Field Screen for Identification of Resistance to -transmitted in Winter Lindsay Overmyer1, Elliot A. Knoell1, Anthony J. McMechan1, Robert A. Graybosch2,3, P. Stephen Baenziger2, Teshome Regassa2, and Gary L. Hein1 Department of Entomology1, Department of Agronomy and Horticulture2, University of Nebraska-Lincoln, Lincoln, NE, USDA-ARS3, Lincoln, NE

Introduction Fig 2. Field screen of commercial varieties Fig 6. Spring 2016 SPAD readings A complex of three viruses (Wheat streak mosaic - 40 WSMV, Triticum mosaic virus - TriMV, and High Plains wheat mosaic virus - HPWMoV) causes significant yield loss in winter wheat in the Great Plains. All three of these viruses 30 are transmitted by the wheat curl mite ( tosichella Keifer). A wheat screen has been developed to screen developing and advanced lines of hard red and white winter 20 wheat varieties for greater resistance to WSMV and the other mite-vectored viruses. Varieties with Wsm1 (Graybosch et al. 10 2009) and Wsm2 (Lu et al. 2011) genes are WSMV resistant.

The objective of this study was to identify varieties that Justin McMechan (SPAD) RelativeChlorophyll have greater resistance to WSMV and the other viruses. 0 8 15 25 4 13 20 1 April May June Materials and Methods Mace Snowmass TAM 112 Tomahawk ▪ Two separate wheat screens were established with Mace (WSMV resistant - Wsm1) and Tomahawk (susceptible) included as check varieties. Results • Varieties commercially available or advanced breeder Gary Hein ▪ Two viruses, WSMV and TriMV, present in the screen lines were compared in a randomized complete block resulted in extensive differentiation between varieties. design (plots 1 row x 7 m with 3 reps). Fig 3. Screen of breeder lines • Commercial variety comparisons (Fig. 2). • Breeding lines potentially carrying resistance genes to identify virus resistant and • Resistant and segregating breeder lines identified screened (plots 1 row x 1.2 m with 2 reps). (Fig. 3). segregating lines ▪ This screening process was done under field conditions by ▪ A combination of relative chlorophyll content (SPAD Justin McMechan using natural infestations of and virus. readings) and plant height provide good metric of virus • An artificial green bridge was established to enable mite impact on varieties (Fig. 4-5). survival through the summer to infest the fall planted Fig 4. 2016 percentage of maximum plant height (A) and SPAD readings (B) • Mace provided a higher level of resistance than all screen (Fig. 1). other entries. 100 • After the winter wheat screen was planted in September, LSD (P=.05) A • Wheat varieties with Wsm2 gene or mite resistance mites moved into the screen and infected the newly 80 had greater SPAD readings than susceptible planted wheat with viruses. 60 varieties, but they also had significant height reduction. ▪ Visual percentage of maximum plant height and relative 40 chlorophyll readings (SPAD) were taken to monitor virus • Severe chlorosis and stunting occurred for all virus 20

impact in the spring. WSM 1 Gene susceptible varieties. Height Percentage Percentage Height • For select varieties SPAD readings were taken weekly. 0 WSM 2 Gene ▪ Severity of symptoms via SPAD readings increased 40 LSD (P=.05) B Mite Resistant through the spring (Fig. 5-6). 30 Mite & Virus • Mace significantly higher over all dates. Susceptible 20 • Tomahawk significantly lower April 15 - June 1.

Fig 1. Diagram of green bridge and wheat screen Chorophyll Sequential wheat plantings through summer allowed natural wheat (SPAD) 10 curl mite population build up and infestation of the wheat screens

Relative 0 planted in September. Significance ▪ The screen process has enabled breeders to more st 1 Volunteer Wheat Planting in Late May * Samples taken May 20 confidently select lines with high levels of resistance and identify resistance in segregating lines. nd 2 Volunteer Wheat Planting Mid-July Fig 5. Examples of the range of SPAD readings resulting from virus impact ▪ Resistance levels and limitations in resistance of commercial lines were identified. # Variety SPAD reading ▪ The development and increased availability of more Wheat Screen varieties with effective resistance to these viruses will 1 Tomahawk 18.6 enable growers to better manage this important risk to 2 Mace 39.4 yield and quality. 3 Snowmass 33.6 Wheat Screen 4 Settler CL 23.4 1 2 3 4 Gary Hein * Samples taken May 20 Acknowledgements References We gratefully acknowledge the support of the Nebraska Wheat Board and the USDA-ARS. Graybosch et al., 2009. Plant Registrations 3:51–56. Lu et al. 2011. Crop Science 51: 5-12.