Genetic Diversity Of Agronomic And Quality Traits On Wheat Landraces From The Yangtze River Region

Yangtze River basin is complex terrain with diversitifed climates. Abundant local wheat varieties have been developed in this area. The research on agronomic and quality characteristics has always been the key of crop improvement in agricultural production. Even when the molecular markers are developing fast these days, fully understanding and scientific assessment of the representing reality of the agronomic and quality characteristic of germplasm materials is still of great importance for rational use of germplasm resources and parent selection. Unfortunately, systematic analysis on the genetic variation of agronomic and quality characteristics of local wheat varieties in the Yangtze River basin is still lacking. The previous researches mainly focused on the genetic diversity of agronomic and quality characteristics of regional or partial varieties. No study was conducted on the analysis of High-molecular-weight glutenin subunits(HMW-GS) of local varieties in Hubei province. We characterized genetic diversity and HMW-GS in477wheat varieties from the Yangzi River basin. using agronomic and quality characteristics. The major findings of SDS-PAGE analysis and MALDI-TOF-MS analysis on the HMW-GS are reported as follows.1. Generally speaking, the wheat varieties in Yangzi River basin studied showed high stalk, precocity, short head, small spikelet number and grain number per spike, high kernel weight. The majority of them have weak stem, poor ear characters, small grain, and are susceptible to lodging. Among the characters studied, spike grain weigh showed wide range of variation followed by the grain number per spike, and the distance from main spike neck to flag leaf pulvinus. No significantly differences were found for plant height, heading date and the number of spikelet number among the varieties.The agronomic traits studied showed significantly difference among different ecological zones and within each zone except for main panicle length, spike numbers of main spike, grain number per spike The averaged plant height of Hubei varieties, which is above120cm, is higher than that of materials from Tibetan Plateau and Australia. The grain number per spike, spike grain weight and kernel weigh in Tibetan varieties are than those in the varieties from Yangtz river region. For the varieties from Australia, The grain number per spike and spike grain weight showed the lowest variation, and the spike grain weight and kernel weigh showed the highest variation among the varieties studied. The results indicated that the agronomic characters of wheat materials from Tibetan Plateau and Australia perform well in Hubei, thus they could be used for wheat breeding. The varieties from the ecological zones in Hubei displyed some undisrable chatacters,it needs better strategy to eccifcetly use the germplasm from Hubei for breeding program.Correlation analysis found significant correlation between grain number per spike, spike grain weight and kernel weigh, indicating that the increase of grain number per spike and kernel weight could redult in the increase of spike grain weight. However, the grain number per spike was nagetively correlated with kernel weigh, increase of grain number per spike could cause the decrease of kernel weight, which is similar to the reports on Polish wheat, Tibet wheat, orient wheat and macha wheat. The negative correlation between plant height, main panicle length and kernel weight indicated that the increase of plant height and panicle length would decrease the kernel weight, which is consistent with the correlation analysis on the261wheat materials collected from all over the country; but is inconsistent with the study on Polish wheat, Tibet wheat, orient wheat and macha wheat.2. The results indicated that the wheat landraces from Yangtze River valley were rich in medium-gluten, few with strong gluten and weak gluten, which was consistent with proposal made in the 《Special-purpose Wheat Regional Development Plan (2003-2007)》.14.14%,77.85%and8.01%of wheat landraces are with protein content reaching high strength gluten index (≥14.00%), middle strength gluten index(14.00%-11.50%), low strength gluten index (≤11.50%) p, respectively. Wheat landraces of wet gluten content reaching high-strength-gluten index (≥32%), middle-strength-gluten index (32.00%～22.00%),low-strength-gluten index (≤22.00%) accouted for0.21%,99.58%,0.21%, respectively. The percentage of local varieties with zeleny reaching high-strength-gluten index (≥45.00mL), middle-strength-gluten index (45.00-30.0mL), low-strength-gluten index (≤30.0mL) were10.97%,88.82%,0.21%, respectively. Therefore, landraces in Yangtze River region of China are valuable resources in wheat breeding.The correlation analysis indicated that starch content was significantly negatively correlated with protein content, wet gluten content, zeleny Starch quality was closely associated with protein quality, wet gluten content, zeleny. These four components determine wheat processing quality. The wet gluten content showed a highly positive correlation with the protein content, with correlation coefficient of0.93.. The wet gluten content can be used as a quality index to evaluate wheat quality. The protein content, wet gluten content, zeleny in the Tibetan local varieties of wheat were significantly higher than those invarieties from other ecological areas. Both protein and starch content did not showed significantly difference among landraces from South-eastern Hubei, East of Hubei, Jianghan plain, West of Hubei, North of Hubei, North-west of Hubei.The starch content of Tibetan local varieties was significantly lower than that in samples from other ecological areas. The results demonstrated that protein content, wet gluten content, zeleny of landraces from Qingzang plateau were superior to those in the local varieties from Hubei Province. Most of the landraces from Qingzang plateau planted in winter in Hubei could normally mature and yield. Therefore they are useful germplasm to improve the wheat quality.3. Among the varieties tested,7+8and2+12subunits are detected in most varieties; and5+10subunit is also very common, and32.14%varieties possessed this subunit. The combinations of high molecular weight glutenin subunits in these varieties tested were mainly divided into3types.286(60.4%) varities contained7+8and2+12subunits,26(5.50%) varieties contained7+8and5+10subunits, and50(10.57%) varieties contained undefined subunits.A total of22alleles are found among the varieties tested, with3alleles for Glu-Al;16alleles for Glu-Bl; and3alleles for Glu-D1locus. Of the3alleles on Glu-A1,0,1,2*, the frequency of0subunit is the highest (89.22%), followed by1subunit (9.73%); and the frequency of2*subunit(1.05%) is the lowest one. Of the16detected subunit types (alleles) at Glu B1,65.96%are7+8subunit followed by?+8subunit (9.51%); the13+16,17+18,7, and20subunits are rare types, with their frequency ranking from1.69%to3.59%. At Glu-Dl site,2+12subunit type is the most common (89.64%), followed by high quality subunit5+10(9.30%).A total of44HMW-GS combination forms are revealed in the varieties. Generally, each combination is consist of3-6subunits. The frequency of subunit combination forms detected in473varieties are quite difference from each other, among which combination form (0,7+8,2+12) is the most frequent(54.97%), followed by (0,?+8,2+12)(8.46%),(1,7+8,2+12)(5.07%),(0,7+8,5+10)(4.23%) and (0,7+9,2+12)(4.23%); the rest are rare subunit combinations, with frequency of0.21%～2.96%. The high quality subunits at Glu-A1site were detected in51varieties (18.68%); at Glu-B1site were detected in73varieties (15.43%); and at Glu-D1site in44varieties (16.12%). Eight varieties have high quality subunits at all the3Glu-1sites, accounting for1.69%of the total;518materials have high quality subunits at2of the3Glu-1sites, accounting for10.78%of the total;351materials have high quality subunits at1of the3Glu-1sites, accounting for74.21%of the total.Although the proportion of high quality subunit combinations is not high among the studied materials, the ratio of high quality subunits is relatively high; especially50unidentified subunit materials are found. They are precious resource for genetic breeding of wheat. Future study on these materials to reveal their contribution to the wheat quality, is of very importance to wheat quality breeding.4. Extensive allelic variation in HMW glutenin subunits was detected among the studied landraces. A total of453of the accessions were homogeneous for HMW-GS composition,32were heterogeneous and37accessions contained abnormal subunits. A total of22normal alleles for the Glu-1loci were detected,3belonged to Glu-A1,13at Glu-B1and6at Glu-D1, resulting in63different allele combinations.In our study, apart from the22normal alleles, twelve alleles encoding abnormal subunits with molecular weights of69,100,69,900,73,000,73,100,75,140,75,600,76,800,79,000,79,100,79,800,83,200,84,300were also detected. This represented a higher rate of abnormal alleles than previous reports, which is likely due to the enhanced resolution in determining the molecular mass of the MALDI-TOF technology. In this study, a large numer of lines had one or two HMWGS genes silenced, especially16lines with the1Bx gene silenced, of which the silencing mechanism is still unclear. These null alleles are valuable resources for dissecting specific allele effects in wheat quality.To conclude, this study characterized the HMW glutenin subunit compositions of485wheat landraces in the Yangtze-River region of China. The information obtained in this study may be used by wheat breeders for breeding new cultivars to meet specific end-product needs. In general,22HMW-GS alleles with16abnormal subunits were identified in a collection of485landraces from the Yangtze-River region of China. Further studies of these novel alleles are currently undergoing to obtain their coding sequences in order to match them with previously reported novel alleles.