Inheritance of spineless leaves in Aechmea (Bromeliaceae)

Bromeliaceae are tropical ornamentals with a variety of colors and inflorescence shapes. Leaves with spined margins are characteristic for the genus Aechmea. Crosses between spineless and spined Aechmea cultivars were attempted in order to obtain a spineless offspring. Crossing spined and spineless genotypes resulted in a progeny with on average 50% spineless plants. The hybrids of two spineless plants had on average 75% spineless leaves. This indicated that the spineless character was dominant. Homozygous plants were selected; these plants are interesting for further breeding and propagation by seed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pollen germination,pollen tube growth and fertilization following self and interspecific pollination of Paspalum species

Summary Crossability between most Paspalum species is very low. This study was undertaken to identify the impediments to hybridization. Accessions of P. intermedium Munro. ex Morong, P. jurgensii Hackel and P. dilatatum Poir were self-pollinated and crossed with one anther. Paspalum intermedium is essentially self-sterile but P. jurgensii and P. dilatatum are highly self-fertile. Following pollination, pollen germination and tube growth were studied by observing the pollinated pistils with fluorescent microscopy. Examination of self-pollinated pistils revealed that the pollen germinated shortly after contacting the stigmas. Germination was over 80% for the P. intermedium and P. dilatatum accessions but only 57% for P. jurgensii. Pollen tubes grew to the micropyle within 45 minutes after pollination in P. dilatatum and 1 hour and 15 minutes in P. jurgensii. However, in the P. intermedium accessions most tubes did not grow beyond the stigma and very few penetrated the style and ovary. Apparently stylar-incompatibility is the reason for the low selfed seed set. In the cross-pollinations, pollen germinated shortly after pollination and germination ranged from 57 to 88% for the different crosses. In all crosses the pollen tubes grew to the micropyle within 30 minutes to 2 hours after pollination indicating that a cross-incompatibility system is not the cause for low crossability among these species. By examining embryo sacs from P. intermedium × P. dilatatum, its reciprocal and P. intermedium × P. urvillei crosses, it was determined that gametes failed to unite in some crosses and this is a major reason for low crossability.     

Pollen grain germination and pollen tube growth following in vivo and in vitro self and interspecific pollinations in annual Cicer species

Summary Germination of pollen grains and growth of pollen tubes were studied to determine the cause of barreness in crosses among annual Cicer species. In vivo and in vitro time-course studies and fluorescent microscopy revealed no pollination incompatibility among the selfs, crosses and reciprocals of C. arietinum L., C. reticulatum Lad. and C. cuneatum Rich. In general, Cicer pollen grains germinated and grew on styles of Cicer species. Pollen tube growth was characterized by irregularly spaced and intermittent callose deposits. Failure of seed formation in interspecific pollinations may be attributed to the slowness of pollen tube growth or collapse of fertilized ovules. In addition to these causes, shortness of stamens and sparsity of pollen grains were responsible for flower drop in natural selfs. Although the number of pollen tubes entering the micropyle in interspecific pollinations was low, it may be possible to grow the fertilized ovules on an artificial medium to obtain F₁ plants.     

Manipulation of in vivo pollination techniques to improve the fertilization efficiency of interspecies crosses in the genus Phaseolus

Phaseolus angustissimus A. Gray contains genes for traits of interest for dry bean (P. vulgaris) breeders. F₁ hybrids can be produced but introgression through backcrossing has been a problem. One of the main impediments is the time required between pollination and fertilization when F₁ hybrids of P. vulgaris/P. angustissimus are backcrossed with P. vulgaris. In an attempt to reduce this time, the effect of alternative pollination techniques was studied. The rate and the time of fertilization were ascertained using three different pollen types (pollen germinated in vitro, fresh pollen (FP) mixed in pollen‐germinating media and FP), and two methods of pollination (cut‐style and stigmatic pollinations). An optimal in vitro pollen germination medium for Phaseolus pollen was developed. Low temperatures (6–9°C) were demonstrated to be necessary for Phaseolus pollen germination. Pollination using a cut‐style technique coupled with pregerminated pollen reduced the time for fertilization in the backcrosses of interspecies hybrids by approximately 28 h. This technique improved the success rate of fertilization in wide crosses of Phaseolus designed to introgress genes from wild relatives.     

Pollen and pollination experiments. VI. Heat resistance of pollen

Summary Pollen of dry apple, pear, lily and rose pollen was heated up to 48 h at a range of temperatures. About half or more than half of the pollen grains survived 48 h at 40 C, 24 h at 50 C, 8 16 h at 60 C. 4 8 h at 70 C, more than one hour at 80 C. and between 10 and 20 min at 90 C. Presumably, pollen able to withstand low humidity is also heat resistant, a property which may be usable to make pollen virus free through heat treatment and perhaps to overcome incompatibility.     

Pollen tube growth in crosses between Porteresia coarctata and Oryza sativa

Summary Comparative study with fluorescence microscopy revealed that the pollen tubes of the self-pollinated rice variety BR-9 reached the ovary within 75 min after pollination. In P. coarctata it took 150 min. In the cross between P. coarctata and BR-9, pollen tubes reached the ovary in 165 min but seed setting was not observed. In the cross between BR-9 and P. coarctata, small and deformed pollen tubes were formed and they failed to grow through the stylodium.     

Pollen and pollination experiments. II. The influence of the first pollination on the effectiveness of the second one in apple

Summary Pollinating apple cultivars twice with compatible pollen at an interval of one or two days produced about twice as many seeds per pollinated flower as a single pollination. With the aid of scab- or mildew resistant marker pollen, it could be shown that the second pollen formed on average twice as many seeds as the first. The first pollen appears to pave the way-partly at its own cost-for the second and was therefore called pioneer pollen.     

In vitro interspecific fertilization,embryo development and formation of hybrid seedlings between Gossypium hirsutum and G. arboreum

Summary In vitro hybridization between Gossypium hirsutum, and G. arboreum was carried out. Hybrid seedlings were obtained after successive use of the following five kinds of media: 1) pollen grain germination medium, 2) double-fertilization medium, 3) embryo development medium, 4) seedlings formation medium, 5) green seedlings growth medium. The factors affecting in vitro interspecific fertilization, embryogenesis and seedling formation were studied. The key factors were temperature and relative humidity (RH). The optimum RH for in vitro interspecific fertilization was 65%, and a suitable temperature range was 26–30°C. Pollen grain germination ratio decreased rapidly at a RH of 80%. When the temperature and the RH were higher than 32°C and 80%, respectively, the fertilization rate decreased to zero.Effects of petals and calyces of the maternal flowers on in vitro interspecific fertilization and ovule growth were identified. Even though the petals or calyces were excised, hybrid plantlets were also obtained after media were improved and a shake culture was used. In addition, the process of double-fertilization and embryo development were studied cytologically. The developmental characteristics of the hybrid embryos derived from in vitro interspecific fertilization were a later occurrence of the double-fertilization process and a much lesser division of endosperm cells. But the embryo development was not affected by these characteristics, and young hybrid embryos can develop to their cotyledon stage finally on artificial media.     

Viability and storage of bromeliad pollen

Several bromeliad species from two different subfamilies, were used to develop a reliable method to evaluate pollen viability. Pollen germination on a medium containing 20% sucrose, 0.001%H₃BO₃ and 0.5% agar was comparable to germination on a compatible stigma. Maximum germination was reached within 2 to 10 hours depending on the species. Based on this test, six species were considered as being good pollen donors with germination percentages between 49%and 83%. Furthermore, pollen from these species and cultivars could be stored in liquid nitrogen (–196 ^°C) without a considerable loss of viability. For all species, a dehydration period of 4 hours prior to cryopreservation and a rehydration period of 1 hour after cryostorage were essential. Greenhouse humidity influenced anther moisture content and cryostorability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stability of cassava plants at the DNA level after retrieval from 10 years of in vitro storage

Summary Cassava (Manihot esculenta Crantz) germplasm collections are conventionally maintained by continuous vegetative propagation in the field. Tissue culture techniques provide a more convenient way to conserve germplasm. The cassava in vitro gene bank held in trust at CIAT comprises nearly 6000 accessions. A study was carried out to determine whether any DNA rearrangements resulting from in vitro storage under slow growth could be detected by molecular analysis in retrieved plants. RFLPs with homologous probes, RAPDs with twenty primers and DNA fingerprinting with M13 probe were tested to detect variation at DNA level in cassava plants after ten-years in vitro storage. The molecular marker data obtained in this study supports the stability of the cassava germplasm under the in vitro storage conditions described in this work.     

Results of multiple pollination in blueberry (Vaccinium elliottii Chapm.)

Blueberry (Vaccinium section Cyanococcus, family Ericaceae) is a shrub that produces multiple-seeded berries in which only a fraction of the ovules develop into viable seeds. A recessive yellowleaf marker gene was used to evaluate the efectiveness of a single pollination versus multiple pollinations in producing seeds in Vaccinium elliottii Chapm. A multiple-pollination experiment was conducted to see if the first pollen applied or the second produced more progeny, and to see if multiple pollinations increased the number of seedlings produced. Flowers of diploid yellowleaf Vaccinium elliottii were pollinated from one to four times at daily intervals. Pollen from redleaf and yellowleaf plants was used to produce two types of seedlings that could be distinguished visually. Generally, percent berry set, seeds per berry, and seed germination were not increased by multiple pollination. After multiple pollination, the pollen applied first always produced the most seedlings. Prior pollination greatly reduced seed set from subsequent pollination, but subsequent pollination caused little or no decrease in the number of seeds set by the first pollination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Embryo development in two barley genotypes after self pollination and pollination with Hordeum bulbosum L.

Summary Embryo development in vivo was compared in the two barley genotypes VK 16032 and Vogelsanger Gold after self pollination and after pollination with H. bulbosum. Embryo growth in VK 16032 after crossing with H. bulbosum showed a similar growth pattern to that of the self pollinated embryos, although the size increase was smaller. The hybrid embryos continued to grow until day 18 after pollination. The embryos from the cross between Vogelsanger Gold and H. bulbosum ceased to grow 8 days after pollination. Arrested embryo growth with subsequent abortion in Vogelsanger Gold was associated with a very early depletion and break down of the endosperm. Use of barley genotypes less sensitive to the genomic disturbances after crossing with H. bulbosum in combination with genotypes like Vogelsanger Gold is recommended in haploid breeding work.     

In vitro techniques for selecting wheat (Triticum aestivum L.) for Fusarium-resistance. II. Culture filtrate technique and inheritance of Fusarium-resistance in the somaclones

Summary Calli of resistant, intermediary and susceptible wheat (Triticum aestivum L.) varieties were selected using culture filtrates of Fusarium graminearum and F. culmorum and the regenerants were evaluated for resistance up to R₃. Czapek-Dox broth medium was inoculated with mycelia of Fusarium isolates and incubated for 2–6 weeks. Filtrates were added to MS callus growing medium, then 5 weeks-old calli were transferred onto this medium (MST) for 4–5 weeks. MST containing 30% filtrate was found to be suitable for selection. Resistant calli were transferred again to fresh MST for further two selection cycles. The surviving calli produced less fertile regenerated lines (R₀) than the non-selected ones. Among 18 R₁ lines tested for Fusarium-resistance in the seedling stage by artificial inoculation in the greenhouse, two (11.1%) were significantly more resistant, one (5.6%) was more susceptible than the original cultivar and the rest (83.3%) behaved similarly to the donor plants. Among unselected R₃ lines of three varieties, practically the same number of resistant plants were found as among the related selected ones. When the R₃ selfed generations obtained through double-layer and culture filtrate selection techniques were tested for Fusarium-resistance, 35.7% of the lines were found to be more resistant than the original cultivars, none was more susceptible and 64.3% had a reaction similar to that of the source materials. Thus, inheritance of the disease reaction was not stable in all cases. Success of in vitro selection for Fusarium-resistance depended also on the genotype, and toxin analysis showed that although being effective, the selective media contained deoxynivalenol only exceptionally. In selecting wheat for Fusarium-resistance in vitro, the culture filtrate technique proved better than the double-layer procedure.     

Improvement of snow mould resistance by conventional and in vitro techniques

Summary Under our climatical conditionsMicrodochium nivale is the main pathogen which causes snow mould in grasses. Like manyFusarium species,M. nivale is able to produce toxins like Deoxynivalenol (DON). In vitro selection with callus cultures from two populations of perennial ryegrass and DON as selective agent was carried out in a one step (subculture) or two step procedure (induction plus subculture). The regenerants from in vitro selection and a seed derived control from the two populations were artificially inoculated withM. nivale. Significant improvement of snow mould tolerance in the high DON variant could be found. Additionally, a toxin test was established which allows to screen large numbers of mature embryos without laborious callus culture. The sexual progenies (R1) of the regenerants were subjected to both the snow mould and the toxin test. Toxin and pathogen resistance were not always in good accordance. The application of both tests in practical plant breeding is discussed.     

Interrelationships of allozymes and ribosomal DNA alleles in wild barley

Summary A genetic resources preservation program led to an in vitro germplasm collection of yam (Dioscorea spp.), obtained by nodal cutting and maintained under slow growth conditions with ((Knop, 1865) in George & Sherrington, 1984) modified medium. The collection comprises accessions of 14 species from Africa and Asia, including edible varieties from the humid intertropical areas, viz 10 wild species (D. abyssinica, D. bulbifera, D. burkilliana, D. dumetorum, D. hirtiflora, D. mangenotiana, D. minutiflora, D. praehensilis, D. schimperana, D. togoensis), 5 edible species (D. alata, D. bulbifera, D. cayenensis-D. rotundata complex, D. dumetorum and D. esculenta) and 1 interspecific hybrid (D. cayenensis-D. rotundata complex, cv. Krengle x D. praehensilis). Three factors that may influence the success in transfer from the in vivo to the in vitro conditions have been studied. These are: the type of introducted material (nodal cutting fragments, seeds and exchanged microplants), the introduction date and the genotype. Some significant differences in success were due to the type of introduced material, whereas the introduction date had no effect. On the other hand, some species showed a greater success in the transfer from the in vivo to the in vitro conditions than others. The three tuberization types (basal tuberization, aerial tuberization and boulage (tuberization without vegetative development) phenomena), according to species, are discussed.     

Vegetative and floral characteristics of interspecific Brassica chimeras produced by in vitro grafting

Summary Interspecific Brassica chimeras (Brassica campestris+B. oleracea) were synthesized according to an in vitro graftculture method, and propagated by tissue culture of axillary buds or chimeric explants. A total of 127 regenerants obtained were investigated. The mericlinal chimera type was more easily produced than the other periclinal and revertant types. No sectorial chimera was produced. The flowering habit and inflorescence type of the chimeras were found to be controlled by the constitution of three tissue layers, but the petal shape and color were controlled only by the two outer tissue layers. Pollen viability of the chimeras were generally lower and more variable in parts than those of the parental types.     

In vitro pollen germination and tube growth of tomato (Lycopersicon esculentum Mill.) and its relation with plant growth

Summary In vitro pollen germination at 10°C, 14°C and 22°C of four groups of two pure line tomato varieties was compared with their plant growth at 19°C D/10°C N under controlled environmental conditions. Generally, pollen germination was slow at 10°C but after 6 h the percentage of germination was similar to that at 22°C. Maximum germination was obtained at 14°C already after 4 h. The longest pollen tubes occurred at 22°C. The two varieties within each group differed significantly from each other for percentage of pollen germination. For one group, this difference was greater at 10°C than at 22°C. The varieties in two groups also differed significantly for pollen tube growth. These differences in pollen tube growth rate were greater at 22°C than at 10°C. There was no clear relationship between pollen germination, pollen tube growth and plant growth in any of the four pairs of varieties. The results are discussed with regard to the possibility of pollen selection at low temperature in order to improve the efficiency of breeding for growth at low temperature.     

Relation between wheat-rye crossability and seed set of common wheat after pollination with other species in the Hordeae

Summary Cultivars of common wheat (Triticum aestivum L. em. Thell.) of high wheat-rye (Secale cereale L.) crossability set more seed with pollen of other related species than did wheats of low wheat-rye crossability. This was found to be true for pollen parents from the genera Triticum, Aegilops, Secale, Agropyron and Elymus.     

The assessment of in vitro characters and their influence on the success rates of doubled haploid production in barley

Summary A assessment of in vitro characters: embryo size, differentiation stage and germination time of haploid embryos, was carried out with a view to developing a selection procedure to increase the efficiency of doubled haploid (DH) production using the Hordeum bulbosum system. The differentiation stage of haploid embryos at the time of excision was found to be the most promising character for selection. In the two spring crosses examined 55% of excised embryos were undifferentiated and 45% were differentiated, with overall success rates, in terms of the percentage of DHs produced, of 7.91% and 25.16%, respectively. 17% of excised embryos produced callus. These embryos performed poorly in terms of regeneration and subsequent growth. It is suggested that only differentiated non-callusing embryos are maintained in order to maximize the efficiency of DH production. It is also shown that the overall success rate depends not only on initial stages such as seed setting but also on genotypic differences in response to colchicine treatment at later stages.     

Pollen retention following natural self pollination in peach,almond, and peach × almond hybrids

Summary Retention of pollen grains following natural self-pollination was evaluated in 15 cultivars (cvs.) of almond, 4 peach and 2 nectarine cvs., and 37 interspecific peach × almond hybrids compared to 7 almond seedlings. The level of pollen retention was presumed to reflect and integrate the degree of homogamy, the amount of pollen produced by the flower, the extent of anther-stigma contact during anthesis, and the level of pollen germination. Pollen retention averaged 5 times greater in the peach and nectarine cvs. than in the almond cvs. The greater pollen retention, characteristic of the peach, was dominant in expression in the interspecific F₁ hybrids over the lower levels of pollen retention, characteristic of the almond. Thus, gametophytic self-incompatibility is not the only trait supporting outcrossing in the almond. Our data are consistent with the concept of co-evolution of floral traits relating to different breeding strategies. The level of pollen retention could often be anticipated at anthesis on the basis of blossom phenotype. That is, stigma-anther contact was observed frequently in the blossoms of peach, nectarine, and the peach × almond F₁ hybrids, but only infrequently in almond.