotype of the alien species for crossing with low crossable wheats, and of the physical factors for improving embryo rescue in wide crosses.Contribution No. 11,825, Purdue Agric. Exp. Stn., West Lafayette, Indiana 47907, USA. The research was supported in part by Public Varieties of Indiana.     

How wide can a wide cross be?

Summary Wide crosses in wheat are reviewed in relation to various factors that facilitate wide crossing to show that wide crosses can be as wide as one can make them. Included in this review is a particular reference to wheat-wheatgrass (Agropyron complex) crosses and an update on wide crosses of wheat with various genera of Agropyron complex. Hybrid seed set is too variable to predict whether a wide hybrid, where no seed was obtained in one attempt, will not be possible. High crossability genes seem to facilitate not only fertilization but also seed development, enabling embryo rescue. Variability for crossability occurs not only in wheat but also in alien species. Contrary to conventional thinking, several wide hybrids with wheat can be produced when species with lower chromosome numbers are used as female parents. Pre-and post-fertilization barriers to wide crosses do not appear to be equally strong, and can be overcome by the development and application of various technologies. Considering these aspects of wide hybridization, and based on recent successes in producing previously unsuccessful and very wide hybrids, it is concluded that how wide cross between plant species can be made is an open question and that many new and wider hybrids can be produced in future.     

Influence of selected wheat and rye genotypes on the direct synthesis of hexaploid triticale

Summary In the synthesis of primary hexaploid triticale, a cross-incompatibility barrier exists when tetraploid wheat (4X) is crossed with diploid (2X) rye. Fertilization may occur, however, abnormal endosperm development usually leads to premature embryo death. Four selected tetraploid wheat lines were crossed as females with seven open-pollinated rye lines and the resulting embryos were rescued in vitro 13–16 days after pollination. The wheat genotypes showed a major influence on crossability (seed set), embryo development and plant recovery. The highest efficiency of amphihaploid plant recovery (18.3 plants per 100 pollinated florets) was obtained from one 4X wheat line originally selected from the cross T. carthlicum × T. dicoccoides. Some of the 3X amphihaploid plants (ABR) derived from two wheat lines showed relatively high level of partial fertility presumably as a result of meiotic restitution. Correlation analysis showed that crossability (seed set), normal hybrid embryo development in vivo and embryo culturability were independent of each other.     

Crossability of tetraploid and hexaploid wheats with ryes for primary triticale production

Summary Crossability of wheat and rye was investigated during thirteen crop cycles in two contrasting locations to 1) evaluate tetraploid and hexaploid wheat parents in crosses with rye, 2) identify genotypes with high crossability and 3) assess the impact of environment on seed development. The majority of the tetraploid wheats crossed with rye had seed set around 20%, but very low embryo viability. Several wheat genotypes with seed set above 50% were identified. The hexaploid wheats crossed with rye showed poor seed set, but plant recovery was relatively high. The majority of the hexaploid wheats with highest seed set (20–30%) were from China. The results suggest differences in crossability between the rye populations, and wheat species by rye interactions. The crossability of the tetraploid and hexaploid wheats was affected by climate in the two locations.     

Parental effects on crossability,embryo differentiation and plantlet recovery in wheat x rye hybrids

Summary One hexaploid wheat cultivar (Triticum aestivem) and two tetraploid wheat lines (T. durum) were crossed with seventeen inbred lines of rye (Secale cereale). Seed set, degree of hybrid embryo differentiation at the time of excision for in vitro culture and recovery of amphihaploid plantlets from various embryo categories were studied. Degree of embryo differentiation was predominantly determined by maternal wheats, paternal rye genotypes appearing to be of minor importance. T. aestivum x rye hybrid embryos were superior to those produced from T. durum for degree of differentiation. The proportion of plantlets developing from differentiated embryos was high for all wheat parents, whereas undifferentiated embryos were mostly unsuitable for plantlet production. The results revealed that cross-incompatibility in hexaploid wheat x rye crosses was due to failure of fertilization, while in tetraploid wheat x rye crosses it was caused by lack of embryo differentiation. Correlation analyses showed that seed set provided a criterion to predict the amphihaploid plantlets to be expected from a particular wheat x rye combination.     

Cross compatibility between Abelmoschus esculentus and A. moschatus

Interspecific cross compatibility between cultivated and wild okra (Abelmoschus esculentus and A. moschatus) and pollen tube growth behaviour in the crosses among a local cultivar of A. esculentus, A. moschatus and their F₁s were studied. Fruit set was observed in all the crosses except one and seed setting was absent in two of the crosses which set fruit. All seed produced were shrivelled but F₁ plants were obtained from two crosses where cultivated okra was used as the seed parent. The F₁ plants were perennial in nature with very low pollen viability and seed set. A high percentage of pollen germination and profuse pollen tube penetration in the style were observed in the cross A. esculentus × A. moschatus but low pollen tube penetration with abnormal pollen tubes was observed in the reciprocal cross. The number of pollen tubes was very low but they appeared to be normal in the backcross A. esculentus × F₁, but were generally abnormal in the reciprocal cross. Both pre- and postzygotic barriers seemed to occur in crosses between the two species. The present studies indicate that these barriers can be overcome and desirable characters from A. moschatus transferred to cultivated okra using conventional hybridisation techniques. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chromosome Locations of Additional Barley Enzyme Loci Identified Using Wheat-Barley Addition Lines

Disomic wheat-barley addition lines carrying a full hexaploid set of chromosomes of the wheat cultivar Chinese Spring, plus a pair of either chromosome 1, 2, 3, 4, 6, or 7 from the barley cultivar Betzes, were assayed electrophoretically. Comparisons of zymograms of each addition line with the Chinese Spring wheat and Betzes barky parents of the addition lines gave direct (presumptive in the case of chromosome 5) evidence of the chromosomal locations of nine enzyme loci which have been useful genetic markers in studies of the population genetics, ecogeneties and breeding of barley. Previously reported chromosome locations of several loci were confirmed and evidence was presented for the existence and probable chromosome locations for additional enzyme loci.     

Influence of suboptimal temperature on biomass production of potato populations of Andean and European origin

Summary Plants grown from seed derived by crossing conventional European S. tuberosum material were compared with plants grown from seed derived by crossing S. tuberosum with various, Andean frost resistant tuberbearing Solanum species. Biomass growth at optimal (20°/10°) and suboptimal (10°/4°) temperatures was studied.Differences in increase of fresh and dry matter were found between populations of Andean and European orgins at 10°/4°. At 20°/10° no such differences were found.At suboptimal temperature, Andean hybrids produced significantly more fresh and dry matter than European crosses in two harvests (64 and 178 days old plants). Statistically, Andean hybrids were found to produce the same amount of dry matter per day at both temperatures, over the complete growth period.Height increase and flower development were strongly depressed in European crosses under the suboptimal temperatures, but much less so in Andean crosses.The Andean material appears to be an under utilized resource in potato breeding for cool climates.     

Transfer of the recessive crossability allele kr1 from Chinese Spring into the winter wheat variety Martonvásári 9

Summary The recessive of crossability allele kr1 was transferred from the spring wheat variety Chinese Spring (CS) into the winter wheat variety Martonvásári 9 (Mv9) by backcrossing the Mv9 × CS hybrids with Mv9. The Mv9 variety possesses dominant Kr1 alleles and is heterogeneous at the kr2 locus, so that some individual plants carry recessive kr2 alleles. The selection of plants possessing the recessive kr alleles from the (Mv9 × CS)Mv9 BC₁ generation was carried out according to the seed set achieved when pollinated with rye (Secale cereale L. cv. Mercator). The partial dominance of the Kr alleles made it possible to differentiate between plants heterozygous at the Kr1 locus and Kr1Kr1 homozygous dominant plants. Two selfed consecutive progenies were tested by pollination with rye to select the homozygous recessive kr1kr1kr2kr2 plants and to check the result of the selection after each backcross.As a result of three backcrosses with Mv9 and two selfings after each backcross the selected progenies had 61.6% seed set with rye tested on sixty individual plants. These data confirm that after the third backcross the selected Mv9 kr1 line carries necessive crossability alleles Kr1 and Kr2, but the genotype is 93.75% Mv9.     

Interspecific hybridization between Vicia faba (L.) and Vicia narbonensis (L.): Early pod growth and embryo-sac development

Summary Fertilized embryo-sac development and pod growth was studied in one Vicia faba cultivar, one Vicia narbonensis population and their reciprocal crosses. The initial development of endosperm and embryo was at least four days faster in V. narbonensis than in V. faba. Pods and ovules developed also faster in V. narbonensis than in V. faba. The growth rate of the hybrid pods followed the growth rate of the mother species, but was slower than that of the pods from selfed flowers. In the cross V. narbonensis × V. faba the ovules stopped growing 9 days after pollination, while in the reciprocal cross they stopped growing 15 days after pollination. Hybrid embryo-sacs from V. faba × V. narbonensis were aborted before they reached the stage of 256 endosperm nuclei or 200 embryo cells. Selfed V. faba embryo-sacs reached this stage in less than 9 days after pollination. In the reciprocal cross the embryo-sacs were aborted before they reached the stage of 128 endosperm nuclei or 80 embryo cells. Selfed V. narbonensis embryo-sacs reached this stage at the 4th day after pollination. Given that at these stages the embryo has less than 200 cells it was concluded that an in-ovule embryo culture technique should be developed to obtain hybrid plants.     

Tolerance to paraquat is correlated with the traits associated with water stress tolerance in segregating F2 populations of barley and wheat

To identify scorable marker traits that can be used in cereal breeding programs for selecting drought tolerant individuals, we investigated the correlation among the drought-associated traits in two F₂ populations derived from the crosses made between drought tolerant and sensitive barley and wheat parental genotypes. The parental genotypes of these crosses also differed by at least three other traits – paraquat tolerance, leaf size, and the relative water content. These three traits were scored in two F₂populations of 80 individuals for each barley and wheat cross. Analysis of results indicated that the enhanced tolerance to paraquat was correlated with reduced leaf size and increased relative water content, two traits associated with water stress phenotypes of the drought tolerant barley and wheat parents. Our results suggested that the selection based on paraquat tolerance istechnically less demanding and thus useful for rapid screening of individuals for enhanced drought tolerance in segregating populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interspecific cross of Brassica oleracea var. alboglabra and B. napus : effects of growth condition and silique age on the efficiency of hybrid production, and inheritance of erucic acid in the self-pollinated backcross generation

Interspecific hybrids were produced from reciprocal crosses between Brassica napus (2n = 38, AACC) and B. oleracea var. alboglabra (2n = 18, CC) to introgress the zero-erucic acid alleles from B. napus into B. oleracea. The ovule culture embryo rescue technique was applied for production of F₁ plants. The effects of silique age, as measured by days after pollination (DAP), and growth condition (temperature) on the efficiency of this technique was investigated. The greatest numbers of hybrids per pollination were produced under 20°/15°C (day/night) at 16 DAP for B. oleracea (♀) × B. napus crosses, while under 15°/10°C at 14 DAP for B. napus (♀) × B. oleracea crosses. Application of the ovule culture technique also increased the efficiency of BC₁ (F₁ × B. oleracea) hybrid production by 10-fold over in vivo seed set. The segregation of erucic acid alleles in the self-pollinated backcross generation, i.e. in BC₁S₁ seeds, revealed that the gametes of the F₁ and BC₁ plants carrying a greater number of A-genome chromosomes were more viable. This resulted in a significantly greater number of intermediate and a smaller number of high-erucic acid BC₁S₁ seeds.     

The effect of temperature on fruit set,seed set and seed germination in ‘Sonia’ × ‘Hadley’ hybrid Tea-rose crosses

Summary The effect of temperature on fruit set, seed set and seed germination was studied in Sonia × Hadley Hybrid Tea-rose crosses. Sonia mother bushes were grown at constant temperatures (10, 14, 18, 22, 26°C) in the greenhouses of the phytotron until fruit ripening. Fruit set, fruit weight and number of seeds increased as temperature was higher. Optimum temperatures were found for days to fruit ripening (18°C), seed germination (22°C) and number of seedlings per pollinated flower (22°C). Fruit weight and number of seeds were positively correlated. For crossing and the subsequent growing of seed-bearing plants 22°C was the most favourable temperature. Effects of temperature on pollen tube growth, fertilization and seed germination are discussed.     

Reciprocal cross differences in a 6×6 diallel set of groundnut (Arachis hypogaea L.) in the F1 generation

Summary Reciprocal cross differences were studied in a 6×6 diallel full set comprising of thirty hybrid combinations of groundnut in the F₁ generation.Reciprocal cross differences were observed for growth habit in four pairs of crosses, for leaf colour, flower colour and stem pigmentation in two pairs of crosses each. It was observed that the inheritance of flower colour, stem pigmentation and testa colour which exhibited different shades of purple colour was likely to be governed by pleiotropic gene(s). Among the quantitative characters significantly positive reciprocal effects were observed in different crosses for number of mature pods per plant, weight of pods per plant and shelling percent. Marked reciprocal cross differences were observed for pod and kernel characters like pod filling, pod beak, pod constriction and testa colour.     

Detection of wheat-barley translocations by genomic in situ hybridization in derivatives of hybrids multiplied in vitro

Wheat-barley translocations were identified by genomicin situ hybridization (GISH) in backcross progenies originating from in vitro regenerated wheat (Triticum aestivum L. cv. Chinese Spring) × barley (Hordeum vulgare L. cv. Betzes) hybrids. The regenerated hybrids were pollinated with the wheat line Martonvásári 9 kr1. Five translocated wheat-barley chromosomes were recovered among 51 BC₂F₂ progeny from the in vitro regenerated wheat × barley hybrids. All were single breakpoint translocations with the relative positions of the breakpoints ranging from the centromere to about 0.8 of the relative arm length. Of the four translocations with intercalary breakpoints, three were transfers of terminal barley segments to wheat chromosomes; one was a transfer of a terminal wheat segment to a barley chromosome. Because of the absence of diagnostic N-bands, the identity of three barley segments could not be determined; in one translocation the barley chromosome involved had a NOR so it must have been 5H or 6H, and the centric translocation was 4HS.2BL. Following selfing, homozygotes of four translocations were selected. The experiment suggests that in vitro culture conditions are conducive for major genome rearrangements in wheat-barley hybrids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genotypic variation and polymorphism of 2S albumins of sunflower

Summary An early postfertilization ovule culture technique in Alstroemeria was described in which young ovules were cultured in vitro two days after pollination. This resulted in the direct production of seedlings in a normally incongruous cross combination. A histological study of the in vitro cultured ovules revealed the development of the embryo inside the ovule in the absence of normal endosperm. The in vivo grown ovules showed a total breakdown of the developing seed within four weeks after pollination due to a postfertilization barrier. This ovule culture technique was applied in a diallel cross of seven Alstroemeria species, five from Chile and two from Brazil. The selfings and the reciprocal crosses between the Brazilian species A. inodora and A. brasiliensis were congruous and gave seed set. The cross A. inodora x A. pelegrina gave viable seeds. In all other 39 combinations no viable seeds were harvested. In those cross combinations both pre-and postfertilization barriers were found. After early ovule culture hybrid plants were obtained in 27 of the 39 incongruous species combinations of the diallel.Abbreviations DAP days after pollination - MS medium medium according to Murashige & Skoog (1962)     

Interspecific hybridization in Cucumis L. II. The crossability of species,an investigation of in vivo pollen tube growth and seed set

Summary The crossability of 12 Cucumis species of African and Asiatic origin was studied in a diallel cross, in order to find ways to realise the cross between the common cucumber (C. sativus L.) and its wild relatives which carry resistances against diseases and pests.Self-pollinations and cross-pollinations within species gave normal pollen tube growth and seet set. The different accessions within a species, as a rule reacted alike in interspecific crosses. In crosses between African species different crossing patterns were found, viz. bilateral congruity, bilateral incongruity and unilateral incongruity. Within C. sativus all accessions intercrossed freely, except one, which displayed unilateral incongruity.Good seed was harvested from several crosses and in some cases embryo culture was needed for further development of seeds. No good seeds were obtained from any cross between a species of the African group and C. sativus L.     

Temperature as a component of the expression of developmental responses in wheat

Summary Studies were made of days to ear emergence under the constant temperatures of 9, 14, 19 and 25°C and 16 h photoperiod in three sets of wheat lines each possessing genotypes differing for developmental responses.Days to ear emergence in three near-isogenic lines of the wheat cultivar Triple Dirk, which differed for vernalization response, increased as the strength of the response increased. At the four temperatures Triple Dirk D (Vrn 1 vrn 2) was not significantly different from normal Triple Dirk (Vrn 1 Vrn 2) but Triple Dirk B (vrn 1 Vrn 2) was significantly (P=0.01) later than normal Triple Dirk at each temperature. This indicates that the vrn 1 allele confers stronger vernalization response than vrn 2 over the range of temperatures (9–24°C). However, Triple Dirk C (vrn 1 vrn 2) failed to head after 120 days at each temperature indicating strong interaction between vrn 1 and vrn 2 with each other (and possibly the Triple Dirk back-ground) to give a much stronger vernalization response than predictions from additivity of their individual effects.The second set comprised the four Chinese Spring/Thatcher chromosome substitution lines CS/T 3B, 6B, 7B and 5D, plus Chinese Spring and Thatcher, and were grown in the unvernalized condition. CS/T 5D was similar in days to ear emergence as Chinese Spring at all four temperatures but the other three lines were earlier to ear emergence, particularly as the temperature increased. Days to ear emergence was fastest at 14°C in all lines, except CS/T 3B, in which it decreased progressively from 9 to 24°C.The third set of Chinese Spring and Thatcher and the homoeologous group 2 chromosomes of Thatcher substituted in Chinese Spring, the group which is considered to be involved in the control of photoperiod sensitivity. The three substitution lines responded differently to temperature compared with Chinese Spring and with each other, with chromosome 2D being the least, and chromosome 2B the most, responsive to temperature.     

Expression of barley yellow dwarf virus and Russian wheat aphid resistance genes in and fertility of spring wheat × triticale hybrids and backcross lines

Summary The Barley Yellow Dwarf Virus disease (BYDV) and the Russian wheat aphid (RWA) Diuraphis noxia (Mordvilko) have caused significant losses to wheat and barley in several areas of the world. Important sources of resistance to both BYDV and RWA have been found in Triticale. Different generations of interspecific wheat x Triticale crosses were produced and the progenies were screened for BYDV and RWA tolerance. Plants with equal chromosome numbers showed different levels of fertility. A significant correlation was observed between pollen fertility and seed set in primary florets (r=0.57). In generaL, pollen fertility, seed set and the number of euploid plants (2n=42) increased from one generation to the next. The expression of BYDV tolerance varied from population to population. Additive effects were predominant in F₁ and some backcross populations. A dominant effect of rye tolerance genes was also observed in few populations. A monogenic trait or a quantitative (polygenic) character would not agree with the observed segregation patterns. The heritability of this oligogenic tolerance was quite different between populations and in many populations the tolerance genes were only partially expressed. Some transgressive segregation for tolerance and sensitivity was demonstrated. The genes controlling tolerance to RWA in Triticale lines, Muskox 658 and Nord Kivu were not expressed in advanced lines resistant to BYDV. This indicates that tolerance genes for BYDV and RWA in these lines are located on different chromosomes.