Speed Breeding Of New Waxy Wheat Lines

Starch is the main component of wheat grains,accounts for about 50-70%of the dry weight of its grain,and is the main source of energy for humans.Granule-bound starch synthase I（GBSSI）,also known as Waxy protein,is the key enzyme for synthesizing amylose.Waxy proteins in common wheat include three homologous subunits,Wx-A1,Wx-B1 and Wx-D1.The wheat lacking all three Waxy protein is called as Waxy wheat of which the amylopectin content is more than 90%,has unique processing characteristics and nutritional quality,and has great value in flour food..Therefore,the creation of new waxy wheat lines can provide materials for the breeding of special wheat new varieties,which is of great significance for wheat quality improvement.In this study,SM133 is a national approved variety developed by Triticeae Research Institute of Sichuan Agricultural University,was crossed with waxy wheat germplasm WN15 to generate elite waxy wheat lines by combining varied breeding techniques.To add generation propagation,plant tissue culture was adopted.By this method,eight generations in two years can be achieved.The integrated application of pollen iodine staining,KASP molecular markers,and SDS-PAGE methods has shortened the breeding period of 3 or 4 years compared with the traditional breeding program.Finally,a set of Waxy wheat lines lacking all Wx proteins were created,and the agronomic characters,starch content and composition,processing quality index and physicochemical properties of the new waxy wheat line were further analyzed.The main research results are as follows:1.In this study,SM133（Wx-AAbb DD）was selected as the recipient parent,and WN15（Wx-aabbdd）was selected as the null Wx gene donor parent to cross each other,plant tissue culture and adding generation in greenhouse were used to quickly and efficiently create elite waxy wheat lines.The F₁generation was crossed in the greenhouse,and the embryos of the F₁generation materials were selected for tissue culture,followed by rapid generation advancement in a greenhouse.After backcrossing with SM133 three times and self-crossing with SM133 five times,the BC₃F₅generation was obtained.2.The methods of pollen odine staining and KASP molecular marker,iodine staining of grain slice and SDS-PAGE were used to identify and verify the genotypes and phenotypes of backcross and self-cross progenies,which greatly improved the selection efficiency.Heterozygous progenies with 1/4 waxy pollen（reddish brown）were selected for further backcrossing with recurrent parents.Due to the natural absence of Wx-B1 site in SM133,we developed Wx-A1 and Wx-D1 gene specific KASP markers based on the gene sequence.Twenty-nine lines with two recessive homozygous mutations at Wx-A1 and Wx-D1 were identified from 217 BC₃F₂generations by KASP marker,and these lines were further verified by iodine section staining and SDS-PAGE,indicating all Waxy proteins were absent in them.And 29lines were self-crossed to generate Waxy wheat lines with elite agronomic traits.This program greatly improved the breeding efficiency and shortened the time of 3-4 years compared with traditional breeding methods.3.The Wx-1 gene was introduced into the new waxy wheat line,and the excellent agronomic characters were inherited from the parents.Compared with SM133,there was no significant difference in the main agronomic characters of BC₃F₅generation,such as grain length,surface area,100 grain weight,plant height,flag leaf length,spikelet number and tiller number.In this study,Wx-A1,Wx-B1 and Wx-D1 were successfully transferred to elite lines by back crossing.The generated lines inherited excellent traits of high yield,lodging resistance and stress resistance from the donor parent line.The results showed that the introduction of waxy gene had no negative effects on agronomic traits.4.The total starch content,amylose content,sedimentation value,RVA parameters and silty parameters of the waxy wheat lines were analyzed comprehensively,the results showed that the waxy wheat lines had unique starch composition and physicochemical properties.The determination of grain composition showed that the amylose content of the new material varied from 0 to 10%,which met the requirements of starch composition in Sichuan waxy wheat variety.The microstructure analysis of glutinous wheat starch showed that the average polymerization degree of starch particle morphology and starch chain length was not significantly different from SM133,but the branching degree of starch was increased.Although the crystallinity of starch in waxy wheat increased significantly,the crystal structure type has not been changed.In terms of physicochemical properties,the peak gelatinization temperature,end temperature and enthalpy of waxy wheat decreased significantly.The determination of quality parameters showed that the settling value,RVA gelatinization time and silty stability time of the new waxy wheat lines decreased compared to parent lines.Therefore,the novel Waxy wheat lines formed by the absence of Wx protein has a very low amylose content,which significantly changes its starch composition and characteristics,conferring it unique processing quality characteristics and applications.