Identification of QTLs controlling heading date on the short arm of chromosome 3 in rice (Otyza sativa L.)

Heading date (flowering time) in rice is a major factor in regional and seasonal adaptation. The shaping of adaptability to local areas has advantages for rice growth. In this study, we identified a quantitative trait locus (QTL) controlling heading date with a small effect in advanced backcrossed progenies. A near isogenic line (NIL) of rice variety Hoshinoyume for a major QTL controlling low-temperature germinability on chromosome 3, qLTG3-1, from Italica Livorno was developed. This NIL showed not only vigorous low-temperature germinability but also early heading with short culms compared with Hoshinoyume. QTL analysis revealed that a QTL controlling heading date, qDTH3, is located in the same chromosomal region as qLTG3-1. The late heading parent Italica Livorno-derived allele at qDTH3 showed early heading. Substitution mapping using a series of introgression lines carrying chromosomal segments from Italica Livorno revealed that qDTH3 involves multiple sub-QTLs, which have different genetic effects on the control of heading date. Recombination within the target region of qDTH3 provides new opportunities for altering heading date in local populations to shape adaptability.