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Abstract
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.
Highlights
The wheat curl mite, Aceria tosichella Keifer, is a global pest of bread wheat Triticum aestivum L
Genetic distance values between haplotypes based on internal transcribed spacer 1 region (ITS1) polymorphism ranged from 0.003 to 0.028 (S3 Table), whereas these values ranged from 0.002 to 0.177 based on cytochrome oxidase I region (COI) polymorphism (S4 Table)
Sequencing ITS1 and COI polymorphisms in A. tosichella samples obtained in the current study indicate that these genes remain useful genomic regions for A. tosichella biotype discrimination
Summary
The wheat curl mite, Aceria tosichella Keifer, is a global pest of bread wheat Triticum aestivum L. Yield losses caused by A. tosichella feeding may be up to 30% [4, 8] due to leaf rolling and trapping [9]. Aceria tosichella transmits three damaging viruses to the wheat plant—Wheat Streak Mosaic Virus (WSMV, family Potyviridae, genus Tritimovirus), High Plains wheat mosaic virus (HPWMoV, genus Emaravirus, formerly High plains virus; www.ictvonline.org/proposals-15/2015.018aP.A.v3.Emaravirus_sp.pdf), and Triticum Mosaic Virus (TriMV, family Potyviridae, genus Poacevirus). WSMV causes wheat yield losses ranging from 2.5 to 7% on at least five different continents [18] depending on climate, virus acquisition time and wheat cultivar [13, 19,20,21,22,23,24]. The cultural practice of controlling over-summering hosts such as volunteer wheat and weed grass hosts can provide effective management of the A. tosichella-virus complex if producers use this management approach [34]
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