Intolerant Cultivars Research Articles

Comprehensive analyses of microtubule-associated protein MAP65 family genes in Cucurbitaceae and CsaMAP65s expression profiles in cucumber.

MAP65 is a microtubule-binding protein family in plants and plays crucial roles in regulating cell growth and development, intercellular communication, and plant responses to various environmental stresses. However, MAP65s in Cucurbitaceae are still less understood. In this study, a total of 40 MAP65s were identified from six Cucurbitaceae species (Cucumis sativusL., Citrullus lanatus, Cucumis melo L., Cucurbita moschata, Lagenaria siceraria, and Benincasa hispida) and classified into five groups by phylogenetic analysis according to gene structures and conserved domains. A conserved domain (MAP65_ASE1) was found in all MAP65 proteins. In cucumber, we isolated six CsaMAP65s with different expression patterns in tissues including root, stem, leaf, female flower, male flower, and fruit. Subcellular localizations of CsaMAP65s verified that all CsaMAP65s were localized in microtubule and microfilament. Analyses of the promoter regions of CsaMAP65s have screened different cis-acting regulatory elements involved in growth and development and responses to hormone and stresses. In addition, CsaMAP65-5 in leaves was significantly upregulated by salt stress, and this promotion effect was higher in cucumber cultivars with salt tolerant than that without salt tolerant. CsaMAP65-1 in leaves was significantly upregulated by cold stress, and this promotion was higher in cold-tolerant cultivar than intolerant cultivar. With the genome-wide characterization and phylogenetic analysis of Cucurbitaceae MAP65s, and the expression profile of CsaMAP65s in cucumber, this study laid a foundation for further study on MAP65 functions in developmental processes and responses to abiotic stress in Cucurbitaceae species.

Effect of Sodium Chloride Salt on Germination, Growth, and Elemental Composition of Alfalfa Cultivars with Different Tolerances to Salinity

The aim of this study was to evaluate physiological responses and elemental composition of three salt tolerant alfalfa (Medicagosativa L.) cultivars, ‘Halo’, ‘Bridgeview’, ‘Rugged’, and two intolerant cultivars ‘Rangelander’ and ‘Vernal’ under five salinity levels (0 dSm−1, 4 dSm−1, 8 dSm−1, 12 dSm−1 and 16 dSm−1) in a sand based hydroponic system in the greenhouse. The germination percentage among the cultivars was highest for ‘Halo’ under salt stress. ‘Rugged’ and ‘Halo’ had higher seed vigor than the other cultivars in 16 dSm−1 EC. Among the alfalfa cultivars, ‘Rugged’ had the highest chlorophyll content at 0–12 dSm−1 EC. There was variation for root (p = 0.01) and shoot (p = 0.03) biomass among the alfalfa cultivars. Salt stress reduced (p < 0.001) plant height and shoot biomass, with 4.2% and 7.9% reduction for each 1 dS m−1 increase, respectively. Shoot biomass showed a positive correlation with plant height (p < 0.001, r = 0.80), chlorophyll content (p < 0.001, r = 0.56), root biomass (p < 0.001, r = 0.51), but was not correlated with seed vigor. This study demonstrated that seed vigor in the germination stage can not be used to predict salt tolerance of alfalfa at mature growth stages, however plant height and leaf chlorophyll content can serve as physiological markers for high shoot biomass selection at mature growth stages under salt stress.

Cereal and Pulse Crops with Improved Resistance to Pratylenchus thornei Are Needed to Maximize Wheat Production and Expand Crop Sequence Options

In the subtropical grain region of eastern Australia, two experiments were conducted, one initially with 2490 P. thornei/kg soil, the other with 8150 P. thornei/kg soil at 0–0.9 m soil depth. We determined the effect of P. thornei, residual from a weed-free fallow and pre-cropping with several cultivars each of barley (Hordeum vulgare), faba bean (Vicia faba), chickpea (Cicer arietinum), and wheat (Triticum aestivum) (Phase 1), on the growth of wheat cultivars with intolerance or tolerance to P. thornei (Phase 2). Pratylenchus thornei substantially increased after growing all cultivars of the Phase 1 faba bean, barley, and most cultivars of chickpea and wheat, and decreased after two moderately resistant wheat cultivars and the fallow treatment. The biomass of the Phase 2 tolerant cultivar ranged from 5070 to 6780 kg/ha and the intolerant cultivar 1020 to 4740 kg/ha. There was a negative linear relationship between P. thornei population densities and biomass of the Phase 2 intolerant cultivar but not of the tolerant cultivar. Growers are at risk of financial loss because they are restricted in their choice of crops to reduce damaging population densities of P. thornei. The development of resistant and tolerant crop genotypes can maximize production in P. thornei-affected farming systems.

A tradeoff between tolerance and resistance to a major fungal pathogen in elite wheat cultivars

Tolerance and resistance represent two strategies that hosts evolved to protect themselves from pathogens. Tolerance alleviates the reduction in host fitness due to infection without reducing a pathogen's growth, whereas resistance reduces pathogen growth. We investigated the tolerance of wheat to the major fungal pathogen Zymoseptoria tritici in 335 elite wheat cultivars. We used a novel digital phenotyping approach that included 11152 infected leaves and counted 2069048 pathogen fruiting bodies. We discovered a new component of tolerance that is based on the relationship between the green area remaining on a leaf and the number of pathogen fruiting bodies. We found a negative correlation between tolerance and resistance among intolerant cultivars, presenting the first compelling evidence for a tradeoff between tolerance and resistance to plant pathogens. Surprisingly, the tradeoff arises due to limits in the host resources available to the pathogen and not due to metabolic constraints, contrary to what ecological theory suggests. The mechanism underlying this tradeoff may be relevant for many plant diseases in which the amount of host resources available to the pathogen can limit the pathogen population. Our analysis indicates that European wheat breeders may have selected for tolerance instead of resistance to an important pathogen.

Differential responses of certain field pea and cowpea cultivars to root-knot nematode, Meloidogyne incognita for commercial release

BackgroundLegumes are considered staple foods for many countries in different areas of the world. Cultivation of nematode-resistant newly introduced field pea and cowpea cultivars is an important, cheap, and economical way to reduce damaging the nematode population that comes from improper use of nematicides and pesticides.ResultsThe cultivars of two examined crops were planted in pots inoculated with second-stage juveniles of M. incognita under screen house conditions. The results proved significant differences (P ≤ 0.05) among the tested cultivars regarding their responses to M. incognita. Host resistance/susceptibility was rated on the basis of potential reproduction index (PRI). Host reaction was based on average percent reduction potentials of plant growth and yield. The combination between host resistance/susceptibility and host reaction rates was used to give clear and accurate determination to these cultivars. According to the later scale, field pea cultivars were grouped into three categories of highly susceptible (Consessa), moderately susceptible (Diacole), and intolerant cultivars (Cerdon, Samantha and 337), while cowpea cultivars were grouped into two categories of highly susceptible (Kafr El-Sheikh) and susceptible cultivars (Dokki and 331).ConclusionsNone of the tested cowpea and field pea cultivars was found to be resistant or immune to root-knot nematode, M. incognita. Subsequently, plant growth and yield of the tested cultivars seemed to be severely damaged by root-knot nematode that might be attributed to less nutrient uptake by field pea and cowpea roots due to nematode infection. Planting of highly susceptible or susceptible cultivar in progression with resistant cultivars may help in limiting or reducing these defects. This is keeping management processes and production more economical. Further studies are needed to evaluate more cultivars/accessions against root-knot nematode.

Physiological changes and DREB1s expression profiles of tall fescue in response to freezing stress

Tall fescue is a widely used cool season turfgrass. In this study, we screened freezing tolerance of six tall fescue cultivars based on TEL50 (temperature causing 50% electrolyte leakage). We observed that freezing tolerant tall fescue cultivar exhibited lower EL, accumulated higher soluble sugar and proline, and showed higher CAT and SOD activities when compared with freezing intolerant cultivar. Based on bioinformatics analysis, 6 FaDREB1 unigenes were identified from publicly available transcriptomic data. Expression profiles showed that freezing tolerant cultivar only activated specific FaDREB1 unigenes, while freezing intolerant cultivar activated all six FaDREB1s during cold acclimation period. These findings indicated that cold stress modulated diverse physiological process in different tall fescue cultivars and activated various gene networks through regulating different subsets of FaDREB1s.

Effect of PEG8000 and NaCl on germination and seedling traits of tropical maize (Zea mays L.)

Among the different types of abiotic stresses, water isthe most damaging for crops. In the current research, the effect ofwater stress, induced with Polyethylene Glycol 8000 (PEG8000)and Sodium chloride (NaCl) solutions, was studied in maize genotypes.A randomized block design (RBD) with a factorial arrangementand four replications of 25 seeds each was used. The studiedmaize genotypes were RC2C39, RC2C51 (wild varieties of the Stateof Tabasco backcrossed with the endogamic line CML247 of the InternationalCenter for the Improvement of Maize and Wheat), wildTamulte, VS536, and Asgrow 7573 hybrid, study osmotic pressures(OP) were 0, -1.0, and -2.0 MPa. The percentage seed germination(G%), and seedling length (SL, in cm), root length (RL, in cm), freshseedling weight (FSW, in g), and fresh root weight (FRW, in g) wereevaluated on seedlings after 12 days of treatment imposition in thefive corn genotypes (Zea mays L.). The results showed significant differencesin the study variables before and after the stresses as theconcentrations of PEG8000 and NaCl increased. In general, theRC2C39, RC2C51, and VS536 genotypes had a better response toPEG8000 and NaCl as compared to wild Tamulte and Asgrow 7573hybrid for all measured variables. The OP of -2.0 MPa is suggestedto separate drought-tolerant from intolerant corn cultivars in theMexican tropical areas.

Agronomic manipulations can enhance the productivity of anaerobic tolerant rice sown in flooded soils in rainfed areas

Poor seedling emergence and establishment are a major restraint for adopting direct seeding in rice. This is especially critical in rainfed lowlands where floods can occur immediately after sowing, creating anaerobic conditions during germination and early seedling growth. Developing rice cultivars that can germinate in flooded soils will ensure good crop establishment. Several major quantitative trait loci (QTLs) for tolerance of anaerobic conditions during germination (anaerobic germination; AG) were identified from different landraces; and near isogenic lines (NILs) containing one of these QTLs (qAG-9-2, AG1) in the background of IR64 were developed. This study is an attempt to determine the effectiveness of AG1 QTL in improving germination of two IR64-AG NILs; IR 93312-30-101-20-3-66-6 (IR64–AG131) and IR93312-30-101-20-13-64-21 (IR64-AG132) sown under flooded conditions. The study also evaluated selected agronomic practices anticipated to further enhance crop establishment in flooded soils. IR64-AG NILs showed 81% and 217% higher plant populations over IR64-Sub1 and IR64, respectively, and this was also reflected as significantly higher grain yields. IR64-AG NILs mobilized relatively more starch into soluble sugars while submerged and maintained higher soluble sugar supply to the developing embryo resulting in faster and higher germination rates than the non-AG genotypes. Agronomic manipulations like higher seed rate (60kgha−1), better seeding methods and nutrient application improved seedling growth after germination and emergence, increasing plant height, leaf area, number of tillers and biomass accumulation. These improvements were reflected as higher grain yield even in the intolerant cultivar IR64. Application of 20% more phosphorus with the recommended N-P-K resulted in 21%, 16% and 19% higher grain yield in IR64-AG, IR64-Sub1 and IR64, respectively, over the control. The results established that combining proper crop establishment practices with tolerant genotype could enhance crop establishment in flooded soils using direct seeding methods, with consequent reduction in production costs and water use and subsequent increase in farmers’ income.

Role of silica and nitrogen interaction in submergence tolerance of rice

Submergence is an intensifying problem in major rice producing areas, when intolerant cultivars are submerged, they show a number of morpho-physiological changes such as elongation and chlorosis which is markedly developed after desubmergence probably due to oxidative damage. We studied the effects of submergence on survival, photosynthesis, nonstructural carbohydrate content, enzymatic activities, growth and yield of Sub1 and non-Sub1 cultivars. The interaction effect of nitrogen (N) and silica (Si) application was also examined for the submergence tolerance in rice. The photosynthetic rate, survival, growth of all the cultivars decreased during submergence but to a greater extent in IR64 and Swarna. After desubmergence, both the type of cultivars experienced oxidative damage, however, the oxidation of lipids was maintain at lower levels in Sub1 cultivars and anti-oxidants activities was increased more than intolerant cultivars. Application of basal Si was beneficial whereas, pre- and post-submergence Si spray was detrimental in relation to submergence tolerance. Basal Si resulted in significantly reduced elongation, lodging, leaf senescence, and chlorosis; when combined with post-flood N application either as broadcasting or spray, it led to significantly highest survival, photosynthesis, anti-oxidant activity and ultimately yields. Interaction of basal Si and post-flood N spray was the most promising method of nutrient application which not only resisted the damage during submergence but also enhanced the survival, growth after recovery in terms of number of green leaves emergence, leaf area and photosynthetic rate leading to significantly higher yield. The findings of the investigation propounds that a simple alteration in the time and method of nutrient application can significantly contribute to higher survival, crop establishment and yield in flash-flood prone areas.

RNA-seq analysis reveals genetic response and tolerance mechanisms to ozone exposure in soybean.

BackgroundOxidative stress caused by ground level ozone is a contributor to yield loss in a number of important crop plants. Soybean (Glycine max) is considered to be ozone sensitive, and current research into its response to oxidative stress is limited. To better understand the genetic response in soybean to oxidative stress, an RNA-seq analysis of two soybean cultivars was performed comparing an ozone intolerant cultivar (Mandarin-Ottawa) and an ozone resistant cultivar (Fiskeby III) following exposure to ozone.ResultsAnalysis of the transcriptome data revealed cultivar-specific expression level differences of genes previously implicated in oxidative stress responses, indicating unique cultivar-specific responses. Both Fiskeby III and Mandarin (Ottawa) exhibit an increased expression of oxidative response genes as well as glutathiones, phenylpropanoids, and phenylalanine ammonia-lyases. Mandarin (Ottawa) exhibited more general stress response genes whereas Fiskeby III had heightened expression of metabolic process genes. An examination of the timing of gene responses over the course of ozone exposure identified significantly more differentially expressed genes across all time points in Mandarin (Ottawa) than in Fiskeby III. The timing of expression was also considered to identify genes that may be indicative of a delayed response to ozone stress in Fiskeby III, We found that Mandarin (Ottawa) exhibits an higher level of expression in early time points for oxidative and general stress response genes while Fiskeby III seems to maintain expression of defense and stress response genes. Of particular interest was the expression of wax and cutin biosynthetic genes that we found to be expressed in Mandarin (Ottawa) in all sampled time points, whereas the expression of this pathway is only in the first time point for Fiskeby III.ConclusionsWe were able to identify differentially expressed genes that correspond to each of the known or expected categories of genes previously implicated in other species for ozone stress. Our study shows evidence that at least part of the observed ozone tolerance of Fiskeby III may be due to its thicker, denser leaves providing passive resistance thereby limiting the degree of ozone exposure. The observed diminished genetic response is then likely a consequence of this reduced exposure.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1637-7) contains supplementary material, which is available to authorized users.

Cereal cultivars can be ranked consistently for resistance to root-lesion nematodes (Pratylenchus thornei & P. neglectus) using diverse procedures

The root-lesion nematodes (RLN) Pratylenchus thornei and P. neglectus are widely distributed in Australian grain producing regions and can reduce the yield of intolerant wheat cultivars by up to 65 %, costing the industry ~123 M AUD/year. Consequently, researchers in the northern, southern and western regions have independently developed procedures to evaluate the resistance of cereal cultivars to RLN. To compare results, each of the three laboratories phenotyped a set of 26 and 36 cereal cultivars for relative resistance/susceptibility to P. thornei and P. neglectus respectively. The northern and southern regions also investigated the effects of planting time and experiment duration on RLN reproduction and cultivar ranking. Results show the genetic correlation between cultivars tested using the northern and southern procedures evaluating P. thornei resistance was 0.93. Genetic correlations between experiments using the same procedure, but with different planting times, were 0.99 for both northern and southern procedures. The genetic correlation between cultivars tested using the northern, southern and western procedures evaluating P. neglectus resistance ranged from 0.71 to 0.95. Genetic correlations between experiments using the same procedure but with different planting times ranged from 0.91 to 0.99. This study established that, even though experiments were conducted in different geographic locations and with different trial management practices, the diverse nematode resistance screening procedures ranked cultivars similarly. Consequently, RLN resistance data can be pooled across regions to provide national consensus ratings of cultivars.

Pratylenchus thornei populations reduce water uptake in intolerant wheat cultivars

Pratylenchus thornei is a major pathogen of wheat crops in the northern grain region of Eastern Australia with an estimated annual yield loss of $38 million. Damaged crops show symptoms of water and nutrient stress that suggest uptake is significantly affected. In order to understand the mechanisms involved in reducing water uptake and consequently plant yield, detailed measurements of water extraction and leaf area were conducted on a range of wheat cultivars with differing levels of tolerance and resistance to P. thornei.Planting wheat into high populations of P. thornei reduced the extraction rate (kl) in the intolerant cultivars; this in turn caused a delay in the root extraction velocity and effectively changed the crop lower limit. The early season stress applied by the reduced extraction rate impeded canopy development that consequently reduced demand for water and nutrients, growth and yield potential. The resulting yield loss was consistent across both a wet and a dry wheat growing season with the intolerant cultivar yielding 34% less than the tolerant cultivar. Understanding the mechanism with which P. thornei reduces yield allows the impact of P. thornei to be included in simulation models to better understand how to manage this constraint to the Australian grain industry.

Genetic analysis of tolerance to the root lesion nematode Pratylenchus neglectus in the legume Medicago littoralis

BackgroundThe nematode Pratylenchus neglectus has a wide host range and is able to feed on the root systems of cereals, oilseeds, grain and pasture legumes. Under the Mediterranean low rainfall environments of Australia, annual Medicago pasture legumes are used in rotation with cereals to fix atmospheric nitrogen and improve soil parameters. Considerable efforts are being made in breeding programs to improve resistance and tolerance to Pratylenchus neglectus in the major crops wheat and barley, which makes it vital to develop appropriate selection tools in medics.ResultsA strong source of tolerance to root damage by the root lesion nematode (RLN) Pratylenchus neglectus had previously been identified in line RH-1 (strand medic, M. littoralis). Using RH-1, we have developed a single seed descent (SSD) population of 138 lines by crossing it to the intolerant cultivar Herald. After inoculation, RLN-associated root damage clearly segregated in the population. Genetic analysis was performed by constructing a genetic map using simple sequence repeat (SSR) and gene-based SNP markers. A highly significant quantitative trait locus (QTL), QPnTolMl.1, was identified explaining 49% of the phenotypic variation in the SSD population. All SSRs and gene-based markers in the QTL region were derived from chromosome 1 of the sequenced genome of the closely related species M. truncatula. Gene-based markers were validated in advanced breeding lines derived from the RH-1 parent and also a second RLN tolerance source, RH-2 (M. truncatula ssp. tricycla). Comparative analysis to sequenced legume genomes showed that the physical QTL interval exists as a synteny block in Lotus japonicus, common bean, soybean and chickpea. Furthermore, using the sequenced genome information of M. truncatula, the QTL interval contains 55 genes out of which five are discussed as potential candidate genes responsible for the mapped tolerance.ConclusionThe closely linked set of SNP-based PCR markers is directly applicable to select for two different sources of RLN tolerance in breeding programs. Moreover, genome sequence information has allowed proposing candidate genes for further functional analysis and nominates QPnTolMl.1 as a target locus for RLN tolerance in economically important grain legumes, e.g. chickpea.

Alleviation of salinity-induced perturbations in ionic and hormonal concentrations in spring wheat through seed preconditioning in synthetic auxins

The experiments were conducted to examine the effects of seed priming in solutions (100, 150 and 200 mg L−1) of different synthetic auxins, i.e., 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), α-naphthaleneacetic acid (NAA) on growth, grain yield, gaseous exchange characteristics, ionic and hormonal concentrations in two spring wheat (Triticum aestivum L.) cultivars MH-97 (salt intolerant) and Inqlab-91 (salt tolerant). The primed (soaked for 12 h) and non-primed seeds were sown in Petri plates in a growth room as well as in a field treated with 150 mM NaCl. Generally, all synthetic auxins did not increase germination percentage and rate in both cultivars when compared with hydropriming (control), and even decreased these attributes when applied at higher concentrations (200 mg L−1). Nonetheless, under salt stress, NAA (150 mg L−1) was most effective in increasing seedling shoot dry weight, fertile tillers per plant, number of grains per ear and grain yield in both cultivars. The plants raised from seed treated with NAA (150 mg L−1) had lower shoot [Na+] in the salt intolerant cultivar. Moreover, NAA treatment improved root [Ca2+] in both cultivars. Priming agents affected leaf free indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) concentrations differently in both cultivars. Treatment with NAA (150 mg L−1) lowered leaf free abscisic acid (ABA) and putrescine (Put) concentrations and raised salicylic acid (SA) and spermidine (Spd) concentrations in the salt intolerant cultivar. In conclusion, pre-treatment with NAA (150 mg L−1) showed consistent promotive effects on growth and grain yield in the two cultivars, which were partially attributed to the beneficial effects of NAA-priming on ionic and hormonal homeostasis under salt stress.

Contrasting responses of salinity-stressed salt-tolerant and intolerant winter wheat (Triticum aestivum L.) cultivars to ozone pollution

Contrasting winter wheat cultivars, salt-tolerant DK961 and intolerant JN17, which sown in no salinity (-S) and salinity (+S) boxes were exposed to charcoal filtered air (CF) and elevated O(3) (+O(3)) in open top chambers (OTCs) for 30 days. In-S DK961 and JN17 plants,+O(3) DK961 and JN17 plants had significantly lower light-saturated net photosynthetic rates (A(sat), 26% and 24%), stomatal conductance (g(s), 20% and 32%) and chlorophyll contents (10% and 21%), while O(3) considerably increased foliar electrolyte leakage (13% and 39%), malondialdehyde content (9% and 23%), POD activity and ABA content. However, responses of these parameters to O(3) were significant in DK961 but not in JN17 in+S treatment. Correlation coefficient of DK961 reached significance level of 0.01, but it was not significant in JN17 under interaction of O(3) and salinity. O(3)-induced reductions were larger in shoot than in root in both cultivars. Results indicate that the salt-tolerant cultivar sustained less damage from salinity than did the intolerant cultivar but was severely injured by O(3) under+S condition. Therefore, selecting for greater salt tolerance may not lead to the expected gains in yield in areas of moderate (100mM) salinity when O(3) is present in high concentrations. In contrast, salinity-induced stomatal closure effectively reduced sensitivity to O(3) in the salt-intolerant cultivar. Hence we suggest salt-tolerant winter wheat cultivars might be well adapted to areas of high (>100mM) salinity and O(3) stress, while intolerant cultivars might be adaptable to areas of mild/moderate salinity but high O(3) pollution.

Estimating and screening of drought resistance indexes of peanut

Aims Our objective was to define an index of peanut (Arachis hypogaea) drought resistance and comprehen- sively evaluate drought resistance of peanut varieties under controlled water conditions. Methods The experiment was conducted on the farm of Qingdao Academy of Agricultural Science with 29 pea- nut varieties. Two levels of water content (80%-85% and 45%-50% of field moisture capacity) were used in a randomized complete block design with four replications. We measured 13 morphological and physiological characters such as plant height, branch numbers, biomass, leaf water content and photosynthetic pigment content in seedling and pod-pin stages. Important findings The 29 peanut cultivars can divided into four classes: high-, mid- and low-tolerant cultivars and intolerant cultivars. The high-tolerant cultivars included 'Tangke 8', 'Jihua 2', 'Datangyou', 'Huayu 25', 'Huayu 17', 'Luhua 14' and 'Fenghua 1'. Subordinate function values of the morphological indexes including main stem height, branch number and biomass, and photosynthetic pigments contents of the same cultivars at seedling stage were different. In addition, the subordinate function value of the seedling stage was unrelated to drought resistance, so a single physiological index cannot be used to identify the drought resistance of peanut. But the values drought resistance comprehensive evaluation (D) of physiological indexes were significantly related to drought resistance and can be used to identify the drought resistance of peanut. At the pod-pin stage, the D values of morphological indexes and physiological indexes were both significantly related to drought resistance, so the

Gibberellic acid mediated induction of salt tolerance in wheat plants: Growth, ionic partitioning, photosynthesis, yield and hormonal homeostasis

In order to elucidate the GA3-priming-induced physiochemical changes responsible for induction of salt tolerance in wheat, the primed and non-primed seeds of two spring wheat (Triticum aestivum L.) cultivars, namely, MH-97 (salt intolerant) and Inqlab-91 (salt tolerant) were sown in a field treated with 15dSm−1 NaCl salinity. Although all the three concentrations (100, 150 and 200mgL−1) of GA3 were effective in improving grain yield in both cultivars, the effect of 150mgL−1 GA3 was much pronounced particularly in the salt intolerant cultivar when under salt stress. Seed priming with GA3 altered the pattern of accumulation of different ions between shoots and roots in the adult plants of wheat under saline conditions. Treatment with GA3 (150mgL−1) decreased Na+ concentrations both in the shoots and roots and increased Ca2+ and K+ concentrations in the roots of both wheat cultivars. GA3-priming did not show consistent effect on gaseous exchange characteristics and the concentrations of auxins in the salt stressed plants of both wheat cultivars. However, all concentrations of GA3 reduced leaf free ABA levels in the salt intolerant, while reverse was true in the salt tolerant cultivar under saline conditions. Priming with GA3 (150mgL−1) was very effective in enhancing salicylic acid (SA) concentration in both wheat cultivars when under salt stress. Treatment with GA3 (100–150mgL−1) lowered leaf free putrescine (Put) and spermidine (Spd) concentrations in the plants of both wheat cultivars. The decrease in polyamines (Put and Spd) and ABA concentrations in the salt stressed plants of the salt intolerant cultivar treated with GA3 suggested that these plants might have faced less stress compared with control. Thus, physiologically, GA3-priming-induced increase in grain yield was attributed to the GA3-priming-induced modulation of ions uptake and partitioning (within shoots and roots) and hormones homeostasis under saline conditions.

Expression of vacuolar H+-pyrophosphatase (OVP3) is under control of an anoxia-inducible promoter in rice

Vacuolar H(+)-pyrophosphatase (V-PPase) expression increases in a number of abiotic stresses and is thought to play a role in adaptation to abiotic stresses. This paper reports on the regulation of six V-PPase genes in rice (Oryza sativa L.) coleoptiles under anoxia, using flood tolerant and intolerant cultivars to test our hypothesis. Quantitative PCR analysis showed that one vacuolar H(+)-pyrophosphatase (OVP3) was induced by anoxia, particularly in flood-tolerant rice. Regulation of OVP3 expression under anoxia was investigated by analysing putative OVP promoters. The putative OVP3 promoter contained more previously identified anoxia-inducible motifs than the putative promoters of the other five OVP genes. GUS activity in transgenic rice plants containing the OVP3 promoter region linked to the GUS reporter gene was induced only by anoxia. Salt and cold treatments had little effect on OVP3 promoter-driven GUS expression when compared to the anoxic treatment.

Resistance to the root-lesion nematodePratylenchus thorneiof Iranian landrace wheat

Pratylenchus thornei is widespread throughout the wheat-growing regions in Australia and overseas and can cause yield losses of up to 70% in some intolerant cultivars. The most effective forms of management of P. thornei populations are crop rotation and plant breeding. There have been no wheat accessions identified as completely resistant to P. thornei, therefore breeding programs have used moderately resistant parents. The objective of the present research was to evaluate 274 Iranian landrace wheats for resistance to P. thornei and identify accessions with resistance superior to the current best resistance source (GS50a). Plants were grown in P. thornei inoculated soil under controlled conditions in a glasshouse pot experiment for 16 weeks. Ninety-two accessions found to be resistant or moderately so were retested in a second experiment. From combined analysis of these experiments, 34 accessions were identified as resistant with reproduction factors (final population per kg soil/initial inoculum rate per kg soil) ≤1. In total, 25 accessions were more resistant than GS50a, with AUS28470 significantly (P<0.05) more resistant. The resistant Iranian landraces identified in the present study are a valuable untapped genetic pool offering improved levels of P. thornei resistance over current parents in Australian wheat-breeding programs.

Grazing‐Tolerant Alfalfa Cultivars have Superior Persistence under Continuous and Rotational Stocking

Grazing-tolerant alfalfa (Medicago sativa L.) cultivars are developed and evaluated under continuous stocking, but this does not reflect the grazing method used by most farmers. The objective of this experiment was to compare persistence of grazing-tolerant and intolerant cultivars grown in pure stands under continuous and rotational stocking in central Iowa. Small-plot trials were established in 2001 using the tolerant cultivars ‘Alfagraze’ and ‘Samurai’ and the intolerant cultivars ‘Apollo’ and ‘5454.’ Plots were not grazed in 2001, but continuous or rotational stocking was applied from mid-May through mid-September in 2002 and 2003. All cultivars had similar stands at the end of the establishment year. Under continuous stocking, the tolerant cultivars had superior survival after 1 year compared with the intolerant cultivars, but no differences among cultivars were seen under rotational stocking after the first year. After the second year of grazing, tolerant cultivars had superior persistence compared to the intolerant cultivars under both stocking methods. This supports a conclusion that evaluation under continuous stocking accurately reflects the performance of cultivars under rotational stocking. Given that continuous stocking allows faster separation of cultivars, it should be the preferred method of evaluation.