Biotype composition and virulence distribution of wheat curl mite in the North Central United States

Doctor of PhilosophyDepartment of EntomologyC. Michael SmithThe wheat curl mite, Aceria tosichella (Keifer), is an important global pest of bread wheat, Triticum aestivum L. Chronic and often severe reductions of winter wheat yield due to A. tosichella infestations have occurred in North America and all other wheat-production areas for over five decades. Moreover, A. tosichella is the only vector which transmits the three most important wheat viruses in the Great Plains, which are Wheat Streak Mosaic Virus (WSMV), the most economically important wheat virus in North America; Triticum Mosaic Virus (TriMV) and High Plains Wheat Mosaic Virus (HPWMoV). Mite infestation alone causes stunted, chlorotic plants in susceptible wheat varieties. To date, mite resistant wheat cultivars have been the only sufficient method to control A. tosichella. The discovery of new genes for A. tosichella resistance and their introgression into wheat cultivars are essential steps to combat the development of new and/or different A. tosichella biotypes which can develop to overcome resistance genes. Both A. tosichella biotype 1 and 2 exist in U. S. Great Plains wheat producing areas. Elucidating and predicting A. tosichella population composition changes based on climatic and geographic variables is a key to continued effective mite management. Experiments were conducted to: 1) assess A. tosichella virulence in mites collected from 25 sample sites in six states to wheat plants harboring the Cmc2, Cmc3 and Cmc4 mite resistance genes and the Wsm2 WSMV resistance gene in 2014 and 2015, and determine the distribution of WSMV, TriMV and HPWMoV present in mites collected; 2) assess A. tosichella biotype composition using internal transcribed spacer 1 (ITS1) and cytochrome oxidase I (COI) polymorphisms; 3) use generalized additive modeling to capture the spatio-temporal factors contributing to the prevalence of A. tosichella biotypes 1 and 2; and 4) screen Kansas advanced breeding lines for resistance to A. tosichella biotypes 1 and 2. Results indicated that A. tosichella collected from 92% of the sample area were virulent to susceptible Jagger wheat plants with no Cmc resistance genes; that mites from 36% of the sample area were virulent to the Cmc2 gene, and that mites collected from 24% of sample area were virulent to Cmc3. Mite populations from only 8% of the sample sites exhibited virulence to plants containing Cmc4 + Wsm2 or Cmc4. The WSMV virus was predominant and present in 76% of all mites sampled. HPWMoV and TriMV were less apparent and present in 16% and 8% of all mites sampled, respectively. These results will enable breeders to increase the efficiency of wheat production by releasing wheat varieties containing A. tosichella resistance genes that contribute to reducing virus transmission. Results of spatio-temporal factor modeling provide new, more accurate information about the use of ground-cover and precipitation as key predictors of biotype prevalence and ratio. Experiments to determine if Kansas State University advanced breeding lines contain A. tosichella resistance found no resistance to biotype 1, resistance to biotype 2 in breeding lines AYN3-37 and AYN3-34; and moderate resistance to biotype 2 in breeding lines AYN2-28 and AYN2-36. The demonstrated correlation between reduced A. tosichella population size and avirulence; characterization and prediction of the A. tosichella biotype composition; and the identification of new sources of A. tosichella resistance in wheat can help entomologists and wheat breeders increase wheat production efficiency by releasing additional wheat cultivars containing A. tosichella resistance genes

Development of Single Nucleotide Polymorphism Markers for the Wheat Curl Mite Resistance Gene Cmc4

Wheat curl mite (Aceria tosichella Keifer) is an important wheat (Triticum aestivum L. em. Thell.) pest in many wheat-growing regions worldwide. Mite feeding damage not only directly affects wheat yield, but A. tosichella also transmits Wheat streak mosaic virus (WSMV). Wheat resistance to A. tosichella, therefore, helps control WSMV. OK05312 (PI 670019) is an advanced breeding line released from Oklahoma that shows a high level of A. tosichella resistance. To map the gene(s) conditioning wheat resistance to A. tosichella in OK05312, a genetic linkage map was constructed using single nucleotide polymorphism (SNP) markers derived from genotyping-by-sequencing (GBS) and a population of 186 recombinant inbred lines (RILs) from the cross ‘Jerry’ (PI 632433)/OK05312. Seedlings of both parents and the RIL population were infested by A. tosichella Biotype 1 in greenhouse experiments. One major quantitative trait locus was identified on the short arm of chromosome 6D, which corresponds to the previously reported gene Cmc4 for A. tosichella resistance. This gene explained up to 71% of the phenotypic variation and was delimited in a 1.7-Mb (?3.3-cM) region by SNPs 370SNP7523 and 370SNP1639. We successfully converted 12 GBS-SNPs into Kompetitive allele specific polymerase chain reaction (KASP) markers. Two of them tightly linked to Cmc4 were validated to be highly diagnostic in a US winter wheat population and can be used for marker-assisted breeding for incorporation of Cmc4 into new wheat cultivars

GRAPEVINE VEIN-CLEARING VIRUS IS MEALYBUG-BORNE BUT NOT MEALYBUG-TRANSMITTED

This article investigates the ability of two types of mealybugs, citrus (Planococcus citri) and longtailed (Pseudococcus longispinus) mealybugs, of acquiring and transmitting Grapevine vein-clearing virus (GVCV) in a greenhouse setting. Mealybugs are the primary vectors for most Badnaviruses, and only a few species have been shown to be aphid-transmitted. In this study, we tested the acquisition and transmission ability of two mealybug species using GVCV-infected and healthy grapevines in a greenhouse setting for three consecutive seasons. This study determined that acquisition time by the mealybugs could be as low as three days, yet the transmission of GVCV from infected grapevines to healthy grapevines by these two mealybug species was unsuccessful. Additionally, with the use of previously-developed species-specific primers, this study determined that those mealybugs captured in the greenhouse facilities at the University of Missouri could not be identified using these primers, and required primers that were specific to their regional diversity. This study contributes to the wider understanding of the acquisition and transmission of GVCV by certain mealybug species. 

Barley Varieties Stoneham and Sydney Exhibit Mild Antibiosis and Antixenosis Resistance to the Wheat Curl Mite, Aceria tosichella (Keifer)

The wheat curl mite, Aceria tosichella (Keifer), devastates cereal crops worldwide by direct feeding damage and transmission of several deadly viruses. Deployment of cereal crop varieties resistant to A. tosichella is key for reduction of crop yield losses, and management of this mite and associated viruses that it transmits. Barley varieties resistant to A. tosichella are not known to exist. The objectives of this study were to determine if A. tosichella resistance exists in the barley varieties Sydney and Stoneham, which are resistant to the Russian wheat aphid, Diuraphis noxia (Kurjumov), and, further, to determine which categories mediate the resistance. Categories of resistance to both A. tosichella biotypes were evaluated independently in non-choice and choice experiments using wheat varieties Ike and OK05312 as susceptible and resistant controls, respectively. Sydney barley displays mild antixenosis and antibiosis resistance to A. tosichella biotype 1 and 2, respectively. Stoneham barley exhibits only mild antibiosis to biotype 2. No evidence for plant tolerance was found in either barley variety to either mite biotype

Two-step method for rapid isolation of genomic DNA and validation of R81T insecticide resistance mutation in Myzus persicae

Isolation and amplification of nucleic acid (DNA) is considered a vital and potent instrument in molecular biological research. However, its functioning outside of a laboratory setting is difficult because of complex procedures that demand expert personnel and expensive equipment in addition to the fulfillment of several additional requirements. DNA isolation from minute insects is sometimes difficult, making diagnostic and genotyping procedures problematic. Thus, the current work offers a high-throughput, cost-effective, straightforward, and faster approach for isolating DNA from the aphid Myzus persicae. Intriguingly, two-step DNA extraction process yielded a high yield of extremely pure genomic DNA and required only 10 s to complete. PCR investigation aiming at amplifying the non-synonymous R81T region on the loop D site of the nAChR gene of M. persicae was subsequently utilized to successfully validate the recovered DNA. Moreover, the proposed method was compared in terms of yield and purity with conventionally used DNA isolation methods including, phenol:chloroform, salt out, and commercially available kits. In conclusion, this newly developed method would enable researchers to quickly process many biological samples used to analyze genetic diversity, mutant screening, and large spectrum diagnosis both in laboratory and field conditions

Modeling Aceria tosichella biotype distribution over geographic space and time.

The wheat curl mite, Aceria tosichella Keifer, one of the most destructive arthropod pests of bread wheat worldwide, inflicts significant annual reductions in grain yields. Moreover, A. tosichella is the only vector for several economically important wheat viruses in the Americas, Australia and Europe. To date, mite-resistant wheat genotypes have proven to be one of the most effective methods of controlling the A. tosichella-virus complex. Thus, it is important to elucidate A. tosichella population genetic structure, in order to better predict improved mite and virus management. Two genetically distinct A. tosichella lineages occur as pests of wheat in Australia, Europe, North America, South America and the Middle East. These lineages are known as type 1 and type 2 in Australia and North America and in Europe and South America as MT-8 and MT-1, respectively. Type 1 and type 2 mites in Australia and North America are delineated by internal transcribed spacer 1 region (ITS1) and cytochrome oxidase I region (COI) sequence differences. In North America, two A. tosichella genotypes known as biotypes are recognized by their response to the Cmc3 mite resistance gene in wheat. Aceria tosichella biotype 1 is susceptible to Cmc3 and biotype 2 is virulent to Cmc3. In this study, ITS1 and COI sequence differences in 25 different populations of A. tosichella of known biotype 1 or biotype 2 composition were characterized for ITS1 and COI sequence differences and used to model spatio-temporal dynamics based on biotype prevalence. Results showed that the proportion of biotype 1 and 2 varies both spatially and temporally. Greater ranges of cropland and grassland within 5000m of the sample site, as well as higher mean monthly precipitation during the month prior to sampling appear to reduce the probability of occurrence of biotype 1 and increase the probability of occurrence of biotype 2. The results suggest that spatio-temporal modeling can effectively improve A. tosichella management. Continual integration of additional current and future precipitation and ground cover data into the existing model will further improve the accuracy of predicting the occurrence of A. tosichella in annual wheat crops, allowing producers to make informed decisions about the selection of varieties with different A. tosichella resistance genes

Resistance to Wheat Curl Mite in Arthropod-Resistant Rye-Wheat Translocation Lines

The wheat curl mite, Aceria toschiella (Keifer), and a complex of viruses vectored by A. toschiella substantially reduce wheat yields in every wheat-producing continent in the world. The development of A. toschiella-resistant wheat cultivars is a proven economically and ecologically viable method of controlling this pest. This study assessed A. toschiella resistance in wheat genotypes containing the H13, H21, H25, H26, H18 and Hdic genes for resistance to the Hessian fly, Mayetiola destructor (Say) and in 94M370 wheat, which contains the Dn7 gene for resistance to the Russian wheat aphid, Diuraphis noxia (Kurdjumov). A. toschiella populations produced on plants containing Dn7 and H21 were significantly lower than those on plants of the susceptible control and no different than those on the resistant control. Dn7 resistance to D. noxia and H21 resistance to M. destructor resulted from translocations of chromatin from rye into wheat (H21—2BS/2RL, Dn7—1BL/1RS). These results provide new wheat pest management information, indicating that Dn7 and H21 constitute resources that can be used to reduce yield losses caused by A. toschiella, M. destructor, D. noxia, and wheat streak mosaic virus infection by transferring multi-pest resistance to single sources of germplasm

Comparative evaluation of sublethal doses of different insecticides on the ovipositional behavior of whitefly (Bemisia tabaci) in Brinjal

The world's worst invading insect is the whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae). For B. tabaci's thorough field control, research on the sublethal impacts of popular insecticides is crucial. We examined the effects of sublethal insecticide concentrations on whiteflies' predilection for oviposition on treated plants of brinjal (Solanum melongena L. cv. Hisar Shyamal) using a multiple-choice test during the 2019 and 2020 growing seasons. The insecticide efficacy was evaluated on the basis of the oviposition preference of B. tabaci on brinjal plants that were raised in pots and repeatedly treated with a distinct dosage of insecticides. The biochemical changes of treated brinjal leaves were also examined in this research, along with their connection to oviposition tendency. The findings showed that whiteflies favored fenpropathrin 30 % EC and deltamethrin 2.8 % EC treated plants for oviposition over diafenthiuron 50 % WP and thiamethoxam 25 % WG. In comparison to untreated control plants, most eggs were deposited on sublethal doses of fenpropathrin 30 % EC treated plants at 50 g a.i./ha and deltamethrin 2.8 % EC at 7.5 g a.i./ha. The findings of biochemical tests showed that with the exception of lesser dosages of fenpropathrin (30 % EC) as well as deltamethrin (2.8 % EC), all insecticidal treatments reduced total sugar and amino acids. Additionally, all the pesticides reduced the overall phenol level and significantly altered the crude protein content. The treated brinjal plant with deltamethrin 2.8 % EC and fenpropathrin 30 % EC attracted whiteflies for oviposition because it provides an improved site for them in terms of nourishment