| Popis: |
Genetic diversity underlies breeding advancement, and selection is the act of concentrating relevant genes (alleles) in populations for ultimate deployment to growers. Measures of genetic diversity indicate perhaps fewer than 25% of the alleles present in Beta vulgaris are present in sugarbeet, suggesting future genetic gains will be found within wild and unadapted germplasm. Germplasm collections exist, but attention to deploying their allelic diversity is stymied, with notable exceptions. Systematic efforts to deploy this germplasm held in public trust are needed, coupled with systematic efforts to identify, map, and catalog relevant agronomic genes. Both objectives can benefit from development of RILs, which represent 'immortal' segregating genetic populations. RILs have not been developed for sugarbeet, and their utility lies in the simple (if lengthy) construction process, their defined genetic relationships within populations, their homozygosity which limits phenotypic diversity to environmental variance components, and the ability a single molecular map to phenotypic values from many environments. RILs are derived via single seed decent (facilitated by self-fertility) from an initial segregating population, are highly inbred progeny derived from a single parent, and sample the genetic diversity of parental lines used to construct the hybrid. Our strategy has been to use a common male sterile (nuclear or cytoplasmic) self fertile seed parent (e.g. C869) to which one of 37 pollen donors has been mated to date, generally followed by selection for vigor and fecundity of the F 1 hybrid, then by single-seed descent for five generations. As of October 2004, 5,968 S21 819 S3 , 245 S4, and 102 S 5 plants are in process. Phenotypic, sucrose, and water content evaluations on one in-process population (C869 X Table beet) indicate the general utility of RILs for genetic analyses, and effectively couples the process of gene discovery with gene deployment in sugarbeet. |
