THE INTERACTION OF GENOTYPE, EXPLANT AND MEDIA ON THE REGENERATION OF SHOOTS FROM COMPLEX EXPLANTS OF BRASSICA-NAPUS L

The relative importance of explant type, genotype and growth regulator regime in the determination of shoot regeneration frequencies from complex explants of Brassica napus L. has been evaluated. Cotyledon, hypocotyl and stem sections taken from one spring (Westar) and three winter (Ariana, Cobra, Libravo) varieties of B. napus were cultured on three different growth regulator regimes, 0.5 mg dm-3 NAA + 2.0 mg dm-3 BAP, 0.5 mg dm-3 NAA + 4.0 mg dm-3 BAP and 1.0 mg dm-3 NAA + 4.O mg dm-3 BAP. The most significant effects on shoot regeneration were due to explant type and variety. The regeneration from stem segments was not only two to three times higher than from hypocotyls or cotyledons, in all varieties, but the response was also more uniform across the varieties. The explant effect accounted for 44-95% of the regeneration response. In contrast, the contribution of growth regulator regime was negligible. Although the growth regulator regime as an independent effect was unimportant, regeneration from both Ariana and Libravo was significantly affected by the interaction of genotype with growth regulator regime. The importance of both the high shoot regeneration frequency from stem segments and the relative uniformity of response across the four tested genotypes is discussed with respect to the potential benefits of using this explant source in Agrobacterium-based transformation experiments.