Methyl jasmonate stimulates polyamines biosynthesisand resistance against leaf rust in wheat plants

Abstract

Leaf rust of wheat (Triticum aestivum L.), incited by Puccinia recondita ex Desm. f. sp. tritici Eriks, is one of the most important wheat diseases in Egypt. Methyl jasmonate (MJ) is a potential plant elicitor which induces a wide range of chemical and anatomical defense reactions in conifers and might be used to increase systemic resistance against biotic damage. In the greenhouse, different concentrations of MJ (10, 20 and 30 mM) were applied as seed soaking plus foliar spray or only as foliar spray to control leaf rust and induction of secondary compound production in leaves of wheat plants. Foliar spray was applied after 30 and 50 days of sowing. Results indicated that all concentrations and treatments reduced the severity of rust disease caused by P. recondita f. sp. tritici in wheat leaves during 45 days of inoculations. Disease incidence was decreased significantly in MJ-treated plants as seed soaking plus foliar spray with 20 and 30 mM when compared to 10 mM MJ or control plants. The study revealed that, with increasing concentrations of MJ, the secondary metabolites were greatly increased. Endogenous levels of both free and conjugated putrescine, spermidine and spermine increased in response to the elicitor. Activities of polyamine biosynthetic enzymes of ornithine decarboxylase (ODC) and polyamine oxidase (PAO) displayed up to threefold increases relative to untreated control. Moreover, significant increases in activities of plant defense-related protein, enzymes as peroxidase and chitinase as well as free and conjugated phenols contents were recorded in treated plants compared with untreated and infected plants. Furthermore, MJ treatment increased the chlorophyll-a, chlorophyll-b and carotenoids pigments contents, the higher increase was obtained with combined treatment between seeds soaking plus foliar spray at 20 and 30 mM of MJ. Under field conditions, three concentrations of MJ, i.e. 10, 20 and 30 mM as combined treatment between seeds soaking plus foliar spray or only as foliar spray were applied to study their effect against rust disease. Foliar spray was applied after 30 and 80 days of sowing. Results showed that the high reduction in disease severity was obtained with combined treatments between seeds soaking plus foliar spray with MJ at 20 and 30 mM compared with other treatments and control. At the same time, all treatments increased the growth and grain yield of wheat plants. It could be suggested that combination treatment between seeds soaking plus foliar spray with methyl jasmonate might be used commercially for controlling rust disease of wheat plants under field conditions.     

内生拮抗细菌在哈密瓜植株体内的传导定殖和促生作用研究

采用抗生素标记的方法研究了内生拮抗细菌P38和B167菌株在哈密瓜植株体内的定殖动态和对植株生长的影响.结果表明,接种方法显著影响P38菌株在植株体内的定殖和传导,并以浸种处理最佳,蘸根和灌根处理次之,喷叶处理最差;浸种可使P38菌株在根、茎、叶中良好传导和稳定定殖,随着植株的生长,根内菌量呈下降趋势,而茎、叶内的含菌量先上升后下降;P38菌株还具有促进哈密瓜种子萌发和植株生长的作用.B167菌株只在根内定殖,在体内的扩展性较差,不能进入叶片;它对植株的生长表现出一定的抑制作用.     

Functional compatibility in cucumber mycorrhizas in terms of plant growth performance and foliar nutrient composition

Functional compatibility in cucumber mycorrhizas in terms of plant and fungal growth, and foliar nutrient composition from all possible combinations of six cucumber varieties and three species of arbuscular mycorrhizal (AM) fungi was evaluated. Measurements of foliar nutrient composition included N, P, K, Mg, Ca, Na, Fe, Zn, Mn and Cu. Growth of AM fungi was measured in terms of root colonisation, as examined with microscopy and the AM fungus biomarker fatty acid 16:1ω5 from both phospholipids and neutral lipids. Different responses of plant growth and foliar nutrient profiles were observed for the different AM symbioses examined. The AM fungus Claroideoglomus claroideum caused growth depression in association with four out of six cucumber varieties; Rhizophagus irregularis caused growth promotion in one of six cucumber varieties; whereas Funneliformis mosseae had no effect on the growth performance of any of the cucumber varieties examined. All three AM fungi markedly altered host plant shoot nutrient composition, with the strongest contrast observed between cucumber–R. irregularis symbioses and non‐mycorrhizal cucumber plants, independent of cucumber variety. On the other hand, AM fungal growth in roots differed between the three AM fungi, but was unaffected by host genotype. Strong build‐up of storage lipids was observed for R. irregularis, which was more moderate in the two other AM fungi. In conclusion, strong differential responses of cucumber varieties to inoculation with different AM fungi in terms of growth and shoot nutrient composition revealed high functional diversity in AM symbioses in cucumber plants.     

Induction of systemic resistance in rice to bacterial blight by 1,2,3-benzothiadiazole 7-carbothioic acid-S-methyl ester (BTH) treatments

Use of BTH to evaluate the disease severity and induction of systemic resistance in rice to bacterial blight caused by Xanthomonas oryzae pv. oryzae is investigated. A new batch of 25 isolates of Xanthomonas oryzae pv. oryzae was obtained from infected rice lead tissues collected from Pattambi, Kerala, south India. Their identification was confirmed by the plant inoculation test on to IR24 rice plants which produced characteristic bacterial blight lesions. Among the 25 of X.o. pv. oryzae, four of the isolates were also virulent to IRBB21 rice plants (a near isogenic line of IR24) which carry the Xa-21 gene for BB resistance. The results confirm that there are pathogen strains in India which can overcome Xa-21. Development of BB lesions developed in IR24 (BB susceptible) plants after they were treated with BTH applications either as seed treatment or as foliar spray at 0.1, 0.5, 0.1 and 2.0 mM concentrations showed that even at 2.0 mM concentrations, IR24 plants were still susceptible to the pathogen. There was very little or marginal effect of BTH on the induction of resistance to BB in IR24 rice plants. When the same concentrations of BTH were applied to IRBB21 (Xa-21) rice plants, they showed pronounced triggering of systemic resistance to BB pathogen even at 0.1 mM concentration of BTH applied either as seed treatment or as foliar spry. Disease severity index was reduced to 5 (against a score of 9 in untreated) and there was 85–86% reduction in BB incidence in plants that received 0.1 mM BTH. These results provide evidence that BTH-induced systemic resistance complements the R-gene resistance in IRBB21 plants but not in IR24 rice plants.     

Effects of induced plant resistance on soybean looper (Lepidoptera: Noctuidae) in soybean

Soybean looper, Chrysodeixis includens (Walker), is one of the most destructive pests of soybean in the southern U.S. Soybean looper defoliation exceeding 20% from R3 (pod initiation) to R5 (pod fill) can result in significant yield loss. In addition, soybean looper is highly resistant to many insecticides. An alternative to insecticide control is induced host plant resistance. In this study, a total of four experiments over 2 years were conducted in which three different elicitors of SAR (systemic acquired resistance), Actigard 50WG (acibenzolar-S-methyl), Regalia (extract of Reynoutria sachalinensis), and methyl jasmonate (MeJA), were applied to soybean at different plant stages to determine if these chemicals could induce plant resistance and lower soybean looper fitness. None of the elicitors of SAR significantly affected soybean looper mortality. However, Actigard 50WG, MeJA, and Regalia had adverse effects on developmental time, defoliation, and pupal weight of soybean looper. Induced effects by Regalia on soybean looper were very limited compared to Actigard 50WG and MeJA. A single application of MeJA reduced pupal weight by 6.8% and delayed larval development by 14.3%. Soybean seed production was not affected by application of elicitors. In conclusion, the results suggest that exogenous elicitors applied in the field can trigger plant resistance against herbivores and this low level of host plant resistance may effectively lessen pest pressure by favoring natural enemy population regulation without reducing seed production.     

Parents lend a helping hand to their offspring in plant defence

Plants under attack by pathogens and pests can mount a range of inducible defences, encompassing both chemical and structural changes. Although few reports exist, it appears that plants responding to pathogen or herbivore attack, or chemical defence elicitors, may produce progeny that are better able to defend themselves against attack, compared with progeny from unthreatened or untreated plants. To date, all research on transgenerational effects of biotic stress has been conducted on dicotyledenous plants. We examined the possibility that resistance induced by application of chemical defence elicitors to the monocot plant barley, could be passed on to the progeny. Plants were treated with acibenzolar-S-methyl (ASM) or saccharin, and grain harvested at maturity. Germination was unaffected in seed collected from plants treated with saccharin, while germination was reduced significantly in seed collected from ASM-treated plants. The subsequent growth of the seedlings was not significantly different in any of the treatments. However, plants from parents treated with both ASM or saccharin exhibited significantly enhanced resistance to infection by Rhynchosporium commune, despite not being treated with elicitor themselves. These data hint at the possibility of producing disease-resistant plants by exposing parent plants to chemical elicitors.     

Induction of antioxidant enzymes is involved in the greater effectiveness of a PGPR versus AM fungi with respect to increasing the tolerance of lettuce to severe salt stress

This study investigated the influence of inoculation with a plant growth-promoting rhizobacterium, Pseudomonas mendocina Palleroni, alone or in combination with an arbuscular mycorrhizal (AM) fungus, Glomus intraradices (Schenk & Smith) or Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe, on antioxidant enzyme activities (catalase and total peroxidase), phosphatase activity, solute accumulation, growth and mineral nutrient uptake in leaves of Lactuca sativa L. cv. Tafalla affected by three different levels of salt stress. Salinity decreased lettuce growth, regardless of the biological treatment and of the salt stress level. The plants inoculated with P. mendocina had significantly greater shoot biomass than the control plants at both salinity levels, whereas the mycorrhizal inoculation treatments only were effective in increasing shoot biomass at the medium salinity level. At the highest salinity level, the water content was greater in leaves of plants treated with P. mendocina or G. mosseae. At the medium salinity level, G. intraradices- or G. mosseae-colonised plants showed the highest concentrations of foliar P. The P. mendocina- and G. mosseae-colonised plants presented higher concentrations of foliar K and lower concentrations of foliar Na under high salt conditions. Salt stress decreased sugar accumulation and increased foliar proline concentration, particularly in plants inoculated with the PGPR. Increasing salinity stress raised significantly the antioxidant enzyme activities, including those of total peroxidase and catalase, of lettuce leaves compared to their respective non-stressed controls. The PGPR strain induced a higher increase in these antioxidant enzymes in response to severe salinity. Inoculation with selected PGPR could serve as a useful tool for alleviating salinity stress in salt-sensitive plants.     

Restoration of the mycobiome of the endangered Hawaiian mint Phyllostegia kaalaensis increases its resistance to a common powdery mildew

Beneficial microbes such as plant mutualistic fungi, hold the promise of ameliorating challenges faced in native plant conservation such as disease management. As an alternative to costly chemical pest control, conservation efforts could potentially harness the benefits of plant mutualistic fungi to aid in defense and disease resistance, but there are few tests of this notion. We set out to test the efficacy of controlling a common foliar pathogen, the powdery mildew Neoerysiphe galeopsidis, by inoculating the endangered Hawaiian plant species Phyllostegia kaalaensis with potentially beneficial members of its wild-type mycobiome. We tested whether inoculating plants with above or belowground fungal mutualists, or both, led to increased disease resistance in the host. We found that while all treatments reduced average disease incidence, colonization by the foliar yeast Moesziomyces aphidis was the only treatment to do so significantly. These results provide an exciting new strategy for plant conservation practices.     

Enhancing Soybean Rhizosphere Colonization by Rhizobium japonicum

A study was conducted to seek means to increase the colonization of the rhizosphere of soybeans (Glycine max L. Merrill) by Rhizobium japonicum. For this purpose, a strain of R. japonicum that was resistant to benomyl, streptomycin, and erythromycin was used. The numbers of R. japonicum rose quickly in the first 2 days after soybean seeds were planted in soil and then rapidly fell. The decline was slower if the seeds were coated with benomyl. This fungicide reduced the numbers of bacteria and protozoa in the rhizosphere, but the effect became less or disappeared as the plants grew. In sterile soil inoculated with R. japonicum and a mixture of microorganisms, the numbers of R. japonicum were usually lower if protozoa were present than if they were absent. Nodulation and plant yield were increased by the addition of benomyl to soybean seeds sown in sterile soil inoculated with R. japonicum and a mixture of microorganisms. The addition of streptomycin and erythromycin to soil stimulated the growth of R. japonicum but inhibited other bacteria in the presence or absence of soybeans. The data indicate that colonization can be increased by the use of antimicrobial agents and R. japonicum strains resistant to those inhibitors.     

Diversity and Functionality of Arbuscular Mycorrhizal Fungi in Three Plant Communities in Semiarid Grasslands National Park, Canada

Septate endophytes proliferating in the roots of grasslands’ plants shed doubts on the importance of arbuscular mycorrhizal (AM) symbioses in dry soils. The functionality and diversity of the AM symbioses formed in four replicates of three adjacent plant communities (agricultural, native, and restored) in Grasslands National Park, Canada were assessed in periods of moisture sufficiency and deficiency typical of early and late summer in the region. The community structure of AM fungi, as determined by polymerase chain reaction-denaturing gradient gel electrophoresis, varied with sampling time and plant community. Soil properties other than soil moisture did not change significantly with sampling time. The DNA sequences dominating AM extraradical networks in dry soil apparently belonged to rare taxa unreported in GenBank. DNA sequences of Glomus viscosum, Glomus mosseae, and Glomus hoi were dominant under conditions of moisture sufficiency. In total, nine different AM fungal sequences were found suggesting a role for the AM symbioses in semiarid areas. Significant positive linear relationships between plant P and N concentrations and active extraradical AM fungal biomass, estimated by the abundance of the phospholipid fatty acid marker 16:1ω5, existed under conditions of moisture sufficiency, but not under dry conditions. Active extraradical AM fungal biomass had significantly positive linear relationship with the abundance of two early season grasses, Agropyron cristatum (L.) Gaertn. and Koeleria gracilis Pers., but no relationship was found under dry conditions. The AM symbioses formed under conditions of moisture sufficiency typical of early summer at this location appear to be important for the nutrition of grassland plant communities, but no evidence of mutualism was found under the dry conditions of late summer.     

Treatment with acetyl salicylic acid protects muskmelon seedlings against drought stress

Salicylic acid (SA) is a common plant-produced signal molecule that is responsible for inducing tolerance to a number of biotic and abiotic stresses. An experiment was, therefore, conducted to test whether acetyl salicylic acid (ASA) application at various concentrations through seed soaking or foliar spray would protect muskmelon [Cucumis melo L. (reticulatus group)] seedlings, subjected to drought stress. Twenty-three-day-old plants pre-treated with ASA (0, 0.1, 0.25, 0.50 or 1.0 mM) were subjected to drought stress for 1 week in a greenhouse. ASA applied either through seed soaking or through foliar spray was effective within the range of 0.1–1 mM in providing drought stress protection in muskmelon seedlings; however, there was no difference between application methods indicating that both methods provided similar levels of protection. ASA significantly affected all seedling growth and stress indicator variables measured except leaf number and root dry weight. The best protection appeared to be obtained from seedlings pre-treated with lower concentrations of ASA. Even though both methods provided similar means of protection, due to its simplicity and practicality, soaking muskmelon seeds prior to sowing in up to 0.5 mM ASA would be a more desirable method.     

Suppression of tan spot and plant growth promotion of wheat by synthetic and biological inducers under field conditions

Tan spot of wheat caused by Pyrenophora tritici‐repentis (Ptr) is a major leaf spot disease. No single control measure is likely to be successful in controlling tan spot and a fully integrated system of disease management is more likely to achieve a long‐term solution. Research to improve control efficacy has focused on fungicide improvement, resistant cultivars, the use of biological control agents (BCAs) mixtures and combinatorial approaches involving BCAs and plant resistance stimulants with complementary modes of action. Various biotic and abiotic agents can stimulate wheat defence mechanisms and so benefit resistance to Ptr infection. Among them, Trichoderma spp. have been widely used as antagonistic fungal agents against several pathogens as well as plant growth enhancers. Also, the synthetic agents acibenzolar‐S‐methyl (ASM) and thiamethoxam (TM) have provided broad‐spectrum disease and pest control as well as enhanced plant vigour against several fungal diseases. The aim of this research was to evaluate the effectiveness of two Trichoderma harzianum strains and two substances of synthetic origin (ASM and TM) on the suppression of tan spot and plant growth promotion of wheat plants. When BCAs, ASM and TM were applied to field plots on wheat cultivar Klein Escorpion, the severity of tan spot reduced and plant height, fresh weight, dry weight of shoots and dry weight of roots increased in comparison with the control. When applied prior to Ptr inoculation, ASM, TM and the strain Th1 of T. harzianum caused a reduction in necrotic lesions >50% compared to the control treatment. Seed treatment with TM resulted in a significant enhancement of plant height. Application of ASM significantly increased foliar fresh weight by 45% as compared to the control treatment, whereas foliar fresh weight increased 29% and 50% when TM and T. harzianum strain Th1 were applied as seed coating. Acibenzolar‐S‐methyl alone or combined with Th1 increased dry weight to >60%, whereas the effects of TM and Th1 on dry mass showed an increase that ranged from 57% to 25%. Plants treated with Th1 and both synthetic compounds achieved up to sixfold increment in root dry weight over the control.     

Hydrogen Oxidation by the Host-Controlled Uptake Hydrogenase Phenotype of Bradyrhizobium japonicum in Symbiosis with Soybean Host Plants

Symbioses between uptake hydrogenase host-regulated (Hup-hr) phenotypes of Bradyrhizobium japonicum and exotic, agronomically unadapted soybean germ plasm were examined for expression of uptake hydrogenase activity. Determinations for hydrogen evolution and uptake hydrogenase activity identified five plant introduction (PI) lines which formed hydrogen-oxidizing symbioses with strains USDA 61 and PA3 6c. Hup-hr strains belonging to serogroup 94 expressed uptake hydrogenase activity in symbioses with PI 181696 and PI 219655 at rates sufficient to prevent hydrogen from escaping the nodules. The identification of soybean germ plasm forming hydrogen-oxidizing symbioses with Hup-hr bradyrhizobia potentially has implications for enhancing nitrogen fixation efficiency in soybean production.     

Interaction between arbuscular mycorrhizal fungus Glomus mosseae and plant growth promoting fungus Phoma sp. on their root colonization and growth promotion of cucumber (Cucumis sativus L.)

Interaction between arbuscular mycorrhizal fungus Glomus mosseae and plant growth promoting fungus Phoma sp. was studied for its effect on their root colonization and plant growth of cucumber. Two isolates of Phoma sp. (GS8-2 and GS8-3) were tested with G. mosseae. The percent root length colonized by G. mosseae was not adversely affected by the presence of Phoma isolates. In contrast, the root colonization of both isolates GS8-2 and GS8-3 in 4-week-old plants was significantly reduced (80.7% and 84.3%, respectively) by added G. mosseae. Inoculating plants with each Phoma isolate significantly increased the shoot dry weight. However, dual inoculation of each Phoma isolate with G. mosseae had no significant effect on growth enhancement.     

Differential effects of <Emphasis Type="Italic">Paenibacillus</Emphasis> spp. on cucumber mycorrhizas

The effects of 17 Paenibacillus strains on root colonization by Glomus intraradices or Glomus mosseae and plant growth parameters (shoot and root weight) of mycorrhizal cucumber plants were examined. The Paenibacillus strains were originally isolated from mycorrhizal (G. intraradices) and non-mycorrhizal cucumber rhizosphere and/or hyphosphere, except for strain EJP73, which originated from a Pinus sylvestris-Lactarius rufus ectomycorrhiza. Root colonization of cucumber plants by G. intraradices or G. mosseae was unaffected by all seven strains of Paenibacillus polymyxa, but was decreased or increased by four strains of Paenibacillus macerans and strain EJP73 of Paenibacillus sp. Overall, shoot dry weight of cucumber grown in symbioses with either G intraradices or G. mosseae was unaffected by inoculation with all of the Paenibacillus strains, except for strain MB02-429 of P. macerans, which increased the shoot dry weight in the cucumber-G. mosseae symbiosis. On the other hand, several Paenibacillus strains caused altered root growth. Three strains of P. polymyxa and four strains of P. macerans increased the root fresh weight of the cucumber–G. intraradices symbiosis, whereas three strains of P. polymyxa and one strain of P. macerans as well as Paenibacillus sp. EJP73, decreased the root fresh weight of the cucumber–G. mosseae symbiosis. In conclusion, our results show that bacteria from several species of Paenibacillus differentially affect cucumber mycorrhizas.     

The impact of foliar boron sprays on reproductive biology and seed quality of black gram

An experiment was conducted under glass house condition to study the effect of foliar application of boron (B) on reproductive biology and seed quality of black gram (Vigna mungo). Black gram (V. mungo L. var. DPU-88-31) was grown under controlled sand culture condition at deficient and sufficient B levels. After 32 days of sowing B deficient plants were sprayed with three concentrations of B (0.05%, 0.1% and 0.2% borax) at three different stages of reproductive development, i.e. prior to flowering, initiation of bud formation and after bud formation. Deficient B supply decreased the anther and pollen size, pollen tube growth, pollen viability as well as stigmatic receptivity which were increased by foliar B application. Foliar spray at all the three concentrations and at all stages increased the yield parameters like number of pods, pod size and number of seeds formed per plant. Foliar B application also improved the seed yield and seed quality in terms of storage seed proteins (albumin, globulin, glutenin and prolamin) and carbohydrates (sugars and starch) in black gram. The foliar application of B in appropriate doses (particularly 0.1%) after bud formation made quantitative and qualitative improvement in seed yield of black gram by supplementing additional/critical B requirements for reproductive development.     

Control of pearl millet downy mildew caused by Sclerospora graminicola with systemic fungicides in an artificially-contaminated plot

Among four fungicides, viz. metalaxyl (two formulations), fosetyl-Al, pro-pamocarb and cyomaxanil tested in vitro against sporangial germination inhibition of Sclerospora graminicola, cyomaxanil was found to be most inhibitory. In an artificially contaminated plot, when used as seed treatment or foliar spray for the control of downy mildew of pearl millet, only metalaxyl was effective. Metalaxyl 25 (Ridomil) and metalaxyl 35 (Apron) seed treatments protected the pearl millet plants from downy mildew up to 30 days. As a foliar spray, metalaxyl 25 used once at 20 days or twice after 20 and 38 days of plant growth gave less disease at harvest time. Seed treatment (metalaxyl 25 or 35) followed by one metalaxyl 25 spray was found to be effective in controlling the downy mildew. These treatments improved the growth of plants and yield significantly.     

Influence of Paclobutrazol and Application Methods on High-temperature Stress Injury in Cucumber Seedlings

Paclobutrazol (PBZ) is a member of the triazole plant growth inhibitor group that is responsible for inducing tolerance to a number of biotic and abiotic stresses. An experiment was therefore conducted to examine whether the application of PBZ at various concentrations (0, 25, 50, and 75 mg l⁻¹) by seed soaking or foliar spray would protect cucumber (Cucumis sativus) seedlings subjected to high-temperature stress. Thirty-five-day-old seedlings were exposed to heat stress at 40°C for 4 h per day for 5 days. PBZ improved the majority of the physiological (for example, relative chlorophyll content and chlorophyll fluorescence ratio) and morphological parameters (for example, shoot and root fresh and dry weights) measured in cucumber seedlings subjected to high-temperature stress. PBZ ameliorated the injuries caused by heat stress by increasing leaf proline content and preventing an increase in leaf electrolyte leakage. PBZ was more effective at increasing the heat tolerance of cucumber seedlings when using the seed-soaking method rather than the foliar spray method. The best protection was obtained when seeds were soaked in 50 mg l⁻¹ PBZ.     

Relationship between N(2)-Fixing Efficiency and Natural N Enrichment of Soybean Nodules

Non-nodular tissue of soybean (Glycine max L. Merrill) plants grown hydroponically in the absence of added N have a ¹⁵N abundance close to that of atmospheric N₂. In contrast, nodules are usually enriched in ¹⁵N. In this paper, we report measurements of the ¹⁵N abundance of foliar tissue and nodules of soybeans inoculated with 11 variably efficient strains of Rhizobum japonicum and grown hydroponically with no added N. The efficiency of the 11 symbioses varied over a wide range as judged by a 16-fold difference in N content. The degree of ¹⁵N enrichment of nodules was closely correlated with N₂-fixing efficiency (milligrams N fixed per milligram N in the nodules).

These results confirm prior preliminary data based on six variably efficient R. japonicum strains. The strong correlation between ^NN enrichment of soybean nodules and N₂-fixing efficiency is consistent with the hypothesis that new nodule tissue is synthesized from a pool of recently fixed N within the same nodule.