Maize Populations Research Articles

Identifying genetic variants underlying phenotypic variation in plants without complete genomes.

Structural variants and presence/absence polymorphisms are common in plant genomes, yet they are routinely overlooked in genome-wide association studies (GWAS). Here, we expand the type of genetic variants detected in GWAS to include major deletions, insertions, and rearrangements. We first use raw sequencing data directly to derive short sequences, k-mers, that mark a broad range of polymorphisms independently of a reference genome. We then link k-mers associated with phenotypes to specific genomic regions. Using this approach, we re-analyzed 2,000 traits in Arabidopsis thaliana, tomato, and maize populations. Associations identified with k-mers recapitulate those found with single-nucleotide polymorphisms (SNPs), but with stronger statistical support. Importantly, we discovered new associations with structural variants and with regions missing from reference genomes. Our results demonstrate the power of performing GWAS before linking sequence reads to specific genomic regions, which allows detection of a wider range of genetic variants responsible for phenotypic variation.

Inbreeding depression and genetic variability in agricultural traits and resistance to phytopathogens in exotic maize populations

The effect known as depression by inbreeding refers to the reduction on the average value of quantitative traits, related to plant reproduction and physiology, due to the homozygosis of deleterious alleles. This study evaluated the inbreeding depression and the genetic variability of agricultural traits and of the resistance to phytopathogens in inbred families of two exotic maize populations. The experiments were done in the experimental area of the Universidade Federal de Goiás, Regional Jataí, in the second harvest 2015. Fifty and 40 FS1 of NAP5 and NAP7 populations, respectively, were evaluated interplanting one row with a mixture of base population at every ten plots to estimate depression by inbreeding of the traits evaluated. The experimental design was randomized blocks, with three replications. The following traits were evaluated: AP – plant height (cm), AE – ear height (cm), FM – male flowering (days), PQ – number of broken plants, AC – number of lodged plants, PG – kernel production (kg plot-1). The greatest estimates of depression by inbreeding in the agricultural traits were observed for kernel production, with values of 51.2 and 38.9% for the populations NAP5 and NAP7, respectively. Among the traits of resistance to phytopathogens, the greatest estimate was observed for the stunting complex, with values of -58.9% in NAP5 and -74.2% in NAP7. Both populations under study presented genetic potential to be used in breeding programs with recurrent selection and, after some selection cycles, lineages with good agricultural standard and resistance to phytopathogens can be obtained.

Genotypic diversity, heritability and agronomic performance high-oil maize populations

High-oil corn is has greater energy than normal corn. High-oil maize is a high negative genetic correlation between kernel oil content and grain yield. To obtain high oil content and yields maize varieties, breeding procedure design are needed to improve that kind of maize with wide genetic diversity. This study aimed to determine the genotypic variability, heritability, and performance of agronomic traits high-oil maize populations. 129 maize oil populations and three maize population as check varieties were tested in Maros Experimental station (South Sulawesi), and Jambegede Experimental station (East Java). The experimental design was used Randomized Complete Block design with two replications. Each population was grown in single row of 4 m length plot, spaced 70 cm between rows and 20 cm within row. The result showed that the location effect, genotype x environment interaction effect was significant for all traits. The Genotypic variance was considered narrow for all traits, expected maize length, number of rows per ear, and 1000-kernel weight. Broad-sense heritability was low for all observed traits, excepted for 1000-kernel weight. The 20 best populations based on the highest grain yield in both locations were selected from the basic population, MHOC0-9 had highest grain yield and MHOC0-112 lowest grain yield.

Variability in Forage yield of a Silage Maize “Zea mays, L.”Base Population via Two Types of Families

The base population for the recent study which is ayellow seed synthetic variety of maize was provided by Dr. M. Abd El-Sattar Ahmed, professor of crop science, Crop Science Department, faculty of Agriculture, Egypt.Two types of families had formulated, as a step before selection for high yielding ability. Those were half-sib (H.S) fami-lies and the first generation of self-pollination(S1) families. Variability in the base population gene pool had estimated depending on variance components of the families. The ratio of σ2A/ σ2G indicated that, additive genetic variance was more effective in controlling green and dry forage yield. This might indicate the importance of additive genetic vari-ance in maize population, consequently, selection among inbred- progeny would expect to be superior to other meth-ods under most genetic situations. Reduction in mean values of forage yield associated with selfing, reached 0.62 and 0.57 for green forage yield (Kg/ plot) and dry forage yield (Kg/plot), respectively. Values of genotypic variances estimated from S1 families were of larger magnitude amounted to 1.63 and 1.94 times the corresponding values for half- sib families in green forage yield and dry forage yield. Opposite to that, environmental variance estimates from S1 families were 0.56 and 0.55 of the respective values from half- sib families in green forage yield and dry forage yield respectively.Genotypic variations in term of coefficient relative to the overall mean of green yield and dry yield were less than 20%of the character mean when estimated from half-sib and S1 families (10.85 vs. 13.96 and 10.21 vs. 14.31% for green and dry forage, respectively).Dry forage yield expressed the highest estimates of heritability in both family types (0.829 and 0.877 for half –sib and S1 families, respectively). While, the obtained values for green forage yield were of lower magnitude (0.53 and 0.67 for half-sib and S1 families, respectively). This might indicate addition-al environmental influences with green forage yield.

Botanical microbiomes on the cheap: Inexpensive molecular fingerprinting methods to study plant-associated communities of bacteria and fungi.

High‐throughput sequencing technologies have revolutionized the study of plant‐associated microbial populations, but they are relatively expensive. Molecular fingerprinting techniques are more affordable, yet yield considerably less information about the microbial community. Does this mean they are no longer useful for plant microbiome research? In this paper, we review the past 10 years of studies on plant‐associated microbiomes using molecular fingerprinting methodologies, including single‐strand conformation polymorphism (SSCP), denaturing gradient gel electrophoresis (DGGE), amplicon length heterogeneity PCR (LH‐PCR), ribosomal intergenic spacer analysis (RISA) and automated ribosomal intergenic spacer analysis (ARISA), and terminal restriction fragment length polymorphism (TRFLP). We also present data juxtaposing results from TRFLP methods with those generated using Illumina sequencing in the comparison of rhizobacterial populations of Brazilian maize and fungal surveys in Canadian tomato roots. In both cases, the TRFLP approach yielded the desired results at a level of resolution comparable to that of the MiSeq method, but at a fraction of the cost. Community fingerprinting methods (especially TRFLP) remain relevant for the identification of dominant microbes in a population, the observation of shifts in plant microbiome community diversity, and for screening samples before their use in more sensitive and expensive approaches.

Intercropping of maize-mungbean to increase the farmer’s income

The alternative to increase the income of maize farmers is intercropping with legumes. Intercropping of maize-mungbean should be not maize productivity lowest compared to monoculture. Therefore, to avoid the decrease in the yield of maize, the plant population of maize in intercropping should be the same as the optimal population in maize monoculture and mungbean in intercropping does not interfere or compete with the maize crop. To suppress yield reduction of mungbean in intercropping by setting maize plants as such so that the light intensity obtained by mungbean to be optimum. The research was aimed to obtain maize-mungbean intercropping with high farmer income. The field experiment was conducted on dry land at Gowa, South Sulawesi, Indonesia. The treatment i.e 1. Intercropping 1 row of mungbean in maize twin row at plant spacing of (100-50) cm x 20 cm; 2. Intercropping 2 rows of mungbean in maize twin rows at plant spacing of (100-50) cm x 20 cm; 3. Intercropping with 1 row of mungbean in twin row at plant spacing of (110-40) cm x 20 cm; 4. Intercropping 2 rows of mungbean in maize twin rows at plant spacing of (110-40) cm x 20 cm; 5. Maize monoculture with a plant spacing of 75 cm x 20 cm; 6. Mungbean monoculture with a plant spacing of 40 x 20 cm. Both of maize monoculture and intercropping maintained plant population at 66,666 plants ha-1. Monoculture of mungbean population was 125,000 plant ha-1, whereas intercropping whit 1 row of mungbean was 33,333 plant ha-1 and 2 rows of mungbean at 66,666 plant ha-1. The results showed that maize-mungbean intercropping in twin rows of maize was able to obtained maize grain yield 2.9 - 7.0% and profit of 26 - 45% higher than monoculture, had maize equivalent yield 24-50% higher than maize grain yield actual, land equivalent ratio >1, and B-C ratio > 1. Intercropping of maize-mungbean with twin rows plant of maize at spacing (110-40) cm x 20 cm and 2 rows of mungbean can be recommended to increase farmer income because it has the highest land utilities and economic benefit compared to other models.

Genetic Variability in West Timor Landrace Maize Populations

Genetic variability information, which is a heritable difference among maize cultivars, is important to a long-term plant breeding program. In the last decade a number of researchers have studied the correlation between phenotypic and genetic variability in maize by using Deoxyribonucleic Acid (DNA) markers. Maize landraces as maize cultivars grown ‘on farm’ by farmers who reproduce their seed every year, and they can be distinguished by specific traits, so maize landraces are composed of widely variable populations, where the variation can be seen between and within populations. Five white maize landrace seed samples were obtained from five farmers in each of three villages, Nunmafo, Amol and Ajaobaki; five yellow landrace maize seed samples were obtained from five farmers in Nunmafo village only; while the five certified improved open pollinated varieties (Lamuru, Piet kuning, Bisma, Harapan, Kalingga) were obtained from the Indonesia Cereal Research Institute (ICRI) Maros. The banding patterns of the samples’ fingerprint were evaluated in the scoring range of 50-700bp fragment weight using fragment size standard ladder (Figure 6.3). Image data was viewed on the computer screen and saved in the SAGA computer program. The gel images were scored manually in Excel 2010 program for presence (score 1) or absence (score 0) of bands, and the binary data used for further analysis. The results of this study for AFLP analysis of West Timor maize landrace populations from three villages and varieties have confirmed that there are extensivegenetic variations within West Timor yellow and white maize landrace populations and varieties. There were two clusters of genetic variation among all samples. The first cluster was a general West Timor maize landrace population, with more than 80% similarity among individuals, and the second cluster was amuch more diverse grouping with less than 80% similarity. It suggests that even though a high molecular diversity had been found among West Timor maize landrace populations most maize genotypes belong to a West Timor maize landrace cluster. In addition the analysis indicated not only significant difference between maize landraces and maize varieties but also maize landraces from the three villages were genetically significantly different from each other. The molecular marker characterization of West Timor maize landrace populations will be a key step for obtaining an improved understanding of the population so they can be managed carefully for the future. Moreover, due to the genetic diversity captured within local landraces, farmers have the opportunity to perform the phenotypic selections based on plant type and seed yield which are likely to give them significant genetic gain in yield in subsequent seasons. Plant breeders have the additional opportunity of applying molecular marker techniques to assist selection.

Recombination Pattern Characterization via Simulation Using Different Maize Populations.

Efficient recombination is critical to both plant breeding and gene cloning. However, almost all traditional recombination studies and genetic improvements require the slow and labor-intensive population construction process, and little is known about the recombination characteristics of populations of different types, generations, and origins. Here, we provide a simple and efficient simulation method for population construction based on doubled haploid (DH) and intermated B73 × Mo17 maize (IBM) populations to predict the recombination pattern. We found that the chromosomes had 0, 1, 2, and 3 recombination events that occurred at rates of 0.16, 0.30, 0.23, and 0.15, respectively, in the DH and the recombination rate of each chromosome in the IBM population ranged from 0 to 12.1 cM per 125 kb. Based on the observed recombination parameters, we estimated the number of recombination events and constructed the linkage maps of the simulated DH and recombination inbred line (RIL) populations. These simulated populations exhibited similar recombination patterns compared with the real populations, suggesting the feasibility of this simulation approach. We then compared the recombination rates of the simulated populations of different types (DH induced or self-crossed), generations, and origins (using the 8, 16, and 32 multiparent advanced generation intercross (MAGIC) populations), and suggested a rapid and cost-effective population construction procedure for breeders and geneticists, while maintaining an optimal recombination rate. This study offers a convenient method for optimizing the population construction process and has broader implications for other crop species, thereby facilitating future population studies and genetic improvement strategies.

Effect of five modified mass selection cycles on combining ability in two Chinese maize populations

The central goal of maize (Zea mays L.) breeding is to increase the frequencies of favorable alleles in germplasm. Two broad-based composites Cpop.15 and Cpop.16 were subjected to five cycles of modified mass selection (MMS) to increase grain yield, lodging resistance, early maturing and short plant height. We evaluated the direct responses of Cpop.15 and Cpop.16 by analyzing per se performance of the two original populations and that of each resulting population after five cycles of MMS (a total of 12 entries) for days to silking (DS), plant height (PH), ear height (EH), stalk lodging (SL), and grain yield (GY) in four environments. Also, we evaluated trends in general and specific combining ability (GCA and SCA) for these traits in the testcrosses of the above 12 entries with three tester lines (for a total of 36 entries) that represent Chinese heterotic groups. Cpop.15 and Cpop.16 responded significantly to selection for DS, PH, and EH, while SL and GY showed no significant changes. GCA estimates in both populations were improved significantly for DS, PH, EH and GY, but not for DS and GY in Cpop.15, suggesting an increase in the frequency of favorable additive alleles with each cycle of selection for these traits. Promising hybrids could be easily generated by crossing inbred lines developed from later cycles of selection in Cpop.15 and Cpop.16 to Sipingtou germplasm. Our results indicate that MMS effectively improved the performance of both populations per se and testcrosses, taking the best advantage of both GCA and SCA.

Mapping-by-Sequencing via MutMap Identifies a Mutation in ZmCLE7 Underlying Fasciation in a Newly Developed EMS Mutant Population in an Elite Tropical Maize Inbred.

Induced point mutations are important genetic resources for their ability to create hypo- and hypermorphic alleles that are useful for understanding gene functions and breeding. However, such mutant populations have only been developed for a few temperate maize varieties, mainly B73 and W22, yet no tropical maize inbred lines have been mutagenized and made available to the public to date. We developed a novel Ethyl Methanesulfonate (EMS) induced mutation resource in maize comprising 2050 independent M2 mutant families in the elite tropical maize inbred ML10. By phenotypic screening, we showed that this population is of comparable quality with other mutagenized populations in maize. To illustrate the usefulness of this population for gene discovery, we performed rapid mapping-by-sequencing to clone a fasciated-ear mutant and identify a causal promoter deletion in ZmCLE7 (CLE7). Our mapping procedure does not require crossing to an unrelated parent, thus is suitable for mapping subtle traits and ones affected by heterosis. This first EMS population in tropical maize is expected to be very useful for the maize research community. Also, the EMS mutagenesis and rapid mapping-by-sequencing pipeline described here illustrate the power of performing forward genetics in diverse maize germplasms of choice, which can lead to novel gene discovery due to divergent genetic backgrounds.

Spatial Arrangement Management of Maize Hybrids at Semiarid Microclimate

Maize (Zea mays L.) is a plant of the Poaceae family, originating in Central America and cultivated in practically every region of the world. In Brazil, it is the most important cereal for the economy, but the productivity is lower when compared to other countries. This may be due to inadequate plant density per unit area, low soil fertility and spatial arrangement of plants. Thus, the development of better performance hybrids and changes in sowing density and spacing appear as techniques for increasing productivity without increasing production costs. Therefore, the objective of this work is to evaluate the agronomic performance of two maize hybrids as a function of plant population and row spacing in semiarid microclimate to identify those agronomic and microclimatic factors that influence it. Two simultaneous fieldwork were conducted in an experimental area, at the microregion of Paraíba swamp. A randomized complete block design was used with six treatments distributed in a 2 x 3 factorial scheme, resulting from the combination of two maize hybrids (H1 and H2) and three population densities (40,000, 60,000 and 80,000 plants.ha-1) for Experiment 1; and two maize hybrids (H1 and H2) and three spacings (0.40, 0.60 and 0.80 m) for Experiment 2. In general, the results of this study suggest that larger populations of maize provide significant increases in grain yield for microclimatic conditions Paraíba semiarid, and when environmental factors are not limiting.

CNVmap: A Method and Software To Detect and Map Copy Number Variants from Segregation Data.

Single nucleotide polymorphisms (SNPs) are used widely for detecting quantitative trait loci, or for searching for causal variants of diseases. Nevertheless, structural variations such as copy-number variants (CNVs) represent a large part of natural genetic diversity, and contribute significantly to trait variation. Numerous methods and softwares based on different technologies (amplicons, CGH, tiling, or SNP arrays, or sequencing) have already been developed to detect CNVs, but they bypass a wealth of information such as genotyping data from segregating populations, produced, e.g., for QTL mapping. Here, we propose an original method to both detect and genetically map CNVs using mapping panels. Specifically, we exploit the apparent heterozygous state of duplicated loci: peaks in appropriately defined genome-wide allelic profiles provide highly specific signatures that identify the nature and position of the CNVs. Our original method and software can detect and map automatically up to 33 different predefined types of CNVs based on segregation data only. We validate this approach on simulated and experimental biparental mapping panels in two maize populations and one wheat population. Most of the events found correspond to having just one extra copy in one of the parental lines, but the corresponding allelic value can be that of either parent. We also find cases with two or more additional copies, especially in wheat, where these copies locate to homeologues. More generally, our computational tool can be used to give additional value, at no cost, to many datasets produced over the past decade from genetic mapping panels.

Narrow rows and high maize plant population improve water use and grain yield under conservation agriculture

AbstractThe relationship between maize (Zea mays L.) population density and grain yield is influenced by soil and crop management strategies, including Conservation Agriculture (CA). However, little is known about the response of maize grain yield to varying plant population and/or row spacing under CA. A 3‐yr study was conducted under CA to evaluate the effects of plant population and row spacing on maize grain yield, plant available soil water, and soil temperature. Plant populations ranging from 40,000 to 80,000 plants ha−1 were evaluated at three row spacings (0.5, 0.76, and 1.0 m). The response of maize grain yield to plant population was highly variable between seasons: it was not affected by plant population in the season with the highest early season rainfall but increased with increasing plant population in the driest season and in the season with well‐distributed, near average rainfall. Higher plant populations resulted in lower soil water levels, presumably due to greater water extraction. Plant population affected soil water availability in the 20‐ to 80‐cm soil layer in Season 2, while plant population affected soil water availability at all soil layers except the 10‐ to 20‐ and 60‐ to 80‐cm soil layers in Season 3. Rapid maize leaf‐canopy closure provided by increased plant population and narrower row spacing is critical to adequately utilize the benefits associated with CA.

Estimation of Genetic Diversity in Seven Races of Native Maize from the Highlands of Mexico

Characterizing the genetic diversity of maize (Zea mays L.) populations by their morphological and molecular attributes makes it possible to place populations into specific groups; thus, facilitating the design of procedures for their optimum and sustainable use. In this study, data from two lines of evidence were analyzed simultaneously to robustly classify maize populations and to determine their genetic relationships. Seven maize races of the central high plateau of Mexico were characterized using a combined analysis of 13 morphological traits and 31 microsatellite loci. The germplasm assessed included samples of 119 accessions held at Mexican germplasm banks. Cluster and principal component analyses were performed. Also, genetic and geographic relationships among the accessions were determined. Principal component analysis separated the different accessions into well-defined groups using first three principal components. The accessions of Arrocillo Amarillo and Elotes Cónicos races did not exhibit a grouping pattern, indicating greater genetic complexity. Better grounded grouping and phylogenetic relationships were obtained when traits of both lines of evidence were used simultaneously.

Genome-wide association studies of leaf orientation value in maize

<p indent=0mm>Leaf orientation value is a comprehensive index reflecting the two characteristics of “straight” and “vertical” of leaves. The varieties with high leaf orientation value have straight and not curved leaves, and small angle, which are conducive to the wind ventilation and light transmission for maize population. When the planting density is high, it is easier to obtain high yield than the expanded plant-type. It is of great significance for molecular design breeding of ideal plant type to clarify the genetic basis of leaf orientation value. In this study, 285 diverse lines genotyped by the MaizeSNP50 chip were evaluated for leaf orientation in 2017 and 2018. The genome-wide association analysis (GWAS) were used to identified the SNPs, which were significant association with leaf orientation values. The analysis of variance showed that the significant variations were observed for leaf orientation value of different inbred lines (<italic>P</italic> < 0.01). In the selection of the optimal model, it was found that the Q + K model was the most suitable for the leaf orientation association analysis in this study. A total of 15 loci (<italic>P</italic> < 4.05E-5) were detected by GWAS, including 27 SNPs, explaining 5.54%–8.73% of phenotypic variation, and 15 candidate genes were mined in two years. Among them, site 2 in 1.07 bin was an important site found in this study, and its candidate gene might be <italic>Zm00001d032050</italic> encoding cyclin dependent protein kinase, which needed to be further confirmed by map-based cloning.

Quantitative trait loci mapping for resistance to maize streak virus in F2:3 population of tropical maize

Maize streak virus (MSV) continues to be a major biotic constraint for maize production throughout Africa. Concerning the quantitative nature of inheritance of resistance to MSV disease (MSVD), we sought to identify new loci for MSV resistance in maize using F2:3 population. The mapping population was artificially inoculated with viruliferous leafhoppers under screenhouse and evaluated for MSVD resistance. Using 948 DArT markers, we identified 18 quantitative trait loci (QTLs) associated with different components of MSVD resistance accounting for 3.1–21.4% of the phenotypic variance, suggesting that a total of eleven genomic regions covering chromosomes 1, 2, 3, 4, 5 and 7 are probably required for MSVD resistance. Two new genomic regions on chromosome 4 revealed the occurrence of co-localized QTLs for different parameters associated with MSVD resistance. Moreover, the consistent appearance of QTL on chromosome 7 for MSVD resistance is illustrating the need for fine-mapping of this locus. In conclusion, these QTLs could provide additional source for breeders to develop MSV resistance.

Repetitive DNA content in the maize genome is uncoupled from population stratification at SNP loci

BackgroundRepetitive DNA is a major component of plant genomes and is thought to be a driver of evolutionary novelty. Describing variation in repeat content among individuals and between populations is key to elucidating the evolutionary significance of repetitive DNA. However, the cost of producing references genomes has limited large-scale intraspecific comparisons to a handful of model organisms where multiple reference genomes are available.ResultsWe examine repeat content variation in the genomes of 94 elite inbred maize lines using graph-based repeat clustering, a reference-free and rapid assay of repeat content. We examine population structure using genome-wide repeat profiles, and demonstrate the stiff-stalk and non-stiff-stalk heterotic populations are homogenous with regard to global repeat content. In contrast, and similar to previously reported results, the same individuals show clear differentiation, and aggregate into two populations when examining population structure using genome-wide SNPs. Additionally, we develop a novel kmer based technique to examine the chromosomal distribution of repeat clusters in silico and show a cluster dependent association with gene density.ConclusionOur results indicate global repeat content variation in the heterotic populations of maize has not diverged, and is uncoupled from population stratification at SNP loci. We show that repeat families exhibit divergent patterns with regard to chromosomal distribution, some repeat clusters accumulate in regions of high gene density, whereas others aggregate in regions of low gene density.

MAJOR EFFECT QTL ON CHROMOSOME 3 CONFERRING MAIZE RESISTANCE TO SUGARCANE MOSAIC VIRUS

The Sugarcane mosaic virus (SCMV), a maize pathogen epidemic worldwide, is the causal agent of common mosaic, one of the most important viral diseases in Brazil. In this study, we mapped and characterized quantitative trait loci (QTL) conferring resistance to SCMV in a maize population consisting of 127 F2:3 families from the cross between two Brazilian maize inbred lines, L18 (resistant) × L19 (susceptible). Field trials were carried out in two years to evaluate the F2:3 families according to a resistance score after artificial inoculation. QTLs were detected via composite interval mapping, using a linkage map based on 82 SSRs, 3 CAPS and 296 SNPs. The heritability ranged from 73.68 to 95.16% and SCMV resistance QTLs were consistently identified on chromosomes 1 and 3, showing minor and major effects, respectively. The major QTL on chromosome 3 explained a large proportion of the genetic variance, being 50 and 70% in year 1 and 2, respectively, while the minor QTL on chromosome 1 explained 11 and 8% in year 1 and 2, respectively. The SNP marker co-localized with the major QTL peak on chromosome 3 and its right flanking marker are positioned inside the predicted gene GRMZM2G122443 encoding a glucosidase II, and the left flanking marker inside the GRMZM2G140537 that encodes a protein tyrosine kinase. Moreover, within this QTL region there are also the GRMZM2G160902 and GRMZM2G122481 predicted genes, encoding a bZIP transcription factor and a cytochrome C oxidase, respectively. The colocalization with this major effect QTL suggests a putative involvement of these candidate genes with maize responses to SCMV resistance, but further functional studies are required for such validation. Our results provide resistance source and genomic target for marker-assisted breeding aiming the development of maize resistant cultivars to SCMV.

Morphological and molecular characterization of teosinte derived maize population

Germplasm enhancement seems to be an essential part of a breeding programme to improve resiliency, adaptability and productivity of the crops. To develop and diversify the maize germplasm, teosinte a wild relative of maize was integrated in crossing programme and BC1F4 lines were developed. Five BC1F4 lines along with teosinte and maize inbred DI-103 were characterised using quantitative characters and molecular markers. Morphological characterization was done with the help of visual parameters and quantitative traits and for molecular characterization fifty six SSR markers were used. SSR data were analysed with the help of software Mapmaker and twelve linkage groups were generated. Maximum allelic contributions from parent teosinte were found in the introgressed line AM-5 (53.4%) followed by AM-12 (48.9 %), whereas, least contribution of 34.1 % was found in AM-7. The maximum genetic distance among the introgressed lines was observed between AM-2 and AM-9 (0.75) followed by AM-2 and AM-7 (0.70), AM-7 and AM-9 (0.70). The maximum number of cob was found in AM-5 (5.00) followed by AM-2 (4.00). Grain yield per plant was found highest for AM-2 (100.00 g) followed by AM-12 (80.00 g), while, least value was observed for AM-7 (42.00 g). The results indicated differential parental contributions which leads to diversification in the progenies derived from diverse crosses in maize and further opined that such crosses seems to be essential for creating adapted germplasm to whom breeders are looking for.

Identification of quantitative trait loci associated with maize resistance to bacterial leaf streak

AbstractBacterial leaf streak (BLS), a foliar disease of maize (Zea mays L.) caused by Xanthomonas vasicola pv. vasculorum, recently emerged in the Americas as a disease of major importance. Little is known about the disease cycle, and consequently, management is difficult. No chemical control is available. Host resistance will likely play a major role in controlling the disease, but to date, no data regarding the resistance of maize germplasm to X. vasicola pv. vasculorum have been published. The objective of this study was to examine the genetic architecture of resistance to BLS. We conducted quantitative trait locus (QTL) mapping for BLS resistance in three maize populations: the Z022 (B73 × Oh43 recombinant inbred line) nested association mapping (NAM) population, the Z023 (B73 × Oh7B recombinant inbred line) NAM population, and the DRIL78 (NC344 × Oh7B chromosome segment substitution line) population. A total of five QTL were detected across two of the mapping populations. Of the QTL detected, one conferred a moderate effect, whereas the others conferred small effects. We also examined the relationship between resistance to BLS and resistance to three foliar diseases of maize, which had been mapped previously. The only significant correlation we found for BLS was with northern corn leaf blight [caused by Exserohilum turcicum (Pass.) K. J. Leonard &amp; Suggs] in one of the populations, although two of the five BLS regions were involved in resistance to other diseases. These data will be useful for developing maize varieties resistant to BLS to mitigate the impact of bacterial leaf streak on maize production.