infestans isolates, even when plants are heterozygous for this gene ( AVRDC, 1998 Black et al., 1996a, 1996b Chunwongse et al., 1998, 2002 Foolad et al., 2008 Gardner and Panthee, 2010). , is of incomplete dominant inheritance however, it confers strong resistance to a spectrum of P. infestans resistance gene Ph-3, derived from S. This gene confers resistance to the Tospovirus species TSWV, Groundnut ringspot virus, and Tomato chlorotic spot virus ( Bioteux et al., 1993 Stevens et al., 1992 van Zijl et al., 1986). accession unknown) ( Stevens, 1964 Stevens et al., 1992 van Zijl et al., 1986). peruvianum (previously Lycopersicon peruvianum Mill. The TSWV resistance gene Sw-5 was introgressed from S. infestans, were originally introgressed from wild relatives and confer high levels of pathogen resistance. Both genes, Sw-5 for resistance to TSWV and Ph-3 for resistance to P. Several resistance genes have been identified for both pathogens however, two genes have been found to be especially valuable for their broad level of resistance to each of these pathogens ( Foolad et al., 2008 Gordillo et al., 2008). Tomato spotted wilt virus (TSWV) and Phytophthora infestans (Mont.) de Bary (late blight) are responsible for substantial tomato crop losses worldwide ( Foolad et al., 2008 Fry and Goodwin, 1997 Kim and Mutschler, 2005, 2006 Mumford et al., 1996 Roselló et al., 1996). Marker-assisted selection (MAS) offers an opportunity to overcome some of the problems associated with phenotypic selection and facilitates combining multiple resistance genes. It is often further complicated by linkage drag of unacceptable characteristics tightly linked with resistance, emergence of new disease pathogens or new races of existing pathogens, and the necessity of selecting for resistance to multiple pathogens ( Yang and Francis, 2005). This is largely the result of the need for large-scale screening and the lack of available resistance genes in a cultivated genetic background. Keywords: Gene pyramiding molecular marker analysis multiple pathogen resistance recombination suppression resistance breeding SCARĪlthough cultivar development for multiple pathogen resistance in tomato ( Solanum lycopersicum L.) is a desirable goal, the process is often challenging. However, MAS was an efficient tool for selecting the desirable recombination events for these two pathogen resistance genes. Recombination was suppressed fivefold in our F 2 population to 1.11 cM between genes when compared with published maps of the same region. F 3 progeny were generated from the remaining eight F 2 recombinants, and resistance to both pathogens, or Ph-3 and Sw-5 in coupling phase, was confirmed in three of those. From 1152 F 2 plants, 11 were identified with potential recombination events between Ph-3 and Sw-5 of those, three were male sterile ( ms-10). Marker-assisted selection (MAS) using three polymerase chain reaction-based codominant markers (TG328, TG591, and SCAR421) was used in F 2 progeny with the goal of selecting for homozygous coupling-phase recombinant lines. The tomato lines NC592 ( Ph-3) and NC946 ( Sw-5) were crossed to develop an F 2 population and subsequent inbred generations. These two genes are linked (within 5 cM on several maps) in repulsion phase near the telomere of the long arm on chromosome 9. pimpinellifolium) are, respectively, TSWV and late blight resistance genes. Tomato spotted wilt virus (TSWV) and Phytophthora infestans (late blight) in tomato ( Solanum lycopersicum) have a worldwide distribution and are known to cause substantial disease damage.
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