selfed and a homozygous resistant stock was selected from the progeny. Stevens contain L. peruvianum DNA
from TG421 to the end of the chromosome (fig 1) . The size of the introgressed area was reduced in the E6203
resistant NIL by selecting for a crossover between CT96 and CT71 during the backcrossing of Sw-5 from Stevens
into E6203 (fig 1). This homozygous resistant NIL was then crossed with E6203 to produce seed heterozygous for
the Sw-5 gene.
E6203 susceptible plants and nearly isogenic heterozygous resistant plants were transplanted into field
plots of 20 plants each at standard densities in the summer of 1996. The sites were in Akko, Israel (IS); Badajoz,
Spain (SP), Stockton, California (CAH); Woodland, California (CAP); and Numata, Japan (JP). There were 3 reps
of the heterozygous resistant NIL and 9 reps of E6203 at each site. The only exception was J P where there were
2 reps of the resistant NIL and 6 reps of E6203. Details of field condition and cultural practices can be found in
Tanksley et al. (1997a). All plots were harvested at the end of the season and evaluated for plant growth/cover,
maturity, stem scar size, fruit color (internal and external), fruit shape, fruit firmness, pericarp thickness, puffiness,
stem core depth, pH, soluble solid, yield (total, red and green), brix*yield, fruit weight and viscosity. The methods
used for these evaluations are described in Tanksley et al. (1997x). The only exception at CAH where yield was
not measured.
Analysis of variance was used to compare the performance of E6203 and the heterozygous resistant NIL
with respect to each of the measured traits. The linkage drag effects of Sw-5 are less than those reported for two
other resistance genes also introgressed from L. peruvianum, Tm2a (Tanksley et al. 1997a) and Mi (Tanksley et
al. 1997b, this issue of TGC). The lack of linkage drag around Sw-5 may be due to the fact that we used molecular
markers to reduce the size of the introgressed segment during backcrossing. Also, Sw-5 is at the end of the
chromosome where the kilo base pairs of DNA; cM ratio is reduced compared to centromeric regions where Mi
and Tm-2a are located. Thus it is possible that the segment of peruvianum DNA surrounding Sw-5 is much
smaller than those around Mi and Tm-2a. Only two traits, pericarp thickness and green yield, registered a
significant difference between the resistant NIL and E6203 (p <0.1). E6203 had a thicker pericarp (p <0.07) than
the resistant NIL and the resistant NIL had slightly greater green fruit yield than E6203 (P <0.04). However there
was no detectable difference in harvestable yield (red fruit) or brix*yield between E6203 and the resistant NIL. We
conclude that the presence of the segment on chromosome 9 containing Sw-5 and flanking peruvianum DNA has
little or no impact on agronomic traits in the heterozygous state and can be readily deployed for use in processing
tomato hybrids.
Literature cited:
Boiteux LS, Giordano L de B (1993) Genetic basis of resistance against two Tospovirus species in tomato
(Lycopersicon esculentum). Euphytica 71:151-154.
Tanksley et al. (1997a) Yield and Quality Evaluations on a Pair of Processing Tomato Lines Nearly Isogenic for
the Tm2a Gene for Resistance to the Tobacco Mosaic Virus. Euphytica (submitted)
Tanksley et al. (1997b) Comparing the effects of linkage drag in a set processing tomato lines nearly isogenic for
the Mi gene for resistance to root knot nematodes. Rept Tomato Genet Coop (this issue)
Detection of a very tight linkage between Frl and Tm-2 loci in tomato
Vakalounakis, D. J.1, Laterrot, H.2, Moretti, A.2, Ligoxigakis, E. K.1, and Smardas, K.3
1 NAGREF, Plant Protection Institute, 711 10 Heraklio, Crete, Greece
2
INRA - Avignon, Station d' Amelioration des Plantes Maraicheres, 84143 Montfavet, France
3
NAGREF, Institute of Viticulture, Floriculture and Vegetable Crops, 71110 Heraklio, Crete, Greece
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