Interactions between plants and insect herbivores are important determinants of plant productivity in managed and natural vegetation. In response to attack, plants have evolved a range of defenses to reduce the threat of injury and loss of productivity. Crop losses from damage caused by arthropod pests can exceed 15% annually. Crop domestication and selection for improved yield and quality can alter the defensive capability of the crop, increasing reliance on artificial crop protection. Sustainable agriculture, however, depends on reduced chemical inputs. There is an urgent need, therefore, to identify plant defensive traits for crop improvement. Plant defense can be divided into resistance and tolerance strategies. Plant traits that confer herbivore resistance typically prevent or reduce herbivore damage through expression of traits that deter pests from settling, attaching to surfaces, feeding and reproducing, or that reduce palatability. Plant tolerance of herbivory involves expression of traits that limit the negative impact of herbivore damage on productivity and yield. Identifying the defensive traits expressed by plants to deter herbivores or limit herbivore damage, and understanding the underlying defense mechanisms, is crucial for crop scientists to exploit plant defensive traits in crop breeding. In this review, we assess the traits and mechanisms underpinning herbivore resistance and tolerance, and conclude that physical defense traits, plant vigor and herbivore-induced plant volatiles show considerable utility in pest control, along with mixed species crops. We highlight emerging approaches for accelerating the identification of plant defensive traits and facilitating their deployment to improve the future sustainability of crop protection.

Breeding in raspberry is time-consuming due to the highly heterozygous nature of this perennial fruit crop, coupled with relatively long periods of juvenility. The speed and precision of raspberry breeding can be improved by genetic linkage maps, thus facilitating the development of diagnostic markers for polygenic traits and the identification of genes controlling complex phenotypes. A genetic linkage map (789 cM) of the red raspberry Rubus idaeus has been constructed from a cross between two phenotypically different cultivars; the recent European cultivar Glen Moy and the older North American cultivar Latham. SSR markers were developed from both genomic and cDNA libraries from Glen Moy. These SSRs, together with AFLP markers, were utilised to create a linkage map. In order to test the utility of the genetic linkage map for QTL analysis, morphological data based on easily scoreable phenotypic traits were collected. The segregation of cane spininess, and the root sucker traits of density and spread from the mother plant, was quantified in two different environments. These traits were analysed for significant linkages to mapped markers using MapQTL and were found to be located on linkage group 2 for spines and group 8 for density and diameter. The availability of co-dominant markers allowed heterozygosities to be calculated for both cultivars.

Disease resistance is increasing in importance, as consumers require high-quality raspberry fruit at a time when chemical disease control is undesirable. Breeders have limited resources and rarely include a primary screen for each fungal disease. Marker-assisted breeding would facilitate the introduction of resistance into elite germplasm and breeding lines. An additional 20 simple sequence repeats have been added to the existing raspberry linkage map. Gene H, which determines cane pubescence (genotype HH or Hh), the recessive allele of which gives glabrous canes (genotype hh), has been mapped on to linkage group 2 and shown to be closely associated with resistance to cane botrytis and spur blight but not rust or cane spot. Other map regions on linkage groups 3, 5 and 6 associated with disease resistance are reported here.

Consumption of raspberries promotes human health through intake of pharmaceutically active antioxidants, including cyanidin and pelargonidin anthocyanins; products of flavonoid metabolism and also pigments conferring colour to fruit. Raspberry anthocyanin contents could be enhanced for nutritional health and quality benefits utilising DNA polymorphisms in modern marker assisted breeding. The objective was to elucidate factors determining anthocyanin production in these fruits. HPLC quantified eight anthocyanin cyanidin and pelargonidin glycosides: -3-sophoroside, -3-glucoside, -3-rutinoside and -3-glucosylrutinoside across two seasons and two environments in progeny from a cross between two Rubus subspecies, Rubus idaeus (cv. Glen Moy)xRubus strigosus (cv. Latham). Significant seasonal variation was detected across pigments less for different growing environments within seasons. Eight antioxidants mapped to the same chromosome region on linkage group (LG) 1, across both years and from fruits grown in field and under protected cultivation. Seven antioxidants also mapped to a region on LG 4 across years and for both growing sites. A chalcone synthase (PKS 1) gene sequence mapped to LG 7 but did not underlie the anthocyanin quantitative traits loci (QTL) identified. Other candidate genes including basic-helix-loop-helix (bHLH), NAM/CUC2-like protein and bZIP transcription factor underlying the mapped anthocyanins were identified.

Twelve microsatellites were isolated from simple sequence repeat (SSR)-enriched genomic libraries of ‘Meeker’ red raspberry (Rubus idaeus) and ‘Marion’ blackberry (Rubus hybrid). These primer pairs plus one developed from a GenBank red raspberry sequence were evaluated in 48 raspberry and 48 blackberry genotypes. Only RhM031 did not generate a product in raspberry, whereas RiG001 failed to amplify in blackberry and hybrid accessions. The number of polymerase chain reaction products per primer pair in the 12 SSRs that successfully amplified was higher in blackberry genotypes and their hybrids than in raspberry, ranging from three to 29 in blackberry (average, 14.4) and from one to 15 in red raspberry (average, 7.5). Diversity estimates were determined for 10 of 12 SSRs that amplified up to two products in 44 red raspberry genotypes. The best SSR loci based on high observed and expected heterozygosities, high polymorphism information content, and low inbreeding coefficient were RiM019, RhM003, and RhM011. They mapped to three different linkage groups (5, 2, and 7, respectively) in red raspberry and differentiated the unique genotypes identified with the 12 SSRs in each crop type.