Primary Mapping Of A Dwarf Gene And Its Interaction With Sd1 Gene In Rice (Oryza Sativa L.)

Two breakthroughs in rice breeding that led to quantum leaps in productivity were the introduction of semidwarf varieties in the 1950s and of hybrid rice in the 1970s.The first green revolution in rice breeding is the use of semidwarf gene Sd1 to cultivate new varieties of lodging resistance,greatly improving the worl-d grain production.The longterm use of a single semidwarf gene Sd1 is not conducive to maintaining a variety of dwarf source,there are many potential risks.It is still an important task for rice breeding to identify,identify and utilize new dwarfing resources.Single segment substitution lines（SSSLs）each with a single chromoso-me segment from a donor under the same genetic background as the recipient weredeveloped in rice by advanced backcrossing and molecular marker-assisted selection.In this study,the dwarf tiller mutant M22-3-2,a Japonica cultivar,was hybridized with eight Sd1-SSSLs materials from different eight donors.After 5generations of backcrossing and screening,sdm gene and Sd1 gene were introduced into huajingxian 74（HJX74）,an elite Indica cultivar,constructed with HJX74 as the genetic bac-kground of sdm-SSSLs,Sd1-SSSLs and sdm-Sd1 double segment pyramiding lines.The main results are as follows:1.Construction of sdm-SSSLs,Sd1-SSSLs and Sd1-sdm double segment pyramiding lines.In 2013,M22-3-2 was hybridized with eight Sd1-SSSLs,which obtains eight hybrid combinations F₁containing Sd1 gene and sdm gene.From 2013 to 2014,F₁ plants were backcrossedwith HJX74 to develop the BC₃F₁ generation.316 pairs simple sequence repeat（SSR）markers covering 12 chromosomes of rice was selected to detect genome-wide of eight BC₃F₁.It was found that these BC₃F₁ contained 6¹0 segments that were not the genetic background of HJX74.In order to eliminate residual chromosomal segments or nontarget chromosomal segments from donors,the BC₃F₁ plants were backcrossed with HJX74 to develop the BC₅F₁ generation in 2015.Through the whole gene detection,we found that eight BC₅F₁ contain only two fragments containing Sd1 gene and sdm gene and the BC₅F₁ other genetic background was the same to HJX74.BC₅F₁ were selfcrossed to produce the BC₅F₂ generation.sdm-SSSLs,Sd1-SSSLs and sdm-Sd1 double segment pyramiding lines were selected in BC₅F₂ generation.2.Localization of gene sdm using single segment overlap group.In this study,27SSSLs,with HJX74 as genetic background and covering M22-3-2 chromosome 12,were developed from advanced backcrosses between the recipient,HJX74 and the donor,M22-3-2 by microsatellite marker assisted selection（MAS）from 2013 to 2015.According to the principle of single segment overlap group mapping,we used these SSSLs to finally locate the sdm gene in the marker MM1304 and C30,within the range of about 3000 kilo base.3.Interaction between sdm of dwarf tiller gene and Sd1 gene of high stem.In 2016,we planted eight combinations of sdm-Sd1 double segment pyramiding lines and analyzed the interaction effect of gene sdm and Sd1 from plant type,grain type and yield factors,evaluating the breeding potential of those pyramiding lines.Compared with HJX74 in the mature period,the pyramiding lines increased yield by 35%without changing in grain size and 1000 grain weight,the pyramiding lines increased culm length by about 22%and tripled the tiller number.The plant height showed that the internode of stem are elongated in proportion,which is mainly caused by the interaction of Sd1 gene and sdm gene;The increase in tiller leads to an increase in yield,which was mainly due to the effect of sdm gene.In this study,sdm gene and Sd1 gene were introduced into HJX74,and a series of SSSLs and sdm-Sd1 double segment pyramiding lines were cultivated.We initially mapped the sdm gene in the centromere region using a single fragment overlap group,which laid the foundation for fine positioning and map cloning.The results showed that the pyramiding lines improved the plant type of HJX74,increased the yield of HJX74 and realized the design breeding goal of"dwarf seeking high".In short,the pyramiding lines is a new semi-dwarf resource,with strong breeding potential.