The Construction Of Mutant Population For Japonica Rice Variety "Nipponbare" And The Genetic Analysis For Some Mutant Traits In Rice (Oryza Sativa L.)

Now-a-days, rice is markedly diversified from the view-point of genetics, rice mutant has become prerequisite for morphology, physiology as well as functional genomics research, and many genes have been isolated from different mutants in rice. In present study, the seeds of japonica variety (Oryza sativa L. ssp. japonica) Nipponbare were treated by ethyl methane sulphonate (EMS) in order to construct the mutant library. From 40,162 M₂ seedlings, total of 981 mutants were screened with the mutant-induced frequency of 2.44%, in which the albino was highest frequency (1.3%), followed by the dwarf and rolled leaf (0.24% and 0.18%, respectively). By using hydroponics method, whole root system could be observed clearly for screening root mutants. About 117 root mutants comprising of long root, short root, less adventitious root, less lateral root and abnormal root was identified; but only 41 root mutants were found stable in inheritance after M3 validation. After morphological mutants were picked up, the remaining seedlings were sprayed with 0.25% Basta (herbicides) solution or treated with 1.2% NaCl solution or placed in 25% PEG 6000 solution for testing ability of herbicide resistance, salt tolerance and drought tolerance respectively. Fifty three herbicide resistance mutants, 42 salt tolerance mutants and 33 drought tolerance ones were identified with frequency of 0.43, 0.32 and 0.22 respectively. By inspection in M3, only 29 herbicide resistance mutants, 17 salt tolerance mutants and 13 drought tolerance ones could propagate to their offsprings without segregation.In 2006, mutants of morphological traits, after screening in M₁ and transfer to the field were found to occupy 56.15% of mutant library in M₂. Among them, culm and tillering trait mutant was most abundant with frequency of 37.68%, followed by leaf, panicle and spikelet mutants with frequency of 33.5%, 16.75% and 12.07%, respectively. Mutants for root traits, abiotic stress resistance and physiological traits occupied the remaining 43.85%. Besides, present study also identified some special mutants such as polyembryonic mutants and white panicle mutants also were captured, albeit with low frequency and could be propagated stably to next generation. M3 validation carried out in 2007 revealed that different mutants, including leaf, root, plant height, culm, panicle, spikelet, fertility and heading time could be stably inherited from generation to generation. By selecting the typical and stable mutants, a library of 412 EMS-mutagenized mutants, which were mostly stable in inheritance, was constructed in M3. And mutants of morphological traits (consisting of leaf, culm and tillering, panicle and spikelet traits) still occupied highest frequency of 59.95% of mutant library.From 4,043 brown rice materials, a pool of grain quality mutants (including brown rice appearance and rice quality mutants) was conducted. 116 mutants for brown rice appearance (including large chalkiness, big embryo, broad grain, small grain, round shaped grain, slender, glutinous rice, red colored rice). Near infrared spectroscopy (NIRS), which has several well-known advantages, was used for screening rice quality mutants and 435 nutrient characteristics (including amylose content, gel consistency, alkali spread value, protein content and amino acids) were also classified in M3. Validation in M4 showed that about 75 mutants brown rice appearance which were screened in M₃ were stable in inheritance (homozygous).Some typical mutants (such as green yellow, rolled leaf, herbicide resistance, long root) were chosen to make hybridization with wild type. Genetic analysis results showed that, segregation in F₂ of these mutants tallied with 3:1 ratio of Mendelian inheritance for single gene controlled traits. By making an intesubspecific crossing between green yellow mutant of Nipponbare and green yellow mutant of 93-11, segregation in F₂ which suited ratio of 9:7, revealed that two mutants were controlled by two non-allelic genes that interact complementarily. These informations might be essential to elucidate the biological function of rice genes and possibly facilitate genetic analysis and positional cloning.