Exploiting the Genetic Diversity of Wild Ancestors and Relatives of Wheat for its Improvement

Wheat is the third most staple food worldwide but current 1% annual improvement in the wheat production is insufficient to meet the growing demands in future. The narrow genetic base of wheat limits continuous improvement in wheat productivity and tolerance to biotic and abiotic stresses under changing climate. Wild ancestors and relatives of wheat hold a potential in widening the genetic pool of wheat and enhance its resilience to biotic and abiotic stresses. This study was focused towards characterizing the genetic diversity in wild relatives of wheat for disease resistance and efficient association with diazotrophs. In the first study, we evaluated a mini core set of Triticum turgidum subsp. (tetraploid wheat, AABB) for resistance to Fusarium head blight (FHB), leaf rust and tan spot. Three, six, and nine accessions showed resistance response to Fusarium head blight (FHB), leaf rust and tan spot respectively. These germplasm resources could be further exploited in wheat breeding. In the second study, in addition to tetraploid wheat, diploid and hexaploid germplasm of both wild and adapted species were evaluated for efficient association with diazotrophic bacteria by analyzing the N content. We observed significant differences for 15N content among different species, represented as average σ15N. Lower σ15N indicates a higher possibility of biologically fixed nitrogen (BNF). Wild accessions both in diploid (T. boeticum, AmAm, σ15N = 20.85) and tetraploid species (T. turgidum subsp. dicoccoides, AABB, σ15N = 16.44) showed significantly better associations with diazotrophs as compared to domesticated species (T. monococcum, AmAm, σ15N = 26.67) and modern hexaploid varieties (T. aestivum, AABBDD, σ15N =31.74). Our study shows that the wild species hold a promise in identification and characterization of efficient association with diazotrophic bacteria and this interaction can be recovered in modern cultivars of wheat to enhance the performance of wheat in marginal soils. In the final study, we analyzed the genetic diversity in the global collection (178 accessions) of rye using 4,037 high-quality SNPs and developed of a mini core set of 32 accessions of rye that represents more than 95 % of the allelic diversity (PIC = 0.25) of our collection (PIC = 0.26). Genome-wide association study (GWAS) was performed on 160 accessions (Secale cereale subsp. cereale) with 4,037 high-quality SNPs to identify genomic regions conferring tan spot resistance. Nearly 32%, 27%, 24%, and 17% accessions showed resistant, moderately resistant, moderately susceptible and susceptible reaction to Pyrenophora tritici-repentis race 5 (PTR race 5) respectively. Two QTLs conferring resistance to tan spot (PTR race 5) were identified (p= \u3c 0.001) using mixed linear model (GAPIT) on chromosomes 5R and 2R. The QTLs QTs-sdsu-5R and QTs-sdsu-2R explained 13.11% and 11.62 % of the variation. In conclusion, wild relatives and ancestors of wheat hold a potential for wheat improvement especially for tolerance to abiotic and biotic factors

Soil penetration by maize roots is negatively related to ethylene-induced thickening

Radial expansion is a classic response of roots to a mechanical impedance that has generally been assumed to aid penetration. We analysed the response of maize nodal roots to impedance to test the hypothesis that radial expansion is not related to the ability of roots to cross a compacted soil layer. Genotypes varied in their ability to cross the compacted layer, and those with a steeper approach to the compacted layer or less radial expansion in the compacted layer were more likely to cross the layer and achieve greater depth. Root radial expansion was due to cortical cell size expansion, while cortical cell file number remained constant. Genotypes and nodal root classes that exhibited radial expansion in the compacted soil layer generally also thickened in response to exogenous ethylene in hydroponic culture, that is, radial expansion in response to ethylene was correlated with the thickening response to impedance in soil. We propose that ethylene insensitive roots, that is, those that do not thicken and can overcome impedance, have a competitive advantage under mechanically impeded conditions as they can maintain their elongation rates. We suggest that prolonged exposure to ethylene could function as a stop signal for axial root growth

Multiseriate cortical sclerenchyma enhance root penetration in compacted soils

Mechanical impedance limits soil exploration and resource capture by plant roots. We examine the role of root anatomy in regulating plant adaptation to mechanical impedance and identify a root anatomical phene in maize (Zea mays) and wheat (Triticum aestivum) associated with penetration of hard soil: multiseriate cortical sclerenchyma (MCS). We characterize this trait and evaluate the utility of MCS for root penetration in compacted soils. Roots with MCS had a greater cell wall to lumen ratio and a distinct UV emission spectrum in outer cortical cells. Genome-wide association mapping revealed that MCS is heritable and genetically controlled. We identified a candidate gene associated with MCS. Across all root classes and nodal positions, maize genotypes with MCS had 13% greater root lignin concentration compared to genotypes without MCS. Genotypes without MCS formed MCS upon exogenous ethylene exposure. Genotypes with MCS had greater lignin concentration and bending strength at the root tip. In controlled environments, MCS in maize and wheat was associated improved root tensile strength and increased penetration ability in compacted soils. Maize genotypes with MCS had root systems with 22% greater depth and 39% greater shoot biomass in compacted soils in the field compared to lines without MCS. Of the lines we assessed, MCS was present in 30-50% of modern maize, wheat, and barley cultivars but was absent in teosinte and wild and landrace accessions of wheat and barley. MCS merits investigation as a trait for improving plant performance in maize, wheat, and other grasses under edaphic stress

Ploidy alters root anatomy and shapes the evolution of crop polyploids .

<p>Polyploidization has played an important role in plant domestication and has shaped modern agriculture. Although the increased cell size of polyploids is known to increase plant biomass and vigor, its impact on soil exploration is relatively unknown. Using wheat as a model, we report a ploidy-induced belowground domestication syndrome which comprises increased root cortical cell size associated with reduced root nitrogen and phosphorus content, increased metaxylem vessel diameter associated with increased axial hydraulic conductance, and increased root tip bluntness associated with reduced root penetration ability of hard soils. Reduced root nitrogen and phosphorus content increased nutrient use efficiency under suboptimal nitrogen and phosphorus availability, which would have been crucial for continuously cultivated and nutrient depleted agroecosystems of neoilithic Mesopotamia. Polyploids of <em>Gossypium</em> and <em>Poa </em>also have lower root phosphorus content compared to the corresponding diploid species. <em>In silico</em> modelling using <em>RootSlice</em> shows that vacuolar occupancy in larger cells of polyploid species is the driving force for reduced tissue nutrient content. Increased axial hydraulic conductance in polyploids might have provided an adaptive advantage in irrigated neothilic fields as well.  Polyploidy is associated with blunter root tips, thus reducing root penetration ability in compacted soils. However, it is plausible that the domestication of wheat around irrigated riverbanks faced only low soil compaction but nutrient depletion over time. We propose that ploidy-driven changes in wheat root anatomy during domestication were important adaptations to neolithic agriculture.  </p> <p> </p&gt

Effect of media composition and explant type on the regeneration of eggplant (Solanum melongena L.)

Two as well as three way interactions of three eggplant genotypes, media compositions and explants (hypocotyl, cotyledon and leaf) showed significant differences for plant regeneration. Among three explants, hypocotyl induced highest percent callusing, but cotyledon showed best results for somatic embryogenesis on all the media compositions. For three way interactions, cotyledon of BSR-27 induced significantly highest somatic embryogenesis (94.47%) on Murashige and Skooge (MS) fortified with 1.5 mgl-1 indole butyric acid (IBA) + 1.0 mgl-1 6-benzyl aminopurine (BAP). However, hypocotyl of BR-16 was not able to induce somatic embryogenesis on MS media fortified with 1.5 mgl-1 IBA + 1.0 mgl-1 BAP. Moreover, the embryogenic callus from cotyledon of BSR-27 (72.24%) achieved highest plant regeneration from somatic embryos on MS supplemented with 2.5 mgl-1 BAP + 1.0 mgl-1kin + 0.2% activated charcoal. Therefore, the performance of cotyledon explant of BSR-27 is the best on MS fortified with 1.5 mgl-1 IBA + 1.0 mgl-1 BAP and 2.5 mgl-1 BAP + 1.0 mgl-1kin + 0.2% activated charcoal for somatic embryogenesis and plant regeneration, respectively.Keywords: Callus, somatic embryogenesis, hypocotyl, cotyledon, leafAfrican Journal of Biotechnology Vol. 12(8), pp. 860-86

Root phenotypes for improved nitrogen capture

BackgroundSuboptimal nitrogen availability is a primary constraint for crop production in low-input agroecosystems, while nitrogen fertilization is a primary contributor to the energy, economic, and environmental costs of crop production in high-input agroecosystems. In this article we consider avenues to develop crops with improved nitrogen capture and reduced requirement for nitrogen fertilizer.ScopeIntraspecific variation for an array of root phenotypes has been associated with improved nitrogen capture in cereal crops, including architectural phenotypes that colocalize root foraging with nitrogen availability in the soil; anatomical phenotypes that reduce the metabolic costs of soil exploration, improve penetration of hard soil, and exploit the rhizosphere; subcellular phenotypes that reduce the nitrogen requirement of plant tissue; molecular phenotypes exhibiting optimized nitrate uptake kinetics; and rhizosphere phenotypes that optimize associations with the rhizosphere microbiome. For each of these topics we provide examples of root phenotypes which merit attention as potential selection targets for crop improvement. Several cross-cutting issues are addressed including the importance of soil hydrology and impedance, phenotypic plasticity, integrated phenotypes, in silico modeling, and breeding strategies using high throughput phenotyping for co-optimization of multiple phenes.ConclusionsSubstantial phenotypic variation exists in crop germplasm for an array of root phenotypes that improve nitrogen capture. Although this topic merits greater research attention than it currently receives, we have adequate understanding and tools to develop crops with improved nitrogen capture. Root phenotypes are underutilized yet attractive breeding targets for the development of the nitrogen efficient crops urgently needed in global agriculture.ISSN:0032-079XISSN:1573-503

A role for fermentation in aerobic conditions as revealed by computational analysis of maize root metabolism during growth by cell elongation

The root is a well-studied example of cell specialisation, yet little is known about the metabolism that supports the transport functions and growth of different root cell types. To address this, we used computational modelling to study metabolism in the elongation zone of a maize lateral root. A functional-structural model captured the cell-anatomical features of the root and modelled how they changed as the root elongated. From these data, we derived constraints for a flux balance analysis model that predicted metabolic fluxes of the 11 concentric rings of cells in the root. We discovered a distinct metabolic flux pattern in the cortical cell rings, endodermis and pericycle (but absent in the epidermis) that involved a high rate of glycolysis and production of the fermentation end-products lactate and ethanol. This aerobic fermentation was confirmed experimentally by metabolite analysis. The use of fermentation in the model was not obligatory but was the most efficient way to meet the specific demands for energy, reducing power and carbon skeletons of expanding cells. Cytosolic acidification was avoided in the fermentative mode due to the substantial consumption of protons by lipid synthesis. These results expand our understanding of fermentative metabolism beyond that of hypoxic niches and suggest that fermentation could play an important role in the metabolism of aerobic tissues