ALLOZYME VARIABILITY IN BRASSICA OLERACEA AND APPLICATIONS IN PLANT BREEDING (ISOZYMES)

Variation was detected at various regions of the zymogram of six enzymes (phosphoglucomutase, alcohol dehydrogenase, phosphoglucoisomerase, leucine aminopeptidase, glutamate-oxalacetate transaminase and acid phosphatase) in Brassica oleracea plant extracts (Chapter 1). Six isozyme genes were identified after electrophoretic analysis of selfed progeny and backcrosses of putatively heterozygous and homozygous individuals. Two more loci were implied from sporophyte-gametophyte zymogram comparisons. The electromorphs found at two additional zones were preliminarily concluded to be intergenic heterodimers. No tight linkage was found among 17 pairs of these loci.; Variability at ten isozyme genes was studied in nineteen cole open pollinated varieties representing seven horticultural groups (Chapter 2). Results indicated a high level of intrapopulation variation and interpopulation diversification. The mating system of OP varieties was estimated to be approximately random.; Two applications of electrophoresis in B. oleracea breeding were studied in detail:; (a) Hybrid purity testing. The analysis of 65 commercial F(,1) hybrids at six isozymes showed that most of them (89%) could be tested for purity using isozyme markers (Chapter 3). Lack of fixation in the inbred lines appeared to be a widespread phenomenon in B. oleracea parental lines.; Two models were developed for the determination of the sib proportion when one or both inbreds segregate at the test locus (Chapter 4). The variance of the sampling distribution and optimal sample allocation in the hybrid and inbred populations were studied. The scope of use of the unfixed models was discussed.; The proportion of contaminants of eight commercial F(,1) hybrids was determined after analysis of a sample of seeds of each hybrid and corresponding inbred lines at four isozyme loci (Chapter 5). Contamination estimates ranged from 1.5 to 40.1% and were generally higher than grow-out estimates of the same hybrids. Isozymes were proposed as a tool for selecting homozygous and highly self-incompatible inbred lines.; (b) F(,1) hybrid identification. The isozyme phenotype can be used as a sensitive and rapid test of identity for F(,1) hybrids. The analysis of a sample of seeds of 65 F(,1) hybrids for six polymorphic loci was enough to individually distinguish 48 (73%) of them (Chapter 3).