Exploiting physical defence traits for crop protection: leaf trichomes ofRubus idaeushave deterrent effects on spider mites but not aphids

Abstract

Plants possess anti-herbivore defences that could be exploited for crop protection. The potential for deploying physical defence traits for more sustainable pest management (i.e. reduced pesticide application) has not been fully realised. Using a perennial crop (red raspberry, Rubus idaeus), we take the novel approach of quantifying within-and between-genotype variation in a resistance trait, leaf trichome density, to determine precisely the effect of trichomes on host plant preference and suitability for two shoot-feeding arthropods, the European large raspberry aphid (Amphorophora idaei) and two-spotted spider mite (Tetranychus urticae). Additionally, we tested whether this trait influenced searching behaviour of a generalist herbivore predator (lacewing larvae, Chrysoperla carnea). Although there was no consistent genotypic variation in R. idaeus suitability for T. urticae, our hypothesis that T. urticae would avoid high leaf trichome density was supported on certain genotypes. The deterrent effect was mainly on egg deposition rather than leaf selection by adults, with up to sixfold differences in leaf preference depending on the genotypes offered. By contrast, there was significant genotypic variation in R. idaeus suitability for A. idaei (10-fold variation in aphid abundance), but, contrary to our prediction, aphid preference and infestation levels were unrelated to leaf trichome density. Instead, A. idaei performed best on vigorous genotypes, indicating that plant tolerance traits contributed to R. idaeus suitability for aphids. Leaf trichomes had little effect on the behaviour of the beneficial control agent C. carnea larvae. We conclude that physical anti-herbivore defences, specifically leaf trichomes, could be deployed to deter particular arthropod pests. However, the mechanistic approach adopted here is necessary to avoid antagonistic effects on other pests or on natural enemies.

Histochemical assays of secretory trichomes and the structure and content of mineral nutrients in Rubus idaeus L. leaves

“…The hypostomatic type of leaf lamina of the R. idaeus cultivars analysed in this study is present in Prunus laurocerasus (Schreiber et al 1995) as well as plants from the genera Sorbus and Sorbaria (Krivoruchko and Gamulya 2013; Song and Hong 2014). As shown by our investigations and literature data, the abaxial epidermis in R. idaeus had twisted unicellular non-glandular trichomes (Fell and Rowson 1960;Tomaszewski et al 2014;Karley et al 2015). Their length in the epidermis of R. loganobaccus leaves ranged from 0.3 to 0.7 mm (Fell and Rowson 1960).…”

“…The main groups of bioactive compounds present in the glandular trichomes in the epidermis of fresh Rubus idaeus 'Laszka' and 'Radziejowa' leaves were stained with relevant histochemical assays using the following chemical compounds: Nadi reagent (naphthol and dimethyl-paraphenylene diamine) for terpenoids and essential oils (David and Carde 1964), Sudan Red 7B (Brundrett et al 1991) and Sudan Black B (Lison 1960) for total lipids, Nile blue A (Jensen 1962) for neutral and acidic lipids, Lugol's solution for proteins (Jensen 1962), Fehling's reagent (Ayoola et al 2008) for total sugars, PAS reagent (Feder and O'brien 1968) for polysaccharides, and iron chloride (Johansen 1940) and potassium dichromate (Gabe 1968) for phenolic compounds.…”

“…from the genera Amphorophora and Tetranychus (Levin 1973). The presence of trichomes on the epidermis surface was found to reduce the number of pests feeding on R. idaeus leaves (Karley et al 2015). Nonglandular trichomes are involved in adaptation to adverse environmental conditions.…”

“…As reported by Tomaszewski et al (2014), trichomes in the leaf epidermis in plants from the genus Rubus are regarded as one of the most important traits for classification of the representatives of this genus and for determination of taxa at the level of series, sections, and even subgenera. The distribution, size, and shape of trichomes were found to vary between taxa (Upadhyaya and Furness 1998;Tomaszewski et al 2014;Karley et al 2015). Tomaszewski et al (2014) distinguished three types of trichomes in Rubus plants: simple eglandular (unbranched) trichomes, eglandular branched trichomes, and very short secretory uniseriate trichomes.…”

Mind the gap: time to make sure that scientists and practitioners are on the same page

“…Science is crucial to the development of IPM, be it understanding pest phenology, developing and evaluating biocontrol agents or obtaining a basic understanding of the biology and ecology of a particular pest (e.g. Webb et al , ; Dandurand & Knudsen, ; Karley et al , ; Rowley et al , ). Basic science is important, but funding needs to be mainly allocated to more immediately applicable research than to the more academic end of the spectrum which is where it tends to go more often than not (Hokkanen, ).…”