Many plant breeding projects – such as those aiming to increase food production – depend on getting ‘pure lines’ of plants but this can take a lot of time as, most of the time, it depends on self-pollination for several generations. Several years may be required following a traditional process. If such a process can be shortened, the efficiency of genetic analysis and breeding can be significantly increased.
Traditional wheat and barley breeding involves a cross between two parents and selfing the resulting hybrids for 6-8 generations to produce pure breeding lines before selection and field evaluation, as illustrated by the following figure, hence the slow progress from a cross to the release of a new cultivar. In selected crosses, breeders may make use of other methodologies to more rapidly advance generations in a glasshouse. Australian breeders can advance 2 generations per year in the field through use of a summer generation at suitable environments. Doubled haploid (DH) techniques can produce pure lines relatively quickly; however, the success is genotype dependent and expensive and there is only a single opportunity for recombination to occur. The single seed descent (SSD) approach is an alternative method to advance generations and current methodologies enable only two to three generations a year, but with increased opportunities for recombination.
Recently a new system has been developed by the research team led by Professor Yan which allows up to eight to nine generations per year to be achieved in glasshouse SSD breeding. This fast generation system (FGS) involves the culture of young embryos at an early developmental stage (10-15 days after anthesis), accelerated growth at the seedling stage and forced flowering and seeding ready to start the next round of embryo culture. It has significant advantages not only over traditional breeding, but also over DH technology. In traditional breeding procedure, it takes approximately 40-50 days for wheat and barley grains to fully mature, followed by a 20-30 days post-harvest “after-ripening” and dormancy before seeds can be germinated for the next generation. A 3-4 month period is normally required for the cereal developing from seeding to flowering in the field. By forcing flower differentiation through managements of light, temperature, watering and potting mix, the seeding to flowering stage can be shortened into 30 days. The total time for one generation can then be shortened to 40-45 days. By incorporating molecular marker assisted selection we can ensure the selected lines in each generation all contain desired genes. FGS will speed up breeding procedure dramatically without losing any recombination benefit. If such a system is made available to Australian breeders, the efficiency of breeding can be significantly increased. This system is also useful for researchers wanting to quickly produce populations of recombinant inbred lines (RIL) and/or near isogenic lines (NIL) for many areas of research.
- Professor Haibo Wang