REDIPLOID MAIZE LINES: (RESYNTHESIZED FROM A TETRAPLOID POPULATION FOR BREEDING HYBRID MAIZE)

The catalogue was compiled based on the results of studying the breeding value of 200 accessions of rediploid lines isolated from tetraploid maize populations with a description of 37 morphological traits, which have economic and breeding importance. The catalogue is addressed to geneticists, breeders and agronomists to be used as a starting material for breeding hybrid forage and food maize in the Russian Federation.

Trait Association and Prediction Through Integrative K-mer Analysis

Genome-wide association study (GWAS) with single nucleotide polymorphisms (SNPs) has been widely used to explore genetic controls of phenotypic traits. Here we employed an GWAS approach using k-mers, short substrings from sequencing reads. Using maize cob and kernel color traits, we demonstrated that k-mer GWAS can effectively identify associated k-mers. Co-expression analysis of kernel color k-mers and pathway genes directly found k-mers from causal genes. Analyzing complex traits of kernel oil and leaf angle resulted in k-mers from both known and candidate genes. Evolution analysis revealed most k-mers positively correlated with kernel oil were strongly selected against in maize populations, while most k-mers for upright leaf angle were positively selected. In addition, phenotypic prediction of kernel oil, leaf angle, and flowering time using k-mer data showed at least a similarly high prediction accuracy to the standard SNP-based method. Collectively, our results demonstrated the bridging role of k-mers for data integration and functional gene discovery.

Selective sorting of ancestral introgression in maize and teosinte along an elevational cline

While often deleterious, hybridization can also be a key source of genetic variation and pre-adapted haplotypes, enabling rapid evolution and niche expansion. Here we evaluate these opposing selection forces on introgressed ancestry between maize (Zea mays ssp. mays) and its wild teosinte relative, mexicana (Zea mays ssp. mexicana). Introgression from ecologically diverse teosinte may have facilitated maize’s global range expansion, in particular to challenging high elevation regions (> 1500 m). We generated low-coverage genome sequencing data for 348 maize and mexicana individuals to evaluate patterns of introgression in 14 sympatric population pairs, spanning the elevational range of mexicana, a teosinte endemic to the mountains of Mexico. While recent hybrids are commonly observed in sympatric populations and mexicana demonstrates fine-scale local adaptation, we find that the majority of mexicana ancestry tracts introgressed into maize over 1000 generations ago. This mexicana ancestry seems to have maintained much of its diversity and likely came from a common ancestral source, rather than contemporary sympatric populations, resulting in relatively low FST between mexicana ancestry tracts sampled from geographically distant maize populations. Introgressed mexicana ancestry in maize is reduced in lower-recombination rate quintiles of the genome and around domestication genes, consistent with pervasive selection against introgression. However, we also find mexicana ancestry increases across the sampled elevational gradient and that high introgression peaks are most commonly shared among high-elevation maize populations, consistent with introgression from mexicana facilitating adaptation to the highland environment. In the other direction, we find patterns consistent with adaptive and clinal introgression of maize ancestry into sympatric mexicana at many loci across the genome, suggesting that maize also contributes to adaptation in mexicana, especially at the lower end of its elevational range. In sympatric maize, in addition to high introgression regions we find many genomic regions where selection for local adaptation maintains steep gradients in introgressed mexicana ancestry across elevation, including at least two inversions: the well-characterized 14 Mb Inv4m on chromosome 4 and a novel 3 Mb inversion Inv9f surrounding the macrohairless1 locus on chromosome 9. Most outlier loci with high mexicana introgression show no signals of sweeps or local sourcing from sympatric populations and so likely represent ancestral introgression sorted by selection, resulting in correlated but distinct outcomes of introgression in different contemporary maize populations.

Use of recurrent selection in middle late synthetic maize populations. results of the first cycle in synthetic “1/2017”

The present study shows the results of a completed first cycle of recurrent selection in a middle late synthetic population “1/2017” and the inbred lines PAU 1617 and B 113 are used as a recurrent parents. The aim of the improving selection is to obtain from the synthetic inbred lines which are later to be used as parental forms for receiving hybrids of this maturity group. The experimental work was carried out in the period 2017 – 2019 when two hundred and ten testcrosses were tested. After the data was analyzed, eighty even inbred progeny variants displaying the best results have been included for crosspollination and a new cycle of breeding. The genetic variability in the synthetic has been preserved as the selected progeny represent 41,4 % of the initially chosen ones. The index of variability after recurrent selection is 12,2 % which allows for efficient testing in the subsequent stages of the improving selection. As a direct outcome of the research, thirteen crosses have been pointed out – B 113 x 37/1, B 113 x 25/5, PAU 1617 x 71/3, B 113 x 29/1, B 113 x 33/1, PAU 1617 x 97/3, PAU 1617 x 85/3, B 113 x 71/5, B 113 x 71/6, B 113 x 53/1, B 113 x 55/1, B 113 x 77/3 and B 113 x 43/1. They exceed in grain yield the foreign standard in the maturity group respectively with 25.2, 20.0, 16.9, 16.6, 15.1, 15.0, 13.1, 12.5, 10.5, 9.0, 8.8, 8.8 and 8.2%. They are still tested in varietal and ecological trials.

Not so local: the population genetics of convergent adaptation in maize and teosinte

ABSTRACTWhat is the genetic architecture of local adaptation and what is the geographic scale that it operates over? We investigated patterns of local and convergent adaptation in five sympatric population pairs of traditionally cultivated maize and its wild relative teosinte (Zea mays subsp. parviglumis). We found that signatures of local adaptation based on the inference of adaptive fixations and selective sweeps are frequently exclusive to individual populations, more so in teosinte compared to maize. However, for both maize and teosinte, selective sweeps are frequently shared by several populations, and often between the subspecies. We were further able to infer that selective sweeps were shared among populations most often via migration, though sharing via standing variation was also common. Our analyses suggest that teosinte has been a continued source of beneficial alleles for maize, post domestication, and that maize populations have facilitated adaptation in teosinte by moving beneficial alleles across the landscape. Taken together, out results suggest local adaptation in maize and teosinte has an intermediate geographic scale, one that is larger than individual populations, but smaller than the species range.

Trait-QTL-heritability of grain yield and other agronomic traits under low nitrogen conditions in bi-parental maize populations

Limited or low Nitrogen is a wanting abiotic stress in maize mainly in Sub-Sahara Africa, affecting yields and quality development of maize crop. As an approach to getting a breeding solution; mapping of QTLs and understanding the heritability factor can provide useful information and guide for breeders in developing low nitrogen resilient maize. QTL mapping which is a molecular breeding component forms an actual basis in estimation of genomic regions associated to the expression of quantitative traits, and how heritable are such traits. Conducting a selection for Low N-tolerance is challenging due to its complex nature with strong interaction between genotypes and environments; therefore, marker assisted breeding is key to improving such complex traits, but at the same time requires markers associated with the trait of interest. In this study, three bi-parental populations were subjected to either or both low and optimum N conditions to detect and determine the QTLs heritability for grain yield and other agronomic traits. Essential to the study; genotype by environmental interaction, significance and heritability was examined for each population with most traits expressing low (<0.2) and moderate to high heritabilities (0.3>). These QTLs with high heritabilities across environments will be of great value for rapid introgression into maize populations using marker assisted selection approach. The study was a preliminary and therefore require further validation on heritability and fine mapping for them to be useful in MAS.

Adaptation assessment of drought tolerance in maize populations from the Sahara in both shores of the Mediterranean Sea

Drought is the main stress for agriculture, and maize (Zea mays L.) germplasm from the Sahara has been identified as potential source of drought tolerance; however, information about adaptation of semitropical maize germplasm from the Sahara to temperate areas has not been reported. Our objective was assessing the adaptation of maize germplasm from Saharan oases as sources of drought tolerance for improving yield and biomass production under drought conditions in temperate environments. A collection of maize populations from Saharan oases was evaluated under drought and control conditions in Spain and Algeria. Algerian populations were significantly different under drought for most traits, and the significant genotype × environment interactions indicated that drought tolerance is genotype-dependent, but tolerance differences among genotypes change across environments. Based on yield, the Algerian maize populations PI527474, PI527478, PI527472, PI527467, PI527470, and PI527473 would be appropriate sources of drought tolerance for temperate environments. Concerning biomass production, the most interesting populations were PI527467, PI542685, PI527478, and PI527472. These Saharan populations could provide favorable alleles for drought tolerance for temperate breeding programs, and could also be used for studying mechanisms and genetic regulation of drought tolerance.

Cyclical response of maize populations versus base population and standard genotypes across environments

Recurrent selection is a cyclical breeding procedure in which selection is made generation after generation, with a reunion of selected plants to produce a new population for the next cycle of selection. Maize (Zea mays L.) base population 'PSEV3' was developed by using selfed progeny recurrent selection in spring and summer crop seasons during 2014 to 2016. During Summer 2017, two improved maize populations [PSEV3-(S1)-C1 and PSEV3-(S2)-C2], original genotype (PSEV3-C0) and three check varieties (two OPV - open-pollinated varieties - Azam and Jalal, and HV - hybrid variety - Kiramat) were assessed for silking and yield traits across four environments including two planting dates and two sites i.e., Cereal Crops Research Institute (CCRI), Pirsabak - Nowshera, and University of Agriculture (UAP), Peshawar, Pakistan. Genotypes and planting dates enunciated significant (p≤0.01) differences for majority of the traits. Maize improved populations (C1 and C2) enunciated comparable values with early flowering and least cob height compared to base population and check genotypes. On average, PSEV3-(S2)-C2 was foremost and exhibited maximum mean values for yield traits with enhanced grain yield with optimum planting at CCRI, followed by PSEV3-(S1)-C1. Base population - C0 and check genotypes were observed with delayed silking and least grain yield across the environments. Selfed progeny recurrent selection was established as an efficient breeding method in improving maize base populations.