Inheritance of Resistance to Two-spotted Spider Mite and Glandular Leaf Trichomes in Wild Tomato Lycopersicon pimpinellifolium (Jusl.) Mill.

Abstract

<jats:p>Genetics of resistance to <jats:italic>Tetranychus urticae</jats:italic> Koch and of glandular trichomes of <jats:italic>Lycopersicon pimpinellifolium</jats:italic> accession TO-937 in a cross between susceptible <jats:italic>L. esculentum</jats:italic> Mill. `Moneymaker' and resistant TO-937 was studied in a greenhouse experiment. Parents, F<jats:sub>1</jats:sub>, F<jats:sub>2</jats:sub>, and two BC<jats:sub>1</jats:sub> generations, interspersed with susceptible tomato plants to avoid negative interplot interference, were artificially infested. Mite susceptibility was evaluated by a rating based on plant capacity to support mite reproduction. TO-937, BC<jats:sub>1</jats:sub> to TO-937, and F<jats:sub>1</jats:sub> were resistant, `Moneymaker' susceptible, and the F<jats:sub>2</jats:sub> and the BC<jats:sub>1</jats:sub> to `Moneymaker' segregated. Resistance was controlled by a single dominant major locus, but modulated by unknown minor loci. TO-937 presented type IV glandular trichomes, their presence governed by two dominant unlinked loci. Type IV trichome density correlated to resistance; however, a causal relationship between type IV trichomes and mite resistance could not be definitively established. The relatively simple inheritance mode will favor successful introgression of resistance into commercial tomatoes from the close relative <jats:italic>L. pimpinellifolium</jats:italic>.</jats:p>

Genetic mapping of two QTL from the wild tomato Solanum pimpinellifolium L. controlling resistance against two-spotted spider mite (Tetranychus urticae Koch)

“…However, problems related to negative interplot interference, due to the high frequency of resistant genotypes observed in that assay, hindered the precise calculation of the number of genes responsible for this trait. Later, we improved the pest resistance test by interspersing susceptible tomato plants between the tested ones and results obtained indicated that pest resistance might be controlled by a single dominant major locus although it could be additionally modulated by unknown minor loci (Fernandez-Muñoz et al 2003). We have confirmed these previous results indicating that resistance to spider mite in TO-937 should be governed by a major locus, the Rtu2.2 QTL located in the telomere of chromosome 2.…”

“…At this stage, 18 S. pimpinellifolium resistant parental plants, 18 F 1 Theor Appl Genet plants and the segregating plants were transplanted to soil in a plastic-house following a random distribution in which all these plants were surrounded by control susceptible plants of cv. Moneymaker as we previously described (Fernandez-Muñoz et al 2003). The transplants were placed 0.4 m apart in a row whereas distance between rows was 1 m. Plants were watered at 3-to 4-day intervals and fed with soluble fertilizer once a week.…”

“…In order to reduce individual, environmental and methodological variability, six plants of each of the F 4 and F 8 lines, surrounded by control susceptible parental plants, were evaluated. The spider mite attack evaluation followed the protocol optimized by Fernandez-Muñoz et al (2003). According to it, a previous controlled infestation was performed on plantlets in the 10-to 15-leaf stage and a second infestation was done 2 weeks later.…”

“…Inspection with a magnifying glass of the characteristic symptoms of damage, the number of mites and presence of silky webs was made on Theor Appl Genet all the leaves of four canopy heights of the tomato plants: basal (leaves 1 to 5), medium-basal (leaves 6 to 10), medium-apical (leaf 11 to 15) and apical (leaf 16 and above). On each canopy height, a spider mite attack index (SMAI) ranging from 0 to 5 was given considering 0 when no mites were found and 5 when severe leaf damage and large populations of spider mite causing intense webbing was observed (Fernandez-Muñoz et al 2003). A mean SMAI value was assigned to each plant by calculating the average of the four canopy heights SMAI values per plant.…”

“…The advantages of accession TO-937 as a source of genetic resistance, compared with those described in other wild species, are that S. pimpinellifolium is a red-fruited species and it is very closely related to the cultivated tomato, the small size of S. pimpinellifolium fruits being its only undesirable characteristic. On the other hand, first results about the inheritance of resistance to the spider mite in S. pimpinellifolium TO-937, based on the analysis of F 2 populations, indicated that a major locus modulated by minor loci controls this trait (Fernandez-Muñoz et al 2003) although spider miteresistance has been repeatedly reported as polygenic in the other three taxa (Blauth et al 1998(Blauth et al , 1999Saeidi et al 2007). In addition, recent studies have uncovered the role played by acylsucrose accumulation and type IV glandular trichome density in the resistance of TO-937 to the twospotted spider mite (Alba et al 2009).…”