Cytogenetics off interpopulation Cuphea lanceolata hybrids

Cuphea lanceolata Ait. (Lythraceae) is an annual diploid (x = 6) with medium-chain fatty acid rich seed oils. Wild C. lanceolata populations are classified as C. lanceolata f. silenoides or C. lanceolata f. lanceolata on the basis of flower pigment differences. Although these taxa are taxonomically close, their interfertility has not been demonstrated. We describe meiotic phenomena underlying the sterility of hybrids between C. lanceolata f. silenoides (LNS-43) and C. lanceolata f. lanceolata (LNC-78) populations. We assayed metaphase and anaphase I microsporocytes of the parent and hybrid populations. The hybrids were female and male sterile. The mean percentage of stainable pollen was 94.9% for the parents and 1.1% for the hybrids. Chromosomes paired and disjoined normally in the parents (LNS-43 and LNC-78) and abnormally in the hybrids (LNS-43 x LNC-78 and LNC-78 x LNS-43). Univalents, unequal chromosome distributions, and laggards were observed in the hybrids. The mean number of univalents per cell was 0.00 for the parents and 5.95 for the hybrids, the mean number of bivalents per cell was 6.00 for the parents and 1.51 for the hybrids, and the mean number of chiasmata per cell was 9.19 for the parents and 4.04 for the hybrids. The most frequently observed (75%) anaphase I chromosome distribution for the hybrids was 7:5:0 (pole-pole-laggards). The genome affinities of the hybrids were half those of the parents (a mean of 0.5 for the hybrids as opposed to 1.0 for the parents). Although C. lanceolata f. silenoides and C. lanceolata f. lanceolata freely hybridize, their progeny are sterile, and the genetic diversity of LNC-78, and perhaps of C. lanceolata f. lanceolata as a whole, cannot be accessed through hybrids with C. lanceolata f. silenoides or C. viscosissima.

Determination and evaluation of the sequence and textural effects of the puroindoline a and puroindoline b genes in a population of synthetic hexaploid wheat

Aegilops tauschii (2 n=2 x=14, DD) is a rich source of genetic variability for hexaploid wheat ( Triticum aestivum, 2 n=6 x=42, AABBDD) improvement. This variability can be accessed through utilizing synthetic hexaploid wheat lines, which contain genomes from Ae. tauschii and T. turgidum (2 n=4 x=28, AABB). Numerous desirable characteristics can and have been introgressed into common hexaploid wheat with this germplasm. In this work, the genetic variability in the two puroindoline genes (a and b) contained on the D genome, and the relationship that sequence polymorphisms in these genes have on endosperm texture among a population of 75 CIMMYT synthetic hexaploid accessions is described. Kernel texture was evaluated using the single kernel characterization system (SKCS). Kernel texture differed significantly ( P<or=0.0001) among the synthetic hexaploid accessions (range 2.6-40.9) and the parent types, durum or Ae. tauschii. The interaction term between parent types was also a significant effect ( P<or=0.0001). In addition to the 'wild-type' protein sequences of the puroindoline genes (those present in 'Chinese Spring' and all other soft wheats), three other translated sequences were identified in puroindoline a and two others in puroindoline b. These protein sequences were associated with significantly ( P<or=0.0001) softer endosperm textures than the wild-type protein sequences. As the softer alleles are expressed in a hexaploid background, they are immediately available to wheat breeding programs.

Meiosis in allopolyploids -- the importance of 'Teflon' chromosomes

Polyploids possess two or more sets of related chromosomes as a result of either the doubling of chromosomes following sexual hybridization within the same species (autopolyploidy), or between closely related species containing related but not completely homologous (homoeologous) genomes (allopolyploidy). For allopolyploids to produce viable gametes and be fertile, they must behave as diploids during meiosis, so that only identical chromosomes (homologues) pair. A solution to this problem is an enhanced ability to resolve incorrect pairing, which in turn promotes correct pairing. This gives nonhomologous chromosomes an almost 'Teflon'-like status, so that only the correct pairs 'stick'.

Origin, evolution and genome differentiation in Guizotia abyssinica and its wild species

Guizotia abyssinica, G. schimperi and G. scabra are diploid species (2n=2x=30) characterised by 15 bivalents during prophase-I/metaphase-I of meiosis. The former species is cultivated whereas the latter two are wild. Interspecific hybrids between these three species were generated and the F1 hybrids were analysed to assess cytogenetic relationships and crop evolution within the genus Guizotia. Meiotic chromosome configurations at diakenesis/metaphase-I in the pollen mother cells of hybrids averaged 0.25I + 14.60II + 0.15IV for G. abyssinica x G. schimperi, 0.05I + 13.6II + 0.14III + 0.58IV for G. abyssinica x G. scabra, and 0.8I + 12.7II + 0.08III + 0.88IV for G. schimperi x G. scabra. Based upon the results of our investigations we conclude that the genomes of G. abyssinica and G. schimperi are similar and homologous, whereas the G. scabra genome is only partially homologous to that of G. abyssinica/G. schimperi. Furthermore, the crop species G. abyssinica might have originated from G. schimperi through selection and cultivation; chromosome translocations appear to have played a significant role in the divergence and differentiation of these three species.

The 'A' genome donor of Eleusine coracana (L.) Gaertn. (Gramineae)

In an attempt to discover 'A' and 'B' genome donor(s) to finger millet, Eleusine coracana, or its progenitor species, E. africana (both allotetraploid 2n=4x=36), five diploid species, E. Indica, E. Floccifolia, E. multiflora, E. tristachya and E. intermedia, were crossed to finger millet and its progenitor taxon. Crosses were successful only with E. coracana. Three combinations of triploid hybrids E. coracana x E. indica, E. coracana x E. floccifolia, and E. coracana x E. multiflora were obtained and analysed. Meiotic behaviour was perfectly normal in parental species. The regular number of 18 bivalents in E. coracana, 9 bivalents in E. indica, E. intermedia, E. tristachya and E. floccifolia and 8 bivalents in E. multiflora were invariably noticed. In E. coracana x E. indica hybrids a mean chromosome pairing of 8.84I+8.80II+0.03III+0.10IV per cell was found. About 86.5% of the cells showed the typical 9I+9II configuration, suggesting that E. indica (AA) is one of the diploid genome donors to cultivated species E. coracana. A mean chromosome pairing of 11.08I+7.63II+0.16III+0.04IV per cell was found in E. coracana x E. floccifolia hybrids. Two to ten bivalents and varying numbers of univalents were seen in 55% of the cells. About 45% of the cells showed the 9I+9II configuration. Various evidence suggests that perennial E. floccifolia is a primitive member of the 'A' genome group of Eleusine species, and it may not be a genome donor to E. coracana. In E. coracana x E. multiflora hybrids (2n=26) mean chromosome pairing of 21.45I+1.97II+0.13III+0.04IV per cell was found. About 91% of the cells were observed to have 20-26 univalents. Only a small percentage of the cells contained bivalents or multivalents. This pairing behaviour indicates that E. multiflora lacks genomic homology with the 'A' or 'B' genome of E. coracana. Genomically E. multiflora is a distinct species and a genomic symbol of 'C' is assigned to it. Identification of the 'B' genome donor species to cultivated millet. E. coracana remains elusive.

Developments in the meiotic analysis of hybrids. I. Review of theory and optimization in triploids

The theory, construction and optimization of a model of chromosome pairing in triploid hybrids are re-examined and the model reconstructed. A new approach to optimization is described that removes a bias in the estimation of x, the measure of relative affinity, by weighting the observed and calculated meiotic figure frequencies by the number of chromosomes in each figure type. The amended analysis is compared with its antecedent and with other models.

Metaphase I bound arms frequency and genome analysis in wheat-Aegilops hybrids : 1. Ae. variabilis-wheat and Ae. kotschyi-wheat hybrids with low and high homoeologous pairing

Meiotic associations of different wheat-Aegilops variabilis and wheat-Ae. kotschyi hybrid combinations with low and high homoeologous pairing were analyzed at metaphase I. Five types of pairing involving wheat and Aegilops genomes were identified by using C-banding. A genotype that seems to promote homoeologous pairing has been found in Ae. variabilis var. cylindrostachys. Its effect is detectable in the low pairing hybrids but not in the high ones. Pairing affinity has been analyzed on the basis of metaphase I associations in the low and high homoeologous pairing hybrids, and in bivalents and multivalents in the high pairing hybrids. The results indicate that the amount of bound arms of each type of identifiable association relative to the total associations formed (relative contribution) was not maintained, either between the different levels of pairing (low and high) or between different meiotic configurations (bivalents and multivalents). These findings seem to indicate that quantifications of genomic relationships based on the amount of chromosome pairing at metaphase I must be carefully done in this type of hybrid combinations.

The allotetraploidization of maize : Part 3: Gene segregation in trisomic heterozygotes

Allotetraploidization is the creation of artificial allotetraploids. Allotetraploidization of maize can be accomplished by concentrating differential pairing affinity (DPA) factors into lines by a recurrent selection breeding system. Selection will be based on changes in genetic ratios which are the result of changes in the relative frequencies of various pairing configurations caused by DPA. Part 1 of this series gave extensive data on gene segregation in trisomic and tetraploid heterozygotes. Some of these tetraploids behaved like segmental allotetraploids. Part 2 presented a model for gene segregation in segmental allotetraploids. This paper presents an analogous model for gene segregation in trisomic heterozygotes. The pairing configurations of trisomes are analyzed by considering pairing in single arms which then are combined to obtain pairing configurations for whole chromosomes. The chromosome disjunction patterns of the various pairing configurations are hypothesized and expected genetic ratios are given that result from different levels of DPA expressed in several hypothetical trisomes. The model analyzes the effect of random pairing in one arm and non-random pairing in the other arms. Also, the effect of crossing over is taken into account. Because crossing over rates are affected by the environment, part of the variability in the data (Part 1) is explained. In addition, an hypothesis is advanced to explain the frequent enhancement of pairing affinity following x-irradiation.