QTL mapping of resistance to leaf rust in Salix

Abstract

Genetic mapping of quantitative trait loci (QTL) for resistance to Melampsora leaf rust was performed in two willow families: the progeny from a backcross between Salix viminalis and a hybrid S. viminalis×Salix schwerinii (population S 1 ), and the F 1 progeny of a cross between two S. viminalis (population S 3 ). Disease levels were scored in the field for three consecutive years. In the laboratory, five different rust strains were sprayed onto leaf disks and the following resistance components were scored: latent period, diameter and number of uredinia, and flecking. One major QTL and 14 smaller were identified in the S 1 host population. One rust strain, that represents a Melampsora form with limited incidence on S. viminalis, showed lower aggressiveness to the S 1 host population together with a different pattern in QTLs. In the S 3 host population, we detected 13 QTLs for rust resistance, of which two were located to the same genomic regions as those found for the S 1 population. We showed that the strongest QTL cosegregated with a gene homologous to a known Toll/ interleukin receptor-nucleotide binding site-leucine-rich repeat resistance gene in poplar. The importance of the identified QTLs is discussed in relation to breeding for durable resistance.

Genetic diversity, population structure and phenotypic variation in European Salix viminalis L. (Salicaceae)

“…K3 and K8 used by Hanley and Karp (2013) and Hanley et al (2002); and S1 and S3 used by Berlin et al (2010) and Tsarouhas et al (2002). Efforts to link phenotype to genotype have also been undertaken, through QTL mapping in these and other bi-parental populations (Tsarouhas et al 2002(Tsarouhas et al , 2004Semerikov et al 2003;Rönnberg-Wästljung et al 2008;Samils et al 2011;Höglund et al 2012). However, to date, association mapping has not been applied in this species.…”

Identification of a Differentially Expressed TIR-NBS-LRR Gene in a Major QTL Associated to Leaf Rust Resistance in Salix

“…schwerinii cv. ‘Björn’ [13–14]. ‘Björn’ is highly resistant to rust infections whereas ‘78183’ is susceptible [13].…”

“…‘Björn’ [13–14]. ‘Björn’ is highly resistant to rust infections whereas ‘78183’ is susceptible [13]. The markers to construct the map for population S 1 had been designed using primers from coding regions in P .…”

“…viminalis × S . schwerinii ) [13]. The aim of the present work was to analyse the region within this major QTL and to find the genes that underlie the resistant phenotype.…”

Forest tree genomics: 10 achievements from the past 10 years and future prospects

“…Forest tree pathologists and breeders have, therefore, focused on the genetic and molecular basis of quantitative resistance, which is thought to be under more complex genetic control and to be more durable. The results of many fine mapping, candidate region sequencing, genome annotation, and transcriptional studies have blurred the distinction between qualitative and quantitative resistances: (i) major QTLs for quantitative resistance can account for more than 40 % of the observed phenotypic variation in field or laboratory experiments (Jorge et al 2005;Freeman et al 2008); (ii) in artificial inoculation tests controlling for pathogen diversity, some major QTLs display significant strain specificity, resembling that of R genes (Dowkiw et al 2010); (iii) qualitative resistance factors from Populus deltoides and quantitative resistance factors against leaf rust inherited from P. trichocarpa and Salix viminalis have been fine-mapped to genomic regions rich in R genes (Bresson et al 2011;Samils et al 2011); and (iv) the difference in the timing of the activation of similar defense responses between susceptibility and partial or full resistance in the poplar-Melampsora interaction is consistent with the signal conversion model described for Arabidopsis (Nimchuk et al 2003;Duplessis et al 2009). …”