Submitted to: Germplasm Release
Publication Type: Germplasm Release
Publication Acceptance Date: December 21, 2004
Publication Date: N/A
Technical Abstract: These four lines are induced early flowering mutants from two International Rice Research Institute (IRRI) germplasm lines which approach U.S. grain quality standards. The IRRI lines themselves are too late in maturity for U.S. conditions, so the present early flowering mutants were induced. The four mutants are a continuation of a base broadening effort to develop indica germplasm suitable for U.S. rice, in which indica-1 to indica-9 were previously developed by recombining very early maturity of an indica cultivar from China with intermediate amylose content of late maturing experimentals from IRRI (Rutger et al., 2005). In the U.S., very narrow genetic bases, essentially all japonicas, have evolved because of need for adaptation to temperate climate and to specific grain quality requirements. Thus long grain cultivars in the U.S. are tropical japonicas which have such specific grain quality requirements that infusions of germplasm from indica sources usually have been limited to individual characters such as semidwarfing and disease resistance, followed by backcrossing to the japonica parent to recover satisfactory grain quality. The present four indica mutants, and their respective late maturing indica parents, have grain shape and amylose contents similar to U.S. long grain japonica cultivars. The mutants are 16 to 29 days earlier than their indica parents, but are only 10 to 14 days later than a prominent japonica check cultivar. They provide useful sources of indica diversity for U.S. rice improvement programs.