Abstract
Pseudomonas syringae pv. actinidiae (Psa) biovar 3, a virulent, canker-inducing pathogen is an economic threat to the kiwifruit (Actinidia spp.) industry worldwide. The commercially grown diploid (2×) A. chinensis var. chinensis is more susceptible to Psa than tetraploid and hexaploid kiwifruit. However information on the genetic loci modulating Psa resistance in kiwifruit is not available. Here we report mapping of quantitative trait loci (QTLs) regulating resistance to Psa in a diploid kiwifruit population, derived from a cross between an elite Psa-susceptible ‘Hort16A’ and a resistant male breeding parent P1. Using high-density genetic maps and intensive phenotyping, we identified a single QTL for Psa resistance on Linkage Group (LG) 27 of ‘Hort16A’ revealing 16–19% phenotypic variance and candidate alleles for susceptibility and resistance at this loci. In addition, six minor QTLs were identified in P1 on distinct LGs, exerting 4–9% variance. Resistance in the F1 population is improved by additive effects from ‘Hort16A’ and P1 QTLs providing evidence that divergent genetic pathways interact to combat the virulent Psa strain. Two different bioassays further identified new QTLs for tissue-specific responses to Psa. The genetic marker at LG27 QTL was further verified for association with Psa resistance in diploid Actinidia chinensis populations. Transcriptome analysis of Psa-resistant and susceptible genotypes in field revealed hallmarks of basal defense and provided candidate RNA-biomarkers for screening for Psa resistance in greenhouse conditions.
Highlights
Pseudomonas syringae is a hemi-biotrophic bacterial complex[1] that can infect a range of plant species
A 3-dimensional principal components analysis (PCA) on the correlation matrix of the field assessment, stab assay and flood assay displays a high degree of divergence in the rankings of the population for Psa response and resistance when assessed through different approaches (Fig. 2d)
This study provides the first information about genetic loci involved in the host-pathogen relationship between A. chinensis and Psa
Summary
Pseudomonas syringae is a hemi-biotrophic bacterial complex[1] that can infect a range of plant species. It comprises pathovars which cause similar symptoms on their host plants and several pathovars can lead to severe crop loss. Actinidiae (Psa) infects several species of Actinidia (kiwifruit)[2,3] and virulent Psa strains induce a range of symptoms on the main stem of the vine, foliage, floral buds and fruits[4]. Psa pathovar strains can be grouped into five biovars based on their genetic and biological characteristics[4,5]. Strains of biovar 3, previously known as Psa-V (referred to here as Psa), are currently the most aggressive and were responsible for outbreaks from 20086–9. Psa has cost the kiwifruit industry billions of dollars worldwide and its incursion in New Zealand in
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