Characterisation of bird cherry-oat aphid (Rhopalosiphum padi L.) behaviour and aphid host preference in relation to partially resistant and susceptible wheat landraces.

The bird cherry-oat aphid (Rhopalosiphum padi L.) is a major pest of wheat (Triticum aestivum L.) and can cause up to 30% yield losses. Heritable plant resistance to aphids is both an economically and ecologically sound method for managing aphids. Here we report how the behaviour and performance of R. padi differs on two resistant, one susceptible wheat landrace and a susceptible elite wheat variety. Feeding behaviour differed among the genotypes, with aphids on resistant lines spending longer in the pathway phase and less time phloem feeding. These behaviours suggest that both inter- and intracellular factors encountered during pathway and phloem feeding phases could be linked to the observed aphid resistance. Locomotion and antennal positioning choice tests also revealed a clear preference for susceptible lines. Although feeding studies revealed differences in the first probe indicating that the resistance factors might also be located in the peripheral layers of the plant tissue, scanning electron microscopy revealed no difference in trichrome length and density on the surface of leaves. Aphids are phloem feeders and limiting the nutrient uptake by the aphids may negatively affect their growth and development as shown here in lower weight and survival of nymphs on resistant genotypes and decreased reproductive potential, with lowest mean numbers of nymphs produced by aphids on W064 (54.8) compared to Solstice (71.9). The results indicate that resistant lines markedly alter the behaviour, reproduction and development potential of R. padi and possess both antixenosis and antibiosis type of resistance.

Rapid screening for resistance to Sitobion avenae (F.) and Rhopalosiphum padi (L.) in winter wheat seedlings and selection of efficient assessment methods.

BACKGROUND: Sitobion avenae (F.) and Rhopalosiphum padi (L.) are harmful pests of wheat [Triticum aestivum (L.)]. No genetic resistance against the aphids has been identified in commercial wheat varieties and resistance phenotyping can be time-consuming and laborious. Here, we tested a high-throughput phenotyping method to screen 29 commercial winter wheat varieties for alate antixenosis and antibiosis. We validated this method using comprehensive behavioural analyses, including alate attraction to volatile organic compounds (VOCs) and a feeding bioassay using an electrical penetration graph (EPG), subsequently highlighting possible sources of resistance. RESULTS: We observed differences in alate behaviour upon assessing alate settlement on wheat seedlings and attraction towards VOCs, revealing the importance of visual and early post-alighting cues for alate host selection. Aphid settlement was four times higher on the most preferred variety than on the least preferred variety. Using an EPG bioassay, we identified phloem feeding and stylet derailment parameters linked to resistance. We found antibiosis assessment on detached leaves to be an inadequate screen because it produced results inconsistent with intact leaves assessment. Alate and nymph mortality were identified as key traits signifying antibiosis, showing significant positive relationships with alate reproduction and nymph mean relative growth rate. CONCLUSIONS: Overall, antixenosis and antibiosis varietal responses were consistent for both aphid species. Alate settlement on wheat seedlings was a more efficient antixenosis screen than an olfactometer assay using VOCs. In addition to assessing alate and nymph survival for antibiosis, this allows for more rapid phenotyping of large numbers of genotypes to identify novel aphid resistance genes for varietal improvement. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Identifying aphid resistance in the ancestral wheat Triticum monococcum under field conditions.

Wheat is an economically, socially, and nutritionally important crop, however, aphid infestation can often reduce wheat yield through feeding and virus transmission. Through field phenotyping, we investigated aphid resistance in ancestral wheat Triticum monococcum (L.). Aphid (Rhopalosiphum padi (L.), Sitobion avenae (F.) and Metopolophium dirhodum (Wlk.)) populations and natural enemy presence (parasitised mummified aphids, ladybird adults and larvae and lacewing eggs and larvae) on two naturally susceptible wheat varieties, Triticum aestivum (L.) var. Solstice and T. monococcum MDR037, and three potentially resistant genotypes T. monococcum MDR657, MDR045 and MDR049 were monitored across three years of field trials. Triticum monococcum MDR045 and MDR049 had smaller aphid populations, whereas MDR657 showed no resistance. Overall, natural enemy presence was positively correlated with aphid populations; however, MDR049 had similar natural enemy presence to MDR037 which is susceptible to aphid infestation. It is hypothesised that alongside reducing aphid population growth, MDR049 also confers indirect resistance by attracting natural enemies. The observed resistance to aphids in MDR045 and MDR049 has strong potential for introgression into commercial wheat varieties, which could have an important role in Integrated Pest Management strategies to reduce aphid populations and virus transmission.

Unravelling mycorrhiza-induced wheat susceptibility to the English grain aphid Sitobion avenae.

Arbuscular mycorrhizal (AM) fungi are root symbionts that can increase or decrease aphid growth rates and reproduction, but the reason by which this happens is unknown. To investigate the underlying mechanisms of this interaction, we examined the effect of AM fungi on the English Grain aphid (Sitobion avenae) development, reproduction, attraction, settlement and feeding behaviour on two naturally susceptible varieties Triticum aestivum (L.) variety Solstice and T. monococcum MDR037, and two naturally resistant lines, T. monococcum MDR045 and MDR049. Mycorrhizal colonisation increased the attractiveness of T. aestivum var. Solstice to aphids, but there was no effect on aphid development on this variety. Using the Electrical Penetration Graph (EPG) technique, we found that mycorrhizal colonisation increased aphid phloem feeding on T. monococcum MDR037 and MDR045, colonisation also increased growth rate and reproductive success of S. avenae on these varieties. Mycorrhizas increased vascular bundle size, demonstrating that these fungi can influence plant anatomy. We discuss if and how this could be related to an enhanced success rate in phloem feeding in two varieties. Overall, we present and discuss how mycorrhizal fungi can affect the feeding behaviour of S. avenae in wheat, inducing susceptibility in a resistant variety.