The introgression of characters of the wild oat Avena magna (2n=4x=28) into the cultivated oat A. sativa (2n=6x=42)

Summary A study of derivatives from the hybrid Avena sativa × A. magna backcrossed to A. sativa clearly indicate that it is possible to introduce characters of the wild oat into the cultivated oat. Progeny with improved grain characters and crude protein content of the groat have been isolated and their use as breeding material is discussed.     

A maternally inherited DNA marker,descended from Solanum demissum (2n = 6x = 72) to S. tuberosum (2n = 4x = 48)

A Mexican hexaploid wild potato species, Solanum demissum (dms), was only used as a female in previous breeding programs. The resulting clones with dms cytoplasm produced abundant, but non-functional pollen. A 170 bp DNA fragment, named Band 1, was originally detected in the F₁ hybrid between dms and S. tuberosum. In this study, the sequenced region was extended to 1,032 bp; nevertheless, it did not show any homology to known sequences. This extended region harboring Band 1 was, without introns, all transcribed to mRNA and was maternally inherited from dms to S. tuberosum through backcrosses. Three dms accessions, 168 accessions of 38 cultivated and closely related wild species, and 158 varieties and breeding lines were surveyed, which demonstrated that Band 1 was specific to dms and varieties and breeding lines with dms cytoplasm. Thus, Band 1 is a useful marker to distinguish dms cytoplasm, which enables us to design efficient mating combinations in breeding programs.     

Male fertility and cytology of triploid hybrids between tetraploidSolanum commersonii (2n=4x=48, 2EBN) and Phureja-Tuberosum haploid hybrids (2n=2x=24, 2EBN)

Summary Solanum commersonii Dun. is a diploid (2n=2x=24, 1EBN) wild species of potential value for potato breeding. It is a reproductively isolated species and cannot be crossed with Tuberosum haploids (2n=2x=24, 2EBN) or other diploid 2EBNSolanum species. In order to overcome the EBN barriers, triploid hybrids were produced between Phureja-Tuberosum haploid hybrids, which form 2n pollen grains by parallel spindles, and tetraploidS. commersonii. Microsporogenesis analysis of the triploids indicated a trend towards low values of chromosome distribution at Anaphase I; lagging chromosomes were often observed as well. Despite these abnormalities, the percentage of stainable pollen was very high, ranging from 5.0% to 74.3%. A high variation in pollen grain diameter was also evident. Parallel and tripolar orientation of spindles at Metaphase II of microsporogenesis was a common feature of all the triploids analyzed, but dyads and triads were observed at a very low frequency. Therefore, also the frequency of 2n pollen was very low; the different size of stainable pollen appears to represent the ploidy levels which are possible according to the distribution of chromosomes in Anaphase I. The results obtained also suggest thatS. commersonii could have minor genes acting at the end of meiosis in such a way that, despite the presence of parallel/tripolar spindles, dyads/triads are not formed.Contribution no. 124 from the Research Center for Vegetable Breeding.     

A synthetic hexaploid (2n = 42) oat from the cross of Avena strigosa (2n = 14) and domesticated A. magna (2n = 28)

A synthetic hexaploid oat was produced by chromosome doubling of a sterile triploid hybrid between cultivated Avena strigosa (2n = 14) cv. Saia and a domesticated form of A. magna (2n = 28). The synthetic hexaploid was intermediate between its parents in panicle shape and lemma color, similar to the tetraploid parent in spikelet structure, and to the diploid parent in having a single, albeit partially shriveled seed per spikelet, and low protein content. By the third generation, plants with yellowish lemmas, mostly two seeds per spikelet and better filled grains had been selected. Rust resistance of the diploid parent was retained in the synthetic hexaploid, but not tolerance to barley yellow dwarf virus disease (BYDV). Chromosome associations at meiosis in the triploid hybrid was low, with over 60% of them being univalents. Bivalent association was the rule in the synthetic hexaploid with an occasional one or two quadrivalents. Regular meiosis with 21 bivalents was observed in further generations. The preferential pairing of homologous chromosomes in the synthetic hexaploid was probably contributed by the A. strigosa genome which exhibits this tendency in artificial allopolyploid situations. Selection of yellow lemma color and two seeds per spikelet suggests that the genes controlling these traits are located on the chromosomes involved in quadrivalents in the synthetic hexaploid. The potential and limitations of utilizing the synthetic hexaploid in oat research and breeding are briefly discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Parthenogenetic monohaploids (2n=x=12) from Solanum tuberosum L. and S. verrucosum Schlechtd. and the production of homozygous potato diploids

Summary Dihaploid and dihaploid derived clones of Solanum tuberosum and diploid genotypes of S. verrucosum produced 85 viable monohaploids by female parthenogenesis. All were induced using diploid S. phureja clones, homozygous for embryo spot, as pollinator. Frequency of S. tuberosum monohaploids per 100 berries was rather constant in three successive years (14, 17 and 17 respectively). No male and female fertility was found in flowering monohaploids.Colchicine-induced chromosome doubling yielded homozygous s. tuberosum diploids with low pollen quality but good seed fertility.Two diploid self-incompatible species (S. multidissectum and S. berthaultii) produced no monohaploids. The presence of genes for female parthenogenesis in some dihaploids is discussed.