Tomato lines resistant to the South American tomato pinworm, Tuta absoluta Meyr.
(Lepidoptera:Gelechiidae)
Gilardón E., Hernández C., Pocoví M., Collavino G., Gray L., Gorustovich M., Olsen A., Bonomo C.
and Broglia, V.
Facultad de Ciencias Naturales. Universidad Nacional de Salta. Buenos Aires 177. (4400) Salta.
Argentina. E-mail: gilardon@unsa.edu.ar
Tuta absoluta is the main pest of tomato crops in Argentina. The newborn larvae enter into the
mesophyl forming galleries that extend as long as the larvae grow. They also mine stems, flowers
and fruits. The wild accession PI 134417 (Lycopersicon hirsutum f. glabratum) is highly resistant to
the tomato pinworm (Gilardón et al, 1998). In this line larvae die in the first larval stages
(antibiosis). The introgression of the resistance began with the crossing between the cultivar Uco
Plata INTA (L. esculentum) with the line 3-5 selected from PI 134417 for its high resistance to the
tomato pinworm. Genealogical selection was made through nine generations, with special intensity
in the selection for insect resistance and fertility. Natural and artificial infestation tests were made
with first stage larvae in all the generations, and the infestation degree (GI) was assessed using a
scale from 0 to 4. (Gilardón et al, 1998). 0: no galleries; 1: small galleries less than 1 mm length; 2:
small galleries more than 1 mm length but without ramifications; 3: long galleries in a few leaves; 4:
long galleries in many leaves. The results showed that the F1 plants had an intermediate GI with
respect to the parents, and the F2 plants had a mean GI similar to the F1, with a slightly higher
variance, showing a mean additive genic effect (Pocoví et al, 1998). The fruit number per plant,
mean fruit weight, and GI heritability were estimated in the F6 populations. The genotypic
correlations between variables were also estimated (Table 1 and 2) (Gray et al, 1999).
After the selection process, the F10 lines were stable enough for assessing them in a
comparative field trial. It was conducted on Spring 2003, in the field of the Facultad de Ciencias
Naturales, Universidad Nacional de Salta, in the NW of Argentina. It was planted with a randomized
complete block design with three replications. The GI and mean fruit weight were compared by
means of ANOVA and Tukey tests (Table 3). The data were analyzed by means of the software
Infostat (Infostat, 2003).
The most resistant line was 3-5, the wild parent. Even if the breeding lines did not achieve
such low GI values, we consider that plants with GI < 2 resistant to the tomato pinworm. Plants with
GI=2 have small, narrow galleries without ramifications, which is evidence that the larvae stopped
eating. This level of resistance can be useful in a pest integrated management program, because it
allows reduction in the number of pesticide treatments and the size of the insect population
(Gilardón et al, 2002). Because of the strong genotypic correlation between the GI and the fruit
weight, during the selection process it was very difficult to break the strong linkage between both
traits. The lines with higher resistance levels had small fruit weights. The fruit quality characteristics,
like color and soluble solids contents, were similar to those from the cultivated control. The lines
described here also show a good level of resistance to the spider mite Tetranychus urticae Koch.
Actually we have a group of breeding lines with high resistance to Tuta absoluta, and good
commercial and agronomic quality.
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