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Development of a single nucleotide polymorphism-based DNA marker for fall armyworm (Lepidoptera: Noctuidae) biotyping: a case study from the fall armyworm outbreak in Sri Lanka

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Abstract

Crop damage caused by fall armyworm (FAW), Spodoptera frugipera J.E. Smith (1797) (Lepidoptera: Noctuidae), has generated concern among agriculturists globally. In 2019, FAW was first reported in Sri Lanka, where it caused significant losses to corn crops. However, given that the two FAW biotypes – “rice strain” (R-FAW) and “corn strain” (C-FAW) – are morphologically identical, the biotype(s) present in Sri Lanka were unknown. The current study used the mitochondrial cytochrome c oxidase subunit I gene (mt- CO1 ) of FAW to biotype nine FAW samples collected in Sri Lanka. The resulting molecular phylogeny revealed that both R-FAW and C-FAW biotypes were present among the samples. In addition, we used the temperature-switch polymerase chain reaction (PCR) technique to develop a gel-based molecular marker. Two fragments were successfully amplified by the newly developed marker ABUOP0002 , with fragment sizes of 341 bp from R-FAW and 204 bp from C-FAW. This demonstrates that ABUOP0002 can serve as a diagnostic gel-based molecular marker to identify the R-FAW and C-FAW biotypes from samples already identified to species level as S. frugiperda through taxonomical keys and provides a possible alternative to more expensive sequencing-based assays.
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DNA taxonomy including barcoding and metabarcoding is widely used to explore the diversity in biodiversity hotspots. In most of these hotspot areas, chafers are represented by a multitude of species, which are well defined by the complex shape of male genitalia. Here, we explore how well COI barcode data reflect morphological species entities and thus their usability for accelerated species inventorization. We conducted dedicated field surveys in Sri Lanka to collect the species-rich and highly endemic Sericini chafers (Coleoptera: Scarabaeidae). Congruence among results of a series of protocols for de novo species delimitation and with morphology-based species identifications was investigated. Different delimitation methods, such as the Poisson tree processes (PTP) model, Statistical Parsimony Analysis (TCS), Automatic Barcode Gap Discovery (ABGD), Assemble Species by Automatic Partitioning (ASAP), and Barcode Index Number (BIN) assignments, resulted in different numbers of molecular operational taxonomic units (MOTUs). All methods showed both over-splitting and lumping of morphologically identified species. Only 18 of the observed 45 morphospecies perfectly matched MOTUs from all methods. The congruence of delimitation between MOTUs and morphospecies expressed by the match ratio was low, ranging from 0.57 to 0.67. TCS and multirate PTP (mPTP) showed the highest match ratio, while (BIN) assignment resulted in the lowest match ratio and most splitting events. mPTP lumped more species than any other method. Principal coordinate analysis (PCoA) on a match ratio-based distance matrix revealed incongruent outcomes of multiple DNA delimitation methods, although applied to the same data. Our results confirm that COI barcode data alone are unlikely to correctly delimit all species, in particular, when using only a single delimitation approach. We encourage the integration of various approaches and data, particularly morphology, to validate species boundaries.
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We present the latest version of the Molecular Evolutionary Genetics Analysis (MEGA) software, which contains many sophisticated methods and tools for phylogenomics and phylomedicine. In this major upgrade, MEGA has been optimized for use on 64-bit computing systems for analyzing bigger datasets. Researchers can now explore and analyze tens of thousands of sequences in MEGA. The new version also provides an advanced wizard for building timetrees and includes a new functionality to automatically predict gene duplication events in gene family trees. The 64-bit MEGA is made available in two interfaces: graphical and command line. The graphical user interface (GUI) is a native Microsoft Windows application that can also be used on Mac OSX. The command line MEGA is available as native applications for Windows, Linux, and Mac OSX. They are intended for use in high-throughput and scripted analysis. Both versions are available from www.megasoftware.net free of charge.
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Despite maize’s current high productivity, higher than other major cereal crops, it is still below its potential, mainly due to many biotic and abiotic factors causing yield losses. The fall armyworm (FAW, Spodoptera frugiperda) is among the major factors which have contributed to the low productivity of maize in Ethiopia since its introduction in February, 2017. Now its infestation covers about 642.2 thousand hectares of which, 640.8 thousand hectares are in 144 districts of six major maize-growing regional states, namely Benishangul-Gumuz, Amhara, Tigray, Gambella, Oromia, and SNNPs (Southern Nations Nationalities and Peoples). FAW, a new destructive insect pest, is one of the major problems for agricultural crop production, especially maize in Ethiopia under warm and humid conditions. This is due to its ability to breed rapidly, migrate, and feed on a wide range of host plants, all of which makes it very difficult to control. Nonetheless, there are several ways of managing the pest as reported in other parts of the world that can potentially be adapted and/or validated and used in Ethiopia. Hence, to manage this pest we have to use different management options. Integrated pest management (cultural, chemical, and biological) is commonly used for controlling FAW infestations. Therefore, in this paper, we review the status and control measures of the fall armyworm, which could be useful to improve its management in maize fields in Ethiopia.
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The recent discovery of fall armyworm (Spodoptera frugiperda, J.E. Smith) in Africa presents a significant threat to that continent’s food security. The species exhibits several traits in the Western Hemisphere that if transferred to Africa would significantly complicate control efforts. These include a broad host range, long-distance migratory behavior, and resistance to multiple pesticides that varies by regional population. Therefore, determining which fall armyworm subpopulations are present in Africa could have important implications for risk assessments and mitigation efforts. The current study is an extension of earlier surveys that together combine the collections from 11 nations to produce the first genetic description of fall armyworm populations spanning the sub-Saharan region. Comparisons of haplotype frequencies indicate significant differences between geographically distant populations. The haplotype profile from all locations continue to identify Florida and the Caribbean regions as the most likely Western Hemisphere origins of the African infestations. The current data confirm the uncertainty of fall armyworm strain identification in Africa by genetic methods, with the possibility discussed that the African infestation may represent a novel interstrain hybrid population of potentially uncertain behavioral characteristics.
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Fall armyworm (FAW), Spodoptera frugiperda (J E Smith) is an economically important pest native to tropical and subtropical America has recently invaded India, causing more damage to maize and sorghum. It is a notorious pestiferous pest with high dispersal ability, wide host range, high fecundity makes the fall armyworm one of the most severe economic pests. Recently in the month of September its feeding on two months old sugarcane crop, variety (Co 86032) was noticed at Ghogaon village of Sangli District (Maharashtra). Other than sugarcane, it was also reported on maize, sorghum and sweet corn in different districts of Maharashtra. Infestation on sugarcane was less than 5 per cent in Sangli, Kolhapur and Pune districts. On sweet corn (Bhasagi village of Akkalakot Tq) it was 35 per cent. The natural enemies like Campoletis chloridae and Noumuraea rileyi activity was meager. This is the first report of fall armyworm incidence on sugarcane and on other crops from Maharashtra. It is evident from the phylogenetic tree that sugarcane fall armyworm is indeed belongs to 'corn' strain.
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Fall armyworm, Spodopterafrugiperda , is a crop pest native to the Americas, which has invaded and spread throughout sub-Saharan Africa within two years. Recent estimates of 20–50% maize yield loss in Africa suggest severe impact on livelihoods. Fall armyworm is still infilling its potential range in Africa and could spread to other continents. In order to understand fall armyworm’s year-round, global, potential distribution, we used evidence of the effects of temperature and precipitation on fall armyworm life-history, combined with data on native and African distributions to construct Species Distribution Models (SDMs). We also investigated the strength of trade and transportation pathways that could carry fall armyworm beyond Africa. Up till now, fall armyworm has only invaded areas that have a climate similar to the native distribution, validating the use of climatic SDMs. The strongest climatic limits on fall armyworm’s year-round distribution are the coldest annual temperature and the amount of rain in the wet season. Much of sub-Saharan Africa can host year-round fall armyworm populations, but the likelihoods of colonising North Africa and seasonal migrations into Europe are hard to predict. South and Southeast Asia and Australia have climate conditions that would permit fall armyworm to invade. Current trade and transportation routes reveal Australia, China, India, Indonesia, Malaysia, Philippines and Thailand face high threat of fall armyworm invasions originating from Africa.
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The global agriculture often faces new threats from invasive alien insect pests, pathogens, weeds etc requiring immediate attention and co-operative action to manage the pestilence. In this regard, the fall armyworm (FAW), Spodoptera frugiperda is a notorious pestiferous insect with high dispersal ability, wide host range and high fecundity that make it one of the most severe economic pests. The FAW has been restricted to the Americas and recently in 2016 reported from various countries in Africa, posing a serious challenge of sustainability in Sub-Saharan African countries. Herewith we report the occurrence of the FAW on maize in various districts of Karnataka state, India. Identification of FAW has been carried out employing morphological and DNA barcoding. Phylogenetic analysis has revealed that FAW clustered with Florida (rice strain), Ghana, Nigeria, Uganda on maize. India predominantly being a tropical country favours high rate of multiplication round the year and its high pestiferous nature poses a formidable challenge to Indian agriculture warranting immediate action before it assumes a serious proportion.
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The development of molecular markers is essential for improvement of soybean cultivars with modified fatty acid content. The objective of this study was to identify and validate SNP markers in candidate genes for fatty acid content in soybean. Six candidate genes (ARAF, PDAT, ABI3, FAD2-1b, FAD3B, and FAD3C) were selected. Alignment of gene sequences identified 25 SNPs and 3 INDELs. TSP primers were used to identify SNP alleles. 259 recombinant inbred lines (RILs) (FA22 / CD219) and 185 F2 progenies (A29 / Tucunaré) were tested for association of SNPs. An SNP for FAD3B was associated with variation in content of linoleic acid (R2 = 5.84%) and linolenic acid (R2 = 6.79%). In FAD3C, an SNP was associated with linoleic and linolenic acids (R2 of 9.21% and 18.51%, respectively). The ABI3 gene was associated with palmitic acid, with R2 = 5.41%. The SNP markers identified will be used in assisted selection for improvement of fatty acid content.
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BACKGROUND Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a major lepidopteran pest in Latin and North America, but very recently invaded the African and Asian continent. FAW has evolved resistance to different insecticides and transgenic corn expressing Bacillus thuringiensis (Bt) toxins. Here we investigated the extent and mechanisms of resistance to diamide insecticides in a Brazilian field‐collected FAW strain selected with chlorantraniliprole. RESULTS Continuous laboratory selection of a field‐collected FAW strain with chlorantraniliprole resulted in resistance ratios of 225‐fold and >5400‐fold against chlorantraniliprole and flubendiamide, respectively, when compared to a susceptible strain. Pre‐exposure to different synergists known to inhibit detoxification enzymes did not result in significantly increased larval toxicity, suggesting a minor role of metabolic resistance. Sequencing of the FAW ryanodine receptor (RyR) C‐terminal domains II to VI revealed a SNP, resulting in a I4734M mutation recently described to confer target‐site resistance to diamides in lepidopteran pests. Genotyping by pyrosequencing of field‐collected FAW larvae sampled in crop season 2018 suggests a low resistance allele frequency. Furthermore, we developed a fluorescent PCR‐based allelic discrimination assay for rapid genotyping of field‐collected FAW samples, because diamides are increasingly used in Bt‐/ non‐Bt corn. CONCLUSIONS The identified RyR mutation has been recently shown to confer field resistance in other lepidopteran pests such as diamondback moth, tomato leafminer and striped rice stem borer. The developed PCR‐based allelic discrimination assay will help to monitor the frequency and future spread of the diamide resistance allele in FAW field populations and to implement appropriate resistance management measures. This article is protected by copyright. All rights reserved.
Article
The invasive Fall Armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a recently introduced species to India first reported during May 2018. So far, the introduced populations found feeding primarily on maize in addition to sweet corn and sorghum. In this communication, for the first time from India, we report FAW larvae feeding on rice in the state of Karnataka. In order to ascertain the species identity of the fall armyworm, we employed both morphological and molecular approaches. Male genitalia characters of FAW matched with previous publications confirming species identity. DNA Barcoding using mitochondrial cytochrome oxidase subunit I (5') revealed that FAW on rice belongs to "R" strain. In addition to mtCOI we have also used two additional markers such as 16S and ND1to decipher the phylogenetic relationship of FAW samples collected during the study and among the global FAW populations. Although it is not clear at this stage whether the rice is also a preferred host or its only feeding by migrating population, the implication of FAW larvae feeding on rice is discussed.