QTLs linked to leaf epicuticular wax,physio-morphological and plant production traits under drought stress in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Drought stress is the major constraint to rice (Oryza sativa L.) production and yield stability in rainfed ecosystems. Identifying genomic regions contributing to drought resistance will help to develop rice cultivars suitable for rainfed regions through marker-assisted breeding. Quantitative trait loci (QTLs) linked to leaf epicuticular wax, physio-morphological and plant production traits under water stress and irrigated conditions were mapped in a doubled haploid (DH) line population from the cross CT9993-5-10-1-M/IR62266-42-6-2. The DH lines were subjected to water stress during anthesis. The DH lines showed significant variation for epicuticular wax (EW), physio-morphological and plant production traits under stress and irrigated conditions. A total of 19 QTLs were identified for the various traits under drought stress and irrigated conditions in the field, which individually explained 9.6%–65.6% of the phenotypic variation. A region EM15_10-ME8_4-R1394A-G2132 on chromosome 8 was identified for leaf EW and rate of water loss i.e., time taken to reach 70% RWC from excised leaves in rice lines subjected to drought stress. A large effect QTL (65.6%) was detected on chromosome 2 for harvest index under stress. QTLs identified for EW, rate of water loss from excised leaves and harvest index under stress in this study co-located with QTLs linked to shoot and root-related drought resistance traits in these rice lines and might be useful for rainfed rice improvement.     

Fine Mapping QTL for Drought Resistance Traits in Rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) Using Bulk Segregant Analysis

Drought stress is a major limitation to rice (Oryza sativa L.) yields and its stability, especially in rainfed conditions. Developing rice cultivars with inherent capacity to withstand drought stress would improve rainfed rice production. Mapping quantitative trait loci (QTLs) linked to drought resistance traits will help to develop rice cultivars suitable for water-limited environments through molecular marker-assisted selection (MAS) strategy. However, QTL mapping is usually carried out by genotyping large number of progenies, which is labour-intensive, time-consuming and cost-ineffective. Bulk segregant analysis (BSA) serves as an affordable strategy for mapping large effect QTLs by genotyping only the extreme phenotypes instead of the entire mapping population. We have previously mapped a QTL linked to leaf rolling and leaf drying in recombinant inbred (RI) lines derived from two locally adapted indica rice ecotypes viz., IR20/Nootripathu using BSA. Fine mapping the QTL will facilitate its application in MAS. BSA was done by bulking DNA of 10 drought-resistant and 12 drought-sensitive RI lines. Out of 343 rice microsatellites markers genotyped, RM8085 co-segregated among the RI lines constituting the respective bulks. RM8085 was mapped in the middle of the QTL region on chromosome 1 previously identified in these RI lines thus reducing the QTL interval from 7.9 to 3.8 cM. Further, the study showed that the region, RM212–RM302–RM8085–RM3825 on chromosome 1, harbours large effect QTLs for drought-resistance traits across several genetic backgrounds in rice. Thus, the QTL may be useful for drought resistance improvement in rice through MAS and map-based cloning.     

Mapping of post-flowering drought resistance traits in grain sorghum: association between QTLs influencing premature senescence and maturity

The identification of genetic factors underlying the complex responses of plants to drought stress provides a solid basis for improving drought resistance. The stay-green character in sorghum (Sorghum bicolor L. Moench) is a post-flowering drought resistance trait, which makes plants resistant to premature senescence under drought stress during the grainfilling stage. The objective of this study was to identify quantitative trait loci (QTLs) that control premature senescence and maturity traits, and to investigate their association under post-flowering drought stress in grain sorghum. A genetic linkage map was developed using a set of recombinant inbred lines (RILs) obtained from the cross B35 × Tx430, which were scored for 142 restriction fragment length polymorphism (RFLP) markers. The RILs and their parental lines were evaluated for post-flowering drought resistance and maturity in four environments. Simple interval mapping identified seven stay-green QTLs and two maturity QTLs. Three major stay-green QTLs (SGA, SGD and SGG) contributed to 42% of the phenotypic variability (LOD 9.0) and four minor QTLs (SGB, SGI.1, SGI.2, and SGJ) significantly contributed to an additional 25% of the phenotypic variability in stay-green ratings. One maturity QTL (DFB) alone contributed to 40% of the phenotypic variability (LOD 10.0), while the second QTL (DFG) significantly contributed to an additional 17% of the phenotypic variability (LOD 4.9). Composite interval mapping confirmed the above results with an additional analysis of the QTL × Environment interaction. With heritability estimates of 0.72 for stay-green and 0.90 for maturity, the identified QTLs explained about 90% and 63% of genetic variability for stay-green and maturity traits, respectively. Although stay-green ratings were significantly correlated (r=0.22, P ≤ 0.05) with maturity, six of the seven stay-green QTLs were independent of the QTLs influencing maturity. Similarly, one maturity QTL (DFB) was independent of the stay-green QTLs. One stay-green QTL (SGG), however, mapped in the vicinity of a maturity QTL (DFG), and all markers in the vicinity of the independent maturity QTL (DFB) were significantly (P ≤ 0.1) correlated with stay-green ratings, confounding the phenotyping of stay-green. The molecular genetic analysis of the QTLs influencing stay-green and maturity, together with the association between these two inversely related traits, provides a basis for further study of the underlying physiological mechanisms and demonstrates the possibility of improving drought resistance in plants by pyramiding the favorable QTLs. Received: 10 October 1998 / Accepted: 12 July 1999     

Photosynthetic pigments and photosynthetic products of endophyte-infected and endophyte-free Lolium perenne L. under drought stress conditions

Endophyte-infected (EI) seeds of Lolium perenne L. were used to attain endophyte-free (EF) population by heating the seeds at 43°C for 15 min and then 57°C for 25 min. Relative water content (RWC), chlorophyll, soluble sugar and starch content of EI and EF populations under normal and drought stress conditions were compared to investigate the effect of endophyte infection on the host plant. Under severe stress, RWC of EI leaf was significantly higher than that of EF leaf, i.e. EI plants took more advantages over EF plants in water-holding ability. Under mild stress, endophyte could enhance soluble sugars in host plants to improve their osmotic ability. With stress intensification, the improvement of endophyte no longer existed, and more photosynthetic products (such as starch) accumulated in EI plants to survive through the undesirable conditions. In the next spring, EI populations will recover more rapidly than EF populations. The biomass of a population is closely related to its photosynthesis. Under severe stress, EI population significantly accumulated more biomass than EF population. As far as photosynthetic pigments were concerned, contents of Chla, Chlb and Car of EI plants were close to those of EF plants, which suggested that endophyte infection didn’t alleviate photosynthetic pigments from being destroyed by drought stress, and endophyte might improve photosynthesis ability of its host plant in other ways. __________ Translated from Acta Ecologica Sinica, 2005, 25 (2) [译自: 生态学报, 2005, 25(2)]     

Responses of Quercus ilex from Different Provenances to Experimentally Imposed Water Stress

Responses of Quercus ilex L. seedlings from three different localities in Italy to experimentally imposed drought stress were analysed. Predawn (Ψ_pd) and midday (Ψ_m) leaf water potential of stressed seedlings decreased on an average until −4.0 and −4.2 MPa, respectively, in the severe water stress. At the end of the severe water stress the relative water content (RWC) was 72.5 – 83.6 % and the photosynthetic rates (P_N) near zero. The critical threshold value of Ψ_pd for complete stomatal closure was from −4.0 to −4.5 MPa. The leaf damage after the severe water stress was significantly greater in seedlings originated from the acorns of climax area (45 % total leaf injured area and 40 % fallen leaves) than in the other seedlings (on an average 20.5 % total leaf injured area and 21 % fallen leaves). This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of endophytic fungi on some drought tolerance mechanisms of tall fescue in a hydroponics culture

Neotyphodium, a seed-transmissible nonpathogenic fungal endophyte (symbiont) is considered beneficial because endophyte-infected grasses are more drought-tolerant, produce more dry matter, utilize soil nitrogen more efficiently, and deter insects. In this study, the effects of endophytes on physiological mechanisms of drought tolerance in tall fescue (Festuca arundinacea Schreb.) were studied in a greenhouse. Two clonally propagated genotypes of tall fescue (F. arundinacea Schreb.), naturally containing endophyte (EI), and their endophyte-free ramets (EF) were tested at three water stress treatments exerted by PEG 6000 in a hydroponics system. Relative water content (RWC), cell membrane stability (CMS), proline and chlorophyll contents in plant leaves were measured during water stress treatments. After harvest, K⁺, Ca²⁺, and Mg²⁺ contents were measured in plant roots and shoots. After 20 days under stress conditions, plants were transferred to basal hydroponics medium, and their survival after stress relief was evaluated. The results showed that endophyte considerably contributes to host grass water stress tolerance. Both genotypes of EI and EF plants did not differ in RWC, but, regardless of the infection status, genotype 75 had the higher RWC than genotype 83. EI clones of both genotypes maintained slightly higher chlorophyll content and membrane stability than EF clones, although these differences were not significant. The EI plants of genotype 83 concentrated significantly more proline than EF plants, but in the genotype 75, differences between EI and EF clones were not significant. Plant mineral absorption was also influenced by the endophyte presence. EI clones had the higher concentrations of K⁺ in the shoots of both genotypes. The Mg²⁺ and Ca²⁺ contents in EF plants of both genotypes were higher than EI plants in the roots, but in the shoots there were no differences between EI and EF clones. EI clones survived longer after stress removal. These results strongly suggest that Neotyphodium endophytes exert their effects on tall fescue drought tolerance through alteration of various physiological mechanisms involved. Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 4, pp. 563–570. This test was submitted by the authors in English.     

Osmoregulation and osmoprotection in the leaf cells of two olive cultivars subjected to severe water deficit

In this study, we compared the efficacy of defense mechanisms against severe water deficit in the leaves of two olive (Olea europaea L.) cultivars, ‘Chemlali’ and ‘Meski’, reputed drought resistant and drought sensitive, respectively. Two-year old plants growing in sand filled 10-dm³ pots were not watered for 2 months. Changes in chlorophyll fluorescence parameters and malondialdehyde content as leaf relative water content (RWC) decreased showed that ‘Chemlali’ was able to maintain functional and structural cell integrity longer than ‘Meski’. Mannitol started to accumulate later in the leaves of ‘Chemlali’ but reached higher levels than in the leaves of ‘Meski’. The latter accumulated several soluble sugars at lower dehydration. ‘Chemlali’ leaves also accumulated larger quantities of phenolic compounds which can improve its antioxidant response. Furthermore, the activity of three antioxidant enzymes catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) increased as leaf RWC decreased. However, differences were observed between the two cultivars for CAT and POD but not for APX. The activity of the first two enzymes increased earlier in ‘Meski’, but reached higher levels in ‘Chemlali’. At low leaf hydration levels, ‘Chemlali’ leaves accumulated mannitol and phenolic compounds and had increased CAT and POD activities. These observations suggest that ‘Chemlali’ was more capable of maintaining its leaf cell integrity under severe water stress because of more efficient osmoprotection and antioxidation mechanisms.     

Physiological responses to water stress following a conditioning period in berseem clover

Berseem clover (Trifolium alexandrinum L.) is an important crop in semi-arid regions; its herbage and seed yields are often reduced by water stress. Our objectives were (i) to determine the effect of water stress, applied after a conditioning period, on water relations, proline accumulation and plant dry weight, and (ii) to investigate if some physiological responses differed in varieties of berseem. Five cultivars (Axi, Bigbee, Lilibeo, Sacromonte and Saniros) were grown in a controlled environment, and subjected to four irrigation treatments (T1, T2, T3 and T4 referring to plants irrigated to field capacity every 1, 2, 3 or 4 d, respectively) during a conditioning period (12 d). T1 treatment indicated the well-watered control, whereas T2, T3 and T4 treatments represented the conditioned plants. Leaf water potential (Ψ), osmotic potential (Ψπ), relative water content (RWC), gravimetric soil water content (GSWC) and leaf proline concentration were recorded during the conditioning period and a subsequent water deficit period (3 d) applied at early flowering growth stage. The conditioned plants subjected to subsequent water deficit maintained higher values of Ψ, Ψπ, RWC and GSWC, and lower values of leaf proline concentration. Reductions in parameter values were inversely related to the water stress severity that plants had previously experienced. At the end of the experiment, T1 showed 42%, 58% and 31% lower values for Ψ, Ψπ and RWC, respectively, than those of T4. Conditioned plants were also shorter and accumulated less leaf, stem and total dry weight. The conditioning treatments did not affect the relation between Ψ and Ψπ since conditioned plants show similar values of Ψπ as the control at the same Ψ value. Thus, drought acclimation in berseem clover contributed to water stress tolerance by the maintenance of tissue hydration. The berseem cultivars examined showed differences in plant growth parameters, but they were very similar for physiological responses to water deficit. The main genetic difference was recorded for turgor maintenance capacity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Molecular mapping and location of QTLs for drought-resistance traits in <Emphasis Type="Italic">indica</Emphasis> rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) lines adapted to target environments

Drought is a major limitation for rice production in rainfed ecosystems. Identifying quantitative trait loci (QTLs) linked to drought resistance provides opportunity to breed high yielding rice varieties suitable for drought-prone areas. Although considerable efforts were made in mapping QTLs associated with drought-resistance traits in rice, most of the studies involved indica × japonica crosses and hence, the drought-resistance alleles were contributed mostly by japonica ecotypes. It is desirable to look for genetic variation within indica ecotypes adapted to target environment (TE) as the alleles from japonica ecotype may not be expressed under lowland conditions. A subset of 250 recombinant inbred lines (RILs) of F₈ generation derived from two indica rice lines (IR20 and Nootripathu) with contrasting drought-resistance traits were used to map the QTLs for morpho-physiological and plant production traits under drought stress in the field in TE. A genetic linkage map was constructed using 101 polymorphic PCR-based markers distributed over the 12 chromosomes covering a total length of 1,529 cM in 17 linkage groups with an average distance of 15.1 cM. Composite interval mapping analysis identified 22 QTLs, which individually explained 4.8–32.2% of the phenotypic variation. Consistent QTLs for drought-resistance traits were detected using locally adapted indica ecotypes, which may be useful for rainfed rice improvement.     

Physiological changes in them in post-stress emerging <Emphasis Type="Italic">Ctenanthe setosa</Emphasis> plants under drought conditions

The capability of Ctenanthe setosa (Rosc.) Eichler (Marantaceae), pre-exposed to severe drought stress, of adaptation to a new drought conditions was investigated. C. setosa unstressed plants were exposed to drought period of 70 days. These plants were named as primary-stress plants (PS). They were trimmed, and new plants were produced from their rhizomes. New growing plants were named as post-stress emerging (PSE) plants. It was observed that leaf area and petiole length of PSE plants were reduced, as compared to unstressed plants. When PSE plants were exposed to a second drought-stress cycle, it was determined that the degree of their leaf rolling was higher but their relative water content (RWC) was less than these parameters of PS plants during drought period. However, at the 81% rolling degree, RWC in PSE plants was higher than in PS plants. Consequently, it can be said that the PSE plant were more resistant to a new drought stress than unstressed and PS plants. In the leaves of PSE plants, which were exposed to a second drought-stress period, the content of soluble protein decreased in the early period of drought, but increased in the later periods. Also, the content of reducing sugar in PSE plants gradually decreased during the stress period. Proline content increased markedly during drought period, whereas peroxidase activity increased up to the 60th day and then decreased. This text was submitted by the authors in English.     

Several QTLs involved in osmotic-adjustment trait variation in barley (Hordeum vulgare L.)

 Osmotic adjustment (OA) was previously demonstrated to be an important adaptive mechanism of drought tolerance in cereals. In order to determine which genomic regions are involved in OA variation, 187 barley (Hordeum vulgare L.) recombinant inbred lines (RILs) derived from a cross between Tadmor (drought tolerant) and Er/Apm (susceptible) were studied in a growth chamber for their OA capacity (through correlated traits and by calculation), at an early growth stage and under two water treatments (soil moisture of 14% and 100% of field capacity). The continuous distribution of the traits and their broad-sense line heritabilities, ranging from 0.04 to 0.44, indicated that OA and related traits should have a polygenic nature. A subset of 167 RILs were also genotyped using 78 RFLP, 32 RAPD and three morphological markers and a linkage map was constructed. Despite strong environmental effects acting on the traits, interval mapping and single-marker ANOVA allowed the detection of three QTLs for relative water content (RWC), four QTLs for osmotic potential (ψ_π), two QTLs of osmotic potential at full turgor (ψ_π100) and one QTL for osmotic adjustment at a soil moisture of 14% field capacity. For the irrigated treatment, only two QTLs were detected: one for RWC and one for ψ_π100. Two chromosomal regions were involved in several OA-related trait variations and could be considered as regions controlling OA; these were present on chromosome 1 (7H) and chromosome 6 (6H), whereas other regions were specific for one trait. No major QTL was found. However, the genomic region involved in OA-related traits on chromosome 1 (7H) in barley seemed to be conserved for OA variation among cereals. Epistatic effects, with or without additive effects, acted on the traits. Received: 15 July 1997 / Accepted: 29 October 1997     

Evaluation of physiological traits for improving drought tolerance in faba bean (<Emphasis Type="Italic">Vicia faba</Emphasis> L.)

Among grain legumes, faba bean is becoming increasingly popular in European agriculture due to recent economic and environmental interests. Faba bean can be a highly productive crop, but it is sensitive to drought stress and yields can vary considerably from season to season. Understanding the physiological basis of drought tolerance would indicate traits that can be used as indirect selection criteria for the development of cultivars adapted to drought conditions. To assess genotypic variation in physiological traits associated with drought tolerance in faba bean and to determine relationships among these attributes, two pot experiments were established in a growth chamber using genetic materials that had previously been screened for drought response in the field. Nine inbred lines of diverse genetic backgrounds were tested under adequate water supply and limited water conditions. The genotypes showed substantial variation in shoot dry matter, water use, stomatal conductance, leaf temperature, transpiration efficiency, carbon isotope discrimination (Δ¹³C), relative water content (RWC) and osmotic potential, determined at pre-flowering vegetative stage. Moisture deficits decreased water usage and consequently shoot dry matter production. RWC, osmotic potential, stomatal conductance and Δ¹³C were lower, whereas leaf temperature and transpiration efficiency were higher in stressed plants, probably due to restricted transpirational cooling induced by stomatal closure. Furthermore, differences in stomatal conductance, leaf temperature, Δ¹³C and transpiration efficiency characterized genotypes that were physiologically more adapted to water deficit conditions. Correlation analysis also showed relatively strong relationships among these variables under well watered conditions. The drought tolerant genotypes, ILB-938/2 and Melodie showed lower stomatal conductance associated with warmer leaves, whereas higher stomatal conductance and cooler leaves were observed in sensitive lines (332/2/91/015/1 and Aurora/1). The lower value of Δ¹³C coupled with higher transpiration efficiency in ILB-938/2, relative to sensitive lines (Aurora/1 and Condor/3), is indeed a desirable characteristic for water-limited environments. Finally, the results showed that stomatal conductance, leaf temperature and Δ¹³C are promising physiological indicators for drought tolerance in faba bean. These variables could be measured in pot-grown plants at adequate water supply and may serve as indirect selection criteria to pre-screen genotypes.     

干旱-复水对两种石斛属植物叶水势的影响

石斛属植物多附着在其他植物体或岩石上,水分获取困难,其特殊的水分利用策略是其生存和发展的重要保证.为弄清石斛属植物对干旱胁迫的适应能力和机制,该文选用3年生金钗石斛和铁皮石斛,通过盆栽控水进行干旱胁迫和复水处理,探讨在不同干旱历时和干旱后复水条件下两种石斛的叶水势变化情况.结果表明:随着干旱时间的延长,两种石斛叶水势均...     

Effects of exogenous nitric oxide on antioxidation and DNA methylation of <Emphasis Type="Italic">Dendrobium huoshanense</Emphasis> grown under drought stress

Nitric oxide (NO) is an important biological messenger in plants, which has been implicated in response to abiotic stress. To study the effects of exogenous NO on drought menace, the tube seedlings of Dendrobium huoshanense were selected and treated with 10% polyethylene glycol (PEG-6000) to simulate drought stress. After application of sodium nitroprusside (SNP), the relative water content (RWC) and antioxidant enzyme activities were determined. As a result, plant treated with 50 μmol L⁻¹ of SNP maintained high level of RWC and lower content of malondialdehyde (MDA). Furthermore, the antioxidant enzyme activities were obviously enhanced. However, the higher concentration of SNP (100 μmol L⁻¹) enhanced the effects of drought stress for plant. For further analysis of the response mechanism to exogenous NO, the methylation-sensitive amplified polymorphism (MSAP) technique was used to investigate the changes of DNA methylation. When the seedlings of Dendrobium huoshanense were treated with 50 μmol L⁻¹ SNP containing 10% PEG-6000, levels of global DNA methylation of Dendrobium huoshanense were decreased. Nevertheless, the demethylation rate of methylated sites increased, accounting for 12.5% of total methylation sites. These results implied that some expressed genes were involved in the response process to drought stress triggered by NO in Dendrobium huoshanense.     

Plant water relations as selection criteria for drought tolerance in mustard

Genotypes of mustard (B. juncea) were evaluated for concurrent changes in leaf water potential (Ψ), leaf osmotic potential (π), leaf turgor potential (P) and leaf relative water content (RWC) during moisture stress at reproductive stage of growth. The slope ‘b’ in the regression between Ψ and π varied from 0.43 to 0.97 and was positively correlated with P and RWC. The genotypes with ‘b’ around 0.7 were able to maintain P of about 0.5 MPa at Ψ of − 2.5 MPa and thus such value of ‘b’ seems to provide enough degree of tolerance against drought.     

Influence of Exogenous Glycine Betaine and Abscisic Acid on Papaya in Responses to Water-deficit Stress

The effects of exogenous foliar glycine betaine (GB) and abscisic acid (ABA) on papaya responses to water stress were investigated under distinct water regimes. Papaya seedlings (Carica papaya L. cultivar “BH-65”) were pretreated with GB or ABA and subsequently subjected to consecutive periods of drought, rehydration, and a second period of drought conditions. Results indicated that water stress induced ABA, jasmonic acid (JA), and proline accumulation but did not modify malondialdehyde (MDA) concentration. In addition, water deprivation reduced photosynthetic rate, stomatal conductance, relative water content (RWC), leaf fresh weight, and increased leaf abscission. GB applied prior to drought imposition decreased the impact of water stress on ABA, JA, proline accumulation, leaf water status, growth, and photosynthetic performance. However, ABA-pretreated plants did not show alteration of most of these parameters under water stress conditions when compared with non-pretreated plants except a clear induction of JA accumulation. Taken together, the data suggest that GB may modulate ABA, JA, and proline accumulation through the control of stomatal movement and the high availability of compatible solutes, leading to improvement of leaf water status, growth, and photosynthetic machinery function. In contrast, exogenous ABA did not stimulate papaya physiological responses under drought, but interestingly ABA in combination with drought could induce progressive JA synthesis, unlike drought alone, which induces a transitory JA increase and may trigger endogenous ABA accumulation. The data also suggest that irrespective of the pretreatments, papaya did not suffer oxidative damage.     

The effect of drought hardening and chilling on ABA content in xylem sap and ABA - delivery rate from root of tomato plant

This paper is a continuation of our studies related to the response of two tomato cultivars: Robin and New Yorker to chilling: the later is more tolerant to chilling than the former one (Starck et al. 1994). The concentration of ABA in the xylem sap and ABA delivery rate (calculated as the amount of ABA exuded in 2h from the cut stump, following shoot removal) were estimated by ELISA. The relative water content (RWC) of the leaf blades and stomatal resistance (RS) were also measured. Tomato plants were grown in a greenhouse, under noncontrolled conditions. Before chilling some of the plants were drought hardened for 10 days (H). As an consequence of water deficit only New Yorker growth slightly decreased. Plants were chilled to 2–5 °C during three consecutive, 16-h nights, preceded by warm days, which caused a decrease in the RWC of leaf blades. Chilling did not decreased leaf blade hydration significantly, but drastically increased the concentration of ABA in the xylem sap in more chilling tolerant cv. New Yorker only. The delivery rate of ABA was markedly enhanced in both cultivars, but much more in New Yorker. Drought hardening increased ABA delivery rate in cv. Robin only, especially after chilling. The lack of correlation between changes in the RWC of leaf blades after low temperature treatment and the concentration of ABA in the xylem sap as well as its delivery rate suggest, that in both tomato cultivars chilling increased ABA level directly, not as an secondery effect of temperature-induced water deficit.     

Interactive effects of elevated CO2 and drought stress on leaf water potential and growth in Caragana intermedia

We studied the responses of leaf water potential (Ψ_w), morphology, biomass accumulation and allocation, and canopy productivity index (CPI) to the combined effects of elevated CO₂ and drought stress in Caragana intermedia seedlings. Seedlings were grown at two CO₂ concentrations (350 and 700 μmol mol⁻¹) interacted with three water regimes (60–70%, 45–55%, and 30–40% of field capacity of soil). Elevated CO₂ significantly increased Ψ_w, decreased specific leaf area (SLA) and leaf area ratio (LAR) of drought-stressed seedlings, and increased tree height, basal diameter, shoot biomass, root biomass as well as total biomass under the all the three water regimes. Growth responses to elevated CO₂ were greater in well-watered seedlings than in drought-stressed seedlings. CPI was significantly increased by elevated CO₂, and the increase in CPI became stronger as the level of drought stress increased. There were significant interactions between elevated CO₂ and drought stress on leaf water potential, basal diameter, leaf area, and biomass accumulation. Our results suggest that elevated CO₂ may enhance drought avoidance and improved water relations, thus weakening the effect of drought stress on growth of C. intermedia seedings.     

Effect of 24-epibrassinolide on drought stress-induced changes in Chorispora bungeana

Brassinosteroids (BRs) have been proposed to increase the resistance of plants to drought stress. The effect of foliar application of 0.1 μM 24-epibrassinolide (EBR) on chlorophyll (Chl) content, photosystem 2 (PS 2) photochemistry, membrane permeability, lipid peroxidation, relative water content (RWC), proline content, and the antioxidant system in drought-stressed Chorispora bungeana plants was investigated. The results showed that polyethylene glycol (PEG) induced water stress decreased RWC, Chl content and variable to maximum Chl fluorescence ratio (F_v/F_m) less in plants pretreated with EBR than in non-pretreated plants. In addition, lipid peroxidation, measured in terms of malondialdehyde content, membrane permeability and proline content in drought-stressed plants were less increased in EBR pretreated plants, while antioxidative enzyme activities and reduced ascorbate and glutathione contents were more increased in EBR pretreated than in non-pretreated plants. These results suggested that EBR could improve plant growth under drought stress     

Selecting a set of wild barley introgression lines and verification of QTL effects for resistance to powdery mildew and leaf rust

A set of 59 spring barley introgression lines (ILs) was developed from the advanced backcross population S42. The ILs were generated by three rounds of backcrossing, two to four subsequent selfings, and, in parallel, marker-assisted selection. Each line includes a single marker-defined chromosomal segment of the wild barley accession ISR42-8 (Hordeum vulgare ssp. spontaneum), whereas the remaining part of the genome is derived from the elite barley cultivar Scarlett (H. vulgare ssp. vulgare). Based on a map containing 98 SSR markers, the IL set covers so far 86.6% (1041.5 cM) of the donor genome. Each single line contains an average exotic introgression of 39.2 cM, representing 3.2% of the exotic genome. The utility of the developed IL set is illustrated by verification of QTLs controlling resistance to powdery mildew (Blumeria graminis f. sp. hordei L.) and leaf rust (Puccinia hordei L.) which were previously identified in the advanced backcross population S42. Altogether 57.1 and 75.0% of QTLs conferring resistance to powdery mildew and leaf rust, respectively, were verified by ILs. The strongest favorable effects were mapped to regions 1H, 0–85 cM and 4H, 125–170 cM, where susceptibility to powdery mildew and leaf rust was decreased by 66.1 and 34.7%, respectively, compared to the recurrent parent. In addition, three and one new QTLs were localized, respectively. A co-localization of two favorable QTLs was identified for line S42IL-138, which holds an introgressed segment in region 7H, 166–181. Here, a reduction effect was revealed for powdery mildew as well as for leaf rust severity. This line might be a valuable resource for transferring new resistance alleles into elite cultivars. In future, we aim to cover the complete exotic genome by selecting additional ILs. We intend to conduct further phenotype studies with the IL set in regard to the trait complexes agronomic performance, malting quality, biotic stress, and abiotic stress.