Evaluation of resistance and the role of some defense responses in wheat cultivars to Fusarium head blight

Fusarium graminearum and F. culmorum are the causal agents of Fusarium head blight (FHB) in cereal crops worldwide. Application of resistant cultivars is the most effective and economic method for management of FHB and reducing mycotoxin production in wheat. Understanding the physiological and biochemical mechanisms involved in basal resistance of wheat to FHB disease is limited. In this research, after screening resistance levels of eighteen wheat cultivars planted in Iran, Gaskozhen and Falat were identified as partially resistant and susceptible wheat cultivars against Fusarium spp., respectively. Also, we investigated the role of hydroxyl radical (OH−), nitric oxide (NO), callose deposition, lipid peroxidation and protein content in basal resistance of wheat to the hemi-biotrophic and necrotrophic Fusarium species causing FHB. Nitric oxide as a signaling molecule may be involved in physiological and defensive processes in plants. Our results showed that NO generation increased in seedlings and spikes of wheat cultivars after inoculation with Fusarium species. We observed earlier and stronger callose deposition at early time points after infection by Fusarium spp. isolates than in non-infected plants, which was positively related to the resistance levels in wheat cultivars. Higher levels of OH− and malondialdehyde (MDA) accumulation (as a marker of lipid peroxidation) were observed in the Falat than in the Gaskozhen cultivar, under non-infected and infected conditions. So, estimation of lipid peroxidation could be useful to evaluate cultivars’ susceptibility. These findings can provide novel insights for better recognition of physiological and biochemical markers of FHB resistance, which could be used for rapid screening of resistance levels in wheat cultivars against this destructive fungal disease.

Withania somnifera acts as a potential insect growth regulator in the polyphagous pest, Pericallia ricini

Both seed and root extracts of the medicinal plant, Ashwagandha, Withania somnifera exhibit insect growth regulatory activity against the polyphagous pest, Pericallia ricini. Topical administration of W. somnifera seed and root extracts to last instar larvae of P. ricini disrupted moulting and metamorphosis, leading to a number of developmental abnormalities such as delay in larval-pupal and pupal-adult ecdysis, formation of larval-pupal, pupal-adult and larval-pupal-adult mosaics/chimeras, ecdysial failure, suppression of pupation and adult emergence and formation of abnormal pupae and adultoids. The treatment with seed extracts was more severe than that of root extracts as it completely suppressed the pupation and adult emergence. The results clearly suggest that the medicinal plant, W. somnifera acts as a potential insect growth regulatory (IGR) disrupting the moulting and metamorphosis as a consequence of interference with the endocrine system.

Mycorrhizal fungi and microalgae modulate antioxidant capacity of basil plants

Mycorrhizal fungi, algae and cyanobacteria are some of the most important soil microorganisms and major components of a sustainable soil-plant system. This study presents for the first time evidence of the impact of green alga and cyanobacterium solely and in combination with arbuscular mycorrhizal fungi (AMF) on plant-antioxidant capacity. In order to provide a better understanding of the impact of AMF and soil microalgae on Ocimum basilicum L. performance, changes in the pattern and activity of the main antioxidant enzymes (AOEs), esterases and non-enzymatic antioxidants including phenols, flavonoids, ascorbate, and α-tocopherols were evaluated. The targeted inoculation of O. basilicum with AMF or algae (alone and in combination) enhanced the antioxidant capacity of the plants and the degree of stimulation varied depending on the treatment. Plants in symbiosis with AMF exhibited the highest antioxidant potential as was indicated by the enhanced functions of all studied leaf AOEs: 1.5-, 2- and more than 10-fold rises of superoxide dismutase (SOD), glutathione-S-transferase (GST) and glutathione reductase (GR), respectively. The greatest increase in the total esterase activity and concentration of phenols, flavonoids and ascorbate was marked in the plants with simultaneous inoculation of mycorrhizal fungi and the green algae. 2,2-diphenyl-1-pycril-hydrazyl (DPPH) free radical scavenging method and ferric reducing antioxidant power (FRAP) assay proved the increased plant antioxidant capacity after co-colonization of green algae and mycorrhizae.

Ecological applications of Pseudomonas as a biopesticide to control two-spotted mite Tetranychus urticae: chitinase and HCN production

The two-spotted spider mite (Tetranychus urticae Koch) is an important pest of many horticultural crops. A study was conducted to evaluate the effect of three fluorescent Pseudomonas isolates obtained from rhizospheric soil of tomato (Solanum lycopersicon) in Agadir, Morocco: Q110B, Q036B and Q172B, as potential biological control agents for T. urticae. Both acaricide and repellent activities were assessed on homogenous adult mites. The acaricidal activity test evaluated five concentrations of bacterial suspensions: 0 (control), 102, 104, 106, 108, and 1010 cfu · ml−1, while only the 1010 cfu ∙ ml−1 concentration of each bacterium was used for the repellent bioassay. The mortality rate and repellentindex were recorded 24, 48 and 72 h after application. Results indicated that the survival rate of T. urticae was reduced (p ≤ 0.01) by all three bacterial isolates compared to control. Within the 24–72 h time period the mortality rates ranged from 8 to 87%, 16 to 99%, and 13 to 89%, for Q110B, Q036B and Q172B isolates, respectively. The isolate Q036B (LC50 = 0.598 cfu · ml−1) provided higher mortality rates than Q172B and Q110B with LC50 values of 90,846 and 169,585 cfu · ml−1, respectively. Repellent activity was also the highest with Pseudomonas Q036B having a 71% repellence index at 48 h after application. Regarding the mechanism of action, all three isolates produced hydrogen cyanide, and exhibited protease and cellulose activities, although only Q036B and Q172B had potential chitinase action. Identification analysis showed that the isolates were either Pseudomonas putida (Q172B) or P. fluorescens (Q110B and Q036B). Our results indicate that the P. fluorescens isolate Q036B is a promising candidate for biological control of T. urticae, and has potential to contribute to an integrated pest management program to control this important pest. Then the fruits produced will be qualified as safe for consumers and the environment. The present work was customized to give support for policy decision makers as an agroecological potential meeting needs of industries and ecological balance.

The need for the application of modern chemical insecticides and environmental consequences of their use: a mini review

Currently, the use of insecticides is an acute problem. Due to rapid population growth, the primary task is to increase food production. Beyond abiotic factors (drought, soil salinity, etc.) that reduce crop yields, farmers face problems with insect pests that can decrease crop productivity up to 60%. Also, insects are carriers of severe viral and protozoan human diseases. The need for application of insecticides is not questioned but many of them cause resistance of insect pests to them. This, in turn, leads to the necessity to invent new insecticides that are safe and more effective for long-term use. Preparations based on conservative parts of nucleic acids, particularly contact DNA insecticides, could be used to solve insecticide resistance problem as control agents which are well-tailored to target insect pests. This mini review is devoted to these issues.

Side effects of fungicides and insecticides on entomopathogenic fungi in vitro

Products based on different strains of entomopathogenic fungi are now being used in Integrated Pest Management (IPM) programs. Compatibility studies of chemical and biological control agents are necessary to be able to give proper recommendations for their integrated use. The effect of three insecticides based on imidacloprid, spinosad and abamectin, and three fungicides based on chlorothalonil, azoxystrobin and thiophanate-methyl on the activity of the following entomopathogenic fungi: Metarhizium anisopliae (Metschn.) sensu lato, Beauveria bassiana (Bals.-Criv.) Vuill., Acremonium sp. was tested under laboratory conditions. Tests of the influence of the pesticides on growth and production of conidia were performed. From this study, we concluded that all tested insecticides can be applied together with fungus B. bassiana products in IPM programs. They even stimulate sporulation of this fungus at the recommended dose, 0.5 of the recommended dose and 1.5 times the recommended dose. In the case of fungicides we observed inhibition of growth and sporulation of B. bassiana and reduction of growth and sporulation of other species of fungi.

Determination of optimal doses of glyphosate for controlling weeds at several stages in southwestern Buenos Aires province (Argentina)

Efficient weed management is essential for avoiding competition for water, light, and nutrient resources in semiarid zones. Chemical weed control with glyphosate was evaluated on perennial wall-rocket (Diplotaxis tenuifolia), artichoke thistle (Cynara cardunculus), slender wild oat (Avena barbata), and perennial ryegrass (Lolium perenne). Plants at early, middle and advanced vegetative stages were used in this study. Glyphosate potassium salt was applied at rates of 0.0675 (1/16x), 0.135 (1/8x), 0.27 (1/4x), 0.54 (1/2x), 1.08 (x) and 2.16 (2x) kg acid equivalent (ae) · ha−1. Glyphosate combined with 2,4-D amine salt was evaluated at rates of 1.08 kg ae · ha−1and 0.53 kg active ingredient (ai) · ha−1, respectively. The volume of the spray was 100 l · ha−1with 86 droplets · cm−2and a Volume Median Diameter (VMD) of 421.19 μm. In general, all the tested weeds were controlled with a quarter of the label rate. Three sizes of tested plants were controlled in a similar way at the same glyphosate dose rate. Moreover, the addition of 2,4-D to glyphosate did not produce an increase in the control of broadleaf weeds. The results showed that glyphosate was effective in controlling the tested weed species, including low application rates for all the growth stages in the southwestern Buenos Aires province.

Relationship between pathogenicity, race and vegetative compatibility grouping among Algerian populations of Fusarium oxysporum f. sp. pisi causing pea wilt

Fusarium oxysporum f. sp. pisi (FOP) is a significant and destructive pathogen of field pea in Algeria. In the present study, 50 isolates of F. oxysporum f. sp. pisi, the causal agent of pea (Pisum sativum) wilt, collected from different parts of western Algeria and representing four races of the pathogen, were analyzed for virulence. The wilt incidence ranged from 6.66 to 88.33% on a highly susceptible cultivar (Little Marvel). Twenty-one isolates belonging to four races of FOP and one nonpathogenic F. oxysporum (FO) isolate were analyzed for vegetative compatibility in order to reveal the genetic structure of the population and to check the reliability of the method for the identification of physiological races of FOP. Obtained results showed that the FOP isolates could be classified into four main vegetative compatibility groups (VCGs) that corresponded to races l, 2A, 2B and 5. The race 6 isolate fell into the race 1 VCG. To our knowledge, this is the first such study in Algeria of its kind.

Interactions between the entomopathogenic fungus Beauveria bassiana and the Neotropical predator Eriopis connexa (Coleoptera: Coccinellidae): Implications in biological control of pest

Aphids (Hemiptera: Aphididae) are serious pests of crops causing direct damage by feeding and indirect by the transmission of plant viruses. The use of conventional insecticides for controlling aphids has caused different problems and insecticide resistance. Accordingly, there is more interest in alternative control methods such as biological control by natural enemies for sustainable agricultural management. Among biological control agents, entomopathogenic fungi are one of the most significant microbial pathogens of insects. Also, Coccinellidae, as a major group, is a serious natural enemy. Both larval and adult stages of Coccinellidae feed on different soft-body pests, such as aphids. Eriopis connexa (Germar) (Coleoptera: Coccinellidae) is a common species in agroecosystems of the Neotropical region where it is considered to be a potential control agent. Pathogens and arthropod natural enemies may contribute to the control of phytophagous pests; however, it is important to assess potential interactions within biological control agents that share hosts (intraguild interaction) to evaluate their combined use for pest control. Therefore, the aim of this study was to evaluate the compatibility and interaction (lethal and sublethal effects) between E. connexa and the entomopathogenic fungus Beauveria bassiana (Bals.-Criv.) Vuill. (Ascomycota: Hypocreales). Both are important biological control agents of aphids. The pathogenicity of B. bassiana against larvae, pupae and adults of the predator E. connexa was evaluated, and results showed, that B. bassiana infected the coleopteran. On the other hand, interaction between B. bassiana and the predator was evaluated through infected-prey. The effects of fungus on larvae survival were significantly different when we analyzed the accumulated survival (from first larval instar to adulthood). The daily fecundity was significantly reduced at five days compared to control group. By contrast, no significant differences were observed between the five oviposition days in the rate of hatched eggs. This study shows that despite having received a single dose of the fungus in its life cycle, the population parameters of the predator E. connexa are affected. More studies would be necessary to help identify interactions between microbes and natural enemies to increase and enhance opportunities and further develop biological pest control programs.

Biocontrol of bacterial speck of tomato by aqueous extract of Tagetes erecta

Biocontrol of plant diseases has emerged as an eco-friendly measure of plant protection and has experienced a lot of devotion in the last two decades. Biocontrol agents include application of microbial agents, their secretion products and natural extracts from different parts of several plants. The present study, therefore, aimed at evaluating the potency of aqueous extracts of Tagetes erecta L. (marigold) in controlling bacterial speck disease in tomato plants. The experimental design consisted of two groups of 50 plants each: group 1 – sprayed with sterile water (control); and group 2 – sprayed with marigold extract. Spraying was performed under aseptic conditions at the third node from the base of each plant. Challenge inoculation with the bacterial speck pathogen Pseudomonas syringae pv. tomato was performed to analyze the disease severity on the test plants. The parameters of study were analysis of alteration in the activity and gene expression of peroxidase (POX), phenyl ammonia lyase (PAL), and polyphenol oxidase (PPO), as well as isoform expression of POX and PPO. The results demonstrated strong inductive effects of the extract on the activity and genes of POX, PAL and PPO. De novo expression of POX and PPO isoforms following marigold extract treatment was also observed. The observations indicate that marigold extract could be a promising biopesticide.