Molecular diagnostic for detecting the cytochrome b G143S - QoI resistance mutation in Cercospora beticola

The mutation G143S has been associated with high-level strobilurin resistance in laboratory mutant strains of Cercospora beticola, one of the most destructive pathogens in sugar beet plants. By using allele specific primers (PASA-PCR) and agarose gel visualization, a molecular diagnostic was developed for the detection of the G143S resistance mutation. This assay is simple and applicable in low tech laboratory settings, with high reliability when a relatively large proportion of mutated mitochondrial alleles are present in the resistant strains. To achieve detection of resistant alleles at low frequencies, a more sensitive Real Time PCR based assay capable of discriminating resistant (S143) genotypes in frequencies as low as 1:10,000 resistant:sensitive alleles was developed. Both diagnostics were successfully validated in laboratory strains. Subsequently, a large number of C. beticola isolates from QoI-treated sugar beet experimental fields in Greece were screened for resistance to Qo fungicides using these diagnostics and classic bioassays. No proportion of the 143S resistant allele was detected in all field isolates tested, which was in agreement with the phenotypes revealed by the biotests confirming that the efficacy of QoIs against C. beticola has been sustained in Greece 7 years after their introduction.     

Diversity of <Emphasis Type="Italic">Fusarium</Emphasis> species associated with root rot of sugar beet in China

Sugar beet is widely grown throughout the world and represents the second largest crop used to produce sugar. Root rot in sugar beet, caused by Fusarium, significantly reduces yield, juice purity, and sugar concentration. Here, 307 Fusarium isolates were collected from sugar beet roots exhibiting typical root rot symptoms in eight provinces or autonomous regions of China from 2009 to 2012. Based on morphological characteristics and sequence data of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) and the translation elongation factor 1α (EF-1α), Fusarium oxysporum (38.4%) was identified as the most prevalent species, followed by F. solani (20.9%), and F. equiseti (18.9%). These three species were widely distributed in all eight of the provinces and autonomous regions. F. tricinctum (5.9%), F. brachygibbosum (4.6%), F. redolens (3.3%), F. proliferatum (3.3%), F. graminearum (2.3%), F. verticillioides (1.6%), F. nygamai (0.7%), and F. culmorum (0.3%) were less frequently obtained. Of the 307 Fusarium isolates, 117 representing different species and geographic locations were demonstrated to cause tip rot and vascular discoloration in sugar beet roots, with disease incidence ranging from 84.2 to 100.0% and disease index ranging from 41.94 to 75.83. This is the first detailed report of Fusarium species, in particular F. tricinctum, F. brachygibbosum, F. redolens, F. proliferatum, F. nygamai, and F. culmorum, causing sugar beet root rot in China.     

Identification and characterization of <Emphasis Type="Italic">Colletotrichum</Emphasis> spp. associated with chili anthracnose in peninsular Malaysia

Anthracnose fruit rot caused by Colletotrichum spp. is a serious post-harvest disease of chili fruits (Capsicum spp.). One hundred-thirty isolates of Colletotrichum spp. were isolated from anthracnose of green and red cayenne pepper (Capsicum annuum) and bird’s eye chili (Capsicum frutescens). The isolates were morphologically identified as Colletotrichum acutatum sensu lato (62 isolates), Colletotrichum truncatum (54 isolates), and Colletotrichum gloeosporioides sensu lato (14 isolates). Molecular identification and phylogenetic analyses were based on internal transcribed spacer regions, β-tubulin, actin, and glyceraldehyde-3-phosphate dehydrogenase genes, and the isolates were re-identified as C. scovillei (58 isolates), C. truncatum (54 isolates), C. siamense (11 isolates), C. fioriniae (four isolates), and C. fructicola (3 isolates). Maximum likelihood trees using combined sequences showed that isolates of the same species grouped in the same main clade with the isolates used for comparison. Pathogenicity testing showed that the tested isolates from each species were pathogenic towards green and red Capsicum annuum and Capsicum frutescens upon treatment of wounded fruit, using both the mycelial plug and conidial suspension methods. Only five isolates of C. truncatum and seven isolates of C. scovillei were found to be pathogenic upon treatment of unwounded fruit. The occurrence of five Colletotrichum spp. (C. siamense, C. fructicola, C. scovillei, C. fioriniae, and C. truncatum) associated with chili anthracnose in Peninsular Malaysia indicates that correct species identification is important to formulate not only effective disease management, but also effective quarantine policy.     

Pathogenicity and Fungicide Sensitivity of <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> and <Emphasis Type="Italic">R. cerealis</Emphasis> Isolates

The Rhizoctonia solani species consists of multinucleate isolates that belong to anastomosis groups AG1–AG3 and differ in virulence and host affinity. R. cerealis is a binucleate species of anastomosis group AG-D which causes sharp eyespot, a common plant disease in Poland. Rhizoctonia spp. is a ubiquitous soil pathogen that poses a significant threat for global crop production due to the absence of effective crop protection products. The aim of this study was to determine the virulence of R. solani and R. cerealis isolates towards Beta vulgaris, Zea mays, Triticum spelta and T. aestivum seedlings, to confirm the presence of endopolygalacturonase genes pg1 and pg5 in the genomes of the tested isolates and to evaluate the tested isolates’ sensitivity to triazole, strobilurin, imidazole and carboxamide fungicides. All tested isolates infected B. vulgaris seedlings. but none of them were virulent against Z. mays plants. R. solani isolates AG4 PL and AG2-2IIIB PL were characterized by the highest virulence (average infestation score of 2.37 and 2.53 points on a scale of 0–3 points) against sugar beet seedlings. The prevalence of infections caused by most of the analysed isolates (in particular R. solani AG4 J—11.8, and R. cerealis RC2—0.78) was higher in spelt than in bread wheat. The virulence of the analysed isolates was not correlated with the presence of pg1 and pg5 genes. The efficacy of the tested fungicides in controlling Rhizoctonia spp. infections was estimated at 100% (propiconazole + cyproconazole), 98.8% (penthiopyrad), 95.4% (tebuconazole) and 78.3% (azoxystrobin).     

Quantitative phenotyping of grey leaf spot disease in maize using real-time PCR

Grey leaf spot is an important maize foliar disease caused by the fungal pathogens Cercospora zeae-maydis and Cercospora zeina. Although methods exist to detect these Cercospora species in maize, current techniques do not allow quantification of the fungi in planta. We developed a real-time SYBR® Green PCR assay for quantification of grey leaf spot disease in maize based on the amplification of a fragment of a cytochrome P450 reductase (cpr1) gene. In planta fungal DNA content was normalised to a maize glutathione S-transferase III gene (gst3) to yield values of ng Cercospora DNA/mg maize DNA. The assay was specific to the two Cercospora spp., and we observed no amplification of the cpr1 fragment in non-target maize leaf pathogens or saprophytes. The assay was employed to quantify C. zeina in glasshouse inoculated maize plants and grey leaf spot infected field plants of resistant and susceptible maize lines. In both instances, C. zeina DNA content correlated with symptomatic leaf lesion area, and the susceptible maize line contained significantly more C. zeina DNA than the resistant line. Sequence differences between the C. zeina and C. zeae-maydis cpr1 amplicons enabled us to perform melt curve analyses to identify the Cercospora species causing grey leaf spot at a particular location. This assay has application in the early detection and quantification of Cercospora spp., both of which are important tools in grey leaf spot disease management and maize breeding programmes.     

A myosin passenger protein gene (<Emphasis Type="Italic">FaSmy1</Emphasis>) is an essential regulator of cell development,pathogenicity, DON biosynthesis,and resistance to the fungicide phenamacril in <Emphasis Type="Italic">Fusarium asiaticum</Emphasis>

Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) are important viruses of wheat (Triticum aestivum L.) in the Great Plains of United States. In addition to agronomic practices to prevent damage from these viruses, temperature sensitive resistance genes Wsm1, Wsm2 and Wsm3, have been identified. However, threshold temperatures for Wsm1 and Wsm3 have not been clearly defined. To better understand these two resistance genes, wheat lines C.I.15092 (Wsm1), KS96HW10–3 (Wsm1), and KS12WGGRC59 (Wsm3) were evaluated for WSMV resistance at 27, 30, 33 and 35 °C and for TriMV resistance at 18, 21, 24, 27, 30, 33 and 35 °C. The results showed that only C.I.15092 remained resistant at 30 °C for both viruses. This line also tolerated TriMV at 33 and 35 °C with less sever symptom and lower infection rates. Wheat lines KS96HW10–3 and KS12WGGRC59 hold resistance to TriMV up to 21 °C. Molecular marker results suggested that the resistance in C.I.15092 is most probably conditioned by the resistance gene Wsm1 and additional gene(s) other than Wsm2 and Wsm3.     

Characterization of cytochrome b from European field isolates of Cercospora beticola with quinone outside inhibitor resistance

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar disease of sugar beet worldwide. Control strategies for CLS rely heavily on quinone outside inhibitor (Q_OI) fungicides. Despite the dependence on Q_OIs for disease control for more than a decade, a comprehensive survey of Q_OI sensitivity has not occurred in the sugar beet growing regions of France or Italy. In 2010, we collected 866 C. beticola isolates from sugar beet growing regions in France and Italy and assessed their sensitivity to the Q_OI fungicide pyraclostrobin using a spore germination assay. In total, 213 isolates were identified with EC₅₀ values greater than 1.0???g?ml^?1 to pyraclostrobin, all of which originated from Italy. To gain an understanding of the molecular basis of Q_OI resistance, we cloned the full-length coding region of Cbcytb, which encodes the mitochondrial Q_OI-target enzyme cytochrome b in C. beticola. Cbcytb is a 1,162-bp intron-free gene with obvious homology to other fungal cytb genes. Sequence analysis of Cbcytb was carried out in 32 Q_OI-sensitive (<0.080???g?ml^?1) and 27 Q_OI-resistant (>1.0???g?ml^?1) isolates. All tested Q_OI-resistant isolates harboured a point mutation in Cbcytb at nucleotide position 428 that conferred an exchange from glycine to alanine at amino acid position 143 (G143A). A PCR assay developed to discriminate Q_OI-sensitive and Q_OI-resistant isolates based on the G143A mutation could detect and differentiate isolates down to approximately 25?pg of template DNA. Microsatellite analyses suggested that Q_OI resistance emerged independently in multiple genotypic backgrounds at multiple locations. Our results indicate that Q_OI resistance has developed in some C. beticola populations in Italy and monitoring the G143A mutation is essential for fungicide resistance management in this pathosystem.     

Virulence profiling of <Emphasis Type="Italic">Xanthomonas oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis> isolates,causing bacterial blight of rice in India

Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo), remains a major production constraint in rice cultivation especially in irrigated and rainfed lowland ecosystems in India. The pathogen is highly dynamic in nature and knowledge on pathotype composition among the Xoo population is imperative for designing a scientific resistance breeding program. In this study, four hundred isolates of Xoo collected from diverse rice growing regions of India were analyzed for their virulence and genetic composition. Virulence profiling was carried out on a set of differentials consisting of 22 near isogenic lines (NILs) of IR24 possessing different BB resistance genes and their combinations along with the checks. It was observed that different NILs possessing single BB resistance gene were susceptible to about 59–94% of the Xoo isolates except IRBB 13 (containing BB resistance gene xa13), which showed susceptibility to about 35% of the isolates. Based on the reaction of the Xoo isolates on the differentials, they were categorized into 22 pathotypes. Among the 22 pathotypes, IXoPt-1 and IXoPt-2 were least virulent and IXoPt # 18–22 were highly virulent. Pathotype IXoPt-19 which was virulent on all single BB resistance genes except xa13 constituted the major pathotype (22.5% isolates) and was widely distributed throughout India (16 states). This was followed by pathotype IXoPt-22 (17.25%) which was virulent on all the NILs possessing single BB resistance genes. Molecular analysis was carried out using two outwardly directed primers complementary to sequence of IS1112, a repetitive element of Xoo. A high level of genetic polymorphism was detected among these isolates and the isolates were grouped into 12 major clusters. The data indicated complex nature of evolution of the Xoo pathotypes and there was no strong correlation between pathotypes and genetic clusters as each genetic cluster was composed of Xoo isolates belonging to different pathotypes. The study indicated that none of the single BB resistance genes can provide broad spectrum resistance in India. However, two-gene combinations like xa5 + xa13 and different 3 or 4 genes combination like Xa4 + xa5 + xa13, Xa4 + xa13 + Xa21, xa5 + xa13 + Xa21 and Xa4 + xa5 + xa13 + Xa21 are broadly effective throughout India.     

Korean <Emphasis Type="Italic">Brassica oleracea</Emphasis> germplasm offers a novel source of qualitative resistance to blackleg disease

Blackleg disease, caused by the hemibiotrophic fungal pathogen Leptosphaeria maculans, is one of the most devastating disease of Brassica species worldwide. To date, a total of 20 race-specific blackleg resistance (R) genes have been reported and all of those loci are located in either the A or B genomes of various Brassica species. The B. oleracea genome (CC) shares a high ancestral synteny with the A genome of B. rapa, suggesting the presence of qualitative (race specific) resistance to blackleg disease is also possible in B. oleracea germplasm. In the present study the C genome of Korean B. oleracea germplasm was screened for the presence of blackleg R genes. Thirty-two inbred cabbage lines with unknown resistance profiles, along with five control B. napus lines with well-characterised race-specific R genes, were assessed for cotyledon resistance against two L. maculans isolates with known and highly-contrasting avirulence gene (Avr) profiles. Two cabbage accessions were identified which produced a strong resistance when challenged with either isolate, demonstrating the presence of effective blackleg R genes in the cabbage C genome. Additionally, 16 microsatellite markers linked to seven different R genes of the B. napus A genome were converted into markers for their homologous regions on the B. oleracea C genome. These markers were used to screen all B. oleracea lines to assess if the novel C genome R genes were syntenous to known R gene-homologous regions of the A genome. The resistant cabbage lines offer C genome R genes for the protection of B. oleracea varieties against incursion of blackleg disease, as well as novel additional resistance sources for introgression into B. napus and B. carinata breeding material.     

Identification of the G143A mutation associated with QoI resistance in Cercospora beticola field isolates from Michigan,United States

BACKGROUND: Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola, is the most serious foliar disease of sugar beet (Beta vulgaris L.) worldwide. Disease control is mainly achieved by timely fungicide applications. In 2011, CLS control failures were reported in spite of application of quinone outside inhibitor (QoI) fungicide in several counties in Michigan, United States. The purpose of this study was to confirm the resistant phenotype and identify the molecular basis for QoI resistance of Michigan C. beticola isolates. RESULTS: Isolates collected in Michigan in 1998 and 1999 that had no previous exposure to the QoI fungicides trifloxystrobin or pyraclostrobin exhibited QoI EC₅₀ values of ?0.006 µg mL^?1. In contrast, all isolates obtained in 2011 exhibited EC₅₀ values of > 0.92 µg mL^?1 to both fungicides and harbored a mutation in cytochrome b (cytb) that led to an amino acid exchange from glycine to alanine at position 143 (G143A) compared with baseline QoI‐sensitive isolates. Microsatellite analysis of the isolates suggested that QoI resistance emerged independently in multiple genotypic backgrounds at multiple locations. A real‐time PCR assay utilizing dual‐labeled fluorogenic probes was developed to detect and differentiate QoI‐resistant isolates harboring the G143A mutation from sensitive isolates. CONCLUSION: The G143A mutation in cytb is associated with QoI resistance in C. beticola. Accurate monitoring of this mutation will be essential for fungicide resistance management in this pathosystem. Copyright © 2012 Society of Chemical Industry     

Assessing the Belgian potato <Emphasis Type="Italic">Alternaria</Emphasis> population for sensitivity to fungicides with diverse modes of action

Early blight and brown spot, caused by respectively Alternaria solani and Alternaria alternata, can lead to severe yield losses in potato-growing areas. To date, fungicide application is the most effective measure to control the disease. However, in recent years, a reduced sensitivity towards several active ingredients has been reported. To shed light on this issue, Alternaria isolates were collected from different potato fields in Belgium during two growing seasons. Subsequently, the sensitivity of these isolates was assessed using four widely used fungicides with different modes of action. Demethylation inhibitors, quinone outside inhibitors, a dithiocarbamate and a carboxylic acid amide were included in this study. Although all fungicides reduced spore germination and vegetative growth of Alternaria species to some extent, the interspecies sensitivity was very variable. In general, A. solani was more suppressed by the fungicides compared to A. alternata. The effectiveness of the dithiocarbamate mancozeb was high, whereas the quinone outside inhibitor azoxystrobin showed a limited activity, especially towards A. alternata. Therefore, a subset of the A. alternata and A. solani isolates was tested for the presence of, respectively, the G143A substitution and the F129L substitution in the cytochrome b. The frequency of A. alternata isolates bearing the resistant G143A allele (approximately 65%) was comparable in both sampling years, although sensitivity of isolates decreased during the growing season. This finding points to a shift of the population towards resistant isolates. Both the European genotype I and American genotype II were present in the A. solani population, with genotype I being the most prevalent. None of the genotype I isolates carried the F129L substitution, whereas in 83% of the genotype II isolates this substitution was present. Our results demonstrate for the first time that the Belgian Alternaria population on potato comprises a considerable broad spectrum of isolates with different sensitivity to fungicides.     

Insecticidal toxicity of thirteen commercial plant essential oils against <Emphasis Type="Italic">Spodoptera exigua</Emphasis> (Lepidoptera: Noctuidae)

We evaluated the chemical composition of thirteen commercially available plant essential oils and their insecticidal activity against the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). Gas chromatography-mass spectrometry was used to characterize the chemical components of the essential oils. A total of 113 compounds were identified, with terpenes (>80%) and aromatic compounds as primary constituents. The toxicity of each pure essential oil was tested separately on third instar larvae and adult beet armyworms by topical application of 0.5 μl oil/ insect. All plant essential oils were found to be harmful to S. exigua, with third instar larvae showing significantly more susceptibility than adults. Essential oils of Cinnamomum zeylanicum and Juniperus virginiana showed the highest toxicity (mortality above 90%) to larvae, while C. zeylanicum and Pogostemon cablin oils were the most harmful compounds (95% mortality) to adults. Cymbopogon winterianus oil caused delayed mortality (similar to the effects of insect growth regulators) as well as malformations in pupae. C. winterianus, Ocimum basilicum and Rosmarinus officinalis oils significantly reduced fecundity, whereas no significant effects were observed on fertility.     

Seasonal progression of leaf rust in ‘Niagara Rosada’ grapevine in a biannual crop system in Brazil

The soil-borne fungus Fusarium oxysporum can cause both Fusarium yellows and Fusarium root rot diseases with severe yield losses in cultivated sugar beet. These two diseases cause similar foliar symptoms but different root response and have been proposed to be caused by two distinct F. oxysporum formae speciales. Fusarium yellows, caused by F. oxysporum f. sp. betae, presents vascular discoloration, whereas Fusarium root rot, due to F. oxysporum f. sp. radicis-betae, appears as black rot visible on the root surface. The aim of this work was to study the host-pathogen interaction between sugar beet lines and isolates originally characterized as Fusarium oxysporum f. sp. betae. Eight susceptible sugar beet lines, selected by the USDA-ARS (US) and UNIPD (University of Padova, Italy) breeding programs, were inoculated with three different isolates of F. oxysporum f. sp. betae, the causal agent of Fusarium yellows, representing different genetic groups. All inoculated lines developed symptoms, but severity, expressed as area under the disease progress curve (AUDPC), differed significantly (P < 0.05) among lines. Two lines from UNIPD, 6 and 9, were the most susceptible to the disease, whereas the other lines showed similar levels. The three isolates of F. oxysporum f. sp. betae differed significantly (P < 0.05) in disease severity. Five weeks after inoculation the plants were harvested and roots examined. Surprisingly, severe root rot was observed in the susceptible UNIPD lines when inoculated with all three isolates, while this symptom was never observed in the USDA germplasm. The development of this disease symptom obviously depends on the plant genotype.     

Phylogenetic relationship and fungicide sensitivity of members of the <Emphasis Type="Italic">Colletotrichum gloeosporioides</Emphasis> species complex from apple

The members of the Colletotrichum gloeosporioides species complex (CGSC), the dominant pathogens of apple bitter rot in Nagano prefecture, Japan, were reidentified and the relationship between the species and fungicide sensitivity was revealed. Based on phylogenetic analysis of the ApMat locus with the neighbor-joining (NJ) method, isolates from apple contained three species of the CGSC; C. fructicola, C. aenigma, C. siamense, and three clades of the CGSC: Clade V, S and K. Colletotrichum fructicola and Clade S dominated in Nagano Prefecture. Isolates of C. siamense, C. aenigma and Clade V, S and K remained sensitive to benomyl and quinone outside inhibitor (QoI) fungicides, while C. fructicola often developed resistance to benomyl and QoI fungicides. These results suggest that the development of fungicide resistance differs among members of the CGSC.     

Fungicide sensitivity,growth rate,aggressiveness and frost hardiness of <Emphasis Type="Italic">Monilinia fructicola</Emphasis> and <Emphasis Type="Italic">Monilinia laxa</Emphasis> isolates

Monilinia fructicola, the most destructive pathogen of the genus Monilinia, has recently been introduced into Serbia and many other European countries. Since then, many studies have been conducted to evaluate the characteristics of Monilinia species that have a role in the establishment and survival of the pathogen in new areas. The present study assessed the capacity of M. fructicola to repress and replace Monilinia laxa in Serbia based on: fungicide sensitivity, growth rate and aggressiveness at different temperatures, as well as frost hardiness of the isolates of both species. The results showed that the isolates of M. fructicola, compared to M. laxa, were significantly less sensitive to the following fungicides: iprodione, tebucanozole, chlorothalonil, azoxystrobin, fluopyram, and boscalid. In addition, M. laxa isolates exhibited little variation in sensitivity to all of the tested fungicides, whereas M. fructicola isolates displayed a wide range of sensitivity. The temperature of 5°C favored M. laxa growth and aggressiveness, while at 30°C M. fructicola grew faster and had higher lesion expansion rate. These results support an assumption that M. fructicola will continue to spread in Serbian orchards in coming years, particularly on stone fruits harvested during hot summer weather.     

Erhebungen zur Anwendung von chemischen Pflanzenschutzmitteln in Zuckerrüben

Freely available information on the actual use of chemical plant protection products (PPPs) in agriculture is highly necessary for a number of scientific questions and political discussions. Therefore, since 2000, regular surveys on the use of PPPs have been carried out for the most important agricultural and horticultural crops in Germany (NEPTUN projects). In 2011, they were adjusted to legal framework changes. Since then they are known as PAPA surveys with “PAPA” being an abbreviation for Panel Pesticide Applications. For each crop a network of farms was built up. In each network, the PPP application data are collected annually, anonymized and forwarded to the Julius Kühn-Institute (JKI).All surveys and analyses based on the panel refer to the Federal Republic of Germany. The participating farms are distributed throughout Germany proportionally to the production area per crop.In sugar beet cultivation the results of PAPA surveys show that the plant protection intensity has increased slightly in recent years comparing the PAPA results with the years 2005 to 2010. There are diverse reasons for this development. Difficult-to-control weeds occurred on an increasing acreage in recent years. At the same time, an early appearance of foliar diseases (approximately beginning of July) combined with warm and humid weather during the following weeks leads to the development of the main pathogen causing leaf spot diseases in sugar beet (Cercospora beticola) in many regions. A continuing development of leaf spots increases the need for repeated fungicide applications. A high infestation with aphids was the dominating reason for increased insecticide applications in some years. Additional influences on the treatment index are due to changes in the authorization of PPPs.     

Associated bacterial diversity of insecticide-susceptible and -resistant brown planthopper, <Emphasis Type="Italic">Nilaparvata lugens</Emphasis> (Homoptera: Delphacidae) analyzed by culture-dependent and -independent methods

Nilaparvata lugens (Stål) is one of the major pests of rice throughout tropical and temperate Asia. Indiscriminate use of insecticides for suppressing N. lugens has resulted in the development of resistance to multiple insecticide classes, causing frequent control failures in the field. Analysis of gut bacterial diversity within an insect host is the initial step towards understanding the ecological roles of the symbionts. Present study aimed to survey the bacterial diversity associated with laboratory-reared (insecticide-susceptible) and field-collected (insecticide-resistant) populations of N. lugens by culture-dependent and PCR-Denaturing Gradient Gel Electrophoresis (DGGE) methods. Seventeen bacterial isolates were obtained by the culture-dependent method. Molecular characterization using the 16S rRNA gene and phylogenetic analysis revealed that the isolates belonged to Firmicutes and Proteobacteria. Taxonomic assignment placed these isolates into seven families representing 10 genera. Enterobacteriaceae was the most dominant family with its occurrence in four out of the five populations studied. The DGGE profiles indicated a low complex gut bacteria associated with N. lugens with limited number of bands. The Shannon-Wiener index ranged from 0.898 in insecticide-susceptible population to 0.946–1.035 in resistant populations. Sequencing and phylogenetic analysis revealed that the DGGE bands belonged to Firmicutes, Proteobacteria and Bacteriodetes. Results of this study illustrated that gut bacterial community associated with N. lugens is dominated by Proteobacteria and Firmicutes. Present findings could provide the basis for future work on the possible role of the bacterial symbionts in insecticide resistance and to formulate potential resistance management strategies.     

Nonhost resistance of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> against <Emphasis Type="Italic">Colletotrichum</Emphasis> species

Arabidopsis thaliana exhibits a durable resistance called nonhost resistance against nonadapted fungal pathogens. A. thaliana activates preinvasive resistance and terminates entry attempts by nonadapted fungi belonging to the genus Colletotrichum, which cause anthracnose disease in many plants. In the interaction between A. thaliana and nonadapted C. tropicale, the preinvasive resistance involves the PENETRATION 2-related antifungal secondary metabolite pathway and the ENHANCED DISEASE RESISTANCE 1-dependent antifungal peptide pathway. The development of invasive hyphae by C. tropicale owing to the reduction of preinvasive resistance then triggers the blockage of further hyphal expansion via the activation of the second layer of resistance, i.e., postinvasive resistance, which guarantees the robustness of the nonhost resistance of A. thaliana against Colletotrichum pathogens. Both the tryptophan-derived metabolic pathway and glutathione synthesis play critical roles in the postinvasive resistance against C. tropicale, although the molecular mechanism of postinvasive resistance remains to be elucidated. In this review, we describe the current understanding of the molecular background of the Arabidopsis nonhost resistance against Colletotrichum fungi and discuss perspectives for future research on this durable resistance.     

Egg and larval parasitoids of the beet armyworm<Emphasis Type="Italic">Spodoptera exigua</Emphasis> on maize in Turkey

The present study was conducted to determine egg and larval parasitoids of the beet armywormSpodoptera exigua Hübner (Lepidoptera: Noctuidae), which is an important but sporadic pest in Turkey. High beet armyworm population levels were recently observed in fields of first and second crop maize in the southeast Mediterranean region of Turkey. The parasitoid species complex and its impact on the pest were analyzed in a 4-year study in first and second crop maize. The braconid larval parasitoidsMicroplitis rufiventris Kokujev,M. tuberculifer Wesmael,Meteorus ictericus Nees,Chelonus obscuratus (Herrich Schäffer) (an egg-larval parasitoid),Apanteles ruficrus (Haliday); the ichneumonid larval parasitoidsHyposoter didymator (Thunberg) andSinophorus xanthostomus Gravenhorst; and the egg parasitoidTrichogramma evanescens (Westwood) were found to be the natural enemies attacking the pest. Among the parasitoid species the solitary endoparasitoidH. didymator was the most prevalent species, being reared from 40.5% of the parasitized larvae found. Higher parasitism rates were recorded on first crop than on second crop maize in every year. Possible reasons for this difference in larval parasitism between two growing seasons include lower population of the pest and reduced insecticide applications in first crop maize fields which permitted higher parasitism. However, parasitoid activity was insufficient to counterbalance the population growth of the pest on subsequent second crop maize.