Comparison of QTLs for Early Elongation Ability between Two Floating Rice Cultivars with a Different Phylogenetic Origin

Abstract

The ability to initiate stem elongation at the early growth stages of a plant is the major survival mechanism of floating rice in the presence of flooding. We previously identified two quantitative trait loci (QTLs) for this "early elongation ability" on chromosomes 3 and 12 using a Patnai23 (a non-floating cultivar) × Goai (a floating cultivar) F 2 population. The objectives of the present study were: (1) to identify QTLs for early elongation ability in the cross Habiganj Aman VIII (a floating cultivar) × Patnai23, and (2) to confirm the results obtained in our previous diallel analysis indicating that Habiganj Aman VIII might harbour additional gene(s) for early elongation ability compared with Goai. The genotype of a total of 192 F 2 plants was investigated using 85 (9 RFLP and 76 SSR) markers and the plants were assessed for early elongation ability. We scaled early elongation ability based on the position of the lowermost internode that exhibited elongation ("lowest elongated internode", LEI), since the LEI position parallels the time of the onset of stem elongation. As a result, a large QTL detected on chromosome 12 seemed to be common to the two crosses. A small QTL detected on chromosome 1 was unique to the Habiganj Aman VIII × Patnai23 cross, which was consistent with the results obtained in our previous diallel analysis. No QTLs were found on chromosome 3 in this cross. These results suggested that (1) the QTL on chromosome 12 might be the most important one for the expression of early elongation ability in terms of the to percentage of phenotypic variation and consistency in different backgrounds, and (2) diallel analysis might be an effective method for examining differences in genetic control among diverse parents.Key Words: floating rice, QTL, rice, stem elongation. IntroductionFloating rice has been the most important crop in the flood plains of South and Southeast Asia, where water may rise to a height of more than 1 m during the wet season. It characteristically exhibits a remarkable stem elongation in rising water, which is the major survival mechanism in the presence of flooding (Catling 1992). This capacity of stem elongation is mainly ascribed to the early onset of stem elongation. In most rice cultivars, stem elongation starts two months or more after germination, whereas stem elongation might start as early as one month after germination in floating rice cultivars (Takahashi 1988). This ability of floating rice cultivars to start stem elongation at the earlier growth stages is referred to as "early elongation ability" (Mazaredo and Vergara 1979).Previous morphological studies have indicated the following mechanism for the early elongation ability of floating rice. Rice (whether floating or non-floating) stem elongation is determined by the "intercalary meristem" (Kende et al. 1998), which becomes differentiated at a definite stage of plant development, regardless of the water conditions (Takahashi 1988). Generally, in rice, submergence only promotes cell division and cell elongation in the...

Mapping of QTLs for floating ability in rice

“…They identified QTLs for LEI on chromosomes 3 and 12, which were located at almost the same positions as in our results. On the same region of chromosome 12, they also detected QTL affecting LEI from different deepwater variety 'Habiganj AmanVIII' (Tang et al 2005). These QTLs for LEI are probably widely distributed among deepwater rice varieties.…”

Gibberellin biosynthesis and signal transduction is essential for internode elongation in deepwater rice

“…To evaluate deepwater rice traits, it is important to measure the TIL, NEI and LEI (Vergara & Mazaredo 1979;Inouye & Mogami 1980;Nemoto et al 2004;Tang et al 2005;Hattori et al 2007;Kawano et al 2008). However, these measurements do not quantify each internode elongation.…”

“…In this report, we determined whether specific internodes in deepwater rice elongate under DW conditions. Previous studies revealed that three major QTLs regulate DW responses (Nemoto et al 2004;Tang et al 2005;Hattori et al 2007;Kawano et al 2008). In this study, we used a QTL pyramiding line (NIL-1 + 3 + 12) carrying C9285 (deepwater rice) genomic fragments possessing three major QTLs on chromosomes 1, 3 and 12 in the T65 (general cultivated rice) genetic background to examine internode elongation patterns and initiation under DW conditions.…”

Markers Associated with Culm Length and Elongated Internode Length in Japonica Rice

“…Three quantitative trait loci (QTLs) located on chromosomes 1, 3, and 12 controlled internode elongation in deep‐water rice (Tang et al, 2005). Two subsequent studies that used different mapping populations verified the effect and locations of these three QTLs (Hattori et al, 2007; Kawano et al, 2008).…”