Soil drought is one of the major abiotic stresses that inhibits the growth, development, and yield of crops all over the world

Drought is one of the most adverse abiotic factors limiting growth and productivity of crops. Among them is barley, ranked fourth cereal worldwide in terms of harvested acreage and production. Plants have evolved various mechanisms to cope with water deficit at different biological levels, but there is an enormous challenge to decipher genes responsible for particular complex phenotypic traits, in order to develop drought tolerant crops. This work presents a comprehensive approach for elucidation of molecular mechanisms of drought tolerance in barley at the seedling stage of development. The study includes mapping of QTLs for physiological and biochemical traits associated with drought tolerance on a high-density function map, projection of QTL confidence intervals on barley physical map, and the retrievement of positional candidate genes (CGs), followed by their prioritization based on Gene Ontology (GO) enrichment analysis. A total of 64 QTLs for 25 physiological and biochemical traits that describe plant water status, photosynthetic efficiency, osmoprotectant and hormone content, as well as antioxidant activity, were positioned on a consensus map, constructed using RIL populations developed from the crosses between European and Syrian genotypes. The map contained a total of 875 SNP, SSR and CGs, spanning 941.86 cM with resolution of 1.1 cM. For the first time, QTLs for ethylene, glucose, sucrose, maltose, raffinose, α-tocopherol, γ-tocotrienol content, and catalase activity, have been mapped in barley. Based on overlapping confidence intervals of QTLs, 11 hotspots were identified that enclosed more than 60% of mapped QTLs. Genetic and physical map integration allowed the identification of 1,101 positional CGs within the confidence intervals of drought response-specific QTLs. Prioritization resulted in the designation of 143 CGs, among them were genes encoding antioxidants, carboxylic acid biosynthesis enzymes, heat shock proteins, small auxin up-regulated RNAs, nitric oxide synthase, ATP sulfurylases, and proteins involved in regulation of flowering time. This global approach may be proposed for identification of new CGs that underlies QTLs responsible for complex traits.

Environmental stresses (soil compaction, drought, waterlogging) cause changes in plants’ root system structure, also affecting the growth of above-ground parts. The aim of this study was to estimate phenotypic variation among maize and triticale genotypes in root penetration ability through petrolatum-wax-layer (RPA). Also, the effect of shortage or excess of soil water on dry matter of shoots and roots and morphological changes in root system structure in sensitive and resistant maize and triticale genotypes grown in low or high soil compaction level was evaluated. To estimate RPA index, the petrolatum-wax-layer method (PWL) was used. The strength of three petrolatum-wax concentrations 60, 50 and 40 % was 0.52, 1.07 and 1.58 MPa, respectively. High coefficients of variation (CV) were observed in 0.52 and 1.07 MPa and for maize were 19.2 and 21.7 %, and for triticale, 12.5 and 18.3 %, respectively. The data indicate that the use of PWL technique is an effective screening method, and makes it possible to divide the genotypes into resistant and sensitive groups. The second part of this study investigated a multistress effect of soil compaction combined with drought or waterlogging on root and shoot growth and morphological changes in root system structure of maize and triticale genotypes differing in susceptibility to environmental stresses. Seedlings were grown for 4 weeks in root-boxes under conditions of low (LSC 1.1 g cm⁻³) or severe (SSC 1.6 g cm⁻³) soil compaction. Drought or waterlogging stresses were applied for 2 weeks from 14th to 28th day. In comparison to LSC treatment, in SSC treatment the decrease in dry matter of shoots and roots was greater for sensitive genotypes of maize and triticale (Ancora, CHD-147). Soil drought or waterlogging caused greater decrease of dry matter of shoots and roots in seedlings grown in SSC in comparison to LSC. The root penetration index (RPI) was estimated as a ratio of root dry matter in 15–40 cm root-box layer to total root dry matter. On the basis of RPI it was possible to group the genotypes according to their ability to distribute roots in soil profile. In comparison to LSC, SSC exerted a strong influence on the length of seminal and seminal adventitious roots, as well as the number and length of L- and S-type lateral roots developed on seminal and nodal roots. In both species the restriction effect of soil compaction on number and length of roots was more severe in sensitive (Ankora, CHD-147) than in resistant (Tina, CHD-247) genotypes. The restriction in roots propagation was greater in triticale than in maize. Exposure to drought or waterlogging in the case of genotypes grown in LSC and SSC treatments caused a decrease in number and length of particular components of root system structure. In both species the decrease of root number and length in plants grown under waterlogging was greater than under drought. The observed changes in root system were greater in sensitive (Ankora, CHD147) than in resistant (Tina, CHD-247) genotypes. Statistically significant correlations were found between RPA and RPI and also between these indexes and soil compaction, drought and waterlogging susceptibility indexes. This indicates that genotypes resistant to soil compaction were resistant to drought or waterlogging and also that genotypes resistant to drought were resistant to waterlogging.

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