Abstract
The SCAR (Sequence Characterized Amplified Region) 'Sw-421' molecular marker is located at 1.0 cM from the Sw-5 allele, originated from Lycopersicon peruvianum (L.), which confers resistance to the tomato spotted wilt virus (TSWV). However, it had not been tested yet in advanced tomato populations. The goal of this study was to distinguish resistant homozygotes (Sw-5/Sw-5) and heterozygotes (Sw-5/Sw-5+) from susceptible (Sw-5+/Sw-5+) plants in crossing populations with the Stevens cultivar and advanced backcrossing populations by using 'Sw421' SCAR marker. The amplification of 940 bp and 900 bp bands characterized the resistant homozygotes and susceptible controls, respectively. A two band pattern (900 bp and 940 bp) was observed in heterozygote genotypes (Sw-5/Sw-5+), which confirmed the co-dominant inheritance mechanism of the marker. Fifty seven plants from the isogenic progenies were characterized based on bands pattern: 18 plants (31.6%) were identified as resistant homozygotes, 8 plants (14.0%) as resistant heterozygotes and 31 plants (54.4%) were characterized as susceptible. The SCAR 'Sw-421' marker is an important tool for selection and pyramid resistance alleles, mainly when other resistance sources to the TSWV are available, such as the Rey de los Tempranos source.
Highlights
Virus-induced diseases are considered an obstacle for tomato crop with significant losses in production
Fifty seven plants from the isogenic progenies were characterized based on bands pattern: 18 plants (31.6%) were identified as resistant homozygotes, 8 plants (14.0%) as resistant heterozygotes and 31 plants (54.4%) were characterized as susceptible
The results of phenotypical evaluations confirmed the efficiency in the inoculation process and showed the differential reaction of the genotypes according to the presence or absence of the Sw-5 allele
Summary
Virus-induced diseases are considered an obstacle for tomato crop with significant losses in production. In Brazil, Tomato spotted wilt virus - TSWV, Tomato chlorotic spot virus - TCSV, Crysanthemum stem necrosis virus - CSNV - and Groundnut ringspot virus - GRSV are the most important viruses caused by Tospovirus in tomato crop (Lima et al, 2002; Ferraz et al, 2004; Lau et al, 2006). Some resistance alleles were introduced in commercial cultivars, like the Rey de los Tempranos (resistance from L. esculentum) and the Stevens (resistance from L. peruvianum) cultivars. These cultivars are the two main resistance sources used in the genetic control of the TSWV in the breeding programs in progress in Brazil (Juliatti & Maluf, 1995; Lourenção et al, 1999; Ferraz et al, 2004). Resistance in the cultivar Stevens is controlled by one gene, denominated Sw-5 with dominant allelic interaction (Stevens et al, 1992; Juliatti & Maluf, 1995), whereas for the cultivar Rey de los Tempranos resistance is controlled by at least 1 to 3 genes with semi-dominant allelic interaction (Juliatti & Maluf, 1995)
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