Kishor K. Bhattarai,2
W. Freddy Tjallingii,5
Richard G. F. Visser,1,6 and
1Wageningen UR Plant Breeding, Wageningen University and Research Center, Droevendaalsesteeg 1, 6708PB Wageningen, The Netherlands; 2Department of Nematology, University of California, Riverside 92521, U.S.A.; 3Horticulture College of Northeast Agricultural University, Haerbin 150030, China; 4Laboratory of Nematology, Wageningen University, Droevendaalsesteeg 1, 6708PB Wageningen, The Netherlands; 5Laboratory of Entomology, Wageningen University, and EPG systems, Dillenburg 12, 6703CJ Wageningen, The Netherlands; 6Centre for BioSystems Genomics, The Netherlands Genomics Initiative/Netherlands Organization for Scientific Research, PO Box 98, 6700AA Wageningen, The Netherlands
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Accepted 13 December 2010.
On the short arm of tomato chromosome 6, a cluster of disease resistance (R) genes have evolved harboring the Mi-1 and Cf genes. The Mi-1 gene confers resistance to root-knot nematodes, aphids, and whiteflies. Previously, we mapped two genes, Ol-4 and Ol-6, for resistance to tomato powdery mildew in this cluster. The aim of this study was to investigate whether Ol-4 and Ol-6 are homologues of the R genes located in this cluster. We show that near-isogenic lines (NIL) harboring Ol-4 (NIL-Ol-4) and Ol-6 (NIL-Ol-6) are also resistant to nematodes and aphids. Genetically, the resistance to nematodes cosegregates with Ol-4 and Ol-6, which are further fine-mapped to the Mi-1 cluster. We provide evidence that the composition of Mi-1 homologues in NIL-Ol-4 and NIL-Ol-6 is different from other nematode-resistant tomato lines, Motelle and VFNT, harboring the Mi-1 gene. Furthermore, we demonstrate that the resistance to both nematodes and tomato powdery mildew in these two NIL is governed by linked (if not the same) Mi-1 homologues in the Mi-1 gene cluster. Finally, we discuss how Solanum crops exploit Mi-1 homologues to defend themselves against distinct pathogens.
This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2011.