| Scab is a disastrous disease for common wheat (Triticum aestivum) in warm and humid areas and exhibits a trend of rapid expansion and aggravation along with the global climate warming and introduction of less- or non-tillage. Development and utilization of resistant cultivars in wheat production has been considered as the most economical and effective strategy. However, the scab-resistance source of wheat in current breeding programs is particularly narrow since most of the resistant cultivars released in past decades originated from only a few varieties, e.g. Sumai 3 and Frontana. Leymus racemosus (2n=4x=28), a perennial and distant relative species of wheat, possess preferred characteristics for wheat improvement, such as salt and drought tolerance, diseases resistance. More recently, this species is becoming a new and potential source for wheat scab resistance. The introduction of new resistance genes from relative species to wheat to broaden the genetic base of breeding materials is essential for an effective and successful breeding program. T.aestivum-L. racemosus alien addition lines of Lr2 (7Lr), Lr7 and Lr14 (5Lr) with high resistance to scab were developed by Cytogenetics Institute, Nanjing Agricultural University. In present study, the microsporocytes and pollens of T. aestivum-L. racemosus alien addition lines were irradiated by 60Co-γray to produce various chromosome structural change materials with scab-resistance, especially small fragment translocation line, and provide new genetic resources for breeding of the scab-resistance wheat.1. Plants of the T. aestivum-L.racemosus addition line DA5Lr during meiosis were irradiated by60Co-y-rays 800R (l00R/min) and were emasculated and bagged after heading. The emasculated flowerets were pollinated by pollens of T. aestivum cv. Chinese spring after 2-3 days. Six T. aestivum- L.racemosus translocations and six telosomics were selected from seventy-nine M1 plants. The frequency of plant with structural aberrance of alien chromosome was 15.2%.In M1 progenies, a plant with a chromosome 5Lr and a small alien fragment intercalary translocation chromosome was identified by chromosome GISH at metphase of root tip cells. In its self-crossing progenies, the homozygous plant with small fragment intercalary translocation was selected. The sequential C-banding and GISH showed that the translocation chromosome might be involved in the chromosome of A or D genome of wheat. The wheat segment of translocation chromosome has only dispersible signals of BAC 676D4 when 676D4 specific to A genome and pAsl specific to D genome was used as probe in double color FISH, indicating that the translocation chromosome was involoved in chromosome of A genome. The obvious site of 5SrDNA on the short arm of the translocation chromosome was observed after FISH using 5SrDNA as probe. Combination the results of C-banding and in situ hybridization, this translocation chromosome was involved in 1A and was designated as TilAS-lAL-5LrL-lAL. Chromosome configuration of the homozygous translocation line at MI of PMCs after GISH was 17.47(?)w+0.90(?) Ti+2.53(?)w+0.10(?)Tu. In heterozygous plants, the intercalary translocation chromosome with small alien fragment paired with 1A as stable bivalent. Meanwhile, non-sister chromatids exchange occurred in the region between alien intercalary fragment and centromere was observed and could be reflected through the segregation of translocation chromosome exchanged or non-exchanged at anaphase I, telophase I and anaphaseⅡ, and tetrad types. The self-crossing progenies of translocation heterozygote produced three types of plants with homozygous, heterozygous translocation and no translocation chromosome respectively. Their proportion fits 1:2:1 statistically. The evaluation of scab resistance showed that plants with alien intercalary translocation chromosome had high resistance to wheat scab.Two translocation lines, WLS5-2 and WLS6-3, both involved in the long arm and partial short arm of 5Lr, one small fragment of unknown wheat chromosome (W?-5LrS-5LrL) were obtained and showed high genetic stability, seed set and scab resistance.One plant with two translocation chromosomes involved in two arms of 5Lr, respectively, was detected in M1 by C-banding and GISH analysis. The plant was crossed with disomic addition DA5Lr. There were one 5Lr and two translocation chromosomes in the F1 plants. The shape of cross and ring or chain quadrivalent were observed at diploma and MI respectively, indicating that two translocation chromosomes were reciprocal translocation chromosomes. The results of C-banding showed that translocation chromosomes were involved in the chromosome of A or D genome. After in situ hybridization using BAC 676D4 and pAsl as probe, only signals of pAsl on wheat segment of two translocation chromosomes were observed. According to the pattern of pAsl and C-banding of these chromosomes, it could be considered the translocation occurred between 5Lr and 7D. The two reciprocal translocation chromosomes were designated as T7DS-5LrL and T5LrS-7DL repectively. Gemate transmission analysis showed that two reciprocal translocation chromosomes were usually transferred together, and homozygous lines only involved in one translocation chromosome were difficultly obtained. The homozygous translocation line 7DS-5LrL with scab-resistance should be selected through backcross and then self cross.In addition, an alien telosomic addition line 5Lr#1L was also obtained. It had high genetic stability and scab-resistance, and is becoming a useful resource.2. The results of gamete transmission analysis showed that L.racemosus chromosome 5Lr, translocation chromosome TW-5LrS-5LrL(in WLS6-3) and TW-5LrS-5LrL (in WLS5-2), and telocentric chromosome 5Lr#1L appeared obviously pollens preferential transmission. Their transmission rate was 88.4%,86.7% and 92.5% through male gamete respectively, significantly higher than theoretical value of 50%, and suggesting a pollen preferential transmission gene on long arm of 5Lr. Because the pollens without 5Lr chromatin showed high fertility, the preferential transmission in these materials was different from the effect of gametocidal chromosome, and should belong to a new type of preferential transmission.3. The pollen of T. aestivum-L. racemosus monosomic addition line MA7Lr was treated by irradiation with 1200 rad 60Co-y-rays prior to pollinating to emasculated wheat cv. Mianyang85-45. Nine telosomics and six T.aestivum-L.racemosus translocations of fifty-seven progenies plants were obtained. The frequency of plant with structural aberrance of alien chromosome was 26.3%.Nine plants with a telocentric chromosome 7Lr#1S were identified by the sequential C-banding and GISH of root tip cells chromosome in M1 plants, and one ditelosomic substitution line 7Lr#1S was selected from self-crossing progenies and confirmed by chromosome C-banding and GISH. Furthermore, a co-dominant EST-SSR marker CINAU 31 was employed to identify this substitution line. A pair of chromosome 7A of common wheat were found to be replaced by a pair of telocentric chromosome 7Lr#1S, and further investigation showed that chromosome configuration of the substitution line at MI of PMCs after GISH was 17.50(?)W+2.19(?)W+O.42(?)7Lr#1S+1.08 I 7Lr#1s+0.69 I w. Two telocentric chromosomes paired as a bivalent in 59.7%of PMCs. Abnormal chromosome behaviors of telocentric chromosomes were observed in part of PMCs at anaphase I and telophase I, including the moving of two telocentric chromosomes to the same pole, lagging and earlier separation of their sister chromatid. All these abnormal behaviors can be grouped into three distinct types of tetrads according to different numbers of 7Lr#1S in their daughter cells and various micronucleus in some tetrads. However, due to the high transmission frequency of the female and male gametes with a 7Lr#1S,84% of the self-crossing progeny plants had ditelosomic substitution. The substitution line showed high resistance to wheat scab in a successive two-year test both in the greenhouse and field; hence, the line will be particularly valuable for alien gene mapping, small fragment translocation induction and telosomic cytological behavior analysis.An alien translocation line was selected from M2 progenies. The translocation occurred between chromosome 4B of wheat and 7LrS of L.racemosus. It belonged to a distal translocation by C-banding and GISH analysis. The breakpoint of translocation chromosome located in S1.6 region of chromosome 4BS of wheat, and was designated as T4BL-4BS-7LrS.One plant (2n=44) with two homozygous translocation chromosomes involved in 7Lr was detected in M2 by the sequential C-banding and GISH analysis. The results of C-banding showed that the translocation chromosomes were involved in the chromosome of A or D genome. After in situ hybridization using BAC 676D4 and pAsl as probe, only signals of pAs1 on wheat segment of two translocation chromosomes were observed. According to the pattern of pAsl and C-banding of these chromosomes, it could be considered the translocation occurred between 7Lr and 2D. The two translocations were designated as T2DS-2DL-7Lr and T2DL-7Lr repectively. The breakpoint of translocation chromosome located in L1.3 region of chromosome 2D of wheat... |
PDF Full Text Request