Genetic Analysis of a Short-Root Mutant LM 10 induced from Rice(Oryza sativa L.) Cultiver IR 8

We analyzed the inheritance of a mutation that causes short roots. The mutant, called LM 10, was derived from an M2 population of rice (Oryza sativa L., cv. IR8) seeds treated with NaN3. In reciprocal crosses between the mutant and wildtype, all F1 progeny had the same root length as the wildtype, however, F2 progeny segregated wildtype and short root lengths in a 13:1 ratio. Segregation analysis for short-root was also carried out in reciprocal backcrosses, with short root heterozygotes (i. e., LM 10/IR 8) backcrossed onto the short root parent. When the short root parent was female, segregation was 1:1 as expected, but when the short root parent was male, the wildtype to mutant segregation ratio was 6:1. From this result, we infer that the distorted segregation (13:1) in the F2 could be caused by a difference in fertilization ratio between wild type and short-root type pollen (about 6:1 in the F1 population). Altoget:her, these results indicate that the short-root phenotype in LM 10 is controlled by a single recessive gene (srt-2). Additionally, allelism was checked between srt-2 and two other mutations known to cause short ro, ots (srt-1 and rt) by pairwise crosses between the three lines. All such crosses produced only wildtype progeny, indicating that the genes of srt-1, srt-2 and rt are locat, ed at different loci.