EXPRESSION OF THE C-3-C-4 INTERMEDIATE CHARACTER IN SOMATIC HYBRIDS BETWEEN BRASSICA-NAPUS AND THE C-3-C-4 SPECIES MORICANDIA-ARVENSIS

The wild crucifer Moricandia arvensis is a potential source of alien g enes for the genetic improvement of related Brassica crops. In particu lar M. arvensis has a C-3-C-4 intermediate photosynthetic mechanism wh ich results in enhanced recapture of photorespired CO2 and may increas e plant water-use efficiency. In order to transfer this trait into Bra ssica napus, somatic hybridisations were made between leaf mesophyll p rotoplasts from cultured M. arvensis shoot tips and hypocotyl protopla sts from three Brassica napus cultivars, 'Ariana', 'Cobra' and 'Westar '. A total of 23 plants were recovered from fusion experiments and est ablished in the greenhouse. A wide range of chromosome numbers were ob served among the regenerated plants, including some apparent mixoploid s. Thirteen of the regenerated plants were identified as nuclear hybri ds between B. napus and M. arvensis on the basis of isozyme analysis. The phenotypes of these hybrids were typically rather B. napus-like, b ut much variability was observed, including variation in flower colour , leaf shape and colour, leaf waxiness, fertility and plant vigour. CO 2 compensation point measurements on the regenerated plants demonstrat ed that 3 of the hybrids express the M. arvensis C-3-C-4 intermediate character at the physiological level. Semi-thin sections through leaf tissues of these 3 plants revealed the presence of a Kranz-like leaf a natomy characteristic of M. arvensis but not found in B. napus. This i s the first report of the expression of this potentially important agr onomic trait, transferred from Moricandia, in M. arvensis x B. napus h ybrids.