The wheat stem sawfly, Cephus cinctus Norton, causes severe losses in wheat grown in the northern Great Plains. Much of the affected area is planted in monoculture with wheat, Triticum aestivum L., grown in large fields alternating yearly between crop and no-till fallow. The crop and fallow fields are adjacent. This cropping landscape creates pronounced edge effects of sawfly infestations and may be amenable to trap cropping using existing agricultural practices. The behavioral preference for two wheat varieties was assessed in the context of developing trap crops for this insect. In field nurseries, stem lodging assessments indicated that the cultivar 'Conan' was infrequently damaged, whereas 'Reeder' was often heavily damaged. In laboratory choice and no-choice tests, 'Reeder' was significantly preferred by ovipositing wheat stem sawfly females. These two cultivars did not differ significantly in height or developmental stage, factors known to impact sawfly preference. Although Conan received fewer eggs than Reeder in no-choice tests, oviposition was further reduced in choice tests, indicating that females clearly preferred Reeder. In field trials where the overall dimensions of the spatial structure in choice tests was varied, females always selected Reeder over Conan in alternating block, row, and interseeded planting scenarios. Reeder releases greater amounts of the attractive compound, (Z)-3-hexenyl acetate than Conan but is similar to Conan for three other known, behaviorally active volatile compounds. The results are discussed in terms of cultivar selection for large scale trap crop experiments for the wheat stem sawfly.

The wheat stem sawfly (WSS) (Cephus cinctus Nort.) is an important pest of wheat (Triticum aestivum L. em. Thell.) in the Northern Great Plains. This paper reports the genetic analysis of antixenosis for egg‐laying WSS females in recombinant inbred lines (RIL) of hard red spring wheat. Female WSS preferentially choose certain wheat genotypes for egg‐laying, with the cultivar Reeder being preferred and Conan being less preferred. We measured percent stem infestation and percent stem cutting for 91 RIL from a Reeder–Conan cross in four sawfly‐infested locations in Montana. Heritability based on means over environments was h2 = 0.86 for infestation and h2 = 0.75 for cutting. Percent infestation was negatively correlated with heading date (r = −0.57, P < 0.001) and degree of stem solidness (r = −0.31, P < 0.01). A molecular map was created with 431 markers. Quantitative trait loci (QTL) for infestation and cutting were identified as cosegregating with QTL for heading date (controlled by Ppd‐D1 on chromosome 2D) and stem solidness (controlled by Qss.msub.3BL). Additionally, significant QTL for infestation and cutting on chromosomes 2D and 4A were present in several environments, and did not cosegregate with heading date, plant height, or solid stems. These QTL may complement the use of solid stems for host plant resistance by developing wheat lines that vary for attractiveness to the wheat stem sawfly.

The most common genes for semidwarf habit in modern wheat (Triticum aestivum L.) cultivars are found at the Rht‐B1 and Rht‐D1 loci on chromosomes 4B and 4D, respectively. An alternative gene for semidwarf habit, Rht8, has shown potential as a replacement for Rht‐B1b and Rht‐D1b in some environments. The objective of the present study was to assess the impact of the height‐reducing gene Rht8 relative to Rht‐B1b and Rht‐D1b on performance of spring wheat in Montana and Washington environments characterized by terminal drought stress. Evaluation of near‐isogenic lines developed in four genetic backgrounds showed that Rht‐B1b, Rht‐D1b, and Rht8 caused height reduction of 19, 20, and 6.5%, respectively, relative to wild‐type near‐isogenic lines over 12 environments. An increase in grain yield was associated with reduced height for lines containing Rht‐B1b and Rht‐D1b based on means over the four genetic backgrounds and 10 environments. Height reduction and yield increase associated with Rht‐B1b and Rht‐D1b were significant in most environments. Lines with Rht8 yielded less than wild‐type based on means over environments and in 3 of 10 individual environments. Reduced height lines with Rht‐B1b and Rht‐D1b tended to have a higher harvest index and more seed per spike than wild‐type lines and reduced height lines with Rht8. In sum, our results suggest that Rht‐B1b and Rht‐D1b are superior to Rht8 as a source for height reduction for spring wheat in the tested environments.

Several species of wheat stem sawflies (WSS) are pests of wheat, including Cephus cinctus Norton in North America. Larvae feed inside the stems and cut the stem near plant maturity. The primary means of control is resistance due to solid stems, largely controlled by a locus on chromosome 3B (Qss.msub‐3BL). Cultivars that differed for WSS resistance, but with similar stem solidness, were crossed to determine the genetic basis for the differences. The cultivar ‘Scholar’ is susceptible, while ‘Conan’ shows resistance. Scholar and Conan possessed different alleles at Qss.msub‐3BL. Both alleles conferred solidness, yet the Conan allele conferred higher WSS resistance. An allele from Conan on chromosome 4A also decreased infestation and stem cutting. The 3B and 4A alleles from Conan acted in an additive fashion to provide increased WSS resistance without increasing stem solidness. Stem solidness has long been used by breeders as a proxy for WSS resistance because of its simplicity. Our results suggest that other resistance mechanisms may complement solid stems.

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