Cultivated Tetraploids Research Articles

Characteristics of 2N pollen producing triploid hybrids betweenSolanum stoloniferum and cultivated diploid potatoes

Segregants which produce 2n pollen were identified inSolanum stoloniferum and hybridized with 2n pollen producing cultivated diploids. A number of the resulting triploids produced 2n pollen, ranging from less than 1 up to 7.6%. Parallel spindles at Anaphase II were shown to be the probable meiotic mechanism responsible for 2n pollen production. Thus the genetic consequences are equivalent to first division restitution. This 2n pollen produced by triploids should facilitate transfer of genes from wild allotetraploids to cultivated tetraploids. There should be increased gene exchange between nonhomologous wild and cultivated genomes during microsporogenesis of the triploids. This methodology should have merit in crosses with allotetraploid species in the Series Longipedicellata and Acaulia.

Spike type in two cultivars of Triticum dicoccum with the spelta gene q compared with the Q-bearing variety liguliforme.

The vulgare-spelta locus on chromosome 5A of two typical cultivars, Large White emmer and Vernal emmer, of Triticum dicoccum SCHUBL., a species of tetraploid wheat (2n=28. AABB) with keeled glumes and brittle rachis, was genetically studied by crossing them to aneuploid lines of T. aestivum (L.) THELL. ssp. vulgare MK (2n=42, AABBDD). It was found that they have the spelta gene, q Thus, for these two cultivars, a previous assumption, which had been made mainly on the basis of plant morphology, was verified. The differentiation of spike type was rationalized between these varieties and another variety, liguliforme, which had previously been found to carry the vulgare gene, Q. It turns out that the rachis brittleness, a key character to distinguish dicoccum from the rest of the cultivated tetraploids, may not be determined simply by the presence of the spelta gene, q. Besides spike type, glume-coloration pattern is found to be a major difference between the two groups.

Inheritance of Fruit Size in the Cultivated Tetraploid Blackberry [Rubus (Tourn.) L. subgenus Eubatus

Abstract Twelve seedling populations involving large, intermediate, and small-fruited parental clones of tetraploid blackberries were evaluated for fruit size inheritance. The amount and type of variation and the significant deviations from the mid-parent means in seedling distributions indicated that inheritance was quantitative with partial dominance for small fruit size. Maximum heritability, estimated by the genetic variance/phenotypic variance, was 0.76. Narrowsense heritability, estimated by regressing progeny on the mid-parents, was 0.62, indicating that most of the genetic variability (82%) was transmittable through the sexual cycle (gametes). These results suggest that simple breeding procedures based on inter-mating parent clones selected on the basis of their phenotypic performance are likely to produce significant genetic gains in fruit size of blackberries.

Genetics of D3 complementary lethality in Gossypium hirsutum and G. barbadense

The diploid taxon, Gossypium davidsonii Kell., induces embryonic or seedling lethality in crosses with most Gossypium taxa, including the cultivated tetraploid species, Gossypium hirsutum L. and Gossypium barbadense L. Selection of a cross-compatible stock of G. barbadense, 15-4, made possible a study of the genetics of lethal complementation between G. davidsonii and the cultivated tetraploids. Two factors, Le1 and Le2, were identified in the stocks examined. Two other cottons, both G. hirsutum, were apparently monomeric for complementary lethal factors, one displaying evidence of being homozygous for Le1 and the other homozygous for Le2. The 15-4 line was assigned the genotype le1le1le2le2, and G. davidsonii harbors at least one allele, Ledav.

2n pollen formation via parallel spindles in the potato cultivar sebago

Parallel spindles occur during microsporogenesis in the cultivar Sebago (2n=4x =48) and are the basis of 2n pollen production in this clone. The relations between the frequencies of parallel spindles, 2n microspores, and 2n pollen are striking. The predicted frequency of 2n pollen based on the percentage of microsporocytes with parallel spindles is highly correlated with the frequency of 2n pollen observed. The percentage of 2n microspores at the sporad stage also corresponds very closely with the observed percentage of 2n pollen. Sebago is thus nulliplex (psp sp sps) for the meiotic mutant which governs spindle orientation at the second meiotic division in microsporocytes. This finding agrees with the prediction that if parallel spindles were involved in the origin of cultivated tetraploid potatoes, the genesps should be present in some 4x cultivars. It adds further support to the concept that 2n gametes have been a creative factor in the origin and evolution of cultivated tetraploids.

Dry Matter and Morphological Responses to Temperatures of Alfalfa Strains with Differing Ploidy Levels1

AbstractAlfalfa (Medicago sativa L.) is grown in a diversity of temperature areas, but there is little information on the response to temperature of strains of different ploidy levels. The objective was to study the response of alfalfa strains of 2x, 4x, and 6x levels of ploidy when grown at three different temperature levels. Plants were grown from seed in pots of soil in three growth chamber regimes; hot (H) 33 C day/24 C night, warm (W) 27/18 C, and cool (C) 21/12 C. All chambers had 18‐hour daylengths. Plants were harvested with two schedules; (i) by date (43 days after seeding) and (ii) by maturity (at first flower). First flower stage generally was delayed as temperatures decreased. The 2x was the first strain to flower in the H and W regimes and 4x in the C regime, while the 6x strain was last to flower in all regimes. At the 43‐day harvest, shoot height and weight of plant parts for each strain generally were highest in the W regime, followed in order by the H and C regimes. Weights of plant parts at first flower for each strain generally were highest in the C regime, followed in descending order by the W and H regimes, except that 6x yielded least in W. Highest herbage growth rate at first flower was in the C regime for the 2x and in the W or C regime for the 4x, while the rate was similar at all temperatures for the 6x. Total plant growth rates (herbage plus roots) of all three strains at first flower were highest in the C regime followed in descending order by the W and H regimes, except 6x was similar at H and W. Leaf area, leaf weight, and specific leaf weight (SLW) generally increased as temperature decreased. However, leaf area of 2x cut by date and SLW of fix cut at first flower were lowest in W rather than H regime. Thus, the strains reacted differently to temperature. The 2x appeared to grow best in the C regime and the 4x in either the W or C regime. The 6x showed a broad adaptation to temperatures, growing about the same at all temperatures. Development of alfalfas with different ploidy levels than the cultivated tetraploids may be a means of obtaining cultivars with broader temperature adaptation or with better adaptation to low or high growing temperatures.

Wild Cotton in Northeast Brazil

Some additional localities for a wild tetraploid cotton, G. musteliinum Watt, in northeast Brazil are reported, together with field observations on this cotton in its natural habitats. The history of cotton cultivation in northeast Brazil is reviewed and G. mustelinum compared with cottons cultivated in the region from early Colonial times onward. G. mustelinum appears to be specifically distinct from the other tetraploid cottons, and it is not likely that it is a feral derivative of any commercially cultivated cotton. This little-known tetraploid may help in reconstructing the origin of the New World polyploid cottons. THE NEW WORLD CULTIVATED COTTONS, Gossipium hirsutum and G. barbadense, are tetraploids (2n=4x_52) which contain the A genome found in the Old World diploids G. herbaceum and G. aiboreum and the D genome found in American wild diploids. In both the cultivated tetraploids and the A genome diploids the hairs on the seed coat are differentiated into long lint hairs, which become twisted on drying and can thus be spun into thread, and an undercoat of short hairs (fuzz), which have more extensive cellulose thickening and which do not twist on drying. The D genome diploids have seed hairs of various sorts but never bear lint and have never been used by man for fiber. At one time it was thought that man had introduced a domesticated, linted A genome cotton from the Old World to the New, where it hybridized with a native D diploid to produce the tetraploids. Gerstel (1953) showed that G. herbaceuin chromosomes were more similar to those of the New World A genome than were those of G. arboreum, although even G. herbaceum chromosomes differed from the A genome of the tetraploids by two translocations. At present it seems that the diploid most similar to the A genome progenitor of the tetraploids is G. herbaceum var. africanum, a linted, hard-seeded cotton that occurs wild in southern Africa. The D genome diploids are today confined to the western sides of the American continents. The Mexican species, together with G. klotzschianum var. davidsonii from the Galapagos Islands, form a group fairly closely related among themselves but more distantly related to the Peruvian species G. raimondii (Phillips 1966). G. rairnondii is the species most similar to the D genome ancestor of the tetraploids on the criteria of morphology of the seed hairs (Hutchinson, Stephens, and Dodds 1945) and chromosome pairing and chiasma formation in hybrids with the tetraploids (Phillips 1963, 1966). Furthermore, electrophoretic studies on seed proteins have shown that a synthetic mixture of proteins from G. raimondii and G. herbacweum var. africanum gave very similar banding patterns to proteins from G. hirsutum and G. barbadense (Cherry, Katterman, and Endrizzi 1970). However, although G. raimondii is the most similar extant diploid to the D genome ancestor of the tetraploids, there are more dissimilarities between the chromosomes of G. raimondii and the tetraploid D genome than there are between G. herbaceum and the tetraploid A genome (Phillips 1963). Today the ranges of the A and D genome diploids are separated by some thousands of miles (see map, fig. 1), and the origin of the tetraploids poses a considerable phytogeographic problem. Cytogenetic data (Phillips 1963) suggested that the tetraploids are derived from a common ancestor (i.e. originated monophyletically) and that speciation occurred after the tetraploids were established. The different genome groups in Gossypiurm may have diverged when the range of an early prototype cotton became fragmented when Gondwanaland broke up into the land masses which correspond to the southern continents of today. This separation probably began in the early Cretaceous (Raven 1972). The first records of tetraploid cottons are archaeological specimens of domesticated (not wild) cot1 Present address: Department of Botany, University of California, Berkeley, California 94720 U.S.A. 42 BIOTROPICA 7(1): 42-54 1975 This content downloaded from 157.55.39.110 on Tue, 20 Sep 2016 05:48:05 UTC All use subject to http://about.jstor.org/terms

Chromosome Manipulations in Alfalfa: Scaling the Cultivated Tetraploid to Seven Ploidy Levels1

The general scheme used in scaling genomic multiples down and up in ploidy is summarized, and a specific case of scaling chromosomes of a single cultivated alfalfa (Medicago sativa L.) clone to seven ploidy levels is reported. Cultivated tetraploids were scaled down to the diploid level by haploidy. Scaling upward was accomplished by sexual polyploidization, colchicine chromosome doubling, and spontaneous doubling in tissue cultures. The resulting ploidy series is diploid, triploid, tetraploid, pentaploid, hexaploid, heptaploid, and octoploid. For the single clone, this is the greatest range in ploidy levels known to have been produced with the chromosomes of a single individual. It demonstrates the plasticity of the autopolyploid genome of alfalfa and its ability to function at extremes of polyploidy. It further demonstrates how gene flow can be accomplished in a polyploid series through interploid crosses and bridge crosses. Such gene flow may prevent autopolyploids from becoming dead ends in evolution and isolated in breeding programs. Data on seed size at 2x, 4x, and 8x levels are also reported.

Fertility improvement in autotetraploid sorghum. 3. Yields of cultivated tetraploids

The development of tetraploid grain sorghum as a crop plant continues to show promise. Yields from bulk populations and lines withdrawn from such populations are now approaching levels realised by good diploid varieties. It seems that tetraploid grain sorghum populations in which high levels of recombination are attained by the use of the genetic male-sterile ms 3, should respond profitably to the application of recurrent selection.

Isolation of Haploids of Tetraploid Alfalfa1

Isolation of 178 haploids (2n=2x=16) of tetraploid alfalfa (2n=4x=32) by the 4x−2x cross method is described. Haploids were obtained from 28 out of 34 tetraploid seed parents, indicating most cultivated tetraploids are capable of haploid production. Seed parents varied in haploid frequency from 0 to 10 haploids per 1000 flowers pollinated with diploid pollen. The diploid pollinator also affected the frequency of haploids. Use of a seedling marker and distinctive morphological characteristics of haploids minimized the number of plants on which chromosome counts were required. Screening for spontaneously occurring haploids in breeding populations and in twin seedlings was inefficient. The potential use of haploids in alfalfa research was discussed.