Yao He1, You Zhang2,3, Yongxiang Liao1, Elizabeth S Dennis4,5, W James Peacock2,3, Xianjun Wu6. 1. State Key Laboratory of Crop Gene Exploration and Utilization in Southwest China, Rice Research Institute, Sichuan Agricultural University, Chengdu, 611130, China. 2. University of Technology Sydney, Broadway Sydney, NSW, 2007, Australia. 3. CSIRO Agriculture and Food, Canberra, ACT, 2601, Australia. 4. University of Technology Sydney, Broadway Sydney, NSW, 2007, Australia. Liz.dennis@csiro.au. 5. CSIRO Agriculture and Food, Canberra, ACT, 2601, Australia. Liz.dennis@csiro.au. 6. State Key Laboratory of Crop Gene Exploration and Utilization in Southwest China, Rice Research Institute, Sichuan Agricultural University, Chengdu, 611130, China. Wuxj@sicau.edu.cn.
Abstract
MAIN CONCLUSION: We have developed long term stable high yielding rice lines, Hybrid Mimics, from commercial hybrids. The vigour of the Mimic and the hybrid are developmental changes. These Mimics could substitute for hybrid seed for planting. We have used two pre-existing high-yielding hybrid systems (FLY1 and DY527) to develop Hybrid Mimics. In the FLY1 hybrid system we selected, under field conditions, F6 lines which have high grain yields and biomass equivalent to the F1 hybrids, stable over subsequent F7, F8 and later generations. We have termed these lines Hybrid Mimics. The mimics are mostly homozygous as a consequence of selfing in each generation. We have repeated this selection procedure in the second independent hybrid system DY527, producing Mimics with similar characteristics to the F1 hybrid. In both hybrid systems the selection criterion, based on the phenotype of the F1 hybrid, results in the Mimics having grain yield and biomass similar to that of the F1 hybrid. In each generation of the breeding program the plant population has increased phenotypic homogeneity. The genomes of the Mimic plants do not contain any common heterozygous segments negating claims that the vigour of hybrids depends upon heterozygosity of particular loci. Both hybrids and Mimics have early germination and commence photosynthesis before the parents, providing enhanced growth which is maintained throughout the life cycle. The biochemical parameters of photosynthesis in the hybrids and Mimics do not differ from those of the parents. Grain quality and resistance to the two major diseases, bacterial blight and rice blast are similar in the Mimics and hybrids. The Mimics overcome the major disadvantage of hybrids where F2 phenotypic segregation prevents their use as a crop beyond the F1 generation.
MAIN CONCLUSION: We have developed long term stable high yielding rice lines, Hybrid Mimics, from commercial hybrids. The vigour of the Mimic and the hybrid are developmental changes. These Mimics could substitute for hybrid seed for planting. We have used two pre-existing high-yielding hybrid systems (FLY1 and DY527) to develop Hybrid Mimics. In the FLY1 hybrid system we selected, under field conditions, F6 lines which have high grain yields and biomass equivalent to the F1 hybrids, stable over subsequent F7, F8 and later generations. We have termed these lines Hybrid Mimics. The mimics are mostly homozygous as a consequence of selfing in each generation. We have repeated this selection procedure in the second independent hybrid system DY527, producing Mimics with similar characteristics to the F1 hybrid. In both hybrid systems the selection criterion, based on the phenotype of the F1 hybrid, results in the Mimics having grain yield and biomass similar to that of the F1 hybrid. In each generation of the breeding program the plant population has increased phenotypic homogeneity. The genomes of the Mimic plants do not contain any common heterozygous segments negating claims that the vigour of hybrids depends upon heterozygosity of particular loci. Both hybrids and Mimics have early germination and commence photosynthesis before the parents, providing enhanced growth which is maintained throughout the life cycle. The biochemical parameters of photosynthesis in the hybrids and Mimics do not differ from those of the parents. Grain quality and resistance to the two major diseases, bacterial blight and rice blast are similar in the Mimics and hybrids. The Mimics overcome the major disadvantage of hybrids where F2 phenotypic segregation prevents their use as a crop beyond the F1 generation.