MEASURING POPULATION IMPROVEMENT IN THE SRA SUGARCANE BREEDING PROGRAM

EACH YEAR, SUGARCANE breeders in each region plant and assess new populations of clones in Clonal Assessment Trials (CAT, target 2,000–2,500) and Final Assessment Trials (FAT, target 150–250). These clonal populations are selected originally from seedling families that are derived from crosses between two parents. Breeder input annually into parent selection, cross selection, seed selection, family selection and, ultimately, clonal selection, is critical in delivering new varieties to the Australian sugar industry. It could also be assumed that, through continual improvements in all aspects of selection mentioned, the current clonal populations produced are ‘better’ than previous populations for the important traits under selection – i.e. cane yield (TCH), CCS and the combination of these two and other traits as the selection index called relative Economic Genetic Value (rEGV). This concept of ‘Population Improvement’ is important to plant breeders to achieve continual improvement in genetic gain and in the new varieties released. However, currently there are no routine methods developed to quantify this improvement. There are a number of difficulties in comparing the different populations across years. These include large year to year and site to site variation and the appearance of a new disease, such as the recent orange rust (2000) and smut (2006) epidemics. Population statistics relative to a common standard variety or set of standard varieties would be one way to overcome this problem, but the standard varieties used by breeders also change with time. This generally precludes the assessment of populations over long time periods, which would be optimal (e.g. 10 to 20 years). However, data are available to assess populations over much shorter periods. This paper examines methods to measure clonal population improvement within the SRA regional selection programs and reports on the trends in population improvement and their implications and limitations.