Morphological Characteristics And Genetic Mapping On A Clustered Spikelets Mutant In Rice

Rice is one of the most important grain crops in the world.The developmental result of the floral organ directly influences on the output and the quality of rice.Rice is a representative monocotyledon and a gramineous model crop.The research on the genetic and molecular mechanism of the developmental regulation of rice floral organ has been the focal point of research on the developmental biology of plants.The development of the developmental biology of plants has improved the knowledge about the shape and the attribute of the floral organ,which has been the focal point of research on the developmental biology of plants together with the research on floral organ development related gene.The development of flower is the obvious characteristic in the reproductive growth period.The forming process of the floral organ is one of the importance characteristics of plants.The development of flower is the result of transformation from vegetative growth to reproductive growth.Such a transformation causes the formation of a structure more complex than the vegetative organ,that is,inflorescence.Therefore,the process of the morphological development of flower provides a system suitable for the research on the molecular mechanism of the genetic regulation.The rice is the model plant of the monocotyledon so the researches on the reproductive development of rice, especially the molecular genetic mechanisms of flower induction and floral organ generation,are important in theory and in practice.Multiple inflorescence mutants have been found in dicotyledonous Arabidopsis thaliana and Antirrhinum majus;and the related genes thereof,such as LFY and TFL in Arabidopsis thaliana and FLO in Antirrhinum majus,have been cloned.Some inflorescence mutants relating to the mutation of morphological structure,such as spike-stalk curled mutant FZP and lax-spiked mutant Lax,have been also found in monogenus rice.A fascicled mutant(Cl-dz) has been found in the filial generation of maintainer line Kangfeng B and Jin-gu B of indica rice.Such a mutant was identified through observation of spike anatomy and paraffin section,observation under scanning electronic microscope and genetic analysis of the mutant character.The related genes thereof were primarily located by molecular marker.The main results are as follows: 1.Phenotypic characteristic of Cl-dz mutant:Compared with wild type,the mutant tyre is slightly higher;the plant type is not compact;the number of the spikes decreases a little; and the grain is a little bigger.Two or three pieces of spikes at the top of the secondary rachis branch are fascicled in 'W' shape.Flowering and fructification are normal.Being observed under the anatomical lens,the mutant has more cells than the wild type at the growing parts of the last two spikes at the top of the secondary rachis branch.Being observed from the paraffin section,no anomaly was found at the growing part of the spike at the top of the secondary rachis branch.2.Observation of developmental process of mutant spike under scanning electronic microscope:The mutant had no obvious difference from the wild type during the forming process from bract primordium to floral primordium;the mutant was abnormal during the period from floral primordium to closure of flower glume;two to three pieces of spikes at the top of the secondary rachis branch were fascicled due to the abnormal development of the rachis branch of the top spike.3.Genetic analysis of mutant trait:The F₂ and BC₁F₁ populations came from the mutant crossing with other rice materials and investigated mutant characteristics under each kind of background separation,the separate analysis of the mutant character showed that the F₂ separation proportion of the normal plants to the mutant plants was 3:1 and the BC₁F₁ was 1:1.It showed that the mutant character was controlled by a pair of recessive genes,which was temporarily called Cl-dz.4.The F₂ population came from the mutant crossing with G46B was used to map the gene.The publicized SSR marker on the chromosome No.6 was selected for genetic linkage analysis;the gene was located between SSR marker,that is,RM1340 and RM6036;and the genetic distances were 3.6 CM and 7.0 CM,respectively.