Abstract:To evaluate the tolerance of different maize materials to salt stress during the germination period and to explore the salt talerance of hybrid maize materials from different hybridization patterns during the germination stage. This study used a 160 mmol/L NaCl solution to treat 152 maize inbred lines and 303 hybrid varieties under salt stress. Distilled water culture was used as the control， and salt tolerance during germination was identified using a paper bed culture method in a culture dish. The results showed that salt stress treatment significantly reduced the germination potential， germination rate， and germination index of maize materials. Trait correlation analysis revealed a highly significant positive correlation between different traits. Using the salt tolerance rate during the germination period and combining with the clustering analysis results， the inbred and hybrid materials were divided into five salt tolerance levels： Level I （high tolerance， 4 inbred lines， 17 hybrids）， Level II （tolerance， 19 inbred lines， 58 hybrids）， Level III （moderate tolerance， 47 inbred lines， 120 hybrids）， Level IV （sensitive， 33 inbred lines， 71 hybrids）， and Level V （high sensitivity， 49 inbred lines， 37 hybrids）. Based on the analysis of identity-by-descent （IBD） segments， 146 inbred line materials were divided into 8 groups. The salt tolerance of different groups of inbred line materials was as follows： European maternal group>Complex group>Inbred line 330 group>PB group>Lancaster group>Tangsipingtou group>PA group>Reid group. The hybrid materials are divided into 23 hybridization patterns based on the different parent material groups， among which European maternal group×PB group is the optimal heterosis pattern for salt stress tolerance during germination. This study identified the salt tolerance of inbred lines and hybrid materials， and selected 4 high salt tolerant inbred line materials and 17 high salt tolerant hybrid materials.

Abstract:In this study， 134 maize inbred lines were used as experimental materials to identify phenotypic variations at nine root traits at seedling stage， followed by the genome-wide association study （GWAS） using FarmCPU model based on 44935 SNP markers. The results showed that the phenotypic variations at nine root traits ranged from 10.86% to 55.96%， and the correlation between most phenotypes reached a highly significant level （P<0.001）. The correlation coefficient between lateral root length and total root length was the highest （0.996）， followed by that between the number of lateral roots and total roots （0.993）. A total of 32 significantly associated SNPs were identified （P value arranged from 1.01e-11 to 9.74e-5）， with phenotypic contribution rates ranging from 0.54% to 22.34%. Four， eight， three and nine significant SNPs were detected for main root length， total root length， maximum root length and lateral root length， respectively. Ten， seven and one significant SNPs were detected for total root number， lateral root number and adventitious root number， respectively. Fourteen SNPs were identified associating with multiple root traits. Twelve significant association sites were located within the intervals where root-related QTL （Quantitative trait locus） were reported. Forty-nine root-associated candidate genes were annotated， including formerly-identified GRMZM2G028386 （ABI4）， GRMZM2G135713 （PUB23）， GRMZM5G870592 （MYB98）， GRMZM2G156861 （LOX1）， GRMZM2G160005 （AUX16）， GRMZM2G126936 （NAC2） and other important root candidate genes. Thus， this study provided reference for future cloning genes related to root development and analyzing the molecular mechanisms of root development in maize.

Abstract:Soil salinization and alkalization reduce the usability of arable land and impair crop production. Identifying and selecting maize germplasm showing salt-tolerant is of significant importance in the reclamation and utilization of saline-alkali land. To determine the optimal NaCl concentration for screening salt tolerance in maize seedlings， 16 representative inbred lines were treated with 0 （control）， 100， 150， 200， 250， and 300 mmol/L NaCl solutions for seven days. Six indicators， including shoot height， root length， shoot fresh weight， root fresh weight， shoot dry weight and root dry weight， were measured， along with recording the seedling conditions. The results showed that after seven days of salt treatment， significant differences were observed in all indices under 150 mmol/L compared with the control， and the coefficient of variation was greater than at other salt concentrations. Therefore， 150 mmol/L was identified as the optimal concentration for salt tolerance identification in maize inbred lines， and a salt tolerance identification technology was developed. Using this technology， 76 maize inbred lines were analyzed， and a comprehensive salt tolerance evaluation index （D） was calculated using the weighted subordinate function method and cluster analysis. The 76 lines were categorized into four groups： high salt tolerance， salt tolerance， salt sensitivity， and high salt susceptibility. Among them， the inbred lines Ming71， Zhong106， Si-287， and 8112 showed the strongest salt tolerance， serving as valuable resources for salt tolerance maize breeding. The salt tolerance coefficient of the fresh weight of the above-ground tissues showed the highest correction with the D value and could be used as the primary indicator for evaluating salt tolerance in maize inbred lines during the seedling stage.

Abstract:The wheat grain hardness is an important index affecting the commodity classification， milling technology and flour final processing use. Molecular marker-assisted （MAS） technique can effectively improve the breeding efficiency for grain hardness in wheat. In order to explore and develop more molecular markers that are closely linked to the grain hardness of wheat， the recombinant inbred lines （RILs） population was constructed by crossing the hard wheat Yangmai 158 with soft wheat Xifeng， and genotyped by wheat 55K SNP array technique. The genetic linkage map is 2784.9 cM in length with 3830 non-consegregation SNP markers. Based on the kernel hardness phenotype in the 4-year experiment， the QTL affecting wheat grain hardness were mapped in the chromosome. A total of 12 repeatable QTL were identified on chromosomes 1A， 1B， 1D， 2A （2）， 3A， 4D， 5A， 5D， 6B， 6D and 7A， and each single QTL could explain 3.2%-15.2% of grain hardness variation. Among them， eleven QTL were derived from the soft wheat Xifeng， and one QTL from the hard wheat Yangmai 158. Seven QTL showed stable performance and were detected simultaneously in the 4-year experiment， and five QTL were newly identified. The newly discovered QTL， especially QTL on chromosome 5D， could account for up to 15.2% of the phenotypic variation. SNP markers closely linked to these QTL will provide help for marker-assisted selection in soft wheat in the middle and lower reaches of the Yangtze River.

Abstract:Maize key inbred line Huangzaosi had been developed in the 1970s in China， exhibiting meritsincluding robust adaptability， high combining ability， compact plant shape， short growth period and fast grainfilling. To date， hundreds of maize inbred lines with the genetic components derived from Huangzaosi haveformed a core maize germplasm group referring‘ Huanggai’ group（ or Tangsipingtou Group） . The hybridsdeveloped by Huangzaosi and its derived lines have been popularized and cultivated up to hundreds of millionshectares， including the current leading varieties in China， Jingke968 and Zhengdan958. Although this line hasplayed an important role in the maize breeding history in China， its pedigree and origin still remain unclear. Here，according to previous description of the breeding processes of Huangzaosi， we inferred that the white kernelinbred line of Tangsipigtou was initially out-crossed with another maize breeding material with earlier maturationand yellow-colored kernel followed by the backcrossing in the Tangsipingtou field， from which Huangzaosi wasfinally developed through later artificial selfing and selection. The comparison of DNA molecular fingerprintsobtained by the 40 core SSR markers for Huangzaosi， Tangsipingtou and 9 landraces and inbred lines planted inthe early 1970′ s indicated that Huangzaosi and Tangsipingtou shared the same 28 SSR loci， and the rest 12 wereonly identical between Huangsipingtou and Huangzaosi. Whole genome-based IBD genetic structure analysis further demonstrated that Tangshipingtou was the major donor for Huangzaosi， and Huangsipingtou was anotherparent. In addition， the correspondence comparison of phenotypic and morphological traits confirmed that thephenotypic and agronomic characteristics of Huangzaosi were consistent with the conclusion that it was derivedfrom the crossing of Tangsipingtou and Huangsipingtou. To sum up， this study deciphered the long mystery of theorigin of‘ Huangzaosi’ .

Abstract:Stem is an important constituent part of the maize plant， which closely affects lodging and grainyield. A study of the trend of stem-related traits of inbred lines of maize grown in China in different decades from1960 s to 1990 s would provide references for maize breeding for lodging resistance and high yield. In this study，maize stem-related traits， including stem height（ SH）， ear height（ EH）， stem node number（ SN）， ear node（ EN），stem diameter（ SD）， stem moisture content（ MC）， stem soluble sugar content（ Brix）， and ear height coefficient（ EHc） and ear node coefficient（ ENc） derived from some of them were investigated in 65 representative maizeinbred lines of the different decades. Using these stem-related phenotypic data， ANOVA， correlation analysisand the trends in the different decades were studied. The results showed that there were significant differences inthe stem traits among the maize inbred lines， while no significant difference of maize stem-related traits existedamong the different decades； SH， EH， SN， and EN were decreasing from decade to decade； the EH improvedsignificantly in the time period； around the 1980 s， the selection criteria of maize stem thickness reversed fromrobust to slender stems， which might be resulted from the breeding goal of increasing yield through rational denseplanting； in the 1990 s， MC decreased by 3%， which was significantly different from the 1980 s. Maize lodgingresistance has always been an important research in China， with EH improvement coming to a significant effect，and SN and EN becoming important focuses in maize breeding of lodging resistance and high yield.

Abstract:Classifying heterotic groups of super-sweet corn inbred lines， selecting inbred lines of highcombining ability and constructing new stronger heterotic groups could provide basis for breeding excellent sweetcorns. 23 self-bred super-sweet corn inbred lines were used to make up 60（ 3× 20） hybrid combinations withNC Ⅱ design to classify heterotic groups by analyzing the combining ability of yield and 56K SNP markers. Theresults indicated that the average heterozygosity of 23 inbred lines was 2.59%， and the homozygosity was higher.Except for GX06 and GX10， GX14 and GX15， GX16 and GX17， the genetic similarity between the inbred lineswas less than 90%， which could be used as different inbred lines in breeding. The positive effect value of GCAin yield of the tester line GX21 and the tested lines GX01， GX03 GX12， GX13， GX18 was higher and they wereexcellent inbred lines. The results of evolutionary tree， PCA and clustering diagram of SCA classified the 23super-sweet corn inbred lines into GX21 group， GX22 group and GX23 group. GX22（ HJZ33） group was named the male parent group， including 5 inbred lines（ GX02， GX11， GX19， GX20 and the tester line GX22）， GX21（ GTL273） and GX23（ YC26） groups were named the female parent groups， including 18 inbred lines（ GX01，GX03-GX10， GX12-GX18 and the tester lines GX21 and GX23） . The results of SNP markers agreed withSCA of yield basically and using SNP markers to classify heterotic groups could shorten the corn breeding cyclesignificantly.

Abstract:The number of vascular bundles in the stem is a key factor that affects the nutrient transport and the lodging resistance in maize. Here we deployed an association panel including 172 maize inbred lines to analyze the difference between the number of small vascular bundles (NSVB) and the number of large vascular bundles (NLVB) in the uppermost internode of maize stem, followed by the multiple comparison analysis to learn about the difference and the trend in the number of vascular bundles among different heterosis groups. The results showed that coefficients of variation of NSVB and NLVB in the uppermost internode in different inbred lines were 17.47%~21.69% and 25.83%~32.19%, respectively. The highly significant differences on either of NSVB and NLVB were revealed in different inbred lines. The broad-sense heritability on NSVB and NLVB was 78.87% and 82.58% respectively, while a significantly positive correlation on NSVB in relative to NLVB was observed. Both NSVB and NLVB represented a similarity on the tendency in different heterotic groups (Lancaster < Reid < P < LRC < TSPT). Collectively, this study represented a preliminary understanding of the genetic variation in the number of vascular bundles in different maize inbred lines, and laid a foundation for future quantitative trail locus (QTL) mapping and gene cloning.

Abstract:Forty-three maize inbred lines in different heterosis groups were used to analyze the difference on grain filling and dehydration rate, in order to provide insights in breeding for maize varieties with high grain filling and dehydration rate. The results showed that: (1) the average yield of maize inbred lines was 4504.29 kg hm-2, while Jing724 showed the highest yield performance (7140.60 kg hm-2). The performance among different heterosis groups was revealed (X group > Reid group > Improved Reid > Huangzaosi improved lines > Reid group > Iodent group > P group> Lüda red cob group). (2) The average grain filling rate was 0.68 g-100 grain d-1. Jing2416 showed the highest grain filling rate (0.88 g-100 grain d-1), representing 0.28 and 0.19 g-100 grain d-1 higher than Zheng58 and PH4CV. Among different heterosis groups, X group was observed to higher than hat of Reid group, followed by Iodent group, Huangzaosi improved lines, Improved Reid, Lüda red cob and P group. (3) The average grain moisture content at harvest was 22.44%, and that of Jing2416 was 18.91%, which was 6.34% and 3.18% lower than that of Zheng58 (25.25%) and PH6WC (22.09%); the average grain dehydration rate after physiological maturity was 0.65% d-1, among which Jing2416 was the highest (0.82% d-1), 78.26% and 17.14% higher than that of Zheng58 (0.46% d-1) and PH6WC (0.70% d-1). The dehydration rate of different types of maize inbred lines was as follows: X group and Iodent group>Huangzaosi improved lines>Reid group>Improved Reid>Lüda red cob>P group. (4) Four inbred lines including Jing2416, JingB547, JingMC01 and Jing72464 showed higher grain filling rate and dehydration rate. (5) The grain yield was significantly positively correlated with grain filling rate and dry matter transport rate. A significant negative correlation between grain moisture content at harvest and grain dehydration rate after physiological maturity was detected, whereas a significant positive correlation between grain dehydration rate and grain filling rate after physiological maturity was observed. The results showed that the grain filling and dehydration rates of X group were higher than those of other genetic groups; Jing2416, the Huangzaosi improved lines, had the earliest maturity and the highest grain filling and dehydration rates, which had important breeding value for breeding new maize varieties with early maturity and suitable grain yield

Abstract:To study stalk characteristics and diversity of different main groups on maize in China is an important step for harvesting maize by mechanical means. In this study, seventy common maize inbred lines, derived from five groups of Lancaster, PB, Sipingtou, Lüda Red Cob and Reid respectively, were using to investigate their stalk-related traits, i.e. stem height (SH), ear height (EH), ear position coefficient (EPC), stem node number (SN), ear node (EN), ear node coefficient (ENC), internode length of ear (IL), internode diameter of ear (ID), stem fresh weight (FW), stem dry weight (DW), brix and moisture content (MC). A higher phenotypic variation existed in Sipingtou and Lüda Red Cob group, both of which are the local germplasms in China. At the filling stage, the moisture content of maize stalk became stable. A significant correlation in maize plant height and internode length was observed, while the number of internodes between ear and tassel was relatively constant. The sugar content of maize stalk was correlated to the length of internode, the diameter of stem and the location of ear. It’s more effective through lowering ear locating node to reduce ear height. Furthermore, maize stalk exists distint characteristics among different groups. For examples, Lancaster group has less stem node, Reid group has greater internode diameter while PB group has less one, Lüda Red Cob group has greater internode diameter and less internode length, Sipingtou group has shorter stem, less brix and dry weight. There has strong heterosis of biomass and grainyield in Lancaster × Sipingtou and Lancaster × PB. It’s an alternative strategy of mechanization breeding utilizing China localgermplasm with the longer internode and the lower ear node. These results could provide important reference for maize breeding.