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Research article2015Peer reviewed

Willow resistance to a galling insect is driven by a lack of induced susceptibility not an induced defense

Hoglund S, Ronnberg-Wastljung A, Berlin S, Larsson S

Abstract

Gall-forming insects need to manipulate host plant's growth to access food resources. Because of this intimate relationship, a hypersensitive response (HR) is thought to be an important plant defense mechanism to kill the insect before a gall is formed. Few data exist, however, that unambiguously demonstrate that HR is causally linked to resistance against galling insects. Variation in Salix viminalis resistance to the gall midge Dasineura marginemtorquens is governed by only a few genes. Although the HR is considered to be an important resistance mechanism, an earlier study based on quantitative trait locus (QTL) analysis of data sets in which resistance was expressed, has shown that larval mortality is related to a single locus in a genomic region that does not contain a locus for HR, thus challenging previous suppositions that resistance is causally linked to the expression of a HR. The present study aims to test whether or not a HR causes the observed variation in willow resistance to D. marginemtorquens. By increasing the number of markers in the genomic region of interest and reanalyzing the QTL, we have enhanced the level of resolution, so permitting a more conclusive analysis than has previously been possible. The analysis identifies two genomic regions responding to gall midge attack. Importantly, the locus for resistance (measured as neonate larval mortality) and the locus for the HR are located in different regions, strongly contradicting the induced defense hypothesis. The analysis found that resistance and susceptibility were highly correlated because the allele associated with resistance was also associated with an absence of galls. It is suggested that a lack of induced susceptibility, rather than induced defense, explains the 'resistance' of S. viminalis to D. marginemtorquens.

Keywords

Cecidomyiidae; Gall midge; Dasineura marginemtorquens; Salix viminalis; Induced susceptibility; Resistance; Resistant-allele; QTL; HR; Hypersensitive response

Published in

Arthropod-Plant Interactions
2015, Volume: 9, number: 5, pages: 447-455

      SLU Authors

          • Associated SLU-program

          SLU Plant Protection Network

          Sustainable Development Goals

          End hunger, achieve food security and improved nutrition and promote sustainable agriculture

          UKÄ Subject classification

          Genetics
          Ecology

          Publication identifier

          DOI: https://doi.org/10.1007/s11829-015-9389-5

          Permanent link to this page (URI)

          https://res.slu.se/id/publ/70123