Bioinsecticidal activity of conidia and dry mycelium preparations of two isolates of Beauveria bassiana against the sugarcane borer Diatraea saccharalis

Two isolates of Beauveria bassiana (Bb₁ and Bb₅ strains) were grown in solid-state and submerged cultures (SSC and SbC, respectively) in order to obtain conidia and dry mycelium preparations. The samples obtained at laboratory scale were tested as alternatives for their further use as mycoinsecticides to control the sugarcane borer Diatraea saccharalis. The spore yields obtained in SSC indicated that the Bb₅ strain was able to produce around three times more conidia per gram of initial dry matter (3.7×10¹⁰) than the Bb₁ strain (1.3×10¹⁰) in a solid medium composed of wheat bran and bran husk. Under this culture conditions, the former showed not only satisfactory spore yields, but also a higher bioinsecticidal activity than the latter. Laboratory bioassays carried out with conidia of both strains against D. saccharalis larvae indicated that the Bb₅ strain promotes an insect mortality of 82.5% whereas only 21.3% was observed with the Bb₁ strain preparations. Concerning the samples obtained in SbC, in which a culture medium based on glucose and yeast extract was employed, it is interesting to point out that although both strains showed similar behaviors with yields of approximately 1.50×10¹⁰ conidia per gram of dry mycelium, both preparations failed in their bioinsecticidal activities. Despite satisfactory yields, bioinsecticidal activity of the Bb₁ and Bb₅ strains dropped drastically showing a larvae mortality below 2%.     

Mitigation of salinity-induced negative impact on the growth and yield of wheat by plant growth-promoting rhizobacteria in naturally saline conditions

Salinity is one of the major environmental threats for successful crop production, hampering plant growth due to the osmotic effect and nutritional and hormonal imbalances. The application of naturally occurring plant growth-promoting rhizobacteria (PGPR) is an emerging technology aimed at ameliorating the negative impact of salinity. However, the results obtained in the laboratory can sometimes not be reproduced in the field. The aim of the study reported here was to evaluate the effect of PGPR inoculation on seed germination in a saline environment under axenic conditions and on enhancement of the growth and yield of wheat under natural salt-affected field conditions. Wheat seeds were inoculated with pre-isolated strains of Pseudomonas putida, Enterobacter cloacae, Serratia ficaria, and Pseudomonas fluorescens and sown at different salinity levels (1, 2, 3, 6, 9, 12, 15 dS m^-1). Inoculation with these strains was found to enhance the germination percentage, germination rate, and index of wheat seeds up to 43, 51, and 123 %, respectively, over the uninoculated control at the highest salinity level. The potential of these PGPR for improving the growth and yield of wheat was also evaluated at two natural salt-affected sites. Inoculation with PGPR resulted a significant increase in the growth and yield parameters of wheat at both sites. The inoculated plants also improved the nutrient status of the wheat plants. The inoculated plants had low sodium and high nitrogen, phosphorus, and potassium contents. Our results show that such rhizobacterial strains may be used as an effective tool for enhancing plant growth under salinity stress and for maximizing the utilization of salt-affected soils.     

Simultaneous Pretreatment and Biohydrogen Production from Wheat Straw by Newly Isolated Ligninolytic <Emphasis Type="Italic">Bacillus</Emphasis> Sp. Strains with Two-Stage Batch Fermentation System

Biodegradation of agribiomass especially wheat straw to biohydrogen and biomethane is an encouraging approach to the current waste management problem. To do so, the biomass must first be pretreated to break down lignin thereby increasing accessibility of the substrate to fermentative organisms. In the current study, out of 20 isolates from the granular sludge of full-scale anaerobic digester, four ligninolytic Bacillus sp. strains were selected based on their lignin and Azure B degradation. Further, among the four isolates, Brevibacillus agri AN-3 exhibited the highest of 88.4 and 78.1% decrease in COD of lignin and Azure B respectively. These strains were also found to secrete optimum yields of lignin peroxidase (LiP) at pH 3, laccase (Lac) at pH 5, and xylanase and cellulase enzymes at pH 7. The strains demonstrated maximum activity of Lip and Lac at 50 °C and xylanase and cellulase at 60 °C after 72-h growth. Among the four strains, Brevibacillus agri AN-3 showed hydrogen (H₂) yield of 1.34 and 2.9 mol-H₂/mol from xylose and cellulose respectively. In two-phase wheat straw batch fermentation, Brevibacillus agri AN-3 produced 88.3 and 283.7 mL/gVS cumulative H₂ and methane (CH₄) respectively. Biotreatment with ligninolytic Bacillus sp. strains perceived that 261.4% more methane yield could be obtained from the wheat straw than using the untreated wheat straw in batch fermentation. This is the first study establishing not only the hydrogen potential of ligninolytic Bacillus sp. strains but also indicates a vital role of these species in developing standard inoculum and a biocatalyst for processing agribiomass.

Open image in new window

Graphical Abstract ?

     

蜡样芽孢杆菌B3-7在大田小麦根部的定殖动态及其对小麦纹枯病的防治效果

为了阐明蜡样芽孢杆菌B3-7在大田条件下的生态适应性以及对于小麦纹枯病的生防效果,通过利用绿色荧光蛋白编码基因gfp标记生防菌株B3-7,室内比较了GFP标记菌株和原始出发菌株在菌落形态、生长特性,生物薄膜产生以及在小麦根部定殖等方面的特性,结果发现GFP标记菌株和出发菌株在上述特性方面无明显差别。在此基础上,大田条件下测定了GFP标记菌株在小麦根部的定殖动态和对于小麦纹枯病的生防效果。结果发现,GFP标记菌株在小麦根部能够长期定殖,其存在量在小麦分蘖期最大,每克根重达到105CFU,拔节期后,该细菌数量一直维持在104CFU之上。同时发现,生防菌株能够有效降低小麦纹枯病的严重度和提高罹病小麦的产量。小麦分蘖期、孕穗期和灌浆期生防菌对于小麦纹枯病的防治效果分别达到60%、34%,34%,小麦成熟后产量提高13%—15%。结果表明,B3-7在大田条件下具有较好的生态适应性和防治小麦纹枯病的能力。     

Isolation and characterization of <Emphasis Type="Italic">Aspergillus flavus</Emphasis> strains in China

Important staple foods (peanuts, maize and rice) are susceptible to contamination by aflatoxin (AF)-producing fungi such as Aspergillus flavus. The objective of this study was to explore non-aflatoxin-producing (atoxigenic) A. flavus strains as biocontrol agents for the control of AFs. In the current study, a total of 724 A. flavus strains were isolated from different regions of China. Polyphasic approaches were utilized for species identification. Non-aflatoxin and non-cyclopiazonic acid (CPA)-producing strains were further screened for aflatoxin B₁ (AFB₁) biosynthesis pathway gene clusters using a PCR assay. Strains lacking an amplicon for the regulatory gene aflR were then analyzed for the presence of the other 28 biosynthetic genes. Only 229 (32%) of the A. flavus strains were found to be atoxigenic. Smaller (S) sclerotial phenotypes were dominant (51%) compared to large (L, 34%) and non-sclerotial (NS, 15%) phenotypes. Among the atoxigenic strains, 24 strains were PCR-negative for the fas-1 and aflJ genes. Sixteen (67%) atoxigenic A. flavus strains were PCRnegative for 10 or more of the biosynthetic genes. Altogether, 18 new PCR product patterns were observed, indicating great diversity in the AFB₁ biosynthesis pathway. The current study demonstrates that many atoxigenic A. flavus strains can be isolated from different regions of China. In the future laboratory as well as field based studies are recommended to test these atoxigenic strains as biocontrol agents for aflatoxin contamination.     

Prevalences of Shiga Toxin Subtypes and Selected Other Virulence Factors among Shiga-Toxigenic Escherichia coli Strains Isolated from Fresh Produce

Shiga-toxigenic Escherichia coli (STEC) strains were isolated from a variety of fresh produce, but mostly from spinach, with an estimated prevalence rate of 0.5%. A panel of 132 produce STEC strains were characterized for the presence of virulence and putative virulence factor genes and for Shiga toxin subtypes. About 9% of the isolates were found to have the eae gene, which encodes the intimin binding protein, and most of these belonged to known pathogenic STEC serotypes, such as O157:H7 and O26:H11, or to serotypes that reportedly have caused human illness. Among the eae-negative strains, there were three O113:H21 strains and one O91:H21 strain, which historically have been implicated in illness and therefore may be of concern as well. The ehxA gene, which encodes enterohemolysin, was found in ∼60% of the isolates, and the saa and subAB genes, which encode STEC agglutinating adhesin and subtilase cytotoxin, respectively, were found in ∼30% of the isolates. However, the precise roles of these three putative virulence factors in STEC pathogenesis have not yet been fully established. The stx_1a and stx_2a subtypes were present in 22% and 56%, respectively, of the strains overall and were the most common subtypes among produce STEC strains. The stx_2d subtype was the second most common subtype (28% overall), followed by stx_2c (7.5%), and only 2 to 3% of the produce STEC strains had the stx_2e and stx_2g subtypes. Almost half of the produce STEC strains had only partial serotypes or were untyped, and most of those that were identified belonged to unremarkable serotypes. Considering the uncertainties of some of these Stx subtypes and putative virulence factors in causing human illness, it is difficult to determine the health risk of many of these produce STEC strains.     

Alkadiene- and botryococcene-producing races of wild strains of Botryococcus braunii

Samples of the green colonial alga Botryococcus braunii, collected from various localities, were grown in the laboratory and examined for their hydrocarbon content and morphology. Although few differences appeared between the ultrastructures of the samples, the nature of their hydrocarbons, which remains unchanged at any stage of growth, allows the distinction of two physiological races viz algae producing odd-numbered unbranched alkadienes and trienes (C₂₅C₃₁) (the A race) and those producing polymethylated triterpenes C_nH_2n-₁₀ (C₃₀C₃₇), the botryococcenes (the B race). In laboratory culture, the hydrocarbon content of these new strains is very high, from 30 to 60% of the dry biomass. For the two races the greatest hydrocarbon productivity takes place during the active growth phase. The important variability observed in botryococcene distribution could originate both from genetic and environmental factors.     

Isolation and identification of Bacillus subtilis strain YB-05 and its antifungal substances showing antagonism against Gaeumannomyces graminis var. tritici

In this study, 98 putative Bacillus strains were isolated from wheat rhizospheric soil. Among the isolated strains, six showed strong inhibitory effects against the wheat take-all pathogen, Gaeumannomyces graminis var. tritici. One of the strains that showed significant inhibitory activity, YB-05, was identified as Bacillus subtilis based on a phylogenetic analysis of its 16S rDNA gene sequence, the results of the PCR analysis and cloning of its antifungal genes, its morphological characteristics and its physiological and biochemical properties. When tested with a dual-culture, cup–disc method and laboratory greenhouse studies, strain YB-05 was found to be superior to chemical treatment for control of the plant pathogen G. graminis var. tritici. After liquid culture, various antimicrobial substances in the culture medium were detected by high-performance liquid chromatography and high-resolution mass spectrometry, and the existence of their corresponding genes was verified by PCR analysis.     

Assessment of Sublethal and Transgenerational Effects of Pirimicarb on the Wheat Aphids Rhopalosiphum padi and Sitobion avenae

The wheat aphids, Rhopalosiphum padi (Linnaeus) and Sitobion avenae (Fabricius), are key pests on wheat crops worldwide. Management practices rely primarily on insecticides. The pirimicarb (carbamate) is used extensively as an effective insecticide to control these two aphids. In addition to the mortality caused by pirimicarb, various sublethal effects may occur in aphids when exposed to low lethal or sublethal doses. Understanding the general effect of pirimicarb on aphids could help increasing rational use of this insecticide. Under laboratory conditions, we assessed the sublethal effects of a low lethal concentration of pirimicarb (LC₂₅) on biological traits and acetylcholinesterase (AChE) activity of R. padi and S. avenae. Both direct and transgenerational effects, i.e. on parent and the F1 generations were assessed, respectively. We found that R. padi and S. avenae responded differentially to the LC₂₅ of pirimicarb. The parent generation of R. padi showed a 39% decrease in fecundity and multiple transgenerational effects were observed in the F1 generation; overall juvenile development, reproductive period, adult longevity and lifespan were longer than those of the control group. By contrast, LC₂₅ of pirimicarb showed almost no effects on S. avenae biological traits in both the parent and F1 generations; only the pre-reproductive duration was reduced in F1 generations. Demographic parameter estimates (e.g. r_m) showed similar trend, i.e. significant negative effect on R. padi population growth and no effect on S. avenae. However, AChE activity decreased in both R. padi and S. avenae treated by the LC₂₅ of pirimicarb. We demonstrated sublethal and transgenerational effects of pirimicarb in the two wheat aphid species; it hinted at the importance of considering sublethal effects (including hormesis) of pirimicarb for optimizing Integrated Pest Management (IPM) of wheat aphids.     

Environmental Determinants of Transformation Efficiency in Helicobacter pylori

Helicobacter pylori uses natural competence and homologous recombination to adapt to the dynamic environment of the stomach mucosa and maintain chronic colonization. Although H. pylori competence is constitutive, its rate of transformation is variable, and little is known about factors that influence it. To examine this, we first determined the transformation efficiency of H. pylori strains under low O₂ (5% O₂, 7.6% CO₂, 7.6% H₂) and high O₂ (15% O₂, 2.9% CO₂, 2.9% H₂) conditions using DNA containing an antibiotic resistance marker. H. pylori transformation efficiency was 6- to 32-fold greater under high O₂ tension, which was robust across different H. pylori strains, genetic loci, and bacterial growth phases. Since changing the O₂ concentration for these initial experiments also changed the concentrations of CO₂ and H₂, transformations were repeated under conditions where O₂, CO₂, and H₂ were each varied individually. The results showed that the increase in transformation efficiency under high O₂ was largely due to a decrease in CO₂. An increase in pH similar to that caused by low CO₂ was also sufficient to increase transformation efficiency. These results have implications for the physiology of H. pylori in the gastric environment, and they provide optimized conditions for the laboratory construction of H. pylori mutants using natural transformation.     

Strains of <Emphasis Type="Italic">Bacillus</Emphasis> ssp. regulate wheat resistance to <Emphasis Type="Italic">Septoria nodorum</Emphasis> Berk.

The ability of Bacillus subtilis Cohn and Bacillus thuringiensis Berliner to induce systemic resistance in wheat plants to the casual agent of Septoria nodorum Berk., blotch has been studied. It has been shown that strains of Bacillus ssp. that possess the capacity for endophytic survival have antagonistic activity against this pathogen in vitro. A reduction of the degree of Septoria nodorum blotch development on wheat leaves under the influence of Bacillus spp. was accompanied by the suppression of catalase activity, an increase in peroxidase activity and H₂O₂ content, and expression of defence related genes such us PR-1, PR-6, and PR-9. It has been shown that B. subtilis 26 D induces expression levels of wheat pathogenesis-related (PR) genes which marks a SA-dependent pathway of sustainable development and that B. thuringiensis V-5689 and V-6066 induces a JA/ET-dependent pathway. These results suggest that these strain Bacillus spp. promotes the formation of wheat plant resistance to S. nodorum through systemic activation of the plant defense system. The designed bacterial consortium formed a complex biological response in wheat plants infected phytopathogen.     

Processes leading to N2O and NO emissions from two different Chinese soils under different soil moisture contents

Background and Aims

Great attention has been paid to N₂O emissions from paddy soils under summer rice-winter wheat double-crop rotation, while less focus was given to the NO emissions. Besides, neither mechanism is completely understood. Therefore, this study aimed at evaluating the relative importance of nitrification and denitrification to N₂O and NO emissions from the two soils at different soil moisture contents

Methods

N₂O and NO emissions during one winter wheat season were simultaneously measured in situ in two rice-wheat based field plots at two different locations in Jiangsu Province, China. One soil was neutral in pH with silt loam texture (NSL), the other soil alkaline in pH with a clay texture (AC). A ¹⁵?N tracer incubation experiment was conducted in the laboratory to evaluate the relative importance of nitrification and denitrification for N₂O and NO emissions at soil moisture contents of 40 % water holding capacity (WHC), 65 % WHC and 90 % WHC.

Results

Higher N₂O emission rates in the AC soil than in the NSL soil were found both in the field and in the laboratory experiments; however, the differences in N₂O emissions between AC soil and NSL soil were smaller in the field than in the laboratory. In the latter experiment, nitrification was observed to be the more important source of N₂O emissions (>70 %) than denitrification, regardless of the soils and moisture treatments, with the only exception of the AC soil at 90 % WHC, at which the contributions of nitrification and denitrification to N₂O emissions were comparable. The ratios of NO/N₂O also supported the evidence that the nitrification process was the dominant source of N₂O and NO both in situ and in the laboratory. The proportion of nitrified N emitted as N₂O (P _N2O ) in NSL soil were around 0.02 % in all three moisture treatments, however, P _N2O in the AC soil (0.04 % to 0.10 %) tended to decrease with increasing soil moisture content.

Conclusions

Our results suggest that N₂O emission rates obtained from laboratory incubation experiments are not suitable for the estimation of the true amount of N₂O fluxes on a field scale. Besides, the variations of P _N2O with soil property and soil moisture content should be taken into account in model simulations of N₂O emission from soils.     

Adaptation of Musca domestica L. Field Population to Laboratory Breeding Causes Transcriptional Alterations

Background

The housefly, Musca domestica, has developed resistance to most insecticides applied for its control. Expression of genes coding for detoxification enzymes play a role in the response of the housefly when encountered by a xenobiotic. The highest level of constitutive gene expression of nine P450 genes was previously found in a newly-collected susceptible field population in comparison to three insecticide-resistant laboratory strains and a laboratory reference strain.

Results

We compared gene expression of five P450s by qPCR as well as global gene expression by RNAseq in the newly-acquired field population (845b) in generation F₁, F₁₃ and F₂₉ to test how gene expression changes following laboratory adaption. Four (CYP6A1, CYP6A36, CYP6D3, CYP6G4) of five investigated P450 genes adapted to breeding by decreasing expression. CYP6D1 showed higher female expression in F₂₉ than in F₁. For males, about half of the genes accessed in the global gene expression were up-regulated in F₁₃ and F₂₉ in comparison with the F₁ population. In females, 60% of the genes were up-regulated in F₁₃ in comparison with F₁, while 33% were up-regulated in F₂₉. Forty potential P450 genes were identified. In most cases, P450 gene expression was decreased in F₁₃ flies in comparison with F₁. Gene expression then increased from F₁₃ to F₂₉ in males and decreased further in females.

Conclusion

The global gene expression changes massively during adaptation to laboratory breeding. In general, global expression decreased as a result of laboratory adaption in males, while female expression was not unidirectional. Expression of P450 genes was in general down-regulated as a result of laboratory adaption. Expression of hexamerin, coding for a storage protein was increased, while gene expression of genes coding for amylases decreased. This suggests a major impact of the surrounding environment on gene response to xenobiotics and genetic composition of housefly strains.     

Solid-state fermentation,lignin degradation and resulting digestibility of wheat straw fermented by selected white-rot fungi

Summary Lignin biodegradation, carbon loss and in vitro dry matter digestibility (IVDMD) have been investigated during the solid state fermentation of wheat straw by eight previously selected strains of white-rot fungi. A mathematical model of the degradation kinetics is presented. [The time period required to reach maximum rates of ¹⁴CO₂ and unlabeled CO₂ release from (¹⁴C)-lignin-labelled wheat straw and from whole wheat straw, respectively, was generally short (6–10 days).] High rates of ¹⁴C-lignin degradation were achieved by Pycnoporus cinnabarinus (2.9% ¹⁴CO₂ evolved/day), an unidentified strain Nancon (3.0%/day), Sporotrichum pulverulentum Nov. (3.4%/day), Bjerkandera adusta (2.4%/day), and Dichomitus squalens (2.3%). However, only the latter two strains degraded whole wheat straw slowly and Bjerkandera adusta was not able to degrade more than 23% of the ¹⁴C-lignin. Cyathus stercoreus and Dichomitus squalens facilitated the highest improvement in IVDMD (68% against 38% for the sound straw) after 20 and 15 days of cultivation respectively, with low dry matter losses (15–20%). A study of the fate of ¹⁴C-lignin during fermentation using these two fungal strains showed that maximal levels of (¹⁴C)-water-soluble compounds are reached before peak levels of ¹⁴CO₂ evolution suggesting that these compounds are intermediates in lignin degradation. A possible relationship between water-soluble lignins and IVDMD improvement is discussed.     

Inoculation with selected strains of Azospirillum brasilense and A. lipoferum improves yields of maize and wheat in Brazil

Interest in the use of inoculants containing bacteria that promote plant growth is likely to increase in the coming years, due to higher costs of fertilizers, concerns over pollution and emphasis on sustainable agriculture. Although Brazil has a long tradition in research on nitrogen fixation in Azospirillum-grass associations, it has not led to recommendations of strains for use in commercial inoculants. In this study, we report the selection and evaluation of Azospirillum strains for the maize (Zea mays L.) and wheat (Triticum aestivum L.) crops, following protocols established by the Brazilian legislature, i.e. field experiments have to be performed in at least two different localities representing the crop growing regions, and for at least two seasons. In a first set of nine trials performed at Londrina and Ponta Grossa, southern Brazil, nine Azospirillum strains were evaluated after application to seeds as peat-based inoculants. A. brasilense strains Ab-V4, Ab-V5, Ab-V6 and Ab-V7 increased grain yields of maize by 662–823 kg ha^?1, or 24–30%, in relation to non-inoculated controls. Two A. lipoferum strains were tested in two of these experiments and promising results were also obtained. With wheat, A. brasilense strains Ab-V1, Ab-V5, Ab-V6 and Ab-V8 were the most effective, increasing yields by 312–423 kg ha^?1, or 13–18%. In a second trial set with eight field experiments at Londrina an Ponta Grossa, liquid and peat-based inoculants carrying a combination of A. brasilense strains Ab-V5 and Ab-V6 increased maize and wheat yields by 27% and 31%, respectively. Effects of inoculation were attributed to general increases in uptake of several macro and micronutrients and not specifically to biological nitrogen fixation. All experiments received only a low N-fertilizer starter at sowing (24 kg and 20 kg of N ha^?1 for the maize and wheat, respectively) and although yields can be globally considered low, they were compatible with Brazilian mean yields. This study resulted in the identification of the first Azospirillum strains authorized for the production of commercial inoculants in Brazil.     

Permethrin resistance in Aedes aegypti (Linnaeus) collected from Kuala Lumpur,Malaysia

Permethrin resistance status of a laboratory strain, a permethrin-selected strain and three field strains of Aedes aegypti collected in Kuala Lumpur, Malaysia were evaluated using three standard laboratory bioassays: WHO larval bioassay, WHO adult mosquito bioassay, and mixed function oxidase (MFO) enzyme microassay. The LC₅₀ values of field strains from the WHO larval bioassay did not differ significantly. The highest LC₅₀ value was from the Taman Melati field strain (0.39 mg/L). The resistance ratio for the permethrin-selected strain and the field strains ranged from 1.86 fold to 5.57 fold. Pre-exposure to piperonyl butoxide (PBO) in the WHO adult bioassay and MFOs enzyme microassay reduced the LT₅₀ values and reduced the mean optical density of elevated oxidase activity (0.28–0.42) at 630 nm. The LC₅₀ or LT₅₀ values and the level of oxidases were significantly correlated (r = 0.825; p< 0.05). This study confirmed the presence of permethrin resistance in these mosquito populations.     

Straw and Xylan Utilization by Pure Cultures of Nitrogen-Fixing Azospirillum spp

Azospirillum spp. were shown to utilize both straw and xylan, a major component of straw, for growth with an adequate combined N supply and also under N-limiting conditions. For most strains examined, a semisolid agar medium was satisfactory, but several strains appeared to be capable of slow metabolism of the agar. Subsequently, experiments were done with acid-washed sand supplemented with various carbon sources. In these experiments, authenticated laboratory strains, and all 16 recent field isolates from straw-amended soils, of both A. brasilense and A. lipoferum possessed the ability to utilize straw and xylan as energy sources for nitrogen fixation. Neither carboxymethyl cellulose nor cellulose was utilized. The strains and isolates differed in their abilities to utilize xylan and straw and in the efficiency of nitrogenase activity (CO₂/C₂H₂ ratio). Reasonable levels of activity could be maintained for at least 14 days in the sand cultures. Nitrogenase activity (acetylene reduction) was confirmed by ¹⁵N₂ incorporation. The level of nitrogenase activity observed was dependent on the time of the addition of acetylene to the culture vessels.     

Wheat (Triticum aestivum L.) growth enhancement by Azospirillum sp. under drought stress

Plant growth promoting rhizobacteria (PGPR) can enhance plant growth by alleviating soil stresses. Although previously investigated, some new interesting details are presented regarding the alleviating affects of Azospirillum sp. on wheat growth under drought stress in this research work. We hypothesized that the isolated strains of Azospirillum sp. may alleviate the adverse effects of drought stress on wheat (Triticum aestivum L.) growth. Three different strains of Azospirillum lipoferum (B1, B2 and B3) were used to inoculate wheat seedlings under drought. During the flowering stage the seedlings were subjected to three drought levels with five different time longevity, including control. Pots were water stressed at 80% (S0), 50% (S1) and 25% (S2) of field capacity moisture in a 25 day-period. Soil and plant water properties including water potential and water content, along with their effects on bacterial inoculum and wheat growth, were completely monitored during the experiment. While stress intensity significantly affected bacterial population and wheat growth, stress longevity only affected wheat water potential and water content. Compared to uninoculated treatments strain B3 (fixing and producing the highest amounts of N and auxin, respectively, with P solubilizing and ACC-deaminase activities) increased wheat yield at S1 and S2 by 43 and 109%, respectively. However, strain B2 (producing siderophore) was the most resistant strain under drought stress. The results of this experiment may elucidate the more efficient strains of Azospirillum sp. for wheat inoculation under drought stress and the mechanisms by which they alleviate the stress.     

Control of Grapholita molesta (Busck, 1916) (Lepidoptera: Tortricidae) with entomopathogenic nematodes (Rhabditida: Heterorhabditidae,Steinernematidae) in peach orchards

Oriental fruit moth Grapholita molesta (Busck, 1916) (Lepidoptera: Tortricidae) is considered a major pest in temperate fruit trees, such as peach and apple. Entomopathogenic nematodes (EPNs) are regarded as viable for pest management control due to their efficiency against tortricid in these trees. The objective of this study was to evaluate the effectiveness of native EPNs from Rio Grande do Sul state against pre-pupae of G. molesta under laboratory and field conditions. In the laboratory, pre-pupae of G. molesta were placed in corrugated cardboard sheets inside glass tubes and exposed to 17 different EPNs strains at concentrations of 6, 12, 24, 48 and 60 IJs/cm² and maintained at 25 °C, 70 ± 10% RH and photophase of 16 h. Insect mortality was recorded 72 h after inoculation of EPNs. Steinernema rarum RS69 and Heterorhabditis bacteriophora RS33 were the most virulent strains and selected for field application (LC₉₅ of 70.5 and 53.8 IJs/cm², respectively). Both strains were highly efficient under field conditions when applied in aqueous suspension directed to larvae on peach tree trunk, causing mortality of 94 and 97.0%, respectively.     

Characterization and identification of compost bacteria based on 16S rRNA gene sequencing

The aim of this study was to isolate and characterize bacteria from the compost of fruit and vegetable waste (FVW) for plant growth-promoting (PGP) activities and investigate the pro-active influence of bacterial isolates on wheat growth. Fourteen bacterial strains (RHC-1 to RHC-14) were isolated and purified in tryptic soya agar (TSA). In addition to being biochemically characterized, these bacterial strains were also tested for their PGP traits, such as phosphate (P)-solubilization, nifH gene amplification, indole-3-acetic acid (IAA) quantification and the production of ammonia, oxidase and catalase. Based on 16S rRNA gene sequencing, these bacterial strains were identified as belonging to species of Bacillus, Lysinibacillus, Lysobacter, Staphylococcus, Enterobacter, Pseudomonas and Serratia. All bacterial strains solubilized tri-calcium phosphate and produced IAA. Two bacterial strains RHC-8 (Enterobacter sp.) and RHC-13 (Pseudomonas sp.) solubilized the maximum amount of tri-calcium phosphate, i.e. 486 and 464 μg/ml, respectively. P-solubilization was associated with a significant drop in the pH of the broth culture from an initial pH of 7 to pH 4.43. In addition to P-solubilization and IAA production, six bacterial strains also carried the nifH gene and were further evaluated for their effect on wheat (Triticum aestivum) growth under controlled conditions. All six bacterial strains enhanced wheat growth as compared to uninoculated control plants. Two of the bacterial strains, RHC-8 and RHC-13, identified as Enterobacter aerogenes and Pseudomonas brenneri, respectively, were assessed as potential PGP rhizobacteria due to exhibiting characteristics of four or more PGP traits and enhancing wheat growth though their specific mechanism of action.