Heterosis for yield and its component traits between chromosome segments from IR24, an indica variety, and the counterparts from 02428, a japonica rice, was inves- tigated by using a hybrid F1 population composed of 63 com- binations between 02428 and IR24 chromosome segment substitution lines (CSSLs) with the genetic background of Asominori, a japonica variety. Significant differences in het- erosis for yield and yield-component traits were observed among the crosses. Analysis of graphical genotyping showed that 14 substituted segments were responsible for yield het- erosis. All of them were from all the 12 chromosomes of IR24 except chromosomes 8 and 10. Six segments at the intervals of RFLP markers, such as X132—G1340—R459, X48— C393A, R288—R1854, R2918—X52, X257—C1350 and R367 —X189-2—X24-2 on chromosomes 2, 3, 4, 11 and 12 respec- tively, had very significant heterosis for yield at the level of P ≤0.005 based on t-test, individually increasing the hybrid yield by more than 35% compared with the control cross “Asominori×02428”. Most of IR24 chromosome segments were found to have no significant hybrid effect for yield and yield-component traits, and one segment located at R2171 on chromosome 6 possessed significant negative effect with 27% of yield decrease. Advantages of using CSSLs in the heterosis studies were discussed and approaches of the partial and genome-wide exploitation of rice heterosis between indica and japonica by molecular marker-assisted selection were then proposed.
