Two distinct major QTL for resistance to fire blight co-localize on linkage group 12 in apple genotypes ‘Evereste’ andMalus floribundaclone 821

Abstract

Fire blight, caused by the bacterium Erwinia amylovora, is one of the most destructive diseases of apple (Malus xdomestica) worldwide. No major, qualitative gene for resistance to this disease has been identified so far in apple. A quantitative trait locus (QTL) analysis was performed in two F1 progenies derived from two controled crosses: one between the susceptible rootstock cultivar 'MM106' and the resistant ornamental cultivar 'Evereste' and the other one between the moderately susceptible cultivar 'Golden Delicious' and the wild apple Malus floribunda clone 821, with unknown level of fire blight resistance. Both progenies were inoculated in the greenhouse with the same reference strain of E. amylovora. The length of stem necrosis was scored 7 and 14 days after inoculation. A strong QTL effect was identified in both 'Evereste' and M. floribunda 821 at a similar position on the distal region of linkage group 12 of the apple genome. From 50% to 70% of the phenotypic variation was explained by the QTL in 'Evereste' progeny according to the scored trait. More than 40% of the phenotypic variation was explained by the M. floribunda QTL in the second progeny. It was shown that 'Evereste' and M. floribunda 821 carried distinct QTL alleles at that genomic position. A small additional QTL was identified in 'Evereste' on linkage group 15, which explained about 6% of the phenotypic variation. Although it was not possible to confirm whether or not 'Evereste' and M. floribunda QTL belonged to the same locus or two distinct closely related loci, these QTL can be valuable targets in marker-assisted selection to obtain fire blight resistant apple cultivars and form a starting point for discovering the function of the genes controlling apple fire blight resistance.

Inheritance of fire blight resistance in Asian <i>Pyrus</i> species

“…Our observations are in agreement with noted transgressive segregation for a number of traits in many crop species [41][42][43][45][46][47][48][49]. Durel et al [50] observed fire blight transgressive apple individuals more resistant or more susceptible than their respective parents in crosses between rootstock MM.106 and species 'Evereste' and between 'Golden Delicious' and the wild apple species Malus floribunda clone 821.…”

Assessment of fire blight tolerance in apple based on plant inoculations with Erwinia amylovora and DNA markers

“…Considerable differences among apple cultivars in susceptibility to fire blight have been reported, and heritability estimates for field resistance have been determined (Hampson and Sholberg 2008). Major QTLs for fire blight resistance have been found on linkage group (LG) 3 in M. robusta 5 explaining up to 80% of the phenotypic variation (Peil et al 2007(Peil et al , 2008) and on LG 12 in the ornamental cultivar 'Evereste' (possibly a derivative of a wild Malus species) and in M. floribunda clone 821 (Durel et al 2009). Promising sources of fire blight resistance in M. fusca and M. sieversii are also being investigated at present Peil et al 2010;Baumgartner et al 2011).…”

Candidate gene prediction via quantitative trait locus analysis of fruit shape index traits in apple

“…With the development of apple linkage maps, many QTLs have been identified and associated with a wide range of quantitative traits, including disease and pest resistance (Gardiner et al 2007;Durel et al 2009;Wöhner et al 2014), growth and tree habit (Kenis et al 2008;Stoeckli et al 2008), and especially fruit quality (Dunemann et al 2009;Sarah et al 2014;Kunihisa et al 2014). Apple fruit shape, including height, diameter, and FSI, is of strong interest in QTL mapping analysis, but there are few reports on QTLs for FSI in apple.…”