Potential usability of CMS rucola for the breeding process
Rucola is a leafy vegetable from the Brassicaceae family with continuously increasing economic demand. Under this name rocket salad (Eruca sativa) as well as the perennial wall rocket (Diplotaxis tenuifolia) are commercially distributed. So far, for both species no hybrid system is available. Therefore, breeding lines of both species were used to pollinate cytoplasmic male sterile (CMS) cauliflower (Brassica oleracea) plants. Intergeneric Fi-hybrids were achieved by manual crosses and embryo rescue. Allotetraploid plants obtained after colchicine treatment were recurrently backcrossed with the respective rucola parent. The elimination of Brassica genomic DNA was verified using molecular markers, GISH analysis, flow cytometry and chromosome analysis. All backcross plants from BC2 up to the BC6 generation of the B. oleracea x E. sativa (BE) cross showed male sterility and full seed set compared to the E. sativa parent. No further incompatibilities were noticed between the CMS inducing cytoplasm and the E. sativa genome. Agronomical traits such as plant vigor, biomass production, flowering and seed set were recorded for the different backcross generations. The developed alloplasmic lines are diploid with 2n=2x=22 chromosomes and could be introduced without any problems into the breeding process. Also BC1 plants of the cross B. oleracea x D. tenuifolia (BD) had completely male sterile flowers. The phenotype was similar to that of the D. tenuifolia parent. Unlike the BE combination, for BD combination embryo rescue was necessary to establish BC2 plants. The flowers of all BC2 plants of BD combination showed besides the male sterility a pronounced female sterility, expressed by the abort of ovaries and failed seed set. Hence, this combination seems to be not applicable for the breeding process. Reasons for this strikingly different behaviour are under investigation.
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