Hexaploid Level Research Articles

THE EVOLUTION OF THE PHENOL COLOUR REACTION GENE IN WHEAT

Phenol reaction of the seeds in a number of varieties of the diploid species having AA, BB, DD genomes and the tetraploid and hexaploid species having the genomic constitution AABB and AABBDD has been studied. Among the diploid species all the six varieties of T. monococcum (AA) and two of T. boeoticum (AA) have shown black reaction. All the varieties of Ae. speltoides (BB) and Ae. squarrosa (DD) have shown white reaction. A variety of reactions ranging from black, brown to white has been shown by the varieties of tetraploid and hexaploid wheats. It has been concluded that ‘A’ genome is. the source of origin of the phenol reaction gene in the emmers and bread wheats. A variety of reactions in the tetraploid and hexaploid levels might have been brought about by mutation and recombinations. Plausible ways of origin of T. zhukovskyi, having supposed genomic constitution AAAABB from T. timopheevi have been discussed in view of the presence of a desynaptic mechanism in the latter and the phenol colour reaction in both of them.

Genetic variability in quantitative characters induced by thermal neutron treatment of diploid, tetraploid and hexaploid oat seeds

Seed lots from 5 oat varieties (Saia, a diploid; P.I. 193958, a tetraploid; and Andrew, Burnett and Pusa, hexaploids) were treated with thermal neutron irradiation, to provide materials for comparing the relative magnitude of variability and the types of mutations induced at different ploidy levels. We grew 40 lines derived from each irradiated population, and a like number from check populations, in a replicated experiment and measured them for heading date, plant height, number of branches per panicle, flag-leaf length, weight per 100 seeds, groat width and groat length. For a few attributes, irradiation treatment caused a significant shift in the population means, and variability was increased for most of the attributes. In general, variability was shifted in both plus and minus directions from the check population means. At the hexaploid level, the mean induced variability from all attributes as measured by genetic coefficients of variation was as great as or greater than that at the tetraploid and diploid levels. Comparisons of the characteristics of the seed-attribute frequency distributions from irradiation derived and check populations tended to show that: (a) mutations occurring in diploid lines produce more discrete expression than those occurring in hexaploids; and (b) a larger portion of hexaploid than diploid lines carry mutations which show some degree of expression. The presence and/or magnitude of genetic variability induced was influenced by the attribute studied, and the genotype treated. No genetic variability was induced for number of branches (except in Pusa variety) and for flag-leaf length; among the hexaploid varieties, Pusa showed nearly twice as much relative variability as the other two varieties. The genetic correlations indicated that the types of mutations induced by irradiation in hexaploids are similar to those induced in diploids; thus, induced genetic variability in hexaploids should be as heritable as that in diploids. Thermal neutron irradiation increased sterility in two of the treated populations. However, there was no evidence that sterility contributed to the apparent induced variability. Intrapopulation correlations, calculated between groat width and sterility, were not significant.

BIOSYSTEMATIC STUDIES IN THE BOUTELOUA CURTIPENDULA COMPLEX. III. POLLEN SIZE AS RELATED TO CHROMOSOME NUMBERS

Pollen size statistics are presented for 10 closely related species of Bouteloua and relationships between pollen size and chromosome numbers are presented for 13 populations of 5 species and 3 varieties. With 1 exception, all populations of all taxa conformed to a general pattern of pollen size dependent upon chromosome number. Chromosome numbers varied from 2n = 20 to 2n = ca. 103, with several independent aneuploid series. Statistical analyses were made of pollen size as related to chromosome number in the 3 varieties of B. curtipendula. These data showed that tetraploids (2n = 40) of var. tenuis had significantly greater pollen size and coefficient of variation than diploids (2n = 20) of the same variety. Similarly, aneuploids of var. curtipendula with 2n = 45 to 2n = 64 chromosomes had significantly larger and more variable pollen than tetraploids (2n = 40) of the same variety. Highly significant positive regression coefficients were obtained from analyses of chromosome numbers and mean pollen size, and chromosome numbers and coefficient of variation, for var. curtipendula. Regression coefficients for var. caespitosa populations with chromosome numbers over the hexaploid (2n = 60) level were not significant.

Biosystematic Studies in the Bouteloua curtipendula Complex. III. Pollen Size as Related to Chromosome Numbers

Pollen size statistics are presented for 10 closely related species of Bouteloua and relationships between pollen size and chromosome numbers are presented for 13 populations of 5 species and 3 varieties. With 1 exception, all populations of all taxa conformed to a general pattern of pollen size dependent upon chromosome number. Chromosome numbers varied from 2n = 20 to 2n = ca. 103, with several independent aneuploid series. Statistical analyses were made of pollen size as related to chromosome number in the 3 varieties of B. curtipendula. These data showed that tetraploids (2n = 40) of var. tenuis had significantly greater pollen size and coefficient of variation than diploids (2n = 20) of the same variety. Similarly, aneuploids of var. curtipendula with 2n = 45 to 2n = 64 chromosomes had significantly larger and more variable pollen than tetraploids (2n = 40) of the same variety. Highly significant positive regression coefficients were obtained from analyses of chromosome numbers and mean pollen size, and chromosome numbers and coefficient of variation, for var. curtipendula. Regression coefficients for var. caespitosa populations with chromosome numbers over the hexaploid (2n = 60) level were not significant.

CYTOGENETIC STUDIES IN THE GENUS HORDEUM VI. THE MURINUM-COMPLEX

Horclez~nt 7~zzni1zz~nq, the ubiquitous species common to most of Europe and Western Asia, call also be found in many parts of North and South America and Australia. It and two other species, H. lepori~zuwz, another tetraploid, and H . glnucz~~n, a diploid, all having remarltably similar morphological features, are frequently referred to as the murhzz~m-complex (Covas, 1949, and Morrison, 1958). In 1960 W. M. Bowden, Plant Research Institute, Ottawa, received seed samples labelled H. nzz~rinz~m from Turlcey and Afghanistan which had 2n = 42 cl~romoson~es. This new form increased the number of species in the con~plex to four and the chromosonle number to the hexaploid level. The most striking feature of the coinplex is that the plants look very much alike. Therc has, therefore, been much confusion in classification although there are minor differences as shown by IVlorrison (1958). H e also clearly showed that both H . ~ ? T z L ~ ~ ' I ~ z L ~ ~ z and H . leporhzum are allotetraploids. Previous lists of chromoson~e numbers had indicated that H. 7mninum was a diploid (Hubbard 1954), an error that led Covas (1949) to propose that H. lepori1zzr7/1 was an allotetraploid derivative of H. glaz~cz~nz and H. muri7zzmz. The purpose of this study is to clarify the status of the various species, to learn about their interrelationships and to find genetical explanation for thc inorpl~ological uniformity of species in the complex. This is also the first paper in this series which deals with a group of Old World species of Hordenzuz. Since the approach is primarily cytogenetic, hybrids were produced among the four species to study their infertility and chromosome relationships.

Comparative Gene Analysis of Common Wheat and its Ancestral Species, I. Necrosis

1) It has been known that complementary necrosis in common wheat is mainly controlled by three genes, Ne1 located in chromosome 5B (V), Ne2 in 2A (XIII)and Ne3 in 3D (XVI). However, the B1 and F2 data from the cross T. macha subletshchumicum ×T. aestivum Chinese Spring indicated that a recessive gene in addition to the above-mentioned genes must be considered regarding the expression of necrosis.2) Relationships among various varieties of common wheat concerning necrosis are represented in the diagram of Fig. 2.3) Distribution of the three major genes in common wheat and its ancestors, Emmer wheat and Ae. squarrosa, was investigated using T. aestivum Prelude (Ne1ne2Ne3), T. aestivum Kharkov (ne1Ne2Ne3) and T. macha subletshchumicum (Ne1Ne2ne3) as test varieties.In Emmer wheat a majority of varieties were found to have the genotype Ne1ne2, while minor fractions were either ne1ne2 or Ne1Ne2.All strains of Ae. squarrosa so far tested had Ne3.In common wheat, most varieties were either ne1ne2Ne3 or ne1Ne2Ne3, while a small fraction were Ne1ne2Ne3. One variety only was found to be Ne1ne2ne3 and another only one to be Ne1Ne2ne3, both belonging to T. macha.4) From these results, the genotypes of Emmer wheat, that supplied the AB genomes to common wheat, are assumed to be Ne1ne2 or ne1ne2. T. dicoccoides spontaneo-nigrum, some forms of T. dicoccum, T. turgidum, T. persicum and T. orientale, and many varieties of T. durum have these genotypes.The donor of the D genome to common wheat must have possessed Ne3. All strains of Ae. squarrosa so far tested had this allele.5) The presumable hexaploid progenitor must have had either Ne1ne2Ne3 or ne1ne2Ne3. In common wheat, some forms of T. spelta, T. sphaerococcum, T. compactum and T. aestivum have these genotypes. T. macha, that is an exception in possessing the ne3 allele, is considered to be an isolated species among the hexaploids and seems not to have contributed to the origin of common wheat.6) It is suggested that Ne2 in common wheat originated at the hexaploid level rather than to have been derived from Emmer wheat. Possibility of selective advantage of Ne2 and disadvantage of Ne1 at the hexaploid level is suggested.

Cytogenetic relationships of certain artificial and natural species of Avena

1. The desirability of employing the genetic variation present in diploid and tetraploid wild species for the improvement of the cultivated hexaploid species stimulated an investigation into the synthesis of various amphiploid forms in Avena.2. Five amphiploids at the hexaploid level have been produced, but the present investigation is limited to the amphiploids developed from the cross A. barbata (2n = 28)×.A. strigosa subsp. hirtula (2n= 14), their hybrids with the natural hexaploid species and with other amphiploid types.3. These amphiploids, like their parents, possessed black paleae, with hairs and a fairly strong geniculate awn on both the lower and upper grains. The bases of both the lower and upper grains possessed the articulation surfaces characteristic of A. fatua. Their hybrids with A. fatua were similar in spikelet morphology, but the A. sterilis type of spikelet was dominant in both the amphiploid 6x × A. sterilis and amphiploid 6x × A. byzantina. Partial dominance of the cultivated type base over the shedding type was evident in crosses with A. sativa and A. nuda but the naked caryopsis and multiflorous spikelet were recessive in the latter cross. In crosses between the A. barbata/A. hirtula 6x amphiploid and the A. abyssinica/A. strigosa 6x amphiploid (Cc 4387) the hybrid exhibited a reversal of dominance relationships, with the cultivated base type of Cc4387 being completely recessive to the shedding base.

Allopolyploidy in the Melaniid Snails

IN a recent communication1, I recorded the occurrence of apomictic parthenogenesis combined with polyploidy in a few species of Melanoides. One of these species, Melanoides tuberculatus, includes a diploid race with 2n = 32 chromosomes and a polyploid race with 90–94 chromosomes, which thus appears to be more or less at the hexaploid level when compared to the former. Both these races are parthenogenetic, but in the latter there occur exceptional males which are sterile, constituting about 3 per cent of the population. The males show evidence of structural and numerical hybridity in the occurrence of bridge and fragment in the meiotic divisions and in the presence of non-pairing univalents with irregular distribution in the first meiotic metaphase and anaphase.