Intergeneric hybrids and an amphiploid between Elymus canadensis and Psathyrostachys juncea

Summary Fifty four hybrid plants between Elymus canadensis and Psathyrostachys juncea were obtained by handpollination and embryo culture. The average cross compatibility between both species was 31.2 percent. One amphiploid plant was induced by colchicine treatment. The hybrid and amphiploid plants resembled P. juncea in appearance but showed a higher plant height and dry matter yield than the parents. The hybrids showed extremely low pollen stainability and were completely sterile. With the exception of one plant (2n=3x+1=22), all hybrid plants were allotriploids (SHN, 2n=3x=21). The amphiploid plant (SSHHNN, 2n=6x=42) showed 58.9% pollen stainability and 11.6% seed fertility.Mean chromosome associations of the hybrids and amphiploid at metaphase I were 0.02IV+0.06III+2.03II+16.91I and 0.07III+18.00II+5.85I, respectively. Lagging chromosomes, chromosome bridges, abnormal cytokinesis, and micronuclei were occasionally observed at the anaphase, telophase, or tetrad stage.     

Some consequences of pollen storage in the raspberry (Rubus idaeus L.)

Summary Raspberry pollen was stored at 5°C and –13°C for six months and then tested for its ability to induce pyrene set and the production of viable seedlings, and for its effect upon the segregation of a major gene s. Only pollen stored at –13°C gave a pyrene set and germination percentage adequate to produce sufficient seedlings for a breeding programme. It is suggested that tests of pollen viability in the raspberry should include studies of pollen germination, and the effect of this pollen on pyrene set and seed germination. Possible causes of the loss of viability in the pollen stored at 5°C are discussed.     

Fertility improvement in tetraploid pearl millet

Summary Autotetraploid (2n=4x=28) pearl millet inbred lines, Tift 23BE and Tift 239DB, have been developed for use in crosses with other polyploid Pennisetum species. Each line set less than 1% and 3% selfed and open-pollinated seed, respectively. Seed germination was usually less than 17%. First generation (F₁) hybrids between the two inbreds set up to 61% seed while up to 40% of the seed from hybrids germinated.Seed weight per inflorescence for two planting dates averaged 0.32 g and 3.06 g for the two inbreds and the second generation F₂ progeny, respectively. One hundred seed weight was also significantly higher (0.78 g vs 0.48 g) in the F₂ progeny, probably due better endosperm development. Chromosome behavior and pollen stainability were similar in the inbred parents and hybrids. However, the hybrids shed more pollen than the inbred parents.Heterosis was evident in the F₁ hybrids and F₂ progeny which showed significant increases in plant height, leaf length, leaf width, and inflorescence length in addition to fertility improvement.     

Wheat pollen dispersal under semiarid field conditions: potential outcrossing with Triticum aestivum and Triticum turgidum

Isolation distance is the main barrier to crop-to-crop gene-flow. A 3-year study assessed the maximum potential outcrossing under field conditions between two wheat cultivars (Triticum aestivum L.) and between wheat and durum wheat (Triticum turgidum L. var. durum). Outcrossing was measured by seed set on emasculated recipient plants placed at four sides with different distances from a 3 m × 3 m T. aestivum (cultivar Chinese Spring) pollen source. Frequencies of seed set at 0 m distance were 45% (37–56%) for T. aestivum cultivars and 18% (5–30%) with T. turgidum. These values agree with hybridization in non-limiting pollen conditions measured by manual crosses in greenhouse. The number of pollen grains and the outcrossing frequencies decreased at increasing distances influenced by the prevailing wind direction. Under semiarid conditions of this assay, viable pollen was found 14 m from the pollen source, with a maximum distance of 8 m at which cross-pollination decreases below 1%. Ambient conditions affect pollen viability, hybridization and pollen dispersal. Data presented in this paper emphasize the major role played by environmental conditions in outcrossing. Data obtained in one area may therefore not coincide with the prevailing situation in different locations and climates.     

Cytogenetic studies and the occurrence of triploidy in the wild potato species Solanum commersonii Dun.

Summary The South American wild potato species Solanum commersonii Dun. exists as two subspecies, subsp. commersonii and subsp. malmeanum (Bitter) Hawkes and Hjerting, and as both diploid and triploid cytotypes. The two subspecies were completely cross fertile but there were reciprocal differences in the number of seeds set per berry and the mean seed weight. Crosses between diploids and colchicine-induced autotetraploids yielded only a few seeds per berry, but 16 of the 18 germinated seeds were triploid or nearly so. Such a high proportion of triploids is unusual for such crosses in potatoes. Some triploids has a high percentage of stainable pollen. The origin of naturally occurring triploids is discussed in the context of 2n gametes, a triploid block, and endosperm balance numbers.     

Freeze preservation of gladiolus pollen

Viability and fertility profiles of cryopreserved gladiolus pollen from 7 cultivars have shown that it is possible to use cryogenic methods for conservation and management of the haploid gene pool in this species. There was no decline in pollen viability (in vitro) levels after 1 and 10 years of cryogenic storage. Field pollinations with cryogenic stored pollen induced capsule and seed set in varying capacities. Long-term cryogenic storage of gladiolus pollen could enhance breeding efficiency through better management of the haploid gene pool resources. Pollen parents could be made available throughout the breeding programme, ensuring guaranteed supply at the time of peak stigma receptivity. A pollen cryobank facility established for this species would increase genetic diversity conservation at the haploid stage.IIHR Contribution No. 112/93     

Production of 27-, 28-, and 56-chromosome apomictic hybrid derivatives between pearl millet (2n=14) and Pennisetum squamulatum (2n=54)

Summary An interspecific hybridization program designed to transfer gene(s) controlling apomixis from Pennisetum squamulatum Fresen. (2n=6x=54) to induced tetraploid (2n=4x=28) cultivated pearl millet, Pennisetum americanum (L.) Leeke resulted in four offtype plants, two with 27 chromosomes and two with 28 chromosomes. These plants were found among 217 spaced plants established from open-pollinated seed of an apomictic 21-chromosome polyhaploid (2n=21) plant derived from an apomictic interspecific hybrid (2n=41) between tetraploid pearl millet and Pennisetum squamulatum. It appeared that a 21- (or 20-) chromosome unreduced egg from the apomictic polyhaploid united with a 7-chromosome pearl millet (2n=2x=14) gamete to produce a 28- (or 27-) chromosome offspring. Meiotic chromosome behavior was irregular averaging from 3.60 to 4.05 bivalents per microsporocyte in the 27- and 28-chromosome hybrids. The 27- or 28-chromosome hybrids, like the 21-chromosome female parent, shed no pollen, but set from 1.8 to 28 seed per panicle when allowed to outcross with pearl millet. Progeny of the 28-chromosome hybrids were uniform and identical to their respective female parents, indicating that apomixis had been effectively transferred through the egg. In addition, a 56-chromosome plant resulting from chromosome doubling of a 28-chromosome hybrid was identified. Pollen was 68 per cent stainable and the plant averaged 2.3 selfed seeds per panicle. Chromosomes of the 56-chromosome plant paired as bivalents (x=10.67) or associated in multivalents. Three to nine chromosomes remained unpaired at metaphase I. Multiple four-nucleate embryo sacs indicated the 56-chromosome hybrid was an obligate apomict. The production of 27-, 28-, and 56-chromosome hybrid derivatives were the results of interspecific hybridization, haploidization, fertilization of unreduced apomictic eggs, and spontaneous chromosome doubling. These mechanisms resulted in new unique genome combinations between x=7 and x=9 Pennisetum species.     

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

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

Hybrid Tea-rose pollen. I. Germination and storage

Summary Germination and storage trials were carried out with pollen of several rose varieties. The pollen grains germinated well in a 15% sucrose solution with 40 ppm boric acid. Staining the pollen with a 0.1% tetrazolium solution and standardizing the degree of colour at which the pollen grains are counted as viable, provided a good viability estimate, simpler to carry out than in vitro germination. Germination capacity and staining ability of the pollen were greatly impeded-about halved-by dehydration during storage in desiccators at low humidity. This effect could be corrected by humidifying the pollen beforehand for about one hour, though this pre-treatment increased the percentage of germinated pollen grains more than the percentage stained. There was no difference between the two percentages in fresh or in deep-frozen pollen.Pollen stored at 1°C and high relative humidity soon lost its germination capacity: between 0 and 20% humidity a considerable proportion of the pollen remained viable for 9 months and longer. Storage for the same period in vacuum-sealed glass tubes at –24°C maintained viability as well or better and would probably prolong it further. Some of the cold-stored pollen induced a reasonable seed set after one year, a low seed set was obtained even after two years of storage at 1°C and low humidity.     

Cryopreservation of Delphinium pollen at –30 °C

Pollen of garden varieties and species of Delphinium that was cryopreserved at –30 ^°C after 3 hours of air drying and storage on silica gel, had high germination and pollen tube growth in vitroeven after 180-day storage. On the other hand, pollen stored at 25 ^°C showed a marked decrease in the germination rate within 10 days. The best in vitro germination of Delphinium pollen was on a 1% water agar containing 15% sucrose and 0.005 to 0.01% boric acid and at 15 to 20 ^°C. Field pollination with the cryopreserved pollen showed higher fruit and seed set than pollination with pollen stored at 25 ^°C, and was not significantly different from fresh pollen. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fertility,plant morphology,and transmission rates of the extra chromosome in single and double trisomics of Solanum tuberosum L. Group Tuberosum

Summary Initial single and double trisomics of S. tuberosum Group Tuberosum cv. Gineke were successfully crossed with and backcrossed to clones obtained through inbreeding of self-compatible dihaploids of the same variety. Some trisomics showed reduced flowering or flower abnormalities and contributed therefore only to a small extent. Berry-set and seed-set varied considerably. There was no relation between these phenomena, nor was there any relation between either berry-or seed-set and the identity of the extra chromosome in the female parent. Seed-set seemed to be influenced by the male parent. When a more inbred male parent was used in the crosses with trisomics this often resulted in less seed per cross. There was no clear relation between seed-set and stainability of the pollen grains, but both the strong selection for good pollen and the high level of self-compatibility, have apparently contributed to the success of the crosses. The double trisomic plants yielded less seed than most single trisomics. Only three of the single trisomics produced stainable pollen and two of them yielded progeny when used as male parent in crosses or selfings.In the progenies several of the trisomic types could be distinguished on the basis of plant morphology in the young seedling stage. For ten different trisomics the morphotype is being described. The average rate of female transmission of the extra chromosome was about twenty per cent, but there was a wide variation, both between and within the various trisomic types. The results indicated that for chromosomes 3 and 8 the rate of transmission was higher than the average value. In one out of two trisomic types male transmission of the extra chromosome occurred, with a rate of 4.7%. The possible causes for the observed differences in female transmission of the extra chromosome are being discussed.     

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.     

Cryopreservation of pollen from two rose cultivars

Summary An investigation was undertaken on the storage characteristics of pollen collected from two English rose cultivars. A rapid decline in viability was observed in pollen stored at +4° C and –20° C, whereas the viability of pollen, stored at ultra-low temperature (–196° C), remained constant. Cryopreserved pollen was shown to retain its ability for fertilisation. The effects of the stage of flower development and anther dehiscence were assessed on both pre-and post-cryopreservation viabilities. Successful long-term storage of pollen will facilitate hybridisation of rose species and cultivars that do not flower synchronously.     

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.     

Male fertility and cytology of triploid hybrids between tetraploidSolanum commersonii (2n=4x=48, 2EBN) and Phureja-Tuberosum haploid hybrids (2n=2x=24, 2EBN)

Summary Solanum commersonii Dun. is a diploid (2n=2x=24, 1EBN) wild species of potential value for potato breeding. It is a reproductively isolated species and cannot be crossed with Tuberosum haploids (2n=2x=24, 2EBN) or other diploid 2EBNSolanum species. In order to overcome the EBN barriers, triploid hybrids were produced between Phureja-Tuberosum haploid hybrids, which form 2n pollen grains by parallel spindles, and tetraploidS. commersonii. Microsporogenesis analysis of the triploids indicated a trend towards low values of chromosome distribution at Anaphase I; lagging chromosomes were often observed as well. Despite these abnormalities, the percentage of stainable pollen was very high, ranging from 5.0% to 74.3%. A high variation in pollen grain diameter was also evident. Parallel and tripolar orientation of spindles at Metaphase II of microsporogenesis was a common feature of all the triploids analyzed, but dyads and triads were observed at a very low frequency. Therefore, also the frequency of 2n pollen was very low; the different size of stainable pollen appears to represent the ploidy levels which are possible according to the distribution of chromosomes in Anaphase I. The results obtained also suggest thatS. commersonii could have minor genes acting at the end of meiosis in such a way that, despite the presence of parallel/tripolar spindles, dyads/triads are not formed.Contribution no. 124 from the Research Center for Vegetable Breeding.     

Allotetraploid hybrids produced by protoplast fusion for seedless triploid <Emphasis Type="BoldItalic">Citrus</Emphasis> breeding

In connection with crop improvement strategies for marginal regions it has been proposed to increase the outcrossing rate in barley which would presuppose high and persistent pollen viability to ensure successful cross fertilisation. The present study was designed to investigate the viability of mature pollen from extruded and non-extruded anthers of cultivated and wild barley (Hordeum vulgare ssp vulgare and ssp spontaneum, respectively) in comparison with the closely related but obligatory outcrossing species H. bulbosum. Pollen viability (PV) was assessed employing the p-phenylenediamine-peroxidase-test on pollen derived from spikes or anthers immediately after collection and after treatment at 20, 30 and 40 ^∘C for 1, 2, 4, 8 and 16 h. The latter treatment was interposed after 8 h by a 10 h period of darkness at 12 ^∘C and thus called 26 h treatment, consecutively. Initial PV was high with 98% across all genotypes and even at 40 ^∘C did not fall below 80% after 8 h. After the 26 h treatment, PV of two H. vulgare genotypes originating from semi-arid regions and of H. bulbosum fell below 60% while the other genotypes retained a PV of > 80%. Viability of pollen of extruded anthers in H. vulgare ssp. spontaneum was on average slightly but significantly lower than PV of non-extruded anthers but still remained above 90%, even after the 26 h treatment at 40 ^∘C. Pollen viability of the outcrossing species H. bulbosum ranged on a very similar level as PV of H. vulgare. Results indicate that pollen of H. vulgare retains a sufficiently high level of viability to ensure successful cross-fertilisation over a period of at least 26 h even at high temperatures of up to 40 ^∘C.     

Male fertility and occurrence of 2n gametes in East African Highland bananas (Musa spp.)

The quantity and quality of pollen produced by a genotype are important attributes to be considered in the selection of male parents for breeding. The objective of this research was to determine the quantity and quality of pollen in 13 selected East African Highland bananas (EAHB) in relation to six diploids commonly used as male parents. Pollen quantity was scored on a scale of 0–6 while the variation of pollen stainability along the rachis was determined using acetocarmine glycerol jelly. Actual male fertility was determined by using pollen from the EAHB varieties on M. acuminata spp. burmannicoides, ‘Calcutta 4’, as the female. The diameter of 200 viable pollen grains was measured under a microscope with the aid of a graduated eyepiece. Significant differences were obtained for mean pollen stainability and pollen diameter. The pollen stainability for diploids was higher than that for the EAHB. Node numbers contributed significantly to variation of pollen stainability in EAHB (P ≤ 0.01) and ‘Pisang lilin’ (P ≤ 0.001). ‘Pisang lilin’ and the EAHB varieties had about 100 nodes as opposed to about 200 in other diploids. The EAHB varieties produced less pollen than most of the diploids. The actual male fertility of EAHB varieties was low (1 seed/bunch), compared to that of ‘Calcutta 4’ (223.3 seeds/bunch) and ‘Pisang lilin’ (13.7 seeds/bunch). Although the production of 2n pollen in EAHB varieties was low (0–7%), the potential exists for using them in new breeding approaches.     

Storage of sugarbeet pollen

Summary To develop the technology for long-term pollen preservation, sugarbeet pollen was collected from plants grown in the greenhouse and in the field, and was stored 1 day to 1 year at 5, -18, and -196°C. Pollen containing about 12% moisture was successfully stored in liquid nitrogen (LN₂) up to 1 year; this pollen effected fertilization of male-sterile flowers as well as freshly collected pollen. Germination of the resultant seed was good and not different from seed from fresh pollinations. Pollen stored at -18°C for 1 year did not result in as much seed set as fresh pollen, and 1 year at 5°C was essentially lethal. In vitro pollen germination served as a post-storage viability measure, provided the pollen was hydrated before germination. The methods tested in these experiments provided a relatively simple, reliable, and inexpensive means for preservation of sugarbeet pollen for breeding purposes and for preservation of genetic resources.Joint contribution of the Agricultural Research Service, USDA, and the Beet Sugar Development Foundation.     

Interspecific hybrids from cross incompatible relatives of sweetpotato

Summary Hybrids were obtained from Ipomoea interspecific crosses through ovule culture. The hybridity of the progeny obtained from I. triloba × IitI. trifida and (I. triloba × I. lacunosa) × I. batatas (4x) crosses was established by comparisons of floral morphology and analyses of peroxidase and esterase isozymes. The hybrids displayed the inflorescence type and sepal shape and texture of their male parents, while corolla size and anther and nectary color tended to be intermediate to their parents. The isozyme banding patterns of the hybrids contained bands present in the patterns of each of their parents. Pollen grain viability, measured by aceto-carmine stainability, was 44.1%, 92.3% and 82.4%, respectively, for the I. triloba × I. trifida hybrid and the (I. triloba × I. lacunosa) × I. batatas (4x) hybrids, H₁ and H₂. A controlled pollination study revealed that the I. triloba × I. trifida, and the (I. triloba × I. lacunosa) × I. batatas (4x) hybrids, H₁ and H₂ were partially self fertile with 6%, 70% and 13%, respectively, of the pollinated flowers producing viable seed. Success in backcrossing and sib-mating varied with the cross combination.     

Stabilization of new types of diploids (2n=22, 24) through selfing of aneuploids (2n=21, 22) derived from crossing of sesquidiploids (2n=29, AAC) and Brassica campestris (2n=20 AA)

Summary Aneuploids with 2n=21 and 2n=22 derived from crossing of sesquidiploids (2n=29, AAC) and Brassica campestris (2n=20, AA) were selfed successively in order to follow the changes in chromosome number of the progenies for three consecutive generations. Progenies with 2n=22, 23 and 24 obtained after selfing of S₀ generation and the succeeding S₁, S₂ and S₃ generations were analyzed in terms of pollen stainability, % seed set as well as cytogenetically based on meiotic behaviour with the aim of determining the possibility of addition of one or more alien chromosomes into n=10 species which may lead to differentiation of single or plural disomic addition lines. The generation of aneuploids with 2n=21 progressed in such a way that most plants seem to revert to the 2n=20 chromosome number of B. campestris after selfing. From 2n=22 aneuploids, however, the succeeding progenies showed high frequency of plants with two additional chromosomes which accounted for 50.6% and 52.9% of total S₃ progenies via 2n=22 and 2n=24 S₂ generations, respectively. The meiotic behaviour of these progenies indicated evidence for a rule governing the frequency distribution of chromosome number among these addition lines and high possibility to breed such disomic plants with 2n=22. A method of selecting stable aneuploids was suggested in addition to the possible role of pollination biology at various processes of such breeding program.