In vitro microspore mutagenesis and selection was used to produce five fertile double-haploid imidazolinone-tolerant canola plants. The S2 plants of three of the mutants were resistant to at least the field-recommended levels of Assert and Pursuit. One mutant was tolerant to between five and ten times the field-recommended rates of Pursuit and Scepter. Two semi-dominant mutants, representing two unlinked genes, were combined to produce an F1 hybrid which was superior in imidazolinone tolerance to either of the heterozygous mutants alone. Evaluation of the mutants under field conditions indicated that this hybrid and the original homozygous mutants could tolerate at least two times the field-recommended rates of Assert. The field results indicated the mutants were unaffected in seed yield, maturity, quality and disease tolerance. These genes represent a potentially valuable new herbicide resistance system for canola, which has little effect on yield, quality or maturity. The mutants could be used to provide tolerance to several imidazolinones including Scepter, Pursuit and Assert.

Somatic hybrid plants were regenerated from fused mesophyll protoplasts of an albino potato (Solanum tuberosum spp. tuberosum) variant and Solanum brevidens, a non-tuber bearing species which is sexually incompatible with S. tuberosum. These somatic hybrid plants represent the first example of direct hybridization between potato and members of the taxonomic group Etuberosa, and offer the potential for introgressing valuable germplasm from Solanum species outside the sexually compatible range into a worldwide crop species.

Microspores of several genotypes of Brassica campestris ssp. parachinensis have been cultured in vitro and induced to undergo embryogenesis and plant formation. Conditions favourable for embryogenesis in this species include a bud size of 2-2.9 mm, NLN-13 culture medium (Nitsch and Nitsch 1967; Lichter 1981, 1982; Swanson 1990), and an induction through exposure to 32°C for a period of 48 h. Longer periods of an elevated temperature for induction of embryogenesis resulted in embryo abortion at early developmental stages. With the protocol developed here, microspores of 60-80% of donor plants could be induced to produce embryos, although embryo yields were low, i.e. 2-5 embryos per 10 buds. Some genotypes responded to culture conditions with high numbers of embryo formation (100-150 embryos per 10 buds) but most of these subsequently failed to mature. The pattern of cell division and morphological changes of the microspores in culture were studied using various microscopic techniques.

Thirty somatic hybrids between Solanum tuberosum and Solanum brevidens were analysed for mitochondrial and chloroplast genome rearrangements. In all cases, the chloroplast genomes were inherited from one of the parental protoplast populations. No chloroplast DNA alterations were evident but a range of mitochondrial DNA alterations, from zero to extensive intra- and inter-molecular recombinations, were found. Such recombinations involved specific 'recombination hot spots' in the mitochondrial genome. Not all hybrids regenerated from a common callus possessed identical mitochondrial genomes, suggesting that sorting out of mitochondrial populations in the callus may have been incomplete at the plant regeneration stage. Sorting out of organelles in planta was not observed.