Improvement of a Yairipok Chujak Maize Landrace from North Eastern Himalayan Region for β-Carotene Content through Molecular Marker-Assisted Backcross Breeding

In the North Eastern Himalayan region (NEHR) of India, maize is an important food crop. The local people cultivate the maize landraces and consume them as food. However, these landraces are deficient in β-carotene content. Thus, we aimed to incorporate the crtRB1 gene from UMI285β+ into the genetic background of the NEHR maize landrace, Yairipok Chujak (CAUM66), and thereby enhance the β-carotene content through marker-assisted backcrossing (MABC). In this regard, we backcrossed and screened BC1F1 and BC2F1 plants possessing the heterozygous allele for crtRB1 and then screened with 106 polymorphic simple sequence repeat (SSR) markers. The plants having maximum recurrent parent genome recovery (RPGR) were selected in each generation and selfed to produce BC2F2 seeds. In the BC2F2 generation, four plants (CAUM66-54-9-12-2, CAUM66-54-9-12-11, CAUM66-54-9-12-13, and CAUM66-54-9-12-24) having homozygous crtRB1-favorable allele with maximum RPGR (86.74–90.16%) were selected and advanced to BC2F3. The four selected plants were selfed to produce BC2F3 and then evaluated for agronomic traits and β-carotene content. The agronomic performance of the four lines was similar (78.83–99.44%) to that of the recurrent parent, and β-carotene content (7.541–8.711 μg/g) was on par with the donor parent. Our study is the first to improve the β-carotene content in NEHR maize landrace through MABC. The newly developed lines could serve as potential resources to further develop nutrition-rich maize lines and could provide genetic stock for use in breeding programs.

Molecular characterization of a farmer-preferred maize landrace population from a multiple-stress-prone subtropical lowland environment

Makore F, Gasura E, Souta C, Mazamura U, Derera J, Zikhali M, Kamutando CN, Magorokosho C, Dari S. 2021. Molecular characterization of a farmer-preferred maize landrace population from a multiple-stress-prone subtropical lowland environment. Biodiversitas 22: 769-777. The study was conducted to assess genetic diversity of 372 maize lines using 116 single nucleotide polymorphism (SNP) markers. Three hundred and forty-seven lines were S1 lines (coded J lines) from a local maize landrace population and twenty-five were the widely used standard lines. The number of alleles per marker ranged from two to four and the average was three alleles. The average polymorphic information content (PIC) value of 0.405 indicates high genetic diversity for maize lines evaluated in this study. Population structure revealed three distinct sub-populations. Sub-population 1 contained two J lines; sub-population 2 contained five J lines and sub-population 3 contained the rest of the J lines and all the standard lines. Analysis of molecular variance (AMOVA) identified 22% variance among and 78% variance within the three subpopulations, indicating high gene exchange and low genetic differentiation. Hierarchical cluster analysis further divided the lines into nine subgroups placing some of the J lines into known heterotic groups', i.e., J30_3, J393_4, J393_3, and J393_1 in CIMMYT heterotic group B. Allelic variation observed can be a source of allele combination for breeding programs interested in widening their genetic base. The private alleles that were present in the J lines suggest availability of stress-tolerant genes that breeders can incorporate in new hybrids.

Effect of sowing time and density for vegetative and reproductive traits of genotypes of maize landrace in an agroecological system

ABSTRACT: Family farmers preserve the tradition of cultivating maize landrace varieties because these plants have characteristics that hybrids lack. The greatest challenge in conserving in situ on-farm genetic diversity is avoiding gene flow and genetic introgression of transgenes to landrace varieties. Thus, farmers are obliged to change sowing times to guarantee temporal isolation since most farms are small, making spatial isolation impossible. The objective of the present work was to evaluate the behavior of maize landrace varieties submitted to different sowing times and densities in an agroecological system. The test was conducted in sub-sub-divided plots, where the main plot was represented by the sowing time, the sub-plot by the genotype, and the sub-sub-plot by the density, with three replications, for two consecutive years. The results demonstrate the effect of sowing time and density on the characteristics evaluated. In western Santa Catarina, the best time to sow seeds of maize landrace varieties in an agroecological system is in September, which is when the varieties expressed the greatest potential at densities from 45,000 to 50,000 pl.ha-1 , but it will not avoid transgene contamination.

ANALYSIS OF THE GENETIC DIVERSITY IN MAIZE LANDRACE CULTIVARS FROM NORTHERN RIO GRANDE DO SUL, BRAZIL

Maize landraces are important genetic resources for maize breeding. Many of these landrace varieties have not yet been properly studied in order to be distinguished from the others. In this study, multivariate statistical methods were used, beyond the analysis of variance, for estimating genetic dissimilarity among 27 maize landrace accessions. Principal component analysis and clustering analysis were performed using 16 evaluated quantitative characters. The ANOVA results reported the existence of significant differences among the tested accessions for 14 evaluated characters. Two principal components almost explained 49% of found experimental variance. Four different clusters were formed by the used clustering analysis, whose results were plotted into a dendrogram. The graphical integration of this dendrogram with the PCA allowed to conclude that the variation found may be due to the genotypic distinctions existing among the four groups of accesses determined in this study.

Increased seed carbohydrate reserves associated with domestication influence the optimal seminal root number of Zea mays

Background and AimsDomesticated maize (Zea mays ssp. mays) generally forms between two and six seminal roots, while its wild ancestor, Mexican annual teosinte (Zea mays ssp. parviglumis), typically lacks seminal roots. Maize also produces larger seeds than teosinte, and it generally has higher growth rates as a seedling. Maize was originally domesticated in the tropical soils of southern Mexico, but it was later brought to the Mexican highlands before spreading to other parts of the continent, where it experienced different soil resource constraints. The aims of this study were to understand the impact of increased seminal root number on seedling nitrogen acquisition and to model how differences in maize and teosinte phenotypes might have contributed to increased seminal root number in domesticated maize.MethodsSeedling root architectural models of a teosinte accession and a maize landrace were constructed by parameterizing the functional-structural plant model OpenSimRoot using plants grown in mesocosms. Seedling growth was simulated in a low-phosphorus environment, multiple low-nitrogen environments, and at variable planting densities. Models were also constructed to combine individual components of the maize and teosinte phenotypes.Key ResultsSeminal roots contributed about 35% of the nitrogen and phosphorus acquired by maize landrace seedlings in the first 25 days after planting. Increased seminal root number improved plant N acquisition under low-N environments with varying precipitation patterns, fertilization rates, soil textures, and planting densities. Models suggested that the optimal number of seminal roots for nutrient acquisition in teosinte is constrained by its limited seed carbohydrate reserves.ConclusionsSeminal roots can improve the acquisition of both nitrogen and phosphorus in maize seedlings, and the increase in seed size associated with maize domestication may have facilitated increased seminal root number.

The genetic architecture of teosinte catalyzed and constrained maize domestication

The process of evolution under domestication has been studied using phylogenetics, population genetics–genomics, quantitative trait locus (QTL) mapping, gene expression assays, and archaeology. Here, we apply an evolutionary quantitative genetic approach to understand the constraints imposed by the genetic architecture of trait variation in teosinte, the wild ancestor of maize, and the consequences of domestication on genetic architecture. Using modern teosinte and maize landrace populations as proxies for the ancestor and domesticate, respectively, we estimated heritabilities, additive and dominance genetic variances, genetic-by-environment variances, genetic correlations, and genetic covariances for 18 domestication-related traits using realized genomic relationships estimated from genome-wide markers. We found a reduction in heritabilities across most traits, and the reduction is stronger in reproductive traits (size and numbers of grains and ears) than vegetative traits. We observed larger depletion in additive genetic variance than dominance genetic variance. Selection intensities during domestication were weak for all traits, with reproductive traits showing the highest values. For 17 of 18 traits, neutral divergence is rejected, suggesting they were targets of selection during domestication. Yield (total grain weight) per plant is the sole trait that selection does not appear to have improved in maize relative to teosinte. From a multivariate evolution perspective, we identified a strong, nonneutral divergence between teosinte and maize landrace genetic variance–covariance matrices (G-matrices). While the structure of G-matrix in teosinte posed considerable genetic constraint on early domestication, the maize landrace G-matrix indicates that the degree of constraint is more unfavorable for further evolution along the same trajectory.