Abstract
Genic analysis for heading time was conducted in six crosses of rice involving two Japanese representatlve varleties "Koshihikari" and "Shiranui" by the ald of the close linkage with blast resistance. Koshihikari is a leading rice variety that has been grown in the wide area of the temperate region of Japan since the release in 1956, due to its excellent eating quality and earliness. A late maturing variety Shiranui was released in 1964 for the growing in the Kyushu area of Southern Japan. These two varieties are frequently used as the genetic source of quality and yield in the present rice breeding programs in Ja pan. Two lines, an early maturing "ER" and a late maturing "LR", were used as testers for the genic analysis of heading time. ER and LR were developed from a cross between a Malaysian variety "Morak Sepilai" and a Japanese "Fujisaka 5" by four-time backcrosses of Fujisaka 5 as a recurrent parent. They have the Pi-zt gene for blast resistance derived from Morak Sepilai. These two lines were selected from a single plant of BC4F1 and have a plant type similar to Fujisak-a 5 except for the late maturity of the LR line. The Pi-zt gene is linked to the heading locus Lm with 2. 4% of recombination in the linkage group I (YOKOO and FUJIMAKI 1971). LR carries a late allele of the Lm locus, while ER has an early allele and heads at the same time as Fujisaka 5.
