Meiotic behavior in interspecific hybrids between Brachiaria ruziziensis and Brachiaria brizantha (Poaceae)

The meiotic behavior of two half-sib interspecific tetraploid (2n = 4x = 36) promising hybrids, a sexual and an apomictic one, from crosses B. ruziziensis and B. brizantha, was evaluated. Although chromosome paired predominantly as bivalents, a few tri- and quadrivalents were recorded. Results suggest that B. brizantha and B. ruziziensis are closely related and genetic recombination is expected in hybrids. Introgression of specific target genes from B. ruziziensis into B. brizantha and vice-versa may be foreseen. However, abnormalities such as irregular chromosome segregation, chromosome stickiness and abnormal cytokinesis reported in these hybrids affect pollen fertility. More than 65% of pollen grains are sterile. Since the distinctive cytological feature of these hybrids is abnormal cytokinesis, this fact suggests that both parental genomes are unable to coordinate their activities with regard to this cytological phenomenon. Deployment of such hybrids in the process of developing varieties is discussed.     

Nuclear genome constitution and other characteristics of somatic hybrids between dihaploid Solanum acaule and tetraploid S. tuberosum

Eleven somatic hybrids (2n = 68 to 74) obtained between S. tuberosum ssp. tuberosum cv. Dejima (2n = 48) and ATDH-1 (2n = 24), an anther-culture-derived dihaploid of S. acaule (Yamada et al., 1997), were characterized by nuclear RFLP markers using 49 single-copy DNA probes distributed throughout the potato genome (2 to 6 probes per chromosome). One of the somatic hybrids, DA8-2, had 72 chromosomes and all the Dejima- and ATDH-1-specific markers (124 and 103 bands, respectively), suggesting the presence of a whole set of both parental chromosomes. The other somatic hybrids lost varying numbers of markers up to seventeen. The pattern of the loss of markers indicated the elimination of five chromosomes among four somatic hybrids. A nucleolar organizer region of chromosome 2 was often eliminated in the somatic hybrids. The somatic hybrids studied here had higher frequencies of multivalent formation than the S. tuberosum parent. They had reasonably good seed set when pollinated with S. tuberosum pollen. Hence, homoeologous recombination between S. acaule and S. tuberosum chromosomes is possible and useful traits from S. acaule may be transferred to the S. tuberosum gene pool. This revised version was published online in July 2006 with corrections to the Cover Date.     

Origin of Sv Genome of Aegilops variabilis and Utilization of the Sv as Analyser of the S Genome of the Aegilops Species in the Sitopsis Section

Hybrids of Aegilops variabilis (2n = 28, UUS^vS^v) with the low-pairing type lines of Ae. longissima, Ae. bicornis, Ae. searsii, Ae. speltoides and Ae. umbellulata were obtained. This is the first report of successful hybridization between Ae. variabilis and Ae. searsii. Meiotic analysis of these hybrids showed that the U genome of Ae. variabilis donated by Ae. umbelltilata remained nearly unchanged and Ae. longissima is the possible donor species of the S genome to Ae. variabilis. But the S^v genome and the S¹ genome of Ae. longissima are not completely homologous and are structurally differentiated by at least one interchange. According to their levels of homology with S^v through the means of chromosome associations, the four genomes of Sitopsis section species can be classified as follow: S^v? S¹ > S^b > S^s > S. The meiotic behaviour of the hybrids between the wheat ‘Chinese Spring’ and the four Sitopsis section species studied has not supported the view that one of the four species is the donor of the B genome of wheat.     

Effects of substituted D genome chromosomes on photosynthetic rate of durum wheat (Triticum turgidum L. var. durum)

Summary A durum wheat cultivar Langdon (LDN) and fourteen disomic D genome chromosome substitution lines of Langdon, where A or B genome chromosomes were replaced with homoeologous D genome chromosomes of Chinese Spring (CS), were used to assess the compensatory effect of the D genome chromosomes on photosynthetic rates at tetraploid level. The LDN 1D(1B) and LDN 3D(3B) lines showed significantly higher photosynthetic rates than Langdon, whereas LDN 1D(1A) and LDN 3D(3A) lines were not greatly different from Langdon. It appears that chromosomes 1B and 3B decrease photosynthesis. This suggests the differentiation of the effects on the photosynthesis within the first and third homoeologous groups. Substitution with the 2D chromosomes did not compensate the effects of either 2A or 2B chromosomes as it reduced photosynthetic rate compared to plant with either chromosomes 2A or 2B. Tetra CS had a higher photosynthetic rate than CS and Penta CS. The photosynthetic rate of CS was similar to that of Penta CS, which lacked one set of D genome. The results suggest that it may be possible to increase photosynthesis, if both sets of the D genome were entirely removed from hexaploid wheat. However, it is difficult to conclude that the lower rate of photosynthesis of the hexaploids was mainly attributable to D genome chromosome effects, because we did not find a dose dependent effect of D genome. Homoeologous differentiation of chromosomes may be involved in photosynthesis.     

Multivariate analysis of variation among Solanum commersonii (+) S. tuberosum somatic hybrids with different ploidy levels

In order to integrate the outcomes of interspecific somatic fusion experiments in breeding schemes, it is important to understand factors involved in the variability observed among regenerated plants. With such a purpose in mind, a population of Solanum commersonii (+) S. tuberosum somatic hybrids was examined by means of discriminant and cluster analyses. Data were collected on 56 hybrids with different ploidies and on the two diploid parents grown in a greenhouse. The ploidy group was used as discrimination criterion. Three significant canonical variables were extracted by discriminant analysis; they were mainly correlated with the number of leaflets and stems, degree of flowering, plant height, and leaf length. After cluster analysis carried out with the significant canonical variables, parental and hybrid clones were grouped in 7 clusters. In the canonical space of reduced dimensions, patterns of morphological variation depended mainly on ploidy level and non-additive gene interactions. Hybrids were in general more similar to the cultivated than to the wild species, suggesting a good chance of fast introgression of useful traits from S. commersonii into the S. tuberosum genetic background.     

The potential of gene technology and genome analysis for cool season food legume crops: theory and practice

The potential of plant gene technology encompasses a multitude of different techniques ranging from the isolation of useful genes, their characterization and in vitro manipulation to the reintroduction of the modified constructs into target plants, where they are expressed at a rate that alters the phenotype of the plants. Genome analysis, on the other hand, aims at characterizing the genome architecture and function(s).Plant gene technology has catalyzed progress in plant breeding, as will be exemplified by a few examples, but has not yet been applied to food legume improvement on a large scale. Genome analysis, however, has a series of practical implications, as is illustrated by the successful introduction of DNA fingerprint and PCR fingerprint techniques to chickpea (Cicer arietinum L.) breeding and Ascochyta rabiei pathotyping. The present overview addresses both areas of plant molecular biology to illustrate their potential for food legume breeding.     

Fertile somatic hybrids of Solanum etuberosum (+) dihaploid Solanum tuberosum and their backcrossing progenies: relationships of genome dosage with tuber development and resistance to potato virus Y

The wild non-tuberous species Solanumetuberosum is resistant to biotic andabiotic stresses, but is very difficult tocross with cultivated potato. Therefore,interspecific somatic hybrids between adihaploid clone of potato S.tuberosum (2n=2x=24, AA genome) and thediploid species S. etuberosum(2n=2x=24, EE genome) were produced byprotoplast fusion. Among the 7 fertilefusion hybrids analysed by genomic insitu hybridisation (GISH), three groups ofplants were found with the genomicconstitution of AAEE, AAEEEE and AAAAEE.Four fusion hybrids had exactly theexpected chromosome composition, while eachof the three aneuploid hybrids had lost twochromosomes of S. etuberosum. Twobackcross progenies were developed, andGISH analysis was applied to analysetransmission of the parental chromosomesinto the sexual generations. BC₁hybrids derived from the crosses of thehexaploid somatic hybrids with tetraploidpotato were pentaploid with thetheoretically expected genomic compositionor with slight deviation from thisexpectation. In the three BC₂ hybridsanalysed by GISH seven to 12 chromosomes ofS. etuberosum were detected in thepredominant S. tuberosum background.No recombinant chromosomes in the hybridswere detected. Genome dosage affects tuberformation in hybrids and their progenies,but has less effect on resistance to potatovirus Y (PVY) in fusion hybrids. Severalgenotypes of the fusion hybrids andBC₁ progeny did not show viralinfection even in the graftingexperiments.     

The genomes of Arachis hypogaea. 1. Cytogenetic studies of putative genome donors

Summary Cytological studies of wild diploid Arachis species in the same section of the genus (sect. Arachis) as the cultivated peanut A. hypogaea L. show, with one exception, a karyotype characterized by the presence of 9 pairs of larger chromosomes and one pair of small (A) chromosomes. The exceptional species A. batozocoi Krap. et Greg. has a more uniform karyotype. Interspecific hybrids between diploid species of similar karyotype have moderate to high pollen stainability, those involving A. batizocoi have zero pollen stainability and a very irregular PMC meiosis. Such infertile hybrids are the most likely to produce fertile, stable amphidiploids on doubling the chromosome complement. It is suggested that the cultivated peanut could have originated from such a sterile interspecific hybrid and on morphological and phytogeographic grounds the most likely genome donors are A. cardenasii (nomen nudum) and A. batizocoi of the species within section Arachis, which have been collected up to the present time.Paper number 5560 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, NC 27650     

Production and cytogenetics of intergeneric hybrids between Triticum durum-Dasypyrum villosum amphidiploid and Psathyrostachys huashanica

Summary Intergeneric crosses between Triticum durum-Dasypyrum villosum (2n=42, AABBVV), and Psathyrostachys huashanica (2n=14, N ^h N ^h ) were made, the seed set was 1.67%. Intergeneric hybrid were successfully obtained by means of embryo culture for first time. The average chromosome pairing in the hybrid (ABVN ^h ) was 26.61% univalents, and 0.69 bivalents. The chiasmata per cell was 0.69. The chiasmata was higher than that in Triticum durum dihaploid (AB), and lower than that in T. durum-Dasypyrum villosum trihaploid (ABV). The result indicated that the N ^h genome of Psathyrostachys huashanica has no homology with the V genome of Dasypyrum villosum, and the A and B genomes of Triticum durum. The coenocytism, micronuclei cell and variation in chromosome numbers were also observed. The F₁ hybrid was crossed with Triticum aestivum (AABBDD), and resulted in seed set. The hybrid of T. durum-D. villosum amphidiploid x P. huashanica showed partial fertility. It made the possibility for chromosome manipulation among Triticum aestivum, Dasypyrum villosum and Psathyrostachys huashanica.