Polygon of crossability between eleven species of Ipomoea: section Batatas (Convolvulaceae)

Summary Crossability within Ipomoea section Batatas is complex because of genetic, cytogenetic and physiological interactions. This complexity is responsible for the fact that knowledge about phylogenetic relationships within this section remains preliminary. Between 1988 and 1991, studies of planting, pollination and evaluation of progenies were carried out at the facilities of CIP in La Molina and San Ramon, Peru. Self-compatibility was found in nine diploid species. Self-incompatibility was found in diploid I. trifida, tetraploid I. tiliacea and both tetraploid and hexaploid I. batatas. Sexual compatibility is though to be related to a multiallelic sporophytic incompatibility system which is expressed in the stigmatic papillae. Altogether, 4,162 cross pollinations were made between 11 species and 76 interspecific combinations of 110 possible combinations in a diallel 11×11 design. From these 76 interspecific combinations only 38 survived, and in these crossability (= proportion between number of fruits harvested/pollinations made) ranged from 0.01 to 1.00 at La Molina. At San Ramon, 11 out of 17 cross combinations were successful, and in these crossability ranged from 0.01 to 0.71. Crossability appeared to be influenced by latitude which is related to flowering synchrony. The early death of seedlings is hypothesized to be related to a genomic imbalance between embryo and endosperm. Maternal effects were found in crosses between diploids and tetraploids which produced triploid and diploid offspring, and in crosses between hexaploids and diploids which gave rise to hexaploid offspring. This study shows that I. trifida and I. x leucantha may act as bridge species for gene flow from wild Ipomoea species to the genepool of the sweetpotato.     

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.     

Effects of aminoethoxyvinylglycine (AVG), environment,and genotype in overcoming hybridization barriers between Cucumis species

Summary It was attempted to overcome crossing barriers between the cucumber (Cucumis sativus L.), the melon (C. melo L.) and two wild Cucumis spp. (C. metuliferus Naud. and C. zeyheri 2x Sond.) by application of aminoethoxyvinylglycine (AVG) and by limiting the amount of rooting substrate. The reciprocal crosses between both wild species were used as a model system.Crosses between C. metuliferus and C. zeyheri 2x succeeded well if the maternal plants were grown in containers of 10 or 25 1 instead of in open soil. This treatment also improved crossability in the cross C. metuliferus x C. melo. It strongly enhanced the number of female flowers per plant in C. metuliferus. Application of AVG to pollinated flowers initially seemed also to improve crossability in these cross combinations, but later on this effect was not found again.Significant genetic variation for crossability was found in C. zeyheri 2x. Rare plants yielded numerous fruits with embryos after crosses with C. metuliferus and also with C. sativus. Clones from these plants gave similar results.Excessive temperature and radiation decreased crossability especially in crosses with C. metuliferus and C. sativus as maternal parent.     

Natural hybridization between Solanum acaule Bitt. and S. megistacrolobum Bitt. in the province of jujuy,Argentina

Summary Evidence is provided that hybridization of the tetraploid (2n=4x=48), self-fertile tuber-bearing species Solanum acaule Bitt. with the diploid (2n=2x=24), self-incompatible, tuber-bearing S. megistacrolobum Bitt. takes place in several localities of the province of Jujuy in the high, cold plateaux of the Argentine Puna. The triploid hybrids (2n=3x=36) closely resemble S. acaule in growth habit, leaf morphology and floral structures and for this reason they can be easily overlooked for that species in the field. Experimental data show that S. acaule can be crossed with S. megistacrolobum though the crossability is rather low and variable according to the particular cross considered. The artificial hybrid obtained compares well with the natural hybrid in morphology and chromosome number. The hybrids, though almost completely male sterile, are successful colonizers of disturbed areas around farmers' dwellings, cattle enclosures and other areas where the soil is rich in organic matter.There is some evidence that the Tilcara material of S. acaule subsp. aemulans and the hybrids of S. acaule x S. megistacrolobum have some characters in common, which can be interpreted as having a similar origin.It is postulated that S. acaule subsp. aemulans, in Jujuy at any rate, is not a primitive form of S. acaule as thought by Hawkes and Hjerting, but rather a fertile hybrid derivative of S. acaule x S. megistacrolobum through the functioning of 2n gametes.We also provide evidence that S. bruecheri Correll should not be considered a hybrid of S. acaulle x S. megistacrolobum but a synonym for S. gourlayi Hawkes. The new name, S. x indunii Okada et Clausen, is proposed to designate this hybrid.     

Reproductive capacity of F1 hybrids from Rosa rugosa and Chinensis cultivars

Summary Reciprocal crosses were carried out for 6 combinations of 4 R. rugosa with 3 R. chinensis cultivars. The parental combinations were evaluated for successful pollinations, seed germination and flowering and seed setting seedlings in populations of 3 year old plants. Seeds and viable seedlings were obtained from each of the 12 seedling populations. Only 3 populations produced female fertile offssprings. The average of seed setting seedlings was 1.5%. The percentage of flowering seedlings was significantly reduced in the offspring from certain parents. The success of cross pollination, seed germination and the ability to initiate flowers were influenced by cytoplasmic factors.The differences in fertility between the present hybrids and the only other rugosa x chinensis hybrid described, R. calocarpa (Andrê) Willmott, are discussed.Contribution No. 73/2.     

Relationships between African species of the genus Cucumis L. Estimated by the production,vigour and fertility of F1 hybrids

Summary The production, vigour, and fertility of F₁ hybrids between nine African species of the genus Cucumis L. were studied as a measure of the relationships between the species. Hybrid plants were obtained from 29 out of the 72 possible cross combinations. Two F₁ hybrids died as seedlings, and 27 hybrids were raised to maturity. Pollen production and stainability varied greatly amongst these hybrids, as did fruit and seed set following self pollination and backcrossing with either parental species. The fruit shape of the hybrids was always intermediate between that of both parental species.Two species appeared to be closely related: C. prophetarum L. and C. anguria var. longipes A. Meeuse. Most other species produced highly to moderately fertile F₁ hybrids with at least one other species. C. metuliferus Naud. produced only sterile hybrids with C. zeyheri Sond. 2x. The results sustain the recent taxonomic classification of the genus (Jeffrey, 1980).     

The nature of the Bolivian weed potato species Solanum sucrense Hawkes

Summary Two theories for the origin of the Bolivian weed potato species Solanum sucrense Hawkes have been tested. The first was that it had an allopolyploid origin as a hybrid of the cultivated tetraploid S. tuberosum ssp. andigena (Juz. et Buk.) Hawkes with the wild/weed tetraploid cytotype of S. oplocense Hawkes. The second hypothesis postulated that it was a cross of the weed diploid species S. sparsipilum (Bitt.) Juz. et Buk. with S. oplocense.Synthetic hybrids of S. tuberosum ssp. andigena x S. oplocense and of S. sparsipilum x S. oplocense have been compared morphologically with S. sucrense accessions. Their crossability has also been investigated.The crossability and morphological studies strongly suggested that the former hypothesis was the more likely. This was borne out by observations made on the 1974 University of Birmingham Expedition when segregating populations of S. sucrense and S. oplocense were collected growing with feral S. tuberosum ssp. andigena.The evidence from this study indicates that the S. tuberosum ssp. andigena x S. oplocense hybrid has formed the basis of the S. sucrense gene pool. It is suggested that this hybridogenic taxon be maintained under the name Solanum x sucrense.The clarification of the taxonomic relationships of these three species will be of interest to Globodera resistance breeders, in view of the fact that these taxa are resistant to various pathotypes of the golden nematode.     

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.     

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.     

Unreduced pollen frequencies versus hybrid production in diploid-tetraploid Vaccinium crosses

Summary Reciprocal crosses were made between highbush Vaccinium corymbosum L. cultivars (4X) and high, medium and low frequency diplandroid pollen producing diploid clones of V. elliotti (Chapm.) and diploid pubescent forms of V. corymbosum. Pollination of 3,342 flowers produced 15 hybrids-11 tetraploids and 4 triploids. All V. elliottii hybrids were tetraploid while each successful diploid-tetraploid V. corymbosum cross produced at least one triploid. The ratio of tetraploid hybrids to 100 pollinations (H: 100P) was considered to be the best criterion for assessing crossability. Vaccinium elliottii produced a total of 8 4X hybrids while 2X V. corymbosum only produced 3. Vaccinium elliottii was more successful as a female parent and diploid V. corymbosum only produced hybrids as male parents. High frequency diplandroid clones showed a lower mean crossability as pollen parents (H: 100P=0.2) than medium frequency diplandroid clones (H: 100P=0.8). As predicted, 0% diplandroid clones wer unsuccessful as pollen parents. Unreduced pollen production was essential for tetraploid hybrid production in 4X×2X crosses. There appeared to be no consistent, inherent pattern between 2n pollen and 2n egg production in a clone nor was a tetraploid genotype effect on crossability consistently observed.Paper No. 10781 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC., 27695-7601     

The importance of wild potato species resistant to the potato cyst nematode,Globodera pallida,pathotypes P4A and P5A,in potato breeding. II. The crossability of resistant species

Summary Over 2400 pollinations were made to investigate the crossability relationships between cultivated potatoes, and wild diploid species from Series Tuberosa and Circaeifolia, as well as wild polyploid species in Series Tuberosa and Longipedicellata resistant to potato cyst nematode, Globodera pallida pathotypes P₄A and P₅A. Wild diploids in Series Tuberosa crossed easily with cultivated diploid species, except with Solanum lignicaule where most pollinations failed, and seed set was extremely low (0.2 seeds per pollination or less). It is suggested that this species is 1EBN. S. capsicibaccatum is clearly isolated from Series Tuberosa, but can form hybrids with S. lignicaule, which can act as a bridging species to S. tuberosum haploids. S. gourlayi and S. oplocense can be crossed with both subspecies of S. tuberosum, but S. papita, Series Longipedicellata is reproductively isolated from the tetraploid cultigens. The crossability data are discussed in the light of germplasm utilisation for breeding potato varieties resistant to potato cyst nematode.     

The application of in vitro tiller induction in Lolium multiflorum

Summary Eight Lolium multiflorum genotypes were micropropagated for over one year. Using Murashige & Skoog's basal medium, various growth regulators (6-benzylaminopurine, indole acetic acid, adenine sulphate) were tested for their effect on micropropagation. Plantlet handling methods, culture conditions and culture procedures were also compared. Differences were observed in rates of micropropagation between plant genotypes. Under the best conditions for micropropagation, an average of approximately 50 tillers were produced in a 5–6 week period, compared with an estimated 8–15 tillers from soil-grown plants over the same period. Tillers must reach a certain developmental stage before they will grow independently, therefore the number of surviving propagules at subculture under micropropagation and in soil is about half the number of tillers produced. A proposed system for the micropropagation of Lolium multiflorum is described.     

The origin of polyploids via 2n gametes in Vaccinium section Cyanococcus

Summary The production of 2n pollen (pollen with the sporophytic chromosome number) was evaluated in 4x and 6x taxa of Vaccinium section Cyanococcus. Mean frequencies of 2n pollen producers were 17.1% and 8.3% in natural 4x and 6x populations, respectively. The frequency of 2n pollen producers in the 4x species ranged from 8.6% (V. angustifolium) to 23.8% (V. pallidum). Level of 2n pollen production was genotypically variable (1% to 37.4%). The widespread occurrence of 2n pollen in 2x, 4x and 6x taxa suggests that sexual polyploidization was widespread and responsible for the origin of the polyploid species found in this genus. The frequency of 2n pollen producers was not significantly different between the 4x species and their putative 2x ancestors. These results support the origin of 4x and 6x taxa as a consequence of sexual polyploidization. Polyploids derived from sexual polyploidization would be expected to have increased fitness and flexibility due to the mode of 2n pollen formation. In blueberry species the predominant mode of 2n pollen formation is genetically equivalent to a first division restitution mechanism (FDR). FDR 2n pollen transmits a high percentage of the heterozygosity and a large fraction of the epistasis from the 2x parent to the 4x offspring.     

The site of action of crossability genes (Kr 1, Kr 2) between Triticum and Secale. II. Proportion of pistils containing pollen tubes and effects of alternate pollination on seed set

Summary Different wheat genotypes (T. aestivum) were crossed with rye to ascertain the site or sites of manifestation of the crossability genes, Kr ₁ and Kr ₂. By using fluorescence microscopy, it was found that the order of increasing proportion of wheat micropyles containing pollen tubes is strongly correlated with the levels of crossability with rye. High crossable genotypes have more micropyles containing pollen tubes than those of the low crossable ones. Most of the inhibition or retardation of pollen tubes occurred between the style base and top of the embryo sac, expecially with the low crossable genotypes where both Kr-genes are present. The results also indicate that Kr ₁ is a greater inhibitor than Kr ₂. Seed set is also highly correlated with the number or proportion of micropyles having pollen tubes. Alternate pollinations seem to support the view that rye pollen tubes do not reach the micropyles of the low crossable genotypes, and hence when repollinated with wheat selfed seeds are produced.     

Incompatibility in diploid and tetraploid crosses of Cucumis sativus and Cucumis metuliferus

The African horned cucumber (Cucumis metuliferus Naud.; 2x = 2n = 24) contains genes that can confer resistance to many important cucumber (C. sativus L.; 2x = 2n = 14) pests [e.g., root-knotnematode, Meloidogyne incognita (Kofoid & White) Chitwood]. Cucumber is highly susceptible to this root-knot nematode species, and a recent screening of C. sativus accessions in the U.S. National Plant Germplasm collection did not identify sources of resistance. Thus,autotetraploids of Cucumis sativus and C. metuliferus were created to recover fertile resistant interspecific progeny. Autotetraploids were obtained at the highest rate when seeds were immersed in 0.5% colchicine for a period of 6 to 8 hrs. Treatment durations less than 6 hrs produced few tetraploids, and durations of 10 hrs or more were lethal to seeds or developing seedlings. Crosses between C. sativus and C. metuliferus were made using diploid and tetraploid lines in all possible combinations, including reciprocals. Fruit development occurred in crosses when diploid and tetraploid C. sativus were used as the female parent. However, seeds developed only in fruit of C. sativus (4n) ×C. metuliferus (2n) crossings. Seeds from these crosses, however,were flat and not viable. No fruit development occurred in crosses whereC. metuliferus was used as the female parent. This revised version was published online in August 2006 with corrections to the Cover Date.     

A tetraploid hybrid plant from 4x × 2x crosses in Vitis and its origin

To study the origin of unreduced (2n) gametes in diploid Vitis cultivars, we surveyed the occurrence of tetraploid hybrid seedlings from 40 interploid crosses with five tetraploid and seven diploid cultivars. A total of 250 seedlings from the interploid crosses were established through embryo culture and by seed sowing. In 20 2x × 4x crosses, no tetraploid hybrid seedlings were derived from 8,902pollinations. In 20 4x × 2x crosses, two tetraploid hybrid seedlings were obtained from 8,057 pollinations. Investigation of isozyme genotypes of the two tetraploid seedlings using three variable enzyme systems indicated that one of the two seedlings resulted from the union of a diploid egg with a 2n male gamete and that failure of second meiotic division resulted in the formation of the 2n male gamete. The percentage of giant pollen grains in `Muscat Bailey A', a pollen parent of the tetraploid seedling, was relatively high(about 5.9%) and 10.9% of the giant pollen grains germinated on agar medium. These results suggested that 2n pollen of diploid cultivars are useful for breeding tetraploid grape. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ploidy races in Actinidia chinensis

Summary Ploidy levels were examined in 26 accessions of Actinidia chinensis: 20 accessions were diploid (2n=2x=58) and 6 accessions were tetraploid (2n=4x=116). There was no evidence of variation in ploidy level within an accession. Our results are consistent with tetraploid A. chinensis coming from a restricted part of China.Interploid crosses within A. chinensis produced only low numbers of seedlings which were mainly triploid. Crossing hexaploid A. deliciosa with pollen of tetraploid A. chinensis produced a large family of plants and those checked were pentaploid.Counts on 83 genotypes of different ploidy levels (2x, 3x, 4x, and 5x) confirmed that the basic chromosome number in Actinidia is 29.     

Pollen germination and pollen tube growth following self-pollination and intra- and interspecific pollination of Medicago species

Summary Pollen germination and pollen tube growth after self- and intra- and interspecific pollinations of annual [M. scutellata (L.) Mill., M. disciformis DC., and M. rigidula (L.) All.] and perennial (M. sativa L.) Medicago species were studied using a Carl Zeiss microscope with a fluorescence filter attachment.Self-pollination of self-fertile annual and intraspecific pollination of cross-fertile perennials were characterized by high pollen germination and rapid normal pollen tube growth. In contrast pollen germination percentages were very low and many pollen tube growth abnormalities occurred following interspecific pollination and self-pollination of self-sterile plants. The time period from pollination to fertilization for interspecific crosses was about double that following self-pollination of the annual species. However, fertilization occurred frequently following interspecific pollinations. Much of the sterility was due to factor(s) operating after fertilization.Cooperative investigations of the Kansas Agricultural Experiment Station, Dept. of Agronomy and the U.S. Department of Agriculture, Agricultural Research Service. Contribution No. 82-582-J- Mention of a trademark name or proprietary product does not constitute a guarantee or warranty by the U.S. Department of Agriculture, and does not imply its approval over other products that also may be suitable.     

Production and meiotic pairing of intergeneric hybrids of Triticum × Dasypyrum species

Summary Crossing experiments between Dasypyrum villosum (2 x) and 14 taxa of Triticum sensu lato (seven diploids, five tetraploids and two hexoploids) were performed. Adult hybrids were obtained in all but three of the combinations with diploid species. A haploid plant was obtained from the combination T. aestivum x D. villosum. Cytogenetic data on the meiotic pairing in the intergeneric hybrids revealed that, in general, very little pairing occurred between the V genome of Dasypyrum and the different genomes in Triticum. There may be comparatively large differences in pairing behaviour in hybrids including different parental accessions, which shows that the Triticum as well as the Dasypyrum genotypes may influence the pairing. The combination T. aestivum x D. hordeaceum (4 x) was also produced and from the meiotic pairing in the hybrid it is evident that D. hordeaceum is an autoploid.     

Inheritance and transfer of multiple-flower character from Capsicum chinense into Capsicum annuum

Summary Capsicum annuum L. produces a single flower and thus a single fruit per branching node. In contrast, Capsicum chinense Jacq. yields two or more flowers per node. If genes for multiple-flowers per node could be transferred from C. chinese to C. annuum, it might be possible to breed C. annuum varieties with a more concentrated fruit set and potentially higher yield. Using progeny from an interspecific cross between C. annuum cv. NM 6-4 and C. chinense CA4, it has been determined that a minimum of five independently segregating chromosomal regions control the difference in flowering behavior between these two accessions. One of the segments is located on a translocated chromosome. Epistatic interactions among independent chromosomal regions appear to play a major role in the determination of this trait.Although it is unlikely that the multiple-flower character can be transferred to C. annuum in its full intensity while maintaining a horticulturally-acceptable phenotype, it may be possible to breed varieties which produce an average of more than 1.5 flowers per node, a value 50% higher than existing C. annuum varieties.