Comparing the Resynthesis of Brassica napus L. by Interspecific Somatic and Sexual Hybridization. I. Producing and Identifying Hybrids

Abstract

<jats:p><jats:italic>Brassica napus</jats:italic> (genome <jats:italic>aacc</jats:italic>), a natural allotetraploid derived from hybridization between <jats:italic>B. oleracea</jats:italic> L. (genome <jats:italic>cc</jats:italic>) and <jats:italic>B. rapa</jats:italic> L. (genome <jats:italic>aa</jats:italic>), was synthesized by sexual and somatic interspecific hybridizations from the same parent plants to compare the two methods of combining genomes and assess the genetic consequences of bypassing the gametophytic phase before hybrid formation. Highly heterozygous species parents were first produced by intraspecific hybridization between two subspecies each of <jats:italic>B. oleracea</jats:italic> and <jats:italic>B. rapa</jats:italic>. Leaf tissue from young plants of both parental species served as a source of protoplasts for fusion; the same plants were later used for crosses. Seventy-two somatic hybrids were produced using a polyethylene glycol-mediated fusion protocol and 27 sexual hybrids were obtained by embryo rescue. Somatic hybrids were produced between one <jats:italic>B. oleracea</jats:italic> and two sibling <jats:italic>B. rapa</jats:italic> plants. Sexual hybrids were successfully produced with only one of the two <jats:italic>B. rapa</jats:italic> siblings. Hybrids were identified by morphology, isozyme patterns, and total DNA content. Although fertile allotetraploid somatic hybrids were obtained within 7 months after seeding parent lines, &gt;1 year was required to produce fertile sexual hybrids.</jats:p>

Origins of the amphiploid species Brassica napus L. investigated by chloroplast and nuclear molecular markers

“…Re-synthesized B. napus may be generated by crossing both diploid and tetraploid B. rapa and B. oleracea , although only a very small proportion of the attempted pollinations result in a viable hybrid plant [3]. In a current research context, the production of hybrids from diploid parents is commonly enhanced through embryo rescue or somatic hybridisation [4] although such plants often have a relatively high frequency of chromosomal rearrangements and reduced fertility [5,3]. …”

Expression of self-incompatibility and fertility of Brassica napus L. resynthesized by interspecific somatic hybridization

“…These include: the use of similar tissue types from both fusion partners (leaf cells); the highly heterozygous nature of the species parents; and the relatively short period in culture (Ozminkowski & Jourdan, 1993a). Previous studies have used dissimilar tissue types and tess heterozygous parents (Sundberg et al, 1987;Ros6n et al, 1988).…”

“…Several of the effective S-alleles found in B. napus are derived from artificially (via sexual hybridization) synthesized lines (Gemmell et al, 1989) or via introgression from B. rapa (Mackay, 1977). In our previous study (Ozminkowski & Jourdan, 1993a) sexual interspecific hybrids were attempted from the same parent plants used to produce the somatic hybrids discussed here. Crosses between the B. oleracea plant and B. rapa-3 plant (i.e.…”

“…The plants used for analysis were described previously (Ozminkowski & Jourdan, 1993a). Briefly, somatic hybrids were produced from intraspecific hybrids of the two parental species, B. rapa and B. oleracea.…”

“…In an earlier report (Ozminkowski & Jourdan, 1993a) we described B. napus resynthesized from its diploid progenitor species via somatic hybridization between highly heterozygous lines; the B. rapa parent was SI whereas the B. oleracea parent was SC. The pedigree emphasized vegetable forms of the parent species since high fertility would be less critical in novel vegetable cultigens of B. napus derived from these hybrids.…”