| Rice(Oryza sativa L.) is one of the most important cereal crops, being considered as model organism for the functional genomics research of monocots. With the entire genome sequence of rice being completed, the research of its genes functions has become one of the challenges for the scientific community in the post-genomic era. The identification of rice mutant is the first key step of functional genomics research. Chemical mutagenesis is one of important methods in the establishment of rice mutant. Wuyujing3, a good quality japonica cultivar was used as wild type in the present study. This cultivar has premium quality traits:fine palatability, gloss white rice, does not harden after cool, and maintain the stability of high-quality in different regions. On the other hand, it has some limitations in terms of quality and agronomic characteristics such as high chalky grain rate, sensitive to sheath blight, and relatively lower yield. A total of236mutants with stable traits have been identified by treating the seeds of Wuyujing3with Ethyl Methane Sulfonate after selecting and identifying in four consecutive years. These seven types of mutants not only provide elite germplasm for agronomic and quality improvement of the cultivarWuyujing3, but also provide new materials for elucidating genetic and physiological mechanisms or environmental control mechanism relating to grain yield and quality.The main results were as follows:(1) For leaf mutants, a total of51mutants including fourteen leaf color mutants, twenty-five lesion mimic mutants, four leaf shape mutants, three leaf length and width mutants, three phyllotaxy mutants, one leaf angle mutant and two premature senility mutants were obtained. The lesion mimic mutants can be divided into two types, leaf sheaths with lesion mimic and leaf sheaths without lesion mimic, in accordance with whether the leaf sheath has a lesion mimic. Phyllotaxy mutants can be divided into three types, including the upper three, four and five leaves located in the ipsilateral, in accordance with the location of the leaves. (2) A total of eight mutants were obtained for the rice stem mutants that can further be divided into four different types. These mutants include two dwarf mutants, one high-stem mutant, two more-tiller mutant and three brittle culm mutants. The chalky grain rate of the dwarf mutant was only4%, the agronomic traits of which contained shorter plant height (49.7cm), larger tillers number (31.17tillers/plants), higher ratio of grain length to grain width (1.83), lower thousand kernel weight (20.8g).(3) For reproductive organ mutants, a total of54mutants were obtained, including fourteen long-awn mutants, three short-awn mutants, five split-glume mutants, seven long-glume mutants, seven two-brown-rice-in-one-spikelet mutants, seven sheathed panicle mutants, three early-maturing mutants, seven late-maturing mutants, two brown panicle mutants, and one degenerated spikelet in upper part of panicle. The average awn length of the long awns mutants is4.8mm, which grows so fast that it looks like two hull package on the outside of the hull.(4) Biochemical properties of the236mutants were investigated. Amylose ranged from15.7%to21.7%. The range of albumin was0.54%-0.65%. Globulin content varied from0.66%to0.65%. The scope for prolamin was from4.66%to7.66%. The lowest value of copper content was3.49ug/g, being19.27%lower than that of wild type. The highest value was5.54ug/g,28.22%higher than that of wild type. For iron, the lowest value was8.10μg/g,15.33%lower than that of wild type, and the highest value was14.86μg/g,55.43%higher as compared with the wild type. The lowest and highest were18.27μg/g and37.95μg/g for manganese, respectively. For the zinc content, the lowest value was17.29μg/g, being10.99%lower than that of wild type. The highest value was23.29μg/g,15.69%higher than that in wild type.(5) For appearance quality mutants,31mutants with six types were identified. These mutants include one brown rice mutant, one long grain shape mutant (5.80mm/grain), one short grain shape mutant (3.77mm/grain), sixteen high chalky grain rate mutants (which chalky grain rate is higher than70%), four low chalky grain rate mutant (which chalky grain rate is less than10%) and one milky white rice mutant. The highest chalky grain rate was92%whereas the lowest rate was only4%in2011. These chalky grain mutants serve as elite germplasm for the researches on the formation mechanism of white-belly and white-core rice kernel.(6) A total of nine yield component related mutants were identified, including four types: wild type, high-tillering type, large-panicle type, and intermediate type with balance between panicle number and grain number per panicle. In2011, the yield components of wild type were:pannicles3006.0thousand per hectare, grains per panicle105.83, seed setting rate93.73%,1000-grain weight24.75g, theoretical grain yield7380.15kg/hm2. The high-tillerring type M31had same feature:panicles3820.5thousand per hectare,1000-grain weight18.83g, chalky grain rate7.5%, theoretical yield7961.70kg/hm2, which contained higher yield and improved appearance quality than the wild type. The intermediate type M38represented panicles3507.0thousand per hectare, grains per panicle125.1, theoretical yield10593.60kg/hm2, chalky grain rate40.5%, possessed high yield potential and appearance quality. The traits of large-panicle type materials M26include panicles2610.0thousand per hectare, grains per panicle171.60, theoretical yield11822.71kg/hm2, chalky grain rate45.0%) and the traits of M76include panicles2700.0thousand per hectare, grains per panicle196.67, theoretical yield13873.80kg/hm2, chalky grain rate50.5%. Both of the two large-panicle type materials contained high yield potential but poor appearance quality. The results showed that large-panicle type M26and M76can be used as the intermediate materials of the high-yield breeding and high-tillering type M31can be used as the intermediate materials of breeding in the improvement of appearance quality on Wuyujing3.(7)24panicle mutants were selected which can be further classified into three types: erect panicle type, intermediate panicle type, dispersed panicle type (including "chicken toe" panicle type). These mutants serve as a systematic set of materials for the study of yield and quality formation. This study compared the number of secondary branch, grain numbers per unit panicle length and grain numbers per unit branch length. There was significant difference in the secondary branch number among the following mutants, with dispersed panicle type being20.97, erect panicle type17.88, and intermediate panicle type16.17. No significant difference detected among the three types in grain numbers per unit panicle length. The grain numbers per unit branch length among the three types were significantly different:erect panicle type (2.06grains/panicle), intermediate panicle type (1.83grains/panicle) and dispersed panicle type (1.73grains/panicle). Results indicate that grain numbers per unit branch length could be used as a criterion categorizing panicle type. |
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