Genetic Diversity Of Chinese Wheat Landraces As Revealed By Gliadin And SSR Analyses

Chiense wheat (Triticum aestivum L.) landraces account for one third of the total number of wheat germplasm. Historically, wheat landraces have made tremendous contributions to breeding and production of wheat. Chinese wheat landraces possess many useful genes for wheat improvement. For example, gene Pm24 from 'Chiyacao' is effective against a wide range of powdery mildew isolates. "Wangshuibai" can be one of the best sources of resistance to Fusarium head blight. The deployment and utilization of disirable genes from landraces are important in development of modern wheat cultivars. In the present study, gliadin composition and SSR (also known as microsatellite) technique were used to detect genetic diversity of Chinese wheat landraces that originated from various wheat growing regions.Seventy-two accessions were chosen from the primary core collections of Chinese wheat landraces. Thirty seeds from each accession were cut into two parts. The half kernels without embryos were crushed to analyze gliadin composition using acid polyacrylamide gel electrophoresis. The other half parts of kernels with embryos were germinated and the bulked leaf samples were used to extract DNA to be used in SSR analysis. The microsatellite primers used in this study detects 21 loci located on each wheat chromosome.(1) The results from gliadin analysis indicated that 101 gliadin bands were observed in a total of 2160 kernels from 72 accessions. Among them, ω-, γ-,β- and a-gliadins had 32, 23, 23, and 23 bands, respectively, which formed 229 banding patterns. The frequency of each band ranged from 0.002% to 4.848%. The number of bands within an accession ranged from 14 to 24.The polymorphism of gliadin banding patterns was observed among accesions and within an accession. Nine accessions (12.5%) were identical in gliadin banding patterns among different kernels within each accession. The remaining landraces displayed variation in their gliadin patterns among kernels within an accesion. Most of them had two to three variations of gliadin banding patterns, which account for 30.6% and 27.8%, respectively. Accessions with 4 gliadin banding patterns accounted for 12.5%. The percentage of accessions with 5 to 8 gliadin banding patterns ranged from 1.4% to 6.5%. 'Erpihong' (ZM004659) had as many as 14 gliadin banding patterns. The check entry 'Xiaoyan 6', one of the modern improved cultivar, exhibited identical banding patterns among kernels examined.The different gliadin banding patterns that were observed in 'Erpihong' were not grouped together. All the landraces used in this study were differentiated based on gliadin banding patterns. The average genetic distance among all accessions was 0.899, ranging from 0 to 1.375. The total genetic diversity index the accessions tested was 0.9782. The genetic diversity indexes within and between accessions were 0.8393 and 0.1389, respectively. The genetic diversity indexes of different wheat growing regions were all over 0.9. The largest genetic distance between kernels with different gliadin banding patterns in an accession was 1.3933, which was observed in 'Hongmanghong' (ZM003008).(2) Microsatellite analysis indicated that 18 of the 21 primer pairs were polymorphic among different accessions. A total of 93 alleles were detected with an average of 4.42 and a range of 1 to 10 alleles for each primer pair. Cluster analysis indicated that the wheat landraces were differentiated using the 21 primer pairs used. The accessions witin a wheat growing region were not grouped together. The genetic diversity index ranged from 0.9740 to 0.9801. The average genetic distance between accessions was 0.436, ranging from 0.131 to 0.563.(3) Comparison between gliadin banding patterns and SSR analysis indicated that the range and average of genetic diversity between accessions based on gliadin banding patterns were greater than those based on SSR analysis. However, both methods produced similar total genetic diversity. The clustering results based on gliadin and SSR analyseswere not always agreed well, which might be due to different genetic information of chromosome and loci as determined by each method. Similar genetic diversity indexes based on gliadin and SSR analyses were observed among different wheat producing regions. A high level of genetic diveristy was observed by gliadin composition and microsatellite analyses.Based on the results from the present study, we concluded that: (1) the results of gliadin composition analysis indicated that a high percentage of Chinese wheat landraces are genetically heterogeneit populations that are composed of individuals with different gliadin composition;(2) based on the genetic heterogeneity of wheat landraces, a large population should be considered in order to maintain the genetic completeness during their collection and conservation;(3) analyses of gliadin compostion and SSR demonstrated that the genetic diversity indexes of various wheat growing regions were all over 0.9, indicating that Chinese wheat landraces are rich in genetic diversity and are potentially useful in wheat improvement.