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Aphids, including the bird cherry-oat aphid (Rhopalosiphum padi), are significant agricultural pests. The wild relative of barley, Hordeum spontaneum 5 (Hsp5), has been described to be partially resistant to R. padi, with this resistance proposed to involve higher thionin and lipoxygenase gene expression. However, the specificity of this resistance to aphids and its underlying mechanistic processes are unknown. In this study, we assessed the specificity of Hsp5 resistance to aphids and analysed differences in aphid probing and feeding behaviour on Hsp5 and a susceptible barley cultivar (Concerto). We found that partial resistance in Hsp5 to R. padi extends to two other aphid pests of grasses. Using the electrical penetration graph technique, we show that partial resistance is mediated by phloem- and mesophyll-based resistance factors that limit aphid phloem ingestion. To gain insight into plant traits responsible for partial resistance, we compared non-glandular trichome density, defence gene expression, and phloem composition of Hsp5 with those of the susceptible barley cultivar Concerto. We show that Hsp5 partial resistance involves elevated basal expression of thionin and phytohormone signalling genes, and a reduction in phloem quality. This study highlights plant traits that may contribute to broad-spectrum partial resistance to aphids in barley.

Halloysite has fascinated investigators ever since it was first discovered that, in obvious contrast to the other kaolin subgroup minerals, namely kaolinite, dickite and nacrite which occur primarily in planar platy or blocky forms, many halloysites adopt an unusual tubular morphology. Spheroidal halloysite is also very well documented especially from soils, but here our focus will be entirely on the tubular form of halloysite, increasingly referred to as halloysite nanotubes or HNTs due to a rapidly expanding range of applications in a wide variety of technologies. Aside from its unusual morphologies, halloysite is also distinct amongst the other kaolin polytypes in that it is hydrated with H2O molecules positioned in the interlayer space between the fundamental 1:1 layer combination of tetrahedral and octahedral sheets that form the basic kaolin structure.Indeed, according to Churchman & Carr (1975) the single most important characteristic that identifies, defines, and distinguishes halloysite as a distinct kaolin mineral is the presence, or evidence of the former presence, of molecules of H2O in the interlayer space. Interlayer H2O in halloysite is exceedingly labile and in response to changing environmental conditions, both naturally in the field or subsequently in the laboratory, it is readily and irreversibly lost. In its fully hydrated state halloysite contains two interlayer H2O molecules accounting for 12.25 wt. % of the molecular formula unit which can be written as Al2Si2O5(OH)4·2H2O. With this full complement of interlayer H2O halloysite has a primary basal spacing, as observed in X-ray diffraction (XRD) patterns, of approximately 10Å. Because the loss of the interlayer H2O is generally not a 3 Published in Clay Minerals V 51,

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