Molecular And Cytobiology Study On Allopolyploid And Alien Chromosome Lines Of Triticum Aestivum L. And Secale Cereale L.

Wheat(Triticum aestivum L.) is one of the most important crops worldwide. Nowadays,the wheat cultivars have been lossing the tolerance to biotic and abiotic stresses because of the inter-hybridization among the wheat cultivars.Wild relatives of common wheat carry plenty of valuable genes for improvement of cultivated wheat,such as disease resistance,insect resistance,broad adaptation,high yields,and yield stability,etc.Wheat breeders have been trying their best to introduc alien elite gene into wheat cultivars.Wide hybridization is an important way by which wheat cultivars are improved.In addition,wide hybrids are useful for the study on species evolution and phylegenesis.Of these wide relatives,rye(Secale cereale L.) is the earliest and extensively used alien introgressions in wheat breeding programs.In present study,two common wheat 'Chinese Spring' and 'Miangyangl l'were used to hybrid to diploid rye 'AR106BONE','Kustro','Jingzhou-heimai'and S.Vavilovii. Molecular and cytologic methods were used to analysis the F1 plants,the first generation plants after chromosome boubling(S1),the second generation plants after chromosome boubling(S2) and the third generation plants(S3),which were derived from five combinations including Chinese Spring×AR106BONE(CA),Chinese Spring×Jinzhou (CJ),Mianyangll×AR106BONE(MA),Mianyangll×Kustro(MK) and Mianyangll×S.vavilovii(MSV).The following new results were obtained:1.Rye telomeric/subtelomeric repeat DNA pSc200 was used to hybridize root-tip metaphase cells of parental rye,S1 paints,S2 plants and S3 plants.The drastic variation of rye telomere/subtelomere initiated in S1 plants.Both elimination and expansion of pSc200 can occur during allopolyploidization,and the genetic backgrounds of parents determine which one will occur.A possible role for the alteration of parental-specific DNA repeats upon allopolyploids is to satiafy with diploid-like meiosis and to mitigate the genomic incompatibility of parental genomes that would otherwise be too divergent for harmonious coexistence and coordination.2.Low-frequency cheomosome translocation between wheat and rye was observed in wheat-rye allopolyploids.Three translocation patterns occurred:(1) rye-telomeric segments were translocated to wheat centromere;(2) rye-telomeric segments were translocated to wheat telomere;(3) translocation occurred on intercalary regions of chromosomal arm between wheat and rye.These translocation events perhaps occurred in somatic cells and this phenomenon was not reported before.3.Unbalanced segregation of chromosomes in wheat-rye allopolyploids derived from MSV,MK and CA combinations occurred.Three unbalanced segregation pattern were observed:(1) both wheat and rye chromosomes underwent unbalanced segregation during meiosis;(2) for different combination,unbalanced segregation occurred in different generation;(3)unbalanced segregation of rye chromosome also occurred in root-tip cells of allopolyploids derived from MSV combination and this phenomenon was not reported before.4.2R,4R and 5R monosomic addition lines were detected from backcross plants derived from MK combination.4R monosomic addition line exhibited aphid resistance and 5R monosomic addition line was immune to powdery mildew.These results indicate the chromosomes 4R and 5R carry resistance gene to aphid and powdery mildew, respectively.These monosomic addition lines are useful for wheat improvement.5.Some sequences amplified by eight randomly selected wheat EST-SSR from F1,S1 and S2 allopolyploidy plants were sequenced.Two results were obtained:(1) both wheat and rye parental coding sequences were transfen'ed into F1,S1 and S2 plants;(2) parental coding sequences were eliminated from progeny:in different combination, only rye parental coding sequences eliminated at some loci,or only wheat parental coding sequences eliminated at the other loci;some sequence elimination initiated in F1 generation and some sequence elimination initiated in S1 generation.This kind of sequence elimination is to mitigate the genomic incompatibility of different parental genomes for harmonious coexistence and coordination.In addition,sequence alignment revealed that parental coding sequences have altered in progeny and a few sequences have recombined between wheat and rye.These results indicate that new coding sequences were produced during allopolyploidization.New coding sequences were produced by base substitution,sequence repeat and recombination.This phenomenon may imply that allopolyploidization can promote the production of new gene.The results obtained in present offer some new references for the study on allopolyploidy evolution and provide some new resistance resources to wheat breeding program.