Root system traits impact early fire blight susceptibility in apple (Malus × domestica)

Abstract

Background Although it is known that resistant rootstocks facilitate management of fire blight disease, incited by Erwinia amylovora, the role of rootstock root traits in providing systemic defense against E. amylovora is unclear. In this study, the hypothesis that rootstocks of higher root vigor provide higher tolerance to fire blight infection in apples is tested. Several apple scion genotypes grafted onto a single rootstock genotype and non-grafted ‘M.7’ rootstocks of varying root vigor are used to assess phenotypic and molecular relationships between root traits of rootstocks and fire blight susceptibility of apple scion cultivars.Results It is observed that different root traits display significant (p < 0.05) negative correlations with fire blight susceptibility. In fact, root surface area partially dictates differential levels of fire blight susceptibility of ‘M.7’ rootstocks. Furthermore, contrasting changes in gene expression patterns of diverse molecular pathways accompany observed differences in levels of root-driven fire blight susceptibility. It is noted that a singular co-expression gene network consisting of genes from defense, carbohydrate metabolism, protein kinase activity, oxidation-reduction, and stress response pathways modulates root-dependent fire blight susceptibility in apple. In particular, WRKY75 and UDP-glycotransferase are singled-out as hub genes deserving of further detailed analysis.Conclusions It is proposed that low root mass may incite resource-limiting conditions to activate carbohydrate metabolic pathways, which reciprocally interact with plant immune system genes to elicit differential levels of fire blight susceptibility.

Candidate gene mapping identifies genomic variations in the fire blight susceptibility genes HIPM and DIPM across the Malus germplasm

“…For instance, selection of appropriate allelic combinations from HIPM/DIPM genes can lower successful pathogen infection, leading to reduced fire blight susceptibility. The root system can also influence fire blight susceptibility levels through co-regulated gene expression patterns and system-level interactions between carbohydrate and defense pathways 63 . Therefore, allelic combinations for the optimal root system can be used to breed rootstocks to further reduce fire blight susceptibility of grafted scions.…”

No evidence of foliar disease impact on crop root functional strategies and soil microbial communities: what does this mean for organic coffee?

“…Previous research has highlighted the role of belowground plant parts, including roots and endophyte communities, in plant defensive strategies against aboveground pathogens (Erb et al 2009, Busby et al 2016). One such strategy, for example, depends on inter‐organ signaling to reduce the plant's nutrient status via changes to root trait expression, which instigates systemic stress‐responsive pathways to limit aboveground disease (Singh et al 2019). Research has shown that these systemic responses can be induced by specific organic amendments, including different compost types (Kavroulakis et al 2005) and biochar (Elad et al 2010), via biotic and chemical elicitors that trigger specific disease pathways within the host plant (Walters et al 2005).…”

“…When confronted with pests and pathogens aboveground, belowground resource acquisition strategies often indicate plant defence strategies. While previous studies have revealed a decoupling of above and belowground plant traits (Freschet et al 2013, Isaac et al 2017), variations in individual root functional trait expression and root‐associated endophyte communities can play an important role in 1) regulating systemic plant defense strategies (by way of inter‐organ signaling) (Erb et al 2009); 2) altering the plant's nutrient status via shifts in root trait expression (Singh et al 2019); 3) inciting competition for plant resources via collaboration with specific root endophyte community members (Fritz et al 2006, Li et al 2018); and/or 4) enhancing plant tolerance of aboveground disease with compensatory growth via greater root resource acquiring traits or specific beneficial microbial collaborations (Tchameni et al 2011). However, the persistence of established belowground trait relationships within visibly diseased plant environments remains largely unclear (Freschet et al 2021).…”