Genetic dissection of the relationships of biomass production and partitioning with yield and yield related traits in rice

Plant breeders often use biomass (BM) and harvest index (HI) to explain the grain yield (GY) increases in cereal crops as GY can be expressed as the product of BM and HI. In the cur-rent study, traits associated with this multiplicative relationship were investigated in a multi-replication field trial with a doubled haploid population of rice and QTL analyses were performed using QTLMapper1.0. Three QTLs for grain yield with R-2 values ranging 17-23% were resolved. For each of the traits of biomass and harvest index, four QTLs with R-2 values ranging 13-28% and 7-23%, respectively, were detected. Among the three GY QTLs, two co-located with two of the four BM QTLs on chromosomes 1 and 3, respectively, and the remaining one co-located with one of the four HI QTLs on chromosome 1, suggesting that grain yield increase might be genetically explained by either biomass enhancement or harvest index improvement. In each of the chromosomal regions, the co-located QTLs all produced additive effects in the same direction, which was in good agreement with the positive correlation between the traits. In addition, none of the BM QTLs was found to overlap with any of the HI QTLs, thus suggesting that a genotype with biomass and harvest index both increased could be obtained by pyramiding the positive alleles for these two traits. Both correlation analysis and QTL mapping revealed that spikelet number per particle (SNP) was closely associated with all of grain yield, biomass and harvest index but was relatively more closely associated with biomass than harvest index. Five plant height (PH) QTLs with R-2 values ranging 4-29% were detected. These PH QTLs were mapped to two types of chromosomal regions, one that tended to contribute weakly to plant height but strongly to grain yield and/or biomass, and the other that mainly affected plant height. Obviously, due to a close association of plant height with plant lodging susceptibility, distinguishing these two types of chromosomal regions should be critical in breaking the traits' undesired association in rice breeding. (C) 2004 Published by Elsevier Ireland Ltd.