Plant Genome II Conference
Town & Country Conference Center, San Diego, CA, January, 1994.
PG-II: HIGH RESOLUTION MAPPING OF THE TOMATO (Cf-2/Cf-5) LEAF MOULD
RESISTANCE LOCUS
HIGH RESOLUTION MAPPING OF THE TOMATO (Cf-2/Cf-5) LEAF MOULD
RESISTANCE LOCUS.
M. S. Dixon, K. Hatzixanthis, D. A. Jones, J. Keddie, M. Ganal*,
S. D. Tanksley* and J. D, G. Jones, Sainsbury Laboratory, John
Innes Institute for Plant Science Research, Norwich, UK.,
*Department of Plant Breeding, Cornell University, Ithaca, NY,
USA.
The Cf-2 and Cf-5 genes that confer resistance to the leaf
mould pathogen Cladosporium fulvum were originally introgressed
from Lycopersicon pimpinellifolium and L. esculentum var.
cerasiforme respectively. Previous studies have located these
genes to a region close to the centromere of chromosome 6 and
indicate that they are allelic or very closely linked to each
other, and closely linked to Mi, a gene conferring resistance to
root-knot nematodes (M. Dickinson et al. 1993 MPMI,Vol. 6,
pp341-347 and D. A. Jones et al. pp348-357). Using overlapping
YAC clones from the Mi region and DNA from the line Ontario 7620
that carries both Cf-2 and Mi, the region that carries Cf-2 has
been more precisely defined. The YAC that carries L. esculentum
DNA in this region has been used to select cDNAs expressed in
Cf-2 and Cf-5. High resolution mapping using the flanking
markers yv (yellow virescent) and tl (thiaminless) to select for
recombinant plants has permitted adequate definition of the Cf
gene location to a region of a few tens of kilobases. A cosmid
library of the yeast strain carrying the YAC of the L. esculentum
form of this region has been constructed and a cosmid contig
covering this region of tomato has been obtained and
characterised. A binary cosmid library representing
approximately 6 genome equivalents has been constructed from
plants homozygous for the resistance genes Cf-2 and Cf-9.
Cosmids from this library are currently being isolated in
readiness for direct complementation experiments by
transformation of sensitive varieties of tomato.
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