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Field Evaluation of Tomato Hybrids Engineered with Tomato spotted wilt virus Sequences for Virus Resistance, Agronomic Performance, and Pollen-Mediated Transgene Flow

First, fifth, and eighth authors: Istituto di Virologia Vegetale, CNR, Strada delle Cacce 73, 10135 Torino, Italy; second and sixth authors: Istituto Sperimentale per l'Orticoltura, CRA, S.o.p. Montanaso L., Via Paullese 28, 20075 Montanaso Lombardo (LO), Italy; third author: Istituto Sperimentale per l'Orticoltura, CRA, S.o.p. Monsampolo, Via Salaria, 1, 63030 Monsampolo del Tronto (AP), Italy; fourth and seventh authors: Di.Va.P.R.A. Entomologia e Zoologia applicate all'Ambiente, Università di Torino, Via L. da Vinci 44, 10095 Grugliasco (TO), Italy

Tomato hybrids obtained from homozygous progeny of line 30-4, engineered for Tomato spotted wilt virus (TSWV) resistance, were tested under field conditions in two locations with their corresponding nontransgenic hybrids. No transgenic hybrid became infected, but 33 to 50% of plants of each nontransgenic hybrid became infected with a severe reduction of marketable fruit production. The transgenic hybrids conformed to the standard agronomic characteristics of the corresponding nontransgenic ones. Fruit were collected from the nontransgenic plots included in the experimental field and from border rows, and seed were used to estimate the flow of the transgene via pollen. No transgene flow was detected in the protected crops; however, in the open field experiment, 0.32% of tomato seedlings were found to contain the genetic modification. Immunity to TSWV infection in 30-4 hybrids was confirmed in laboratory conditions using mechanical inoculation and grafting. Thrips inoculation in leaf discs of line 30-4 demonstrated that TSWV replication was inhibited at the primary infection site but not in leaf discs of a commercial hybrid containing the naturally occurring resistance gene Sw-5. Due to the high economic value of tomato crops worldwide and the importance of TSWV, the engineered resistance described here is of practical value for breeding into cultivars of commercial interest, because it could be combined with naturally occurring resistance, thus greatly reducing the ability of the virus to develop resistance-breaking strains.

Additional keywords: Italy , Tospovirus .