QTLs and epistasis for seminal root length under a different water supply in rice (Oryza sativa L.)

To identify the genetic background of seminal root length under different w ater-supply conditions, a recombinant inbred (RI) population consisting of 150 lines, derived from a cross between an indica lowland rice. IR1552. and a tropical japonica upland rice, Azucena, was used in both solution cultur e (lowland condition) and paper culture (upland condition). Quantitative tr ait loci (QTLs) and epistatic loci for seminal root length were analyzed us ing 103 restriction fragment length polymorphism (RFLP) markers and 104 amp lified fragment length polymorphism (AFLP) markers mapped on 12 chromosomes based on the RI population. One QTL for seminal root length in solution cu lture (SRLS) and one for seminal root length in paper culture (SRLP) were d etected on chromosomes 8 and 1, and about 11% and 10% of total phenotypic v ariation were explained. respectively. The QTL for SRLP on chromosome I was very similar with the QTL for the longest nodal root referred to in a prev ious report; this QTL may be phenotypically selectable in a breeding progra m using paper culture. Five pairs of epistatic loci for SRLS were detected. but only one for SRLP, which accounted for about 60% and 20% of the total variation in SRLS and SRLP. respectively. The results indicate that epistas is is a major genetic basis for seminal root length, and there is a differe nt genetic system responsible for seminal root growth under different water supply conditions.