This is a brief summary of some of the work published in 2015 by UK Strawberry researchers and it is perhaps unsurprisingly dominated by work undertaken at East Malling Research. Richard Harrison leads two studies that focus on different aspects of the diseases that effect strawberry yield while Louisa Robinson-Boyer heads an investigation into the role that arbuscular mycorrhizal fungi might play in enabling future growth of strawberries in drier condtions.
Elsewhere we introduce a study that the outlines the developement of a commercial SNP-array that will hopefully aid marker-assisted breeding and finally is a Spanish-led investigation into a class of enzymes that contribute to fruit softening.
Antanaviciute L, Šurbanovski N, Harrison N, McLeary KJ, Simpson DW, Wilson F, Sargent DJ, Harrison RJ (2015) Mapping QTL associated with Verticillium dahliae resistance in the cultivated strawberry (Fragaria × ananassa). Hortic Res 2:15009 http://dx.doi.org/10.1038/hortres.2015.9 Open Access
Richard Harrison (East Malling) is the UK lead on this collaboration with Italian researchers in a study that investigates the QTLs that confer resistance to Verticillium dahliae, an important strawberry pathogen. A population of octoploid strawberries that was segregating for pathogen resistance was screened over three field seasons and multiple QTLs were identified. These resistance QTLs appear to be additive in this situation and their associated markers are abundant in cultivated strawberry germplasm. The authors state that genetic gain is clearly possible through marker-assisted breeding in Strawberry.
Bassil NV, Davis TM, Zhang H, Ficklin S, Mittmann M, Webster T, Mahoney L, Wood D, Alperin ES, Rosyara UR, Koehorst-Vanc Putten H, Monfort A, Sargent DJ, Amaya I, Denoyes B, Bianco L, van Dijk T, Pirani A, Iezzoni A, Main D, Peace C, Yang Y, Whitaker V, Verma S, Bellon L, Brew F, Herrera R, van de Weg E (2015) Development and preliminary evaluation of a 90 K Axiom® SNP array for the allo-octoploid cultivated strawberry Fragaria × ananassa. BMC Genomics 16:155 http://dx.doi.org/10.1186/s12864-015-1310-1 Open Access
This international collaboration includes a UK industrial contribution from researchers from AffymetrixUK and describes the development of a SNP-array to aid marker-assisted breeding of allo-octoploid cultivated strawberry. Sequence variants were identified from the sequencing of 19 varieties of available octoploid germplasm along with a diploid progenitor. Following genotyping of over 300 octoploid accessions, SNPs were analysed using Affymetrix software. Ultimately the finished array has SNPs evenly distributed across 28 chromosomes with an average density of one marker/0.5cM. The authors state that this array will allow quality genetic analysis including generation of high density linkage maps and will aid strawberry researchers to identify QTLs and provide a platform for use in future marker-assisted breeding strategies.
Boyer LR, Brain P, Xu XM, Jeffries P (2015) Inoculation of drought-stressed strawberry with a mixed inoculum of two arbuscular mycorrhizal fungi: effects on population dynamics of fungal species in roots and consequential plant tolerance to water deficiency. Mycorrhiza. 25(3):215-27 http://dx.doi.org/10.1007/s00572-014-0603-6
Louisa Robinson-Boyer from EMR is the corresponding author of this study that investigated the ability of cultivated strawberry to grow in drought conditions after inoculation with zero, one or two species of arbuscular mycorrhizal fungi (AMF). They showed that both species of Funneliformis AMF were able to co-colonise roots but that their relative abundance varied under different water stresses (reduced irrigation by up to 40%). The authors found that colonisation was beneficial but that single species inoculation gave similar benefits to a mixed population, irrespective of the amount of irrigation. This shows that the presence of colonisation was of principle importance. Addition of AMF to plants under drought conditions restored growth to the levels observed in plants grown with normally watering. This demonstrated that the growth of cultivated strawberries in drought conditions significantly benefits from the presence of AMF and therefore might suggest a long-term strategy to improve future production of this crop in changing climate conditions.
Xu X, Passey T, Wei F, Saville R, Harrison RJ (2015) Amplicon-based metagenomics identified candidate organisms in soils that caused yield decline in strawberry. Hortic Res. 2:15022 http://dx.doi.org/10.1038/hortres.2015.22 Open Access
This second paper led by Richard Harrison looks into novel soil microbial pathogens that may be a causative agent for declining strawberry yield. Multiple soil samples were collected from four sites, two that showed yield-decline and two without. The authors defined operational taxonomy units (OTU) of bacterial and fungal origin and were able to assign yield decline to four potential factors: 1- Low abundance of helpful bacterial populations, such as Bacillus and Pseudomonas 2- lack of nematophagous fungus (Paecilomyces sp) 3- high levels of two potential fungal root-rot pathogens and 4- overall wet soil conditions. The authors will use this information to identify true causative agents that contribute to strawberry yield decline. Furthermore the authors highlight that this amplicon-based metagenomics approach is useful for profiling novel soil microbiota communities.
It is an exciting time for the Harrison lab as in collaboration with The Genome Analysis Centre, they have just obtained BBSRC funding for a project to sequence the octoploid cultivated strawberry.
Paniagua C, Blanco-Portales R, Barceló-Muñoz M, García-Gago JA, Waldron KW, Quesada MA, Muñoz-Blanco J, Mercado JA (2015) Antisense down-regulation of the strawberry β-galactosidase gene FaβGal4 increases cell wall galactose levels and reduces fruit softening. J Exp Bot. http://dx.doi.org/10.1093/jxb/erv462 Open Access
This Spanish-led study includes UK representation from Keith Waldron at the Institute of Food Research. Softening of fruit is a significant issue when bringing strawberries to the market and is caused by an increase in the solubilization and depolymerization of pectins from cell walls. This study aimed to investigate the role that galactose-release plays in this process, a reaction that is catalyzed by β-galactosidase enzymes. One putative member of this enzyme family, FaβGal4 was identified using a novel strawberry expression array. The authors generated antisense transgenic strawberries that aimed to have reduced expression of FaβGal4. Two out of nine lines showed reduced expression of FaβGal4 (and also the related FaβGal1) that was coincident with fruits that were 30% firmer, analysed over three growing seasons. These plants have higher levels of galactose in their cell walls demonstrating that the role of the β-galactosidase enzyme was indeed inhibited in these lines. Therefore this indicates that the FaβGal4 gene represents an potential target for future breeding or transgenic strategies to generate strawberry plants that have firmer fruit.