Abstract
Key messageRphq2, a minor gene for partial resistance toPuccinia hordei, was physically mapped in a 188 kbp introgression with suppressed recombination between haplotypes ofrphq2andRphq2barley cultivars.Partial and non-host resistances to rust fungi in barley (Hordeum vulgare) may be based on pathogen-associated molecular pattern (PAMP)-triggered immunity. Understanding partial resistance may help to understand non-host resistance, and vice versa. We constructed two non-gridded BAC libraries from cultivar Vada and line SusPtrit. Vada is immune to non-adapted Puccinia rust fungi, and partially resistant to P. hordei. SusPtrit is susceptible to several non-adapted rust fungi, and has been used for mapping QTLs for non-host and partial resistance. The BAC libraries help to identify genes determining the natural variation for partial and non-host resistances of barley to rust fungi. A major-effect QTL, Rphq2, for partial resistance to P. hordei was mapped in a complete Vada and an incomplete SusPtrit contig. The physical distance between the markers flanking Rphq2 was 195 Kbp in Vada and at least 226 Kbp in SusPtrit. This marker interval was predicted to contain 12 genes in either accession, of which only five genes were in common. The haplotypes represented by Vada and SusPtrit were found in 57 and 43 %, respectively, of a 194 barley accessions panel. The lack of homology between the two haplotypes probably explains the suppression of recombination in the Rphq2 area and limit further genetic resolution in fine mapping. The possible candidate genes for Rphq2 encode peroxidases, kinases and a member of seven-in-absentia protein family. This result suggests that Rphq2 does not belong to the NB-LRR gene family and does not resemble any of the partial resistance genes cloned previously.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-015-2627-5) contains supplementary material, which is available to authorized users.
Highlights
Partial resistance is an incomplete host resistance which retards epidemic development despite a compatible infection type (Niks et al 2011; Parlevliet and van Ommeren 1975)
Partial resistance of barley to Puccinia hordei consists of the components lower infection frequency, lower sporulation rate and longer latency period of the pathogen, and such effects are not associated with hypersensitivity
Evidence suggests partial resistance of barley to powdery mildew and rust fungi to be a weak form of non-host resistance based on pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) (Jones and Dangl 2006; Niks and Marcel 2009; Niks et al 2011; Trujillo et al 2004)
Summary
Partial resistance is an incomplete host resistance which retards epidemic development despite a compatible infection type (Niks et al 2011; Parlevliet and van Ommeren 1975). Barley (Hordeum vulgare) is such a marginal host or near-non-host to Puccinia triticina, Puccinia hordei-murini and some other non-adapted rust fungi because a small proportion of barley accessions (less than 10 %) are susceptible (>10 pustules on the first leaf) at seedling stage when inoculum is applied at high density (Atienza et al 2004). SusPtrit is, at the seedling stage, highly susceptible to P. triticina and to at least nine other non-adapted rust fungi (Atienza et al 2004) This experimental line was used to develop mapping populations Vada/SusPtrit (Jafary et al 2006), Cebada Capa/SusPtrit (Jafary et al 2008) and SusPtrit/Golden Promise (Yeo et al 2014), as well as a set of near-isogenic lines for different resistances QTLs (Yeo et al unpublished data). Resistance of barley to non-adapted rust fungi inherits polygenically just as partial resistance to P. hordei, the barley leaf rust fungus (Jafary et al 2006, 2008; Marcel et al 2007b; Niks et al 2000; Qi et al 1998)
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