Abstract
Late blight of potato, caused by Phytophthora infestans, is one of the most economically important diseases worldwide, resulting in substantial yield losses when not adequately controlled by fungicides. Late blight was a contributory factor in The Great Irish Famine, and breeding for resistance to the disease began soon after. Several disease-resistant cultivars have subsequently been obtained, and amongst them Sárpo Mira is currently one of the most effective. The aim of this work was to extend the knowledge about the genetic basis of the late blight resistance in Sárpo Mira and to identify molecular markers linked to the resistance locus which would be useful for marker-assisted selection. A tetraploid mapping population from a Sárpo Mira × Maris Piper cross was phenotyped for foliar late blight resistance using detached leaflet tests. A locus with strong effect on late blight resistance was mapped at the end of chromosome XI in the vicinity of the R3 locus. Sárpo Mira’s genetic map of chromosome XI contained 11 markers. Marker 45/XI exhibited the strongest linkage to the resistance locus and accounted for between 55.8 and 67.9 % of variance in the mean resistance scores noted in the detached leaflet assays. This marker was used in molecular marker-facilitated gene pyramiding. Ten breeding lines containing a late blight resistance locus from cultivar Sárpo Mira and the Rpi-phu1 gene originating from the late blight resistant accession of Solanum phureja were obtained. These lines have extended the spectrum of late blight resistance compared with Sárpo Mira and it is expected that resistance in plants containing this gene pyramid will have enhanced durability.
Highlights
Late blight, caused by the oomycete pathogen Phytophthora infestans, is the most economically important disease in potato production worldwide and can only be controlled by frequent application of fungicides (Haverkort et al 2009)
From the 1st of January 2006 the maximum allowable application rate in The European Union was restricted to 6 kg of copper per hectare per year (Tresnik 2007) and in Germany this was reduced to 3 kg/ha (Tschöpe et al 2010).Cultivar resistance to P. infestans as a strategy for late blight control is gaining its importance (Swiezynski and Zimnoch-Guzowska 2001) due to several factors, including the growing need to produce organic potato crops without the use of copper (Tresnik 2007) and changes to legislation concerning the application of pesticides (Twining et al 2009)
Sárpo Mira was resistant to P. infestans isolates MP324, MP618 and MP650 and susceptible to isolate MP1353, while Maris Piper was susceptible to all tested isolates (Table 1)
Summary
Late blight, caused by the oomycete pathogen Phytophthora infestans, is the most economically important disease in potato production worldwide and can only be controlled by frequent application of fungicides (Haverkort et al 2009). From the 1st of January 2006 the maximum allowable application rate in The European Union was restricted to 6 kg of copper per hectare per year (Tresnik 2007) and in Germany this was reduced to 3 kg/ha (Tschöpe et al 2010).Cultivar resistance to P. infestans as a strategy for late blight control is gaining its importance (Swiezynski and Zimnoch-Guzowska 2001) due to several factors, including the growing need to produce organic potato crops without the use of copper (Tresnik 2007) and changes to legislation concerning the application of pesticides (Twining et al 2009). Whilst desirable traits like texture, tuber shape and starch content may vary over time according to consumer and industry preferences, the need to obtain potato cultivars with late blight resistance remains constant. Due to changes in virulence of P. infestans populations, and the corresponding breakdown of host resistance, breeders must continually introduce new sources of resistance
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