A recombinant inbred line mapping population derived from a Lycopersicon esculentum x L.
pimpinellifolium cross
Graham, EB1,2, Frary, A3, Kang, JJ2, Jones, CM2, and Gardner, RG4
1AVRDC, PO Box 42, Shanhua, Tainan 741, Taiwan, email: graham@avrdc.org 2Department of
Vegetable Crops, UC Davis, Davis, CA 95616
3Department of Biology, Izmir Institute of Technology, Gulbahce Campus Urla Izmir, 35430 Turkey
4MHCREC, NC State University, 455 Research Drive, Fletcher, NC 28732
The availability of permanent, improved germplasm resources has greatly enhanced both
basic and applied tomato research in recent years. Recently developed introgression line libraries
for Lycopersicon pennellii (Eshed and Zamir 1994) and L. hirsutum (Monforte and Tanskley 2000),
and inbred backcross lines for L. pimpinellifolium (Doganlar et al. 2002), provide genetic tools for
mapping, quantitative trait loci (QTL) analysis, gene discovery and cloning, expression analyses,
comparative genomics and a plethora of other research activities. These populations have many
advantages (Zamir 2001) but may be limited in their range of phenotypic variation, the amount of
recombination represented in the populations, the ability to test epistatic effects, and the ability to
confirm allelic contributions to phenotypes within a species. Here we report on the development of
a set of 77 recombinant inbred lines (RILs) from L. esculentum x L. pimpinellifolium which may be
complementary to existing resources.
North Carolina L. esculentum inbred NC 23E-2(93) (Le) was crossed as the pistillate parent
to L. pimpinellifolium LA1269 (Lp) to create an F2 mapping population, which was used for QTL
analysis of resistance to late blight, Phytophthora infestans (Frary et al. 1998). LA1269, also known
in the literature as L3708, was chosen because it was described as being resistant to multiple
strains of P. infestans (Black et al. 1996). RIL lines were created by harvesting seed from individual
F2 plants and using a single seed descent breeding program for subsequent generations. All plants
were grown in the greenhouse, and were manually pollinated, as needed, to insure self pollination.
From 82 F2 plants chosen at random for advance to further generations, 77 F7 lines were obtained
for which both marker data and adequate seed for inclusion in the RIL population were collected.
Genotyping of F7 lines was done with the RFLP markers used in the F2 population. Six plants per
line in the F8 generation were grown in two replications in the field at UC Davis in 2003 for
phenotyping and bulk seed harvest.
Three morphological and 104 RFLP markers were used to genotype the F7 RILs, an average
of 9 markers per chromosome (Figure 1). Several chromosomes require additional markers to
resolve multiple linkage groups into a complete group. These areas may represent significant map
expansion which is expected for RILs. Residual heterozygosity was measured at 6.3% (34% of the
lines had significantly higher than expected heterozygosity). This value is more than the expected
1.5% for this generation, yet less than the 15% reported for a RIL population derived from a L.
esculentum x L. cheesmanii (Le/Lc) cross (Paran et al. 1995). The Le/Lp allele ratio was 1.07 and
the proportion of markers showing significantly skewed segregation was 9%. In contrast, 73% of
the markers in the Le/Lc population showed significant deviation from the expected 1:1 segregation.
Many quantitative traits are segregating in the population, including fruit color, shape and
size, maturity, inflorescence structure, carpel size and degree of reflection, plant architecture,
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