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Montane environments as a source of biotypic diversity in Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), in Colorado

Date

2013

Authors

Chapela, Mariana, author
Peairs, Frank B., advisor
Cranshaw, Whitney, committee member
Haley, Scott D., committee member

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Abstract

The Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), is a small grain pest of worldwide economic importance. The preferred hosts of the Russian wheat aphid are wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and triticale (X Triticosecale Wittmack). The aphid also colonizes noncultivated cool-season grasses, particularly wheatgrasses, and volunteer wheat and barley plants. This pest also has been found on different grass species at elevations between 1,000 and 3,000 m above sea level in Colorado. The objective of this study was to improve our knowledge of Russian wheat aphid biotypic diversity present along the Front Range of northern Colorado. In order to achieve this objective I compared the biotypic diversity of Russian wheat aphids present on alternate grass hosts (crested wheatgrass, intermediate wheatgrass, slender wheatgrass, western wheatgrass and foxtail barley) in montane and prairie environments using plant differentials (wheat and barley lines) currently of interest to the Colorado State University wheat breeding program. The ultimate goal was to determine if noncultivated grass hosts in montane environments are a potential source of the biotypic diversity of Russian wheat aphid affecting wheat production in eastern Colorado. Fourteen Russian wheat aphid isolates were collected in 2010 from prairie and montane sites and characterized in a standard seedling assay using 22 wheat and two barley lines with known reactions to biotype 1 Russian wheat aphid (RWA1) and biotype 2 Russian wheat aphid (RWA2). Thirty-four Russian wheat aphid isolates were collected in 2011 and characterized in a standard seedling assay using seven wheat and one barley lines with know reactions to the RWA1 and RWA2 biotypes. Known biotypes RWA1 and RWA2 were included for comparison. Once the RWA1 susceptible wheat cultivar 'Yuma' and barley cultivar 'Otis' were killed, all plants were rated for leaf chlorosis and leaf rolling. Differences in virulence patterns were observed among the 14 isolates from 2010 and the 34 isolates from 2011 for leaf chlorosis and leaf rolling. The isolates exhibited different levels of damage, and divided into three groups: isolates producing low amount of damage (similar to that expected by biotype RWA1 on plants expressing Dn4 resistance), isolates producing heavy damage (similar to that expected from biotype RWA2 feeding on susceptible plants or plants expressing Dn4 resistance), and isolates with intermediate level of damage. Isolates M5 and P14, collected in 2010, produced more damage than the RWA2 biotype. Isolate M5 produced heavy damage on CO03797, Karee-Dn8, Betta-Dn9, and intermediate damage on 94M370 and Sidney, whereas RWA2 biotype produced intermediate damage on CO03797, Karee-Dn8, and Betta-Dn9, and low amount of damage on 94M370 and Sidney. Isolate P14 produced heavy damage on Karee-Dn8 and intermediate damage on 94M370, whereas RWA2 biotype produced intermediate damage on Karee-Dn8 and low amount of damage on 94M370. Collection date and site did not influence damage in either 2010 or 2011 isolates. For example, isolates M5, M2, M3 and M4 from 2010 were all collected from the same montane site on the same date, but were categorized into three damage groups. Isolates M40, M36 and M37 were also collected from the same montane site on the same date in 2011, but represented two damage groups. The results of these screenings confirmed the presence of two previously unknown biotypes: isolate M5, collected from a montane site, and isolate P14, collected from a prairie site. Both biotypes were more virulent than RWA2 biotype. These results also documented that biotypic diversity of Russian wheat aphid in Colorado montane was greater than the prairie collections.

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