Genetic and environmental regulation of plant architectural traits and opportunities for pest control in raspberry

Abstract

Part of the reason for the under-exploitation of physical resistance traits in plant breeding is that the genetic basis and heritability of these traits is poorly characterised, and any associations of particular traits with pest and disease resistances have yet to be determined. In raspberry, some associations between architectural traits and disease resistances have been demonstrated, for example cane hairs and resistance to cane diseases. The aim of this work is to examine a range of traits, including leaf trichomes, leaf density, cane density, bush density, lateral length and lateral numbers, to determine the heritability and therefore breeding potential of these traits. The effect of these traits against aphids and spider mites, two important pests in raspberry, was examined. Chromosomal regions with candidate genes regulating these traits were identified as the first step to understanding the genetic control.

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

“…Johnson et al , ), although particularly low values might have resulted from slow aphid development, reduced fecundity or high mortality on some genotypes. A recent field study indicated a positive association between aphid abundance and leaf trichome density (Graham et al , ), which might be considered surprising; elevated leaf trichome density frequently has a negative effect on the abundance of aphids feeding on other crop species (Webster et al , ; Khan et al , ), although sap‐feeding herbivores can be unaffected by leaf physical traits (Carmona et al , ). These observations would suggest that, for A .…”

“…These genotypes (varieties and accessions) had been classified previously in field plantations as exhibiting high (Glen Ample, Glen Moy, R239, R174; see Fig. ), intermediate (R232, R253) and low (Latham, R184, R278, R279) abaxial leaf trichome density using a qualitative leaf trichome score (Graham et al , ). Briefly, the leaf was held between thumb and index finger, allowing the index finger to be rubbed gently over the abaxial leaf surface to assign a tactile score between 0 (no trichomes) and 3 (abundant trichomes) for trichome density.…”

“…idaeus is a high‐value crop grown widely in northern temperate regions of Europe and the United States. The system is useful for investigating such interactions in the context of crop protection because this woody perennial is grown in long‐lived plantations (up to 10–15 years) in agronomic conditions that increasingly rely on reduced pesticide inputs (Graham et al , ). We focus on two pest species that predominate in raspberry plantations.…”

“…idaei and T . urticae infestations in raspberry plantations revealed that leaf trichome density correlated positively with aphid presence and negatively with spider mite incidence (Graham et al , ), indicating potentially antagonistic effects of a resistance trait on two arthropod pests. These associations between plant traits and naturally occurring populations of herbivores provide the rationale for the current study, which aimed to investigate rigorously the mechanistic basis of these relationships under controlled conditions and assess the consequences for pest management of deploying this trait.…”

“…idaeus genotypes that differed in leaf trichome density, the aims of this study were to determine whether a physical resistance trait influences (a) host plant suitability for herbivores, (b) herbivore preference for host plants and (c) searching behaviour of larvae of a generalist predator of many arthropod species, particularly aphids (the common green lacewing, Chrysoperla carnea Stephens, Neuroptera: Chrysopidae). Based on observations of naturally infesting arthropods in field plantations (Graham et al , ), our null hypothesis was that genotypes with high leaf trichome densities would be more acceptable to A . idaei and less acceptable to T .…”