Report of the Tomato Genetics Cooperative Number 58

RESEARCH REPORTS TGC REPORT 58, 2008
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the time of infection of the plants, the possibility for infection of plants by different begomoviruses
(Nakhla et al., 2005) or by mixed begomoviral infections, and the variation in the field conditions
associated with each plant and block. Regardless of these factors, which are expected to cause
variation in the DSI‘s for each plant, 85% of the variation among the F3 families was explained by this
SCAR marker (Table 2). This number also includes a family, number 3, with a putative
recombination, which decreases the percentage of variation explained by the marker. These results
are consistent with the similar observation by Ji et al. (2007b), where the Ty-3 introgression was a
major contributor to resistance to Tomato yellow leaf curl virus in an F2 mapping population. Thus,
this introgression has a major effect on begomovirus-resistance, and the molecular SCAR marker
(P6-25F2/R5) can be used for predicting begomovirus-resistance in a tomato breeding program.
Table 2. Influence of different factors on the observed phenotypic variance.
Source Variance Percentage of variance
Marker
Genotype 3.18 85.1%
Block 0.05 1.2%
Interaction
Genotype*Block -0.05 -1.2%*
Error 0.55 14.9%
Since the field in Guatemala can have more than seven bipartite begomoviruses present
Nakhla et al., 2005), it is expected that the resistance locus/loci that are associated with the Ty-3
introgression may be effective in other regions of the world. This is supported by the observation that
FAVI 9, which has the Ty-3 introgression, exhibited resistance to monopartite begomoviruses in
Israel, India (Maruthi et al., 2003) and South Africa (Pietersen and Smith, 2002) and that breeding
lines with begomovirus-resistance traced to the same source of resistance as Gh13 were resistant in
Jordan, Lebanon, Egypt and Morocco (D. P. Maxwell, unpublished data). Also, this co-dominant
SCAR marker for the Ty-3 introgression will facilitate the pyramiding of begomovirus-resistance
genes from different sources (Favi, 2007).
Acknowledgements: This project was funded in part by DIGI grant no. 7-69 from San Carlos
University of Guatemala to L. Montes and A. Sánchez-Pérez, by USAID-CDR (TA-MOU-05-C25-037)
to L. Mejía, by USAID-MERC (GEG—G-00-02-00003-00) grant to D. P. Maxwell, by San Carlos
University, and by the College of Agricultural and Life Sciences, University of Wisconsin-Madison.
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