Quantitative trait loci for phyllochron and tillering in rice

Morphogenetic processes in sequentially growing leaves and tiller buds are highly synchronized in rice (Oryza sativa L.). Consequently, the appearance of successive leaves in the main tiller acts as the 'pacemaker' for the whole shoot system development. The time interval between the appearance of successive leaves (days/leaf) in the main tiller is called the 'phyllochron'. The objectives of the investigation reported here were: (1) to identify quantitative trait loci (QTLs) that control rice phyllochron and (2) to understand the roles of phyllochron QTLs as an underlying developmental factor for rice tillering. For this purpose we developed a set of recombinant inbred lines derived from a cross between IR36 (indica) and Genjah Wangkal (tropical japonica). Composite interval mapping detected three phyllochron QTLs located on chromosomes 4, 10 and 11, where the presence of a Genjah Wangkal allele increased phyllochron. The largest QTL (on chromosome 4) was located on the genomic region syntenic to the vicinity of the maize Teopod 2 mutation, while the QTL on chromosome 10 was close to the rice plastochron 1 mutation. These three phyllochron QTLs failed to coincide with major tiller number QTLs. However, one tiller number QTL was associated with small LOD peaks for phyllochron and tiller-bud dormancy that were linked in coupling phase, suggesting that linked small effects of phyllochron and tiller-bud dormancy might result in a multiplicative effect on tiller number.