Virulence Characterization of Venturia inaequalis Reference Isolates on the Differential Set of Malus Hosts

Abstract

23Caffier, V., Patocchi, A., Expert, P., Bellanger, Durel, M., 24 Broggini, G.A.L, Groenwold, R., and Bus V.G.M. 2014. Virulence characterization of 25 Venturia inaequalis reference isolates on the differential set of Malus hosts. Plant Dis. 26XX:XX-XX.27 28 A set of differential hosts has recently been identified for 17 apple scab resistance genes in an 29 updated system for defining gene-for-gene (GfG) relationships in the Venturia inaequalis- 30 Malus pathosystem. However, a set of reference isolates characterized for their 31 complementary avirulence alleles is not yet available. In this paper, we report on improving 32 the set of differential hosts for h(7) and propose the apple genotype LPG3-29 as carrying the 33 single major resistance gene Rvi7. We characterized a reference set of 23 V. inaequalis 34 isolates on 14 differential apple hosts carrying major resistance genes under controlled 35 conditions. We identified isolates that were virulent on at least one of the following defined 36 Sixteen different virulence patterns were observed. In general, the isolates carried one to 38 three virulences, but some of them were more complex, with up to six virulences. This set of 39 well-characterized isolates will be helpful for the identification of additional apple scab 40 resistance genes in apple germplasm and the characterization of new GfG relationships to 41 help improve our understanding of the host-pathogen interactions in the V. inaequalis-Malus 42 pathosystem.43 44 45 3 Plant DiseaseDurable pest and disease resistance is a major breeding objective for most crops, but 46 achieving it has proven to be a challenge for breeders in the absence of truly non-race-47 specific resistances. Many genes involved in effector-triggered immunity (20) code for highly 48 polymorphic proteins containing nucleotide binding (NB) and leucine-rich repeat (LRR) 49 domains that instigate a resistance reaction in the host following recognition of the 50 complementary pathogen effector protein(s) in this specific gene-for-gene (GfG) relationship 51 (13). However, the high evolutionary potential of the pathogen effector arsenal negatively 52 affects the durability of resistance genes. To counteract, or at least delay the breakdown of 53 resistance genes by virulent races of the pathogen, breeders search for new resistance genes 54 (major genes and quantitative trait loci (QTLs)) that are effective against the already known 55 virulent races (23) and pyramid them (including 'spent' ones) to improve their durability as 56 well as increase the efficacy of the combined genes. This is based on the principle that for a 57 multiple virulent strain to develop, it will have to acquire these virulences simultaneously 58 (11). The effectiveness of this strategy relies on the availability of a set of differential hosts 59 and reference isolates to understand the genetics of the arsenal of both effectors in the 60 pathogen and resistances in the host, and their GfG relationships (34). 61 Apple scab, caused by Venturia inaequali...

Comparative analysis of the predicted secretomes of Rosaceae scab pathogens Venturia inaequalis and V. pirina reveals expanded effector families and putative determinants of host range

“… a Hybrid with hints/ab initio gene predictions for Vi1 b CEGMA analysis using both partial and full gene sequences [ 25 ] c BUSCO analysis using both partial and full gene sequences [ 26 ] d Note the recent race designation change reported for EU-B04 [ 187 ], previously reported as race (1,14) by Bus et al [ 14 ] …”

A Large Family of AvrLm6-like Genes in the Apple and Pear Scab Pathogens, Venturia inaequalis and Venturia pirina

“…The V. inaequalis Vi1 and the V. pirina genomes ( Cooke et al, 2014 ) are publicly available via the MycoCosm genome portal at JGI 1 , 2 . All V. inaequalis and V. pirina isolates used in this study have been reported previously ( Stehmann et al, 2001 ; Le Cam et al, 2002 ; Win et al, 2003 ; Bowen et al, 2009 ; Broggini et al, 2011 ; Cooke et al, 2014 ; Caffier et al, 2015 ). The rest of the genomes were only used to extract the ALVi predicted protein sequences, these are included in the Supplementary Material.…”

Scab resistance in ‘Geneva’ apple is conditioned by a resistance gene cluster with complex genetic control

“…Further investigation of the GfG relationships at the molecular level should be performed to understand why V. inaequalis was able to overcome all five genes. Nevertheless, based on the considerable sporulation on ‘Geneva’ by, for example, EU‐NL24, a race (1,3,6,7) isolate (Caffier et al ., ), we can hypothesize that the R genes do not impose a high penalty to the pathogen for adaptation (Leach et al ., ). Nevertheless, (part of) the ‘Geneva’ R gene complex has demonstrated field resistance in New Zealand (V. Bus et al ., unpublished data), and hence will still be useful for gene pyramiding with other scab genes by breeders applying MAS enabled by our fine mapping of five ‘Geneva’ resistance loci.…”

“…The characterization of host–pathogen interactions was performed at Plant Research International in Wageningen, the Netherlands on F1 and F2 progenies derived from ‘Geneva’ using nine reference monoconidial isolates of V. inaequalis (Caffier et al ., ), including isolate 1774‐1, which was distributed as a race (3) isolate (Bus, ), but recently characterized as race (1,7) (Caffier et al ., ) (Tables and http://onlinelibrary.wiley.com/doi/10.1111/mpp.12269/suppinfo, see Supporting Information).…”