crown rootless

8581 Japan

Many mutants affecting root development have been identified in dicots such as Arabidopsis thaliana and tomato, for genetic studies (Zobel 1991, Okada et al. 1996). However genetic mechanism of root formation in monocots are poorly understood, because few good mutations for this character have been induced.

In the previous paper (Hong et al. 1995), we reported the isolation of three recessive rice mutants (odm 40, odm 115 and odm 123) which fail to form radicle. This type of mutation was named radicleless (ral). Recently, we also isolated recessive another radicleless rice mutant (HK8215), and two recessive rice mutants with a defect in formation of crown roots (odm 202 and BRX334). The latter type of mutation was named crown rootless (cr1). HK8215 and odm 202, and BRX334 were identified among M3 populations of Taichung 65 treated with MNU (N-methyl-N-nit rosourea), and Blue Rose subjected to ‘y-ray irradiation, respectively. Here, the genetic analysis of these six mutants showing radicleless and crown rootless is described.

To determine whether the mutations identified in these lines affected the same or different genes, allelism tests were performed among four radicleless mutants and between two crown rootless mutants. All the F, progeny from a cross of HK8215 x odm 40 were radicleless (Table 1), indicating that HK8215 is an allele of odm 40. In the F2 prog
Table 1. Genetic analysis of radicleless and crown rootless mutants enies from the crosses of odm 40 x odm 115, odm 40 x 0dm 123, and odm 123 x 0dm 115, a wild type to radicleless segregation agreed with the 9:7, 9:7, and 3:1 ratios, respectively (Table 1). Therefore odm40 is not an allele of either 0dm 115 or odm 123, but 0dm 123 is an allele of 0dm 115. On the other hand, a wild type to crown rootless segregation in the F2 progeny from a cross of odn 202 x BRX334 was consistent with the 9:7 ratio (Table 1), indicating that 0dm 202 is not an allele of BRX334. These results indicate that there are at least two different loci each for formation of radicle and crown root. One of radicieless locus was named rail and the alleles were designated rail-i (odm 40) and ral1-2 (HK8215), and the other was named ral2 and the alleles were designated ral2-l (odm 115) and ral2-2 (odm 123). crown rootless loci of 0dm 202 and BRX334 were also designated cr11 and cr12, respectively.

*: Heterozygous plants were used for the allelism tests, since the three homozygous mutants were infertile.