Development of a locus-specific, co-dominant SCAR marker for assisted-selection of the Sw-5 (Tospovirus resistance) gene cluster in a wide range of tomato accessions

Abstract

The best levels of broad-spectrum Tospovirus resistance reported in tomatoes thus far are conferred by the Sw-5 locus. This locus contains at least five paralogues (denoted Sw-5a through Sw-5e), of which Sw-5b represents the actual resistance gene. Here we evaluated a panel of seven PCR primer pairs matching different sequences within a genomic region spanning the Sw-5a and Sw-5b gene cluster. Primer efficiency evaluation was done employing tomato isolines with and without the Sw-5 locus. One primer pair produced a single and co-dominant polymorphism between susceptible and resistant isolines. Sequence analysis of these amplicons indicated that they were specific for the Sw-5 locus and their differences were due to insertions/deletions. The polymorphic SCAR amplicon encompass a conserved sequence of the promoter region of the functional Sw-5b gene, being located in the position -31 from its open reading frame. This primer pair was also evaluated in field assays and with a collection of accessions known to be either susceptible or resistant to tospoviruses. An almost complete correlation was found between resistance under greenhouse/field conditions and the presence of the marker. Therefore, this primer pair is a very useful tool in marker-assisted selection systems in a large range of tomato accessions.

The Tomato spotted wilt virus cell‐to‐cell movement protein (NSM) triggers a hypersensitive response in Sw‐5‐containing resistant tomato lines and in Nicotiana benthamiana transformed with the functional Sw‐5b resistance gene copy

“…After seven generations of backcross breeding (using ‘Santa Clara’ as a recurrent parent), a Tospovirus ‐resistant near‐isogenic line was selected from a segregating F 8 population. This inbred line (named ‘CNPH LAM 147’) was phenotypically very similar to ‘Santa Clara’, differing, however, in its resistance response to Tospovirus , because of the presence of the genomic segment encompassing the locus with the Sw ‐5 gene cluster (Dianese et al ., ). Progeny tests were carried out with ‘Santa Clara’ and ‘CNPH LAM 147’ in order to confirm the homozygous condition of both inbred lines.…”

“…Mechanical inoculation with TSWV (BR‐01 isolate) was performed in 20 plants of ‘Santa Clara’ and 20 plants of the ‘CNPH LAM 147’ line, following standard procedures (Boiteux and Giordano, ). A co‐dominant molecular marker system (Dianese et al ., ), able to discriminate between heterozygous resistant ( Sw ‐5/ sw ‐5) and homozygous resistant ( Sw ‐5/ Sw ‐5) plants, was employed in conjunction with the inoculation assays, aiming to obtain two pure and contrasting near‐isogenic lines. Total genomic DNA was extracted from asymptomatic ‘CNPH LAM 147’ and also from the mock‐inoculated ‘Santa Clara’ plants.…”

Resistance to Tospoviruses in Vegetable Crops: Epidemiological and Molecular Aspects

“…This gene cluster originates from Solanum peruvianum and has been the most widely deployed resistance source against TSWV because of its durability and the ability to provide stable resistance against tospovirus species and isolates from different geographic locations (14, 15, 47,106,127,129,130). Although the Sw-5 gene cluster was cloned and characterized in 2001, only recently have molecular markers that assist in breeding been reported (32,112).…”

Search in Solanum (section Lycopersicon) germplasm for sources of broad-spectrum resistance to four Tospovirus species

“…Molecular markers specifically targeting the Sw-5 genomic region (Dianese et al 2010) could be used for this analysis. In addition, the molecular cloning of the genetic factors associated with this broad-spectrum resistance might provide a new set of transgenic strategies to control resistance to other Tospovirus species described so far affecting tomato as well as other vegetable, ornamental, and field crops (Hassani-Mehraban et al 2005;Whitfield et al 2005).…”