A resistance gene against potato late blight originating from Solanum × michoacanum maps to potato chromosome VII

Abstract

Solanum × michoacanum (Bitter.) Rydb. is a diploid, 1 EBN (Endosperm Balance Number) nothospecies, a relative of potato originating from the area of Morelia in Michoacán State of Mexico that is believed to be a natural hybrid of S. bulbocastanum × S. pinnatisectum. Both parental species and S. michoacanum have been described as sources of resistance to Phytophthora infestans (Mont.) de Bary. The gene for resistance to potato late blight, Rpi-mch1, originating from S. michoacanum was mapped to the chromosome VII of the potato genome. It confers high level of resistance since the plants possessing it showed only small necrotic lesions or no symptoms of the P. infestans infection and we could ascribe over 80% of variance observed in the late blight resistance test of the mapping population to the effect of the closest marker. Its localization on chromosome VII may correspond to the localization of the Rpi1 gene from S. pinnatisectum. When mapping Rpi-mch1, one of the first genetic maps made of 798 Diversity Array Technology (DArT) markers of a plant species from the Solanum genus and the first map of S. michoacanum, a 1EBN potato species was constructed. Particular chromosomes were identified using 48 sequence-specific PCR markers, originating mostly from the Tomato-EXPEN 2000 linkage map (SGN), but also from other sources. Recently, the first DArT linkage map of 2 EBN species Solanum phureja has been published and it shares 197 DArT markers with map obtained in this study, 88% of which are in the concordant positions.

Fig. 1

Distributions of mean leaflet resistance to P. infestans in whole leaf tests performed with the isolate MP847 in 2009 (a) and with the isolate MP921 in 2010 (b) in the mapping population of S. michoacanum. The resistance was assessed in 1–9 scale, where 9 means the most resistant. The fitness to the normal curve: K−S Kolmogorov−Smirnov test, d – coefficient calculated for this test, p – probability, the line indicates the normal curve. Resistance levels of parental clones are marked with their names: 99-12/8 and 99-12/12

Fig. 2

Genetic linkage map of the S. michoacanum 99-12/8 chromosome VII showing the location of the late blight resistance gene marked by black rectangle. The reference PCR markers are bolded. On the left, interval genetic distances in cM are given

Fig. 3

The CAPS marker C2_At1g53670 digested with RsaI mapped 5.7 cM from the Rpi-mch1 gene. PR – resistant parent 99-12/8, PS – susceptible parent 99-12/12, R, S – progeny resistant and susceptible to P. infestans, respectively, - negative control. Arrows indicate the marker bands