Allotetraploid Hybrids Research Articles

Allotetraploid hybrids between citrus and seven related genera produced by somatic hybridization

Allotetraploid hybrids between citrus and seven related genera produced by somatic hybridization

PATHWAYS OF BACKCROSSING ZINNIA ANGUSTIFOLIA × Z. ELEGANS INTERSPECIFIC HYBRIDS TO THE PARENTAL SPECIES

Allotetraploid Z. angustifolia × Z. elegans hybrids (2 n =46) were reciprocally backcrossed to Z. angustifolia (2 n = 22 or 44) and Z. elegans (2 n = 24 or 48). Pollen germination and pollen tube penetration of the stigmatic surface were observed for all 8 cross combinations. At 14 days after pollination, the percentage of florets with embryos ranged from 0 to 69%, and some hybrid embryos exhibited developmental abnormalities. Seed-propagated backcross (BC1) populations were generated with Z. angustifolia (2 n =44)as ♀ or ♂, and Z. elegans (2 n =48) as ♀ BC1 progeny from these 3 crosses demonstrated low to high levels of resistance to bacterial leaf and flower spot (incited by Xanthomonas campestris pv. zinniae) and high levels of resistance to powdery mildew (incited by Erysiphe cichoracearum). BC1 hybrids derived from crossing allotetraploid hybrids as ♀ and Z. elegans (2 n =48) lines have commercial potential as disease-resistant, flowering annuals.

Notch is required for successive cell divisions in the developing Drosophila retina

Following activation by UV-irradiated sperm, diploid eggs of the allotetraploid hybrids (red crucian carp ♀×common carp ♂) developed into normal live gynogens. Cold-shocking these activated diploid eggs failed to induce the expected tetraploidy in them. All these gynogenetic progenies, generated with or without the cold shock, were female diploids with 100 chromosomes, indicating the XXXX genotype of the tetraploid females. The gynogenetic females matured at the age of 2+ suggesting delayed maturity, in comparison to the diploid females of the red crucian carp. Thirty percent of these gynogens were fertile with normal ovary and mature eggs. These gynogens were not morphologically distinguishable from the F2 hybrids. Like the diploid F2 hybrids, these diploid gynogens produced diploid eggs, for these eggs developed into triploids with 150 chromosomes, when crossed with red crucian carp. Without the treatment for doubling the chromosome number, the diploid eggs, produced by the F1 gynogens, developed into the F2 gynogens following activation by UV-irradiated sperm. Production of these diploid eggs from the diploid gynogens may have resulted from the pre-meiotic endoreduplication of chromosomes. For aquaculture, these diploid eggs remain an important gamete source for the production of tetraploids and triploids, and establishment of diploid gynogenetic hybrid line.

Intergeneric somatic hybrid plants from sexually incompatible woody species: Citrus sinensis and Severinia disticha

The fusion of Citrus sinensis cv. Hamlin (sweet orange) protoplasts isolated from an embryogenic suspension culture with Severinia disticha (Philippine box orange) protoplasts isolated from epicotyl-derived callus with organogenic potential, resulted in the regeneration of allotetraploid somatic hybrid plants. Plant regeneration was a function of complementation, combining the capacity for somatic embryogenesis of C. sinensis with the organogenic ability of S. disticha. Confirmation of somatic hybrid identity was based on leaf morphology, chromosome number, and analyses of phosphoglucose mutase (PGM) and malate dehydrogenase (MDH) zymograms. Hybrid plants were multiplied organogenically and exhibited morphology intermediate to that of the parents. This is the first example of somatic hybrid plants produced between sexually incompatible woody genera.

The production of alien monosomic additions in Beta vulgaris as a source for the introgression of resistance to beet root nematode (Heterodera schachtii) from Beta species of the section Patellares

Experiments were carried out for adding the chromosome carrying resistance to beet root nematode (Heterodera schachtii) from the wild Beta species of the section Patellares (B. procumbens, B. webbiana and B. patellaris) to the genome of B. vulgaris. Preliminary experiments indicated that crosses between the wild species and B. vulgaris cultivars of the mangold type yielded on average more viable F1 hybrids than crosses with sugar and fodderbeet. However, crossability varied strongly between individual parental combinations. It was concluded that most types of B. vulgaris can be hybridized with the wild species of the section Patellares if a sufficient number of pair-crosses is made. Crosses between diploid cultivars or species of the section Vulgares and diploid wild species of the section Patellares yielded many hybrids which, however, were highly sterile. From crosses between tetraploid B. vulgaris and the wild species a great number of viable allotriploid and allotetraploid hybrids was obtained. In the backcross progenies of allotriploid hybrids 26% alien monosomic additions occurred, of which 4.1% carried the resistance bearing chromosome of B. procumbens or B. patellaris. The programme will be continued by sereening progenies of the resistant monosomic addition plants for the occurrence of resistant disomic introgression products.

The effect of chromosome doubling on fertility, meiotic behaviour and crossability of Solanum etuberosum × S. pinnatisectum

Doubling the chromosome number of sterile F1 hybrids of S. etuberosum × S. pinnatisectum resulted in fertile allotetraploid hybrids (code 4x-EP) with nearly normal chromosome pairing at meiosis. Many seeds were obtained from selfing and sibbing, but seed set varied considerably. The 4x-EP hybrids were successfully crosses as females with S. stoloniferum and S. polytrichon and as males with S. verrucosum. The crosses with S. stoloniferum and S. polytrichon were carried out reciprocally and unilateral incompatibility was detected. Crosses of 4x-EP hybrids as males onto S. phureja and S. tuberosum cv. Gineke produced parthenocarpic berries only. Nearly 1700 flowers of colchicine-doubled S. pinnatisectum × S. bulbocastanum and the trispecific hybrid (S. acaule × S. bulbocastanum) × S. phureja did not yield a single berry after pollination with a pollen mixture from 20 4x-EP plants.

Cytology and digoxin production in hybrids between Digitalis lanata and D. grandiflora

Digitalis lanata is the only commercial source of the cardiac glycoside digoxin. It is an outbreeder and displays considerable variation. An attempt to increase uniformity was made by making D. lanata × D. grandiflora diploid hybrids and from these produce allotetraploid hybrids using colchicine treatment. Such tetraploid plants would be homozygous. Tetraploid hybrids were shown to contain digoxin but at lower levels than in D. lanata. Progeny of selfed tetraploid hybrids were significantly more uniform than D. lanata grown from commercial seed, but were considerably less vigorous.

Transmission of B-Chromosomes in Dactylis

Summary In diploid and autotetraploid Dactylis glomerata ssp. lusitanica and its allo-tetraploid hybrids with D. glomerata ssp. glomerata, B-chromosomes undergo non-disjunction and preferential segregation to the generative nucleus at first pollen mitosis. This results in transmission by male gametes of double the number of B-chromosomes received by the microspore at completion of meiosis. This mechanism of numerical increase is similar to that reported for a number of other species of Gramineae. On the female side, transmission of B-chromosomes is normal.

CYTOGENETIC STUDIES OF ALLOTETRAPLOID HYBRIDS OF MAIZE AND PERENNIAL TEOSINTE

Shaver, Donald L. (Brookhaven Natl. Lab., Upton, New York.) Cytogenetic studies of allotetraploid hybrids of maize and perennial teosinte. Amer. Jour. Bot. 49(4): 348–354. Illus. 1962.—Euchlaena perennis (4n), “perennial teosinte,” was less fertile when pollinated with 4n Zea mays than when selfed. Cross fertility between the 2 genera was influenced by the particular maize stock involved. Chromosome numbers varied from 36 to 43 in a population of 4n maize maintained by interpollination without regard to chromosome number. In the 4n intergeneric hybrid, nearly every chromosome number from 29 to 44 was found. The expression of the perennial growth habit varied with the proportion of perennial teosinte germ plasm present. Triploid hybrids with 2 perennial teosinte genomes and 1 maize genome were usually perennial. Tetraploid hybrids having 2 genomes of each parent were usually not fully perennial. Tetraploid hybrids with only 1 perennial teosinte genome had no perennial tendency but had a strong tendency to tiller. As compared with autotetraploids of maize having the same genetic markers, intergeneric hybrids showed a highly significant degree of preferential segregation for each of the 12 marker genes studied. In the opinion of the author, these data may represent the best available measure of the relationship of maize to teosinte, and are considered to support the proposal of Reeves and Mangelsdorf that maize and teosinte are congeneric.