A Comparison of effectiveness of selection in rice hybrids between pedigree, mass-selection and bulk system of breedin method.

Abstract

A hybrid population between a Japanese rice "No-rin 36" and a chinese rice "Reishiko" was treated by each of the 3 systems of breeding method, pedigree, mass-selection and bulk. In pecligree system 5, 000 plants were grown and 248 individuals were selected from F2 population. Selection and pedlgree culture were repeated in eclch generation from F2 to F6 as in ordinary way. In mass-selection system, also, 5, 000 plants were grown for individual selection in F2 and their seeds were mixed in groups. Individual selection and bulk of seeds were repeated in each follwing generation untill the F6. Populations in bulk system were raised in 3 Iocations from F2 to F6 where the climatic and biological environmental conditions were different. The number of plants used in bulk system were 1, 500 in F2 and 5000 in each following generation at each location. In F6, individual selection was done in each location. In F7 and F8 generation, the performance test was conducted for all selected lines from each 3 systems of breeding method to compare the effectiveness of selection between these systcms. The results show that the pedigree system had more ones with high yield, strong culm or early maturity as compared to the bulk system. The inferiority of the bulk system in the effectiveness of selection may mainly due to: ( 1 )the weakness of individuals with good characters in the compctition of bulk population, ( 2 ) the shortage of number of individuals in F6 generation and that of lines in F7 used in bulk system and ( 3 ) the effectiveness of individual selection for the grain-weight paralleled with plant-type in F2 of the pedigree system. By the mass-selection system, on the other hand, there were many heterozygous lines in F7 though they were good in growth and yield. They indicated that the individual selection in heterozygous hybrid population had a high possibility to select heterozygous plants with heterosis and it was difficult to fix them in homozygous conditicn without pcdigree culture. The results also revealed that : ( 1 ) the parentoffspring correlation coefficients between individual and line (F2-F3, F5-F6), and that between line to line (F3-F4, F6-F7) calculated in the pedigree system were large for heading-time, culm-length, spikelength, quality of brown rice and disease resistance and small for grain-weight and number of spikes, ( 2 ) the natural selection for the agronomical characters, especially for heading-time and disease resistance, in bulk populations was different for the environ mental conditions of locations where the hybrid population were grown. From the result, it was recognized that environmental conditions of breeding station had significant effects on the effeciency of selection in breeding work, espccially in the bulk system.