Increased grain yield with improved photosynthetic characters in modern maize parental lines

The grain yield of maize has increased continuously in past decades, largely through hybrid innovation, cultivation tech-nology, and in particular, recent genetic improvements in photosynthesis. Elite inbred lines are crucial for innovating new germplasm. Here, we analyzed variations in grain yield and a series of eco-physiological photosynthetic traits after anthesis in sixteen parental lines of maize (Zea mays L.) released during three different eras (1960s, 1980s, 2000s). We found that grain yield and biomass signiifcantly increased in the 2000s than those in the 1980s and 1960s. Leaf area, chlorophyl , and soluble protein content slowly decreased, and maintained a higher net photosynthesis rate (Pn) and improved stomatal conductance (Gs) after anthesis in the 2000s. In addition, the parental lines in the 2000s obtained higher actual photo-chemistry efifciency (ФPSI ) and the maximum PSII photochemistry efifciency (Fv/Fm), which largely improved light partition-ing and chlorophyl lfuorescence characteristic, including higher photochemical and photosystem II (PSII) reaction center activity, lower thermal energy dissipation in antenna proteins. Meanwhile, more lamel ae per granum within chloroplasts were observed in the parental lines of the 2000s, with a clear and complete chloroplast membrane, which wil greatly help to improve photosynthetic capacity and energy efifciency of ear leaf in maize parental lines. It is concluded that grain yield increase in modern maize parental lines is mainly attributed to the improved chloroplast structure and more light energy catched for the photochemical reaction, thus having a better stay-green characteristic and stronger photosynthetic capac-ity after anthesis. Our direct physiological evaluation of these inbred lines provides important information for the further development of promising maize cultivars.

Genetic analysis and QTL mapping of stalk cell wall components and digestibility in maize recombinant inbred lines from B73 × By804

The cell wall composition and structure of the maize stalk directly affects its digestibility and in turn its feed value.Previous studies of stem quality have focused mostly on common maize germplasm,and few studies have focused on high-oil cultivars with high grain and straw quality.Investigation of the genetic basis of cell wall composition and digestibility of maize stalk using high-oil maize is desirable for improving maize forage quality.In the present study,a high-oil inbred line(By804)was crossed as male parent with the maize inbred line B73 to construct a population of 188 recombinant inbred lines(RILs).The phenotypes of six cell-wall-related traits were recorded,and QTL analysis was performed with a genetic map constructed with SNP markers.All traits were significantly correlated with one another and showed high broad-sense heritability.Of 20 QTLs mapped,the QTL associated with each trait explained 10.0%–41.1%of phenotypic variation.Approximately half of the QTL each explained over 10%of the phenotypic variation.These results provide a theoretical basis for improving maize forage quality by marker-assisted selection.

Determination of the Number of SSR Alleles Necessary for the Analysis of Genetic Relationships Between Maize Inbred Lines

The amount of molecular marker information has considerable impact on the results of studies of crop germplasm genetic relationships in crop. The number of alleles required to reveal genetic relationship in maize inbred lines is a theoretical issue that needs to be addressed. In this study, 112 pairs of SSR （simple sequence repeat） primers and 97 maize inbred lines were selected to study the relationship between the number of inbred lines and the number of SSR primers and alleles required for a stable cluster. The results showed that the number of SSR primers is not tightly associated with the stability of the cluster analysis results, while an increase in the number of alleles can significantly improve the stability of cluster analysis results. The number of inbred lines （X） is significantly associated with the number of alleles required for stable cluster analysis （Y）, and the regression equation is Y- 600.8xe（-15.9/x）. This equation can be used to calculate the number of SSR alleles required for a genetic relationship study of maize inbred lines. These results provide a reference for determining of SSR alleles number in genetic relationship analysis of maize inbred line and other crop germplasm.

Determination and Quantification of Susceptibility of Heritance Resistance to Root Rot of Eight Commercial Genotypes of Maize (Zea mays L.)

Maize is susceptible to a number of diseases that can infect all plant organs and serve as a constraint on cereal production. The reduction in cereal production caused by disease is estimated at an average of 9.4%. Corn root rot contributes greatly to the reduction in grain production and quality. The main objective of this work was to review the research on root rot in maize to determine the susceptibility of genotypes to root rot and to quantify the inheritance of resistance to root rot in maize. The methodology used was a complete 8 × 8 diallel design planted during the year 1999/2000. Root discoloration, plant length, root volume, effective volume and yield were the evaluated parameters. To analyze the data and determine the combinatorial abilities, genetic correlations, heritability and correlated response, diallel analysis was used. Eight parental lines;P28, I137TN, MP706, E739, MO17, B37, B73, and B14 were planted. The lines were crossed into each other, all combinations according to the complete diallel model (Model 1). The F1 was harvested after maturation. For statistical analysis, the version of the Agrobase program (2016) was used. Results show that F1 hybrids showed significant differences in root rot discoloration, plant height, root volume, effective root volume and yield. The P28 line and the B73XE739 cross had, respectively, the highest general and specific combinations. Root discoloration had the highest genetic correlation (rA = 0.47) with plant length. Broad and narrow heritability for root rot discoloration were, respectively, h2 = 0.81 and h2 = 0.51. Root rot discoloration showed the highest correlated response (CR = 0.14) on plant length.

Diversity, Structure, and Marker-Trait Association Analysis of the Maize Recombinant Inbred Line Population

Association mapping has emerged as a new tool to elucidate complex quantitative trait loci in maize, but there are few reports about systematic association analysis for the specific SSR markers with agronomic traits of interest in China. We investigated the morphological and genetic diversity and population structure for 76 maize recombinant inbred lines, and then association analysis were further performed between 48 simple sequence repeat loci and 17 morphological traits, consisting of nine ear-related traits and eight other traits. The 48 SSR markers were screened out and further classified into two groups including a group of loci in regions harboring reported quantitative trait loci that affect ear shape and a group of markers distributing on the whole genome randomly. The result indicated that the population of recombinant inbred lines was structured, showing five subpopulations. Our association results revealed that there were 82, 59, and 40 significant associations detected by K-test, logistic regression, and both analysis, respectively. When the 17 traits were considered separately, the significant associations between Q-SSRs and E-traits were raised to 27.8%, whereas the other groups of combinations ranged between 2.3 and 6.3%. As the proportion of significant associations is higher among the Q-SSR subset of markers and the subset of traits related to ear shape than those for all of the other combinations, we conclude that this approach is valid for establishing true positive marker-trait relationships. Our results also demonstrated that association mapping could complement and enhance previous QTL information for marker-assisted selection.

Transfer and Detection of barstar Gene to Maize Inbred Line 18-599 (White) by Particle Bombardment

In China, the purity of maize hybrid strain is discomforting to the development of seed industrialization. Finding a new method for reproduction of maize hybrid strain is necessary. In this study, using particle bombardment, barstar gene was transferred into maize inbred line 18-599 （White）, which is an antiviral and high quality maize inbred line. By molecular detection of the anther of transgenic maize, two plants transferred with barstar gene were gained in this study, which are two restorer lines. The two plants showed normal male spike, and lively microspores. But the capacity of the two restorer lines should be studied in the future. The aim of this study is to find a new method of reproduction of maize hybrid strain using engineering restorer lines and engineering sterility lines by gene engineering technology.

Evaluation of drought tolerance in ZmVPP1-overexpressing transgenic inbred maize lines and their hybrids

The vacuolar proton-pumping pyrophosphatase gene(VPP)is often used to enhance plant drought tolerance via genetic engineering.In this study,the drought tolerance of four transgenic inbred maize lines overexpressing ZmVPP1(PH4CV-T,PH6WC-T,Chang7-2-T,and Zheng58-T)and their transgenic hybrids was evaluated at various stages.Under normal and drought conditions,the height and fresh weight were greater for the four transgenic inbred maize lines than for the wild-type(WT)controls at the germination and seedling stages.Additionally,the transgenic plants exhibited enhanced photosynthetic efficiency at the seedling stage.In irrigated and non-irrigated fields,the four transgenic lines grew normally,but with increased ear weight and yield compared with the WT plants.Moreover,the ear weight and yield of the transgenic hybrids resulting from the PH4CV-T×PH6WC-W and Chang7-2-T×Zheng58-W crosses increased in the non-irrigated field.Our results demonstrated that the growth and drought tolerance of four transgenic inbred maize lines with improved photosynthesis were enhanced by the overexpression of ZmVPP1.Moreover,the Chang7-2 and PH4CV transgenic lines may be useful for future genetic improvements of maize hybrids to increase drought tolerance.

Genetic Diversity for Yield and Yield Contributing Characters of Short Statured Maize Inbred Lines

Genetic diversity is one of the useful tools to select appropriate lines for hybridization. Twenty short-statured maize inbred lines were taken for present study, which were collected from CIMMYT India and Mexico through Plant Breeding Division, Bangladesh Agricultural Research Institute (BARI), Gazipur. This experiment was conducted from November 2015 to April 2016 to identify parental lines to produce single cross short statured maize hybrids. From the genetic diversity studies, the importance of both additive and non-additive gene actions for the expression of yield and yield contributing characters were found. Values of vector I and II revealed that both the vectors had positive values for date of silking, plant height, rows/cob, grains/row and yield. These results indicated that these five characters had highest contribution towards divergence. Based on the relative magnitude of D2 values;20 inbred lines were grouped into five clusters. Seven inbred lines were selected on the basis of genetic diversity and per se performance which will be crossed separately in a half-diallel fashion to develop hybrids.

Adaptability and recovery capability of two maize inbred-line foundation genotypes, following treatment with progressive water-deficit stress and stress recovery

Two maize inbred lines, the foundation genotype Y478 and its derived line Z58, are widely used to breed novel maize cultivars in China, but little is known about which traits confer Z58 with superior drought tolerance and yield. In the present study, responses in growth traits, photosynthetic parameters, chlorophyll fluorescence and leaf micromorphological characteristics were evaluated in Y478 and Z58 subjected to water-deficit stress induced by PEG 6000. The derived line Z58 showed greater drought tolerance than Y478, which was associated with higher leaf relative water content (RWC), root efficiency, and strong growth recovery. Z58 showed a higher stomatal density and stomatal area under the non-stressed condition;in these traits, both genotypes showed a similar decreasing trend with increased severity of water-deficit stress. In addition, the stomatal size of Y478 declined significantly. These micromorphological differences between the two lines were consistent with changes in physiological parameters, which may contribute to the enhanced capability for growth recovery in Z58. A non-linear response of Fv/Fm to leaf RWC was observed, and Fv/Fm decreased rapidly with a further gradual decline of leaf RWC. The relationship between other chlorophyll fluorescence parameters (photochemical quenching and electron transport rate) and RWC is also discussed.

A Dynamic Model of Heavy Ion ~7Li Irradiation Mutagenesis Based on Maize Inbred Line Nutrition Difference

To reveal the saddle-type dose effect relationship, we propose a radiation mutagenesis model based on maize nutrition difference resulting from heavy ion ~7Li radiation. Through irradiation mutagenesis, apparent trait selection, amino acids and fatty acids content determination, and modeling, dynamic evolution from microscopic damage and repair initiation to the final macroscopic biological effects are considered simultaneously. The results show that the steady state nature is independent of evolution time and only relates to different radiation doses.Heavy ion ~7Li radiation could effectively cause maize phenotypic variation and could improve nutritional quality.This model not only gives a good fit to the experimental results on most types of amino acids and fatty acids, but also offers an adequate explanation of the experimental phenomenon underlying the saddle-type bimodal dose effect. By combining experimental results with theoretical analyses, we suggest that the synergy of the stimulus effect and momentum transfer is the main cause of the saddle-type dose effect bimodal curve. This provides an effective strategy for conducting maize germplasm innovation.

Diurnal variation of gas exchange, chlorophyll fluorescence, and photosynthetic response of six parental lines of maize released in three eras

Over the past seven decades, the grain yield of maize(Zea mays L.) has increased continuously in China, mostly due to hybridization innovations, particularly recent genetic improvements in photosynthesis. In order to reveal photosynthetic characters of elite inbred lines in different ears, a field experiment was conducted at the North China Plain of Shandong Province in China. Six parental lines of maize introduced in three eras(the 1960 s, 1980 s, and 2000 s) were investigated diurnal variation of gas exchange, chlorophyll fluorescence, and photosynthetic response characteristic at the grain filling stage. Compared to earlier parental lines, the 2000 s parental lines always had higher net photosynthetic rate(Pn) throughout the day, especially at noon, and a mid-day depression in Pn did not occur in all hybrids parental lines. Moreover, the stomatal conductance(Gs) and water use efficiency(WUE) of the 2000 s’ lines showed higher value than those of the 1960 s’ and 1980 s’ lines. The inbred lines differences in photosynthetic parameters were partly owing to their different quantum carboxylation efficiencies and light synthase activities. Simultaneously, the 2000 s parental lines exhibited lower light and CO2 compensation points, and their higher apparent quantum yield, and carboxylation efficiency. These suggested that the modern parental lines required lower light intensity and less CO2 to maintain a relatively high photosynthetic capacity, substantially increasing leaf physical quality and stress resistance. It provided crucial information of high photo-efficiency and stress-resistance breeding in maize.

Evaluation of maize inbred lines for resistance to pre-harvest aflatoxin and fumonisin contamination in the field

Two important mycotoxins, aflatoxin and fumonisin, are among the most potent naturally occurring carcinogens, contaminating maize(Zea mays) and affecting crop yield and quality.Resistance of maize to pre-harvest mycotoxin contamination, specifically aflatoxin produced by Aspergillus flavus and fumonisin produced by Fusarium verticillioides, is a goal in breeding programs that screen for these important traits with the aim of developing resistant commercial hybrids. We conducted two years of field evaluations on 87 inbred lines originating primarily in China and Mexico and not previously screened for resistance.The objectives of our study were to identify resistant germplasm for breeding purposes and to examine possible relationships between resistances to the two mycotoxins. Aflatoxin and fumonisin were present in samples harvested from all lines in both years.Concentrations of total aflatoxin ranged from 52.00 ± 20.00 to 1524.00 ± 396.00 μg kg^(-1),while those of fumonisin ranged from 0.60 ± 0.06 to 124.00 ± 19.50 mg kg^(-1). The inbred lines TUN15, TUN61, TUN37, CY2, and TUN49 showed the lowest aflatoxin accumulation and CN1, GT601, TUN09, TUN61, and MP717 the lowest fumonisin accumulation. TUN61 showed the lowest accumulation of both mycotoxins. This study confirmed previous observations that high levels of aflatoxin can coexist with fumonisin, with 55 maize lines showing a positive correlation coefficient between the concentrations of aflatoxin and fumonisin and 32 lines showing a negative correlation coefficient. These selected lines,particularly TUN61, may provide sources of resistance to mycotoxin contamination in breeding programs. However, the mechanism of resistance in this germplasm remains to be identified. Future research should also address factors that influence the fungus–plant interaction, such as herbivory and environmental stress.

Changes of the Biomass and Acid Phosphatase Activity in Maize(Zea mays L.) Lines Under Low-P Stress

A pot culture trial was conducted to investigate the changes of the biomass and acid phosphatase （APase） activity in 10 maize lines under low-P stress. P-deficiency significantly decreased the biomass, but induced the significant enhancement of the APase activity. Since P-deficiency had smaller effects on the low-P tolerant maize lines compared with P-sensitive lines, it was demonstrated that differences of tolerance to P-deficiency existed among 10 different maize lines. In addition, the relative biomass and APase activity changed during the vegetative stage of development, and there existed a significant correlation between the biomass and APase activity under low-P stress. These results suggest that the biomass and APase activity can be regarded as indicative traits of maize lines for tolerance to low-P stress at seedling stage.

Line ×Tester Analysis of Tropical High Land Maize (<i>Zea mays</i>L.) Inbred Lines Top Crossed with Three East African Maize Populations

Maize breeding efforts to generate high yielding and adaptive cultivars have recently been given emphasis by national maize breeding program. In Ethiopia, the maize production system is mainly dominated by subsistence farmers where their production is below average. The objectives of this study were to determine the combining ability between lines and testers, and to evaluate the performance of crosses (hybrids) and parents for grain yield and yield component traits. Twenty-seven inbred lines were generated by crossing nine female lines (L1-L9) and three male testers (T1-T3) using line × tester mating system at International Maize and Wheat Improvement Center (CIMMYT), East African high land maize improvement program. The inbred lines along with parents were evaluated in randomized complete block design with two replications at three locations (Ambo, Kulumsa and Haramaya). Significant differences were observed among genotypes for all ten traits considered. Eight crosses (L1 × T2, L1 × T3, L3 × T3, L8 × T1, L4 × T2, L9 × T1, L2 × T1, and L2 × T2) had higher yield performance compared to other crosses across environments. Significant mean square differences were found across locations for general combining ability (GCA) due to lines for all traits except for number of kernel rows per ear, whereas GCA due to testers were significant only for grain yield, ear length and 1000-seed weight. Significant mean square due to GCA × Loc (both for lines and testers) was found for days to maturity (38.71*), 1000-seed weight (4582.36**) and grain yield (2756777**), while significant SCA × Loc interaction was found for all traits except number of kernel rows per ear (1.07), ear length (0.79) and ear diameter (0.12), suggesting that the importance of additive and non-additive gene effects in controlling these characters.

Study of Application of Isozymic Marker to Distinguish the Multiplasmic Lines of Maize

On the basis of previous work, the study of screening marker bands of maize ( Zea mays L. )isozyme was carried out. 11 multiplasmic lines were used as experimental materials. The different tissues at different development stages were taken for each material. DPAGE system and double vertical gel slabs were used. The experimental results are as follows: (1) POD: A total of 20 isozymic bands. (Fli)Mo17 and (su1)Mo17 possessed the POD1 and POD3, while POD7 was absent. (sh2)MoI7-POD15 and POD16. (bt1)Mo17-POD1, POD11. (Pop)Mo17-POD15. (wx)Mo17 did not possess the POD3, 4, 5, 6, 8, 15, 16. The other lines possessed different POD. (2) EST: A total of 18 isozymic bands. (Fli)Mo17 possessed the EST 2, 17,but EST15 was absent. (su1)Mo17-EST13. (bt1)Mo17-EST6, 12, 14. (Pop)Mo17 possessed the EST12, but EST2, 8, 11, 13, 14 were absent. For the other multiplasmic lines, some possessed this EST, some possessed other EST. (3)According to the above data, some specific isozymic bands can be used as biochemical markers to distinguish these multiplasmic lines from each other.

Factors influencing seed reserve utilization during seedling establishment in maize inbred lines

Strong seedlings are essential for high yield.To explore the foundation of strong seedlings,we investigated various factors influencing the conversion and distribution of seed storage reserves during seedling establishment in maize inbred lines.Three maize inbred lines were used to explore the effects of seed size,seed vigor,illumination duration,temperature,water content,and salt concentration of the seedling medium on the utilization of seed storage reserves during seedling establishment.The results showed that the conversion rate of small seeds was 3.69 to 17.71%higher than that of large seeds.Moreover,prolonged illumination time was conducive to the formation of strong seedlings.However,low temperature,drought stress and salt stress reduced the conversion rate of seed storage reserves and increased the root/shoot ratio.These results could be used to guide field management during seedling emergence and develop improved germplasm with a high conversion rate of seed storage reserves.

Genetic Diversity Analysis of 13 Maize Inbred Lines by SSR Molecular Markers

This paper used SSR molecular markers to perform the genetic diversity analysis on 13 ordinary inbred lines of maize of different sources in order to divide heterotic groups of maize inbred line and predict heterosis. Using 12 pairs of SSR primers,a total of 47 allelic variants were detected in 13 inbred lines,2-5 alleles were detected for each pair of primers,an average of 3. 9,and polymorphism information content varied from 0. 379 to 0. 828. According to the cluster analysis,the 13 inbred lines could be divided into 5 groups.

Comparative evaluation of maize inbred lines (zea mays l.) according to dus testing using morphological, physiological and molecular markers

A major challenge facing those involved in the testing of new plant varieties for Distinctness, Uniformity and Stability (DUS) is the need to compare them against all those of 'common knowledge'. A set of maize inbred lines was used to compare how morphological, physiological characterization and RAPD molecular marker described variety relationships. All the inbred lines were confirmed as morphologically and physiologically distinct. At morphological level the maximum genetic distance (10.8) and least genetic distance (1.6) were found. For physiological characters distance varied from 0.35 to 1.92 and results from dendrogram, which was made on the basis of dissimilarity matrix, were grouped into five major clusters. From RAPD, random primers provide polymorphic amplification products;the distance varying 0.42 to 0.65 and dendrogram showed that these lines formed close clusters due to the less variation in these lines at molecular level. In the present study, the molecular markers also exposed useful genetic diversity and the visual displays appeared to disperse the lines somewhat more evenly over the plot than the morphological and physiological methods.

Preliminary Phenotypic and SNP-Based Molecular Characterization of Maize (<i>Zea mays</i>L.)-Mexicana (<i>Zea mays</i>SSP. <i>Mexicana</i>) Introgression Lines under Inbred Background of 48-2

Wild relatives possess potential genetic diversity for maize (Zea mays L.) improvement. Characterization of maize-mexicana introgression lines (ILs) is of great value to diversify the genetic base and improve the maize germplasm. Four maize-mexicana IL generations, i.e. BC1, BC2, BC3, and RIL, were constructed under the elite inbred background of 48-2, elite inbred line that is widely used in maize breeding in Southwestern China, and were phenotyped in different years and genotyped with 56110 SNPs. The results indicated that 48-2 had higher phenotypic performances than all the characterized ILs on most of the agronomic traits. Compared with other ILs, BC2 individuals exhibited more similar performance to 48-2 on most traits and possessed the highest kernel ratio (66.5%). Population structure and principal component analysis indicated that BC3 individuals gathered closer to 48-2 and exhibited the lowest mexicana-introgression frequency (0.50%), while BC2 (29.06%) and RIL (18.52%) showed higher introgression frequency. The high level of genetic diversity observed in the maize-mexicana ILs demonstrated that Z. mays ssp. mexicana can serve as a potential source for the enrichment of maize germplasm.

Genetic Diversity of Chinese Temperate and Exotic Tropical, Subtropical Quality Protein Maize Inbreds by SSR Markers

Information on genetic relationship is of great value to maize (Zea mays L.) breeding. Theobjectives of this study were: 1) to classify 22 quality protein maize (QPM) inbreds intodifferent groups by using simple sequence repeats (SSR) markers, which included exotictropical, subtropical and domestic temperate QPM and normal maize inbreds; 2) to examine theconsistency of grouping results obtained from SSR, specific combining ability (SCA) analysis,and genetic backgrounds of these inbreds. A set of 39 polymorphic SSR primers was selected from70 primer pairs, which detected 136 alleles among the 22 lines. The mean polymorphisminformation content was 0.55. Based on analysis of genetic similarities, five groups wereidentified including Luda Red Cob, Sipingtou, Reid, Lancaster and a miscellaneous group withseveral tropical inbreds which could not be classified into the above four groups. The resultsgenerally agreed with previous results based on analysis of yield combining ability andpedigree data.