Genetic Analyses On Brassica Species (B. Napus, B. Rapa)×Capsella Bursa-pastoris Hybrids And Their Progenies

The rapeseed which is the main source of edible oil, feeding protein and bioenergy plays more important roles in national economy. The first B. napus cultivar 'Oro' with low erucic acid was selected from one local variety 'Liho' in Germany, while the only donor conferring the low glucosinolates in almost all the B. napus varieties was 'Bronowski' from Poland. Thus, the search for new gene source for double-low quality of rapeseed through suitable approaches including wide hybridization is pivotal for further genetic improvement. And Sclerotium blight is one of the most devastating diseases to rapeseed in our country, especially in the Changjiang drainage area and Southeast of our country. The crucifer Capsella bursa-pastoris (L.) Medic of tribe Lepidieae is an annual to biennial predominantly autogamous species with worldwide distribution. It has been used traditionally as vegetable and medicinal plant in China and some other countries for many centuries. A population of this species collected in the campus of Huazhong Agricultural University is found to be a natural double-low germplasm (0.68% erucic acid and 15.68μtmol glucosinolates/g oil free seed meal). C. bursa-pastoris has been reported to be highly resistant to Alternaria brassicae. In the present study we have observed that it possesses high resistance to Sclerotinia sclerotiorum. In this investigation, the intertribal hybrids which contains some important traits, such as low erucic acid, low glucosinolates were obtained through wild hybridization of B. napus and B. rapa with C. bursa-pastoris, and chromosomal/genomic composition analyzed by the methods of cytology, genomic in situ hybridization (GISH) and amplified fragments length polymorphism (AFLP). The results were described as follows.1. Production and morphology of hybrids. Among plants from the crosses with C. bursa-pastoris as pollen parent, thirty-two ones were from cross with B. napus cv. "Zhongyou 821", thirty with B. napus cv. "Huashuang No3", and sixty-three with B. rapa vat. chinesis cv. "Aijuehuang". The majority of hybrids were obtained by embryo resuce, and few from the seeds harvested. All F₁ plants showed the similar morphology of their Brassica females. While three F₁ plants between B. napus and C. bursa-pastoris expressed some traits of C. bursa-pastoris, such as deep-green leaves, cleft leaves, stem lignification, purple stems and siliques, and three F₁ plants with B. rapa expressed nanism, basal clustering branches, and deep-green leaves, from C. bursa-pastoris.2. Cytology and GISH analysis of hybrids. The F₁ plants between B. napus and C. bursa-pastoris were classified into two types according to the chromosome numbers in ovary cells and the chromosome behaviors in pollen mother cells (PMCs): typeâ… (2n=25-29) and typeâ…¡(2n=38). In typeâ… , PMCs mainly had 12â…¡+5â… , 13â…¡+3â… and 14â…¡+â… at diakinesis or metaphaseâ… and showed the 15: 14, 16: 13, 17: 12 segregations at anaphaseâ… (Aâ… ). In typeâ…¡, PMCs mainly had 19â…¡at diakinesis and showed the 19: 19 segregations at anaphaseâ… (Aâ… ). Lagging chromosomes and chromosomal bridges appeared at high frequency in Aâ… and Aâ…¡PMCs of typesâ… . In F₁ plants with 20 chromosomes between B. rapa and C. bursa-pastoris, PMCs mainly had 10â…¡at diakinesis and metaphaseâ… , and showed the 10: 10 or a few 11: 9 segregations at Aâ… . GISH observations on PMCs of partial F₁ plants between B. napus and C. bursa-pastoris showed no intact chromosomes or fragements of C. bursa-pastoris.3. AFLP analysis. Fourteen pairs of AFLP primes were randomly selected and used for AFLP fingerprint analyses. Most female bands could be amplified in all F₁ plants, and the percentage of C. bursa-pastoris-specific bands, deleted bands in females and novel bands for two parents were 0.22-8.37%, 1.17-4.67% and 1.17-3.50%, respectively.4. Cytology of progenies. Ovary cells and pollen mother cells with 2n=29-34 were most frequent in BC₁ plants after the hybrids between B. napus and C. bursa-pastoris were pollinated by B. napus parents, but PMCs with 22 chromosomes had 10â…¡+2â… , 11â…¡at diakinesis or metaphaseâ… , so A genome was intact in F₁ plants and most chromosomes from C genome were lost. F₂ from hybrids between B. rapa and C. bursa-pastoris mainly had 18-20 chromosomes, and their PMCs mainly had 10â…¡at diakinesis and metaphaseâ… , and showed the 10: 10 segregations at Aâ… .Finally, we proposed that hybrid cells experienced chromosome double, partial parent genome separation and preferential elimination of male chromosomes during plant development. C. bursa-pastoris chromatin introgression led to alternation of maternal genome structure and disturbed gene expression, such as new AFLP bands and deviation of morphology.