Phenotypic identification and genetic analysis of two rice (Oryza sativa L.) mutants induced by heavy ion

Objective  To clarify the phenotypic characteristics and genetic patterns of two rice (Oryza sativa L.) mutants.

Method  Two mutants were screened from the M2 generation of the indica rice germplasm BBS (wild type) induced by heavy ion, named m2 and m3 respectively. Firstly, the mutant materials were identified by means of phenotypic observation and agronomic trait comparison. Secondly, the F₂ populations of 02428 (male parent)/m2 and 02428/m3 were constructed for genetic analysis.

Result  Compared with BBS, the leaves of m2 were inner-rolled and the leaf width was significantly reduced during the whole growth period. The rolling index of flag leaf, the 2^nd and 3^rd leaf from the top were 22.30%, 38.15% and 28.84% respectively, which were significantly different from BBS. The mutant m2 showed a high level of sterility. The new leaf tip of m3 main stem started necrosis on the 54^th day after sowing in early season or 30^th day after sowing in late season. The leaf necrosis phenotype sustained about 25 days and then new leaves recovered to normal phenotype. Compared with BBS, the main panicle weight and grain number of m3 dropped highly significantly, but other agronomic traits had no significant difference. Genetic analysis indicated that the frequency distribution of flag leaf width of the F₂ population of m2/02428 was in accordance with normal distribution. The segregation ratio of normal individuals and leaf necrotic individuals fitted 3∶1 in the F₂ generation of m3/02428.

Conclusion  The mutant m2 is a narrow leaf mutant and the narrow leaf trait is controlled by multiple genes, whereas m3 is a leaf necrosis mutant and the mutant phenotype is controlled by a pair of recessive nuclear genes.