Intergeneric Hybridization Between Brassica Rapa Pekinensis And Orychophragmus Violaceus And Cytogenetics Analysis On The Hybrids

The wide hybridization can break limits of species in some extent,promote genetic introgression and communication of different species,which are effective approaches to transfer useful characters to cultivated crops,to produce new species,to introduce alien gene and create variations.At present by this breeding method,a lots of important and special genes have been transferred to Brassica crops from wild relatives.Orychophragmus violaceus(L.) O.E.Schulz(OO,2n=22) is a species of Cruciferae.It was cultivated in some places as an ornamental plant.O.violaceus has many good agronomic characers such as cold-tolerance,shade-tolerance,high protein content and superior oil quality which is characterized by the high contents of linoleic and the low contents of erucic acids.So far lots of concerned study emphasizes particularly on using O.violaceus to improve the oil quality of B.napus.Our research indicates that O.violaceus is also highly resistant to downy mildew,which is one of the three important diseases in B.rapa ssp.pekinensis.In order to improve the genetic background of B.rapa pekinensis and to gain the new resistant genetic resource,distant hybridization between B.rapa ssp.pekinensis and O.violaceus had been made and the charaters of the F₁ plants,the number of the chromosomes,and chromosome components by general cytology and GISH have been investigated.The results are listed as follows.1.In the general hybridization,whether the derect cross or reciprocal cross combination,no hybrids were gained.By successive hand bud pollination and embryo rescue,thirty-one hybrid plants were obtained including seven crosses,the obtaining rate of hybrids was improved to 51.6%.In the process of embryo rescue,the number of survival ovules was different when the stage of embryo development is different.Our result indicated that ten days after pollination is the best time for successful culture.The crossing-compatibilities were higher when B.rapa pekinensis were used as the maternal parents than when O.violaceus as maternal.2.The charaters of the thirty-one F₁ plants,the fertility,the number of the chromosomes and chromosome components were investigated and the results revealed that fifteen of them carried twelve chromosomes of O.violaceus and one hybrid contained thirteen chromosomes of O.violaceus and they were truly intergeneric hybrids.Morphological characters of hybrids(F₁) were investigated and the results revealed that sixteen of them showed an intermediate morphology between the two parents and the pollen fertility was aborted.Cytology identification and GISH analysis of the hybrids showed that fifteen of them had twenty-two chromosomes including twelve chromosomes of O.violaceus except one hybrid (403×565) which had twenty-three chromosomes including thirteen chromosomes of O.violaceus.3.The process of miosis of the hybrids was researched by general cytology methods and GISH.The results indicated that the chromosomes of hybrids couldn't paired rightly in the process of moisis,so the pollen fertility of hybrid plants(F₁) was aborted.It was found that cytoplasm divided simultaneously and the chromosomes behaved innormal in the anaphase of the miosis.The chromosomes of hybrids divided unequally in anaphaseâ… and anaphaseâ…¡of miosis.Some cells with chromosome lagging and multipolarly dividing were observed.Most of the chromosomes paired in the form of univalents in metaphaseâ… .The average configuration of chromosomes was 11.82â… +4.61â…¡+0.19â…¢+0.08â…£.GISH analysis indicated that most bivalents consisted of B.rapa pekinensis chromosomes and O.violaceus chromosomes.