Genetic Analysis of Spreading Stub Using indica/japonica Backcrossed Progenies in Rice

Improving plant type is one of the principal objectives of rice breeding: programs. However, little information about the genetic basis of plant type is available. For progenies derived from indica/Japonica crosses, the variation of plant type is continuous and complex, so genetic analysis of such traits is often difficult. This study was undertaken to clarify the genetic basis of spreading stub, an inferior plant type character for recent Japanese elite rice varieties. Two different plant types, spreading stub and erect, were observed in one population (BC₃F₂) derived from a selected backcrossed plant, in which a japonica variety, Nipponbare, was the recurrent parent and an indica variety, Kasalath, was the donor parent. BC₃F₃ lines derived from each BC₃F₂ individual were also classified into 3 distinct types, erect (9 lines), spreading (12 lines) and segregating into both types (29 lines). Spreading type was observed about 3 times more frequently than erect type in each segregated line. These results suggest that spreading stub was controlled by a single dominant gene. Moreover the tentatively designated locus, Spk(t), was mapped, with RFLP markers, on chromosome 9.