Cytogenetic Analysis On Progenies Of Interspecific Hybridization Between Brassica Napus And Early Maturing Brassica Rapa

Because of its high yield and good quality,B.napus has become the main type of rapeseed.Its A-genome and C-genome derived from the original diploid species “B.oleracea” and “B.rapa”.During the long-term evolution,the genomes of B.napus have changed greatly compared with the original parents,but its domestication history is shorter and the genetic resources are deficient and so on,which limit the genetic improvement of B.napus.Through interspecific hybridization between B.napus and B.rapa,the favorable characters could be transferred and the genetic basis of B.napus could be widened.In this study,interspecific hybridizations between B.napus and early maturing B.rapa were made and the progenies of the early generations were studied by the cytogenetic method to provide a technical support for quickly obtaining novel early maturing B.napus.The main results were as follows:1.Orthogonal combinations with B.napus as the female parent were more likely to harvest hybrids than backcross combinations with early maturing B.rapa as the female parent.In addition,the number of chromosomes was the expected 29 from B.napus as the female parent.In pollen mother cells(PMCs),the chromosome pairing was dominated by divalents,the number of which ranged from 9 to 14 and separation method was mainly 15/14 at anaphase I.When chromosomes separation occured,the lagging chromosome(s)and chromosome bridge(s)could be observed at anaphase I and anpahse II.2.F1 plants were the B.napus-like phenotype.The morphological variation of F2 was broad,could be roughly divided into B.napus-like,intermediate,B.rapa-like and others.Meanwhile,the B.napus-like F2 plants were most and selected in the experiment,their F3 plants were all B.napus-like phenotype.The flowering period of F1 plants were between B.napus and early maturing B.rapa.Both F2 and F3 showed some materials whose flowering period was earlier than the B.napus,and the percentage decreased.3.Among the F2 plants classified from the morphological and cytological analyses,those with the B.rapa-like phenotype showed 2n=20,the same chromosomes number as the B.rapa parent,which were paired as 1.64 I +9.11 II +0.04 III.The F2 plants with 2n=23-28 was intermediate for phenotype,while the others with 2n=29-58 was similar to the B.napus parent,among which the plants with 2n=38 were few and the chromosome pairing configuration was 0.68 I +8.23 II +0.30 III.During meiosis of the PMCs of F2,the lagging chromosome(s)and chromosome bridge(s)were observed at anaphase I and anaphase II.The results showed that F2 plants varied widely,the plants with 2n=20-28 were B.rapa-like and intermediate phenotype.The plants with 2n=38 were few and presented low seed-set after self-pollination,the meiosis was abnormal.In order to obtain novel B.napus,the B.rapa-like and intermediate plants could be eliminated according to the morphological characteristics in the field.4.Cytological analysis of self-bred progeny F3 of the F2 plants with B.napus-like phenotype showed that the F3 plants with 2n=38 was from 20% to 40.00% when the F2 plants was 2n=35-37.Meanwhile,the F3 plants with 2n=38 gave 46.46% when the F2 was 2n=38.It could be concluded that the production of the B.napus-like progenies was rational via the directional selection of the F2 plants with such phenotype and more than 35 chromosomes.During the PMCs meiosis of F3 plants with 2n=38,the chromosome pairing configuration of the plants with 2n=38 was 0.59 I +18.30 II +0.26 III,and the number of divalents ranged from 16 to 19,with mainly 19 divalents accounted for 58.62%,while the number of univalents was from 0 to 3.Compared with F2 plants with 2n=38,the number of univalents and trivalents decreased.5.In order to study the introgression of parental genetic materials in the progenies of the hybridization between B.napus and B.rapa,AFLP and SSR molecular markers were used for the early F2 and F3 generations.The results showed that the A-genome of early maturing B.rapa was introgressed in the hybrid progenies of F2 and F3,accompanied by the double variation of A-genome and C-genome of hybrid progenies.