Comparative Analysis of Coding and Non-Coding Features within Insect Tolerance Loci in Wheat with Their Homologs in Cereal Genomes

Food insecurity and malnutrition have reached critical levels with increased human population, climate fluctuations, water shortage; therefore, higher-yielding crops are in the spotlight of numerous studies. Abiotic factors affect the yield of staple food crops; among all, wheat stem sawfly (Cephus cinctus Norton) and orange wheat blossom midge (Sitodiplosis mosellana) are two of the most economically and agronomically harmful insect pests which cause yield loss in cereals, especially in wheat in North America. There is no effective strategy for suppressing this pest damage yet, and only the plants with intrinsic tolerance mechanisms such as solid stem phenotypes for WSS and antixenosis and/or antibiosis mechanisms for OWBM can limit damage. A major QTL and a causal gene for WSS resistance were previously identified in wheat, and 3 major QTLs and a causal gene for OWBM resistance. Here, we present a comparative analysis of coding and non-coding features of these loci of wheat across important cereal crops, barley, rye, oat, and rice. This research paves the way for our cloning and editing of additional WSS and OWBM tolerance gene(s), proteins, and metabolites.

Estimation of Stem-Solidness and Yield Components in Selected Spring Wheat Genotypes

Solid-stemmed wheat genotypes are better protected from damage caused by wheat stem sawfly (Cephus pygmaeus L.) larvae and at lower risk of lodging, as they are additionally strengthened. The aim of the study was to analyse the stem-solidness of fifty spring wheat cultivars with pith. A field experiment was conducted at the Agricultural Research Station Dłoń, Poland in the years 2012–2014. The method recommended by the International Union for the Protection of New Varieties of Plants (UPOV) and the methodology described by DePauw and Read were used to analyse the stem-solidness. The statistical analysis of the results showed that the stems of the wheat cultivars differed in their, therefore, they were divided into seven classes. There were nine Polish cultivars, two genotypes from Canada (BW 597 and AC Elsa) and one Portuguese genotype (I 836) with hollow stems. There were only nine solid-stemmed cultivars. Both methodologies were used to assess the filling of the stem in the whole plant upon analysis of its filling at the cross-section of the first internode. Both methods gave the same results. The DePauw and Read methodology showed that the internodes in the lower part of the plants were filled to the greatest extent. The same genotypes collected in the consecutive years of the study differed in the filling of their stems with pith. These differences were influenced by the environmental conditions.

Plant Volatiles and Oviposition Behavior in the Selection of Barley Cultivars by Wheat Stem Sawfly (Hymenoptera: Cephidae)

Wheat stem sawfly, [Cephus cinctus (Hymenoptera: Cephidae)], females display complex behaviors for host selection and oviposition. Susceptible hollow stem wheat (Triticum aestivum L.) cultivars release a greater amount of attractive compound, (Z)-3-hexenyl acetate and receive a greater number of eggs compared to resistant solid stem wheat cultivars. However, barley (Hordeum vulgare L.) is becoming a more common host for C. cinctus in Montana. Therefore, how do host selection and oviposition behaviors on barley cultivars compare to what happens when encountering wheat cultivars? To answer this question, we carried out greenhouse experiments using two barley cultivars: ‘Hockett’ and ‘Craft’. Between these cultivars at Zadoks stages 34 and 49, we compared host selection decisions using a Y-tube olfactometer, compared oviposition behaviors on stems, and counted the number of eggs inside individual stems. In Y-tube bioassays, we found a greater number of C. cinctus females were attracted to the airstream passing over ‘Hockett’ than ‘Craft’ barley cultivars. Although the frequencies of oviposition behaviors were similar between these cultivars, the number of eggs was greater in ‘Hockett’. Volatile profiles indicated that the amount of linalool was greater in the airstream from ‘Craft’ than in ‘Hockett’ at Zadoks 34 while the amount of (Z)-3-hexenyl acetate was greater in airstream from ‘Hockett’ at both Zadoks 34 and 49. These results suggest that volatiles of barley plants influenced host selection behavior of ovipositing C. cinctus females, while other discriminating behaviors do not differ between cultivars.

Survey of Wheat Stem Sawfly (Hymenoptera: Cephidae) Infesting Wheat in Eastern Colorado

From 2012 through 2020, a survey of wheat stem sawfly, Cephus cinctus Norton, was conducted in wheat (Triticum aestivum L.) fields in Eastern Colorado. In 2013, results showed sawfly infestations concentrated in the northern part of the state with only a few highly infested sites, with 38 of the 94 sampled sites having any infestation (five of which had >50% infestation levels). By 2020 sawfly had been found in all eastern counties sampled, and 72 of the 106 sites sampled were found to contain sawfly (11 of which had >50% infestation levels). The spread of this pest across the Colorado wheat-growing region will have lasting economic effects. The information gathered from this and future surveys will inform wheat variety development and aid in management decisions made by growers across the state.

Evaluation of resistance of some barley varieties to wheat stem sawfly (Hymenoptera: Cephidae) in Hama Governorate

Wheat stem sawfly (Hymenoptera: Cephidae) is a significant pest on wheat and barley in Syria, and host plant resistance is one of the most effective mitigation of wasps damage. The preference for laying eggs among females of wheat stem sawfly (WSS) was studied in some cultivation barley varieties in Syria, and the reasons for this preference, by comparing the characteristics of plant height in the stages of early wasp propagation, phenological development stages synchronized with late propagation wasps stages that are known having attraction influence for female wasps to put eggs, within the natural conditions at the place of experimenting in Soran region, northern of Hama, about 20 km. The results showed a great variation in the infection rates between the tested barley cultivar varieties. Female of wheat stem sawfly (WSS) preferred to lay eggs in the barley cultivar (Arabi Aswad) (Aswad means black), which was a sensitive variety for infection althoughit is not being the highest height plant in the early stages or the less developed in the late stages of wheat stem sawfly spread, whereas the rest of the tested varieties distinguished (Furat 1, Furat 3, Furat 4, Furat 5, Furat 6, Furat 9, Arabi Abiad, and Arabi Abiad Mohsan) (Abiad means white, Mohsan means improved) by its relative resistance to the injury. Our results suggest conducting other studies to reach the reasons forpredilection preference or lack of preference and benefit from them later for reducing losses resulting from this injury.

Copy number variation ofTdDofcontrols solid-stemmed architecture in wheat

Stem solidness is an important agronomic trait of durum (Triticum turgidumL. var.durum) and bread (Triticum aestivumL.) wheat that provides resistance to the wheat stem sawfly. This dominant trait is conferred by theSSt1locus on chromosome 3B. However, the molecular identity and mechanisms underpinning stem solidness have not been identified. Here, we demonstrate that copy number variation ofTdDof, a gene encoding a putative DNA binding with one finger protein, controls the stem solidness trait in wheat. Using map-based cloning, we localizedTdDofto within a physical interval of 2.1 Mb inside theSSt1locus. Molecular analysis revealed that hollow-stemmed wheat cultivars such as Kronos carry a single copy ofTdDof, whereas solid-stemmed cultivars such as CDC Fortitude carry multiple identical copies of the gene. Deletion of allTdDofcopies from CDC Fortitude resulted in the loss of stem solidness, whereas the transgenic overexpression ofTdDofrestored stem solidness in theTdDofdeletion mutantpithless1and conferred stem solidness in Kronos. In solid-stemmed cultivars, increasedTdDofexpression was correlated with the down-regulation of genes whose orthologs have been implicated in programmed cell death (PCD) in other species. Anatomical and histochemical analyses revealed that hollow-stemmed lines had stronger PCD-associated signals in the pith cells compared to solid-stemmed lines, which suggests copy number-dependent expression ofTdDofcould be directly or indirectly involved in the negative regulation of PCD. These findings provide opportunities to manipulate stem development in wheat and other monocots for agricultural or industrial purposes.

Antixenosis, Antibiosis, and Potential Yield Compensatory Response in Barley Cultivars Exposed to Wheat Stem Sawfly (Hymenoptera: Cephidae) Under Field Conditions

Wheat stem sawfly, Cephus cinctus Norton, is an economically serious pest of cereals grown in North America. Barley cultivars were previously planted as resistant crops in rotations to manage C. cinctus, but due to increasing levels of injury to this crop, this is no longer a valid management tactic in Montana. Therefore, we aimed to understand antixenosis (behavioral preference), antibiosis (mortality), and potential yield compensation (increased productivity in response to stem injuries) in barley exposed to C. cinctus. We examined these traits in eight barley cultivars. Antixenosis was assessed by counting number of eggs per stem and antibiosis was assessed by counting infested stems, dead larvae, and stems cut by mature larvae. Potential yield compensation was evaluated by comparing grain yield from three categories of stem infestation: 1) uninfested, 2) infested with dead larva, and 3) infested cut by mature larva at crop maturity. We found the greatest number of eggs per infested stem (1.80 ± 0.04), the highest proportion of infested stems (0.63 ± 0.01), and the highest proportion of cut stems (0.33 ± 0.01) in ‘Hockett’. Seven out of eight cultivars had greater grain weight for infested stems than for uninfested stems. These cultivars may have compensatory responses to larval feeding injury. Overall, these barley cultivars contain varying levels of antixenosis, antibiosis, and differing levels of yield compensation. Our results provide foundational knowledge on barley traits that will provide a framework to further develop C. cinctus resistant or tolerant barley cultivars.

Phenology and Dispersal of the Wheat Stem Sawfly (Hymenoptera: Cephidae) Into Winter Wheat Fields in Nebraska

Historically, the wheat stem sawfly, Cephus cinctus Norton was a pest in spring wheat-growing regions of the northern Great Plains. However, in the 1980s, it was found infesting winter wheat fields in Montana. Infestations were first detected in western Nebraska in the 1990s, and have since spread throughout the Nebraska Panhandle. Larval damage occurs from stem-mining, but stem girdling that results in lodged stems that are not harvested results in the greatest yield losses. The biology and phenology of the wheat stem sawfly are well described in the northern portion of its range, but they are lacking in Colorado, southeast Wyoming, and Nebraska. In this study, the phenology and dispersal of the wheat stem sawfly in Nebraska winter wheat fields is described using sweep net and larval sampling. During this 2-yr study, adult activity began on May 23 and ended on June 21. Adult sex ratios were 2.32 males per female in 2014 and 0.46 males per female in 2015. Both sexes demonstrated an edge effect within the wheat fields, with greater densities near the field edge. The edge effect was stronger for male wheat stem sawfly than females. Wheat stem sawfly larval density also had an edge effect, regardless of the density of female wheat stem sawfly present. This information will be useful for developing management plans for the wheat stem sawfly in Nebraska and neighboring regions.

Effect of Precipitation and Temperature on Larval Survival of Cephus cinctus (Hymenoptera: Cephidae) in Barley Cultivars

Host plant traits strongly affect survivorship of insect herbivores, and host suitability is especially important for the wheat stem sawfly, Cephus cinctus Norton, which spends its entire egg, larval, and pupal periods in a single stem. Measuring larval survival inside stems from egg hatch through diapause-mediated dormancy is a potential measure of population size for the next year but is also useful in assessing effects of growing season precipitation and temperature. Larval growth is synchronized with host plant growth, and the larva cannot switch hosts. Thus, incorporating plant physiological time, as growing degree days (GDD), may yield a better prediction of larval survival. Therefore, we assessed wheat stem sawfly survival from early larval growth to the beginning of autumnal diapause in barley cultivars selected from across feed, forage, and two- or six-row malt groups. Field experiments were conducted in Gallatin and Chouteau counties, Montana, in 2016 and 2017. We used Kaplan-Meier estimation to assess larval survival among cultivars. We found that the survival of pre-diapause larvae was greatest in ‘Hockett’ (36.5%) and lowest in ‘Celebration’ (15.4%). Precipitation and temperature during the growing season affected temporal patterns for larval survival across study sites. Adjusting survivorship curves using site-specific GDD accumulation allowed cultivar-specific survivorship to be estimated more precisely for each site, despite differing environmental influences. Our findings suggest that measuring wheat stem sawfly survival across barley cultivars and standardizing by site-specific GDDs may provide better recommendations on barley cultivars that impede wheat stem sawfly population growth and reduce economic losses.