Determination of n+1 Gamete Transmission Rate of Trisomics and Location of Gene Controlling 2n Gamete Formation in Chinese Cabbage(Brassica rapa)

A set of trisomics of Chinese cabbage was used for determining the n-I-1 gamete transmission rate and locating the gene controlling 2n gamete formation on the corresponding chromosome. The results showed that the transmission rates of extra chromosomes in different trisomics varied from 0% to 15.38% by male gametes and from 0% to 17.39% by female gametes. Of the nine F2 populations derived from the hybridizations between each trisomic and Bp058 （2n gamete material）, only Tri- 4xBp058 showed that the segregation ratio of plants without 2n gamete formation to plants with 2n gamete formation was 10.38：1, which fitted the expected segregation ratio of the trisomics （AAa） based on the 7.37% of n＋l gamete transmission through female and 5.88% through male. In other populations the segregation ratios varied from 2.48：1 to 3.72：1, which fitted the expected 3：1 segregation ratio of the bisomics （Aa）. These results suggested that the gene controlling 2n gamete formation in Chinese cabbage Bp058 was located on chromosome 4. Further trisomic analysis based on the chromosome segregation and the incomplete stochastic chromatid segregation indicated that the gene locus was tightly linked to the centromere.

Analysis of the meiosis in the F_1 hybrids of Longiflorum × Asiatic(LA) of lilies(Lilium) using genomic in situ hybridization

Longiflorum and Asiatic lilies of the genus Lilium of the family Liliaceae are two important groups of modem lily cultivars. One of the main trends of lily breeding is to realize introgression between these groups. With cut style pollination and embryo rescue, distant hybrids between the two groups have been obtained. However, the FI hybrids are highly sterile or some of them could produce a small number of 2n gametes, and their BC1 progenies are usually triploids. Dutch lily breeders have selected many cultivars from these BC1 progenies based on their variation. It is presumably suggested that such variation could be caused by intergenomic recombination and abnormal meiosis during gamete formation in F1 hybrids of Longiflorum × Asiatic （LA） hybrids in Lilium. Therefore, the meiotic process of ten F1 LA hybrids was cytologically investigated using genomic in situ hybridization and traditional cytological methods in the present research. The results showed that： at metaphase I, the homoeologous chromosome pairing among different F1 hybrids ranged from 2.0 to 11.4 bivalents formed by homoeologous chromosomes per pollen mother cell （PMC）, and very few multivalents, and even very few bivalents were formed by two chromosomes within one genome rather than homoeologous chromosomes in some PMCs; at anaphase I, all biva- lents were disjoined and most univalents were divided. Both the disjoined bivalents （half-bivalents） and the divided univalents （sister chromatids） moved to the opposite poles, and then formed two groups of chromosomes; because the two resulting half-bivalents retained their axes in the cell undisturbed, many crossover types, including single crossovers, three strand double crossovers, four strand double crossovers, four strand triple crossovers, and four strand multiple crossovers between the non-sister chromatids in the tetrads of bivalents, were clearly inferred by analyzing the breakpoints on the disjoined bivalents. The present investigation not only explained the reason for sterility of the Fl LA hybrids and the variation of their BCx progenies, but also provided a new method to analyze crossover types in other F1 interspecific hybrids as well.

Estimating Combining Ability of 4x-2x Crosses in Cultivated Potatoes

Progenies derived from crosses between Solarium tuberosum and 2n pollen-Producing diploid hybrids, exhibit obvious hybrid vigor. The 2n pollen-producing clone can act as a bridge in crossing S. tuberosum and S. andigena with S. phureja. Populations from 4x-2x crosses show more unifomity and less segregation compared with that of 4x-4x crosses.The parent-offspring correlation for the traits, starch content and tuber number, is significant at 0.01 level. The regrssion equations are Y (mp-F1)=1.0 + 1.2x and Y (mp - F1) = 5.3 + 0.8x, respectively. The 2n pollen-producing clones play an impotant role in increasing tuber stach content.Estimates of the combining ability for the main yield components indicate that additive effect prodominatcs for such trais as plot yield, tuber weight per plant and starch content, whereas both additive and non-additive effects lay equal stress on mean tuber weight and non-additive effect is important for tuber number. In general, non-additive effect appears to be important in the progenies of 4x-2x crosses.Tuber number shows apparent heterosis while mean tuber weight dos not. Thus, it is necessary for 2n pollen-producing clones to be selected for high mean tuber weight and low tuber number before their use in commercial potato production.In the double cropping region of Anhui, the 4x - 2x hybrids seem to be more adaptive than S. tuberosum x S. andigena hybrids, but the yield of 4x - 2x cross is lower than that of the cross S. tuberosum x S. andigena in Harbin region.In Harbin region, the better combination type is in the from of S. andigena x (phureja-haploid Group tuberosum), and the best cross is also in the from. In Anhui, the better combination type is S. tuberosum x (phureja - haploid Group tuberosum), and the best cross is that using a variety of S. tuberosum as its parent. The progeny tubers of 4x - 2x cross have a short dormant period and are suitable for the double cropping region.

UNREDUCED MEGAGAMETOPHYTE FORMATION VIA SECOND DIVISION RESTITUTION CONTRIBUTES TO TETRAPLOID PRODUCTION IN INTERPLOIDY CROSSES WITH/ORAH/MANDARIN(CITRUS RETICULATA)

Seedless fruits are desirable in the citrus fresh fruit market.Triploid production via diploid x tetraploid interploidy crosses is thought to be the most efficient and widely-used strategy for the breeding of seedless citrus.Although'Orah'mandarin has desirable organoleptic qualities,seeds in the fruits weaken its market competitiveness.To produce new seedless cultivars that are similar to'Orah'mandarin,we performed three 2x x 4x crosses using'Orah'mandarin as the seed parent to regenerate triploid plantlets.A total of 182 triploid and 36 tetraploid plantlets were obtained.By analyzing their genetic origins using nine novel single nucleotide polymorphism(SNP)markers,all of the triploids and tetraploids derived from these three crosses were proven to be hybrids.Also,we demonstrated that 2n megagametophyte formation in'Orah'mandarin result in tetraploid production in these three interploidy crosses.These tetraploid plantlets were genotyped using eight pericentromeric SNP markers and nine centromere distal SNP markers.Based on the genotypes of the 2n megagametophytes,the parental heterozygosity rates in 16 SNP loci and all 2n megagametophytes were less than 50%,indicating that second division restitution was the mechanism underlying 2n megagametophyte formation at both the population and individual levels.These triploid hybrids enrich the germplasm available for seedless breeding.Moreover,the tetraploid hybrids are valuable as parents for ploidy breeding for the production of seedless citrus fruits.