During summer 2004 samples of a processing tomato variety carrying the Sw5 resistance gene to TSWV were collected from plants with suspected TSWV infection grown in open field condition in Mesagne (BR), Apulia (southern Italy). Leaf extracts from each sample were tested with lateral flow and/or ELISA (Roggero et al. 2002) for the presence of TSWV, INSV, CMV, TMV, PVY. Samples were also observed with the electron microscope and inoculated mechanically onto a set of test plants including some commercial F1 hybrids carrying the Sw5 resistance gene. Only TSWV was detected in all the samples. One of the TSWV isolates, called T992, was further investigated for its capability of overcoming the resistance provided by the presence of the Sw5 gene. It was used to mechanically inoculate 20 individual plants for each commercial tomato F1 hybrid carrying the Sw5 gene (Donald, York, Rovente, Valiente, Hermes, UGX 9233, Diaz, ISI 19343, Es 5302, Scipio, Herdon) with the appropriate control cultivar without the Sw5 gene (Cultivar Marmande). A different set of plants of the same hybrids was mechanically inoculated with strain p105, a wild type strain of TSWV previously characterized (Roggero et al., 2002). Tomato plantlets were inoculated at the 4-5 true leaf stage, and systemic infection was tested 20 days post inoculation through an ELISA specific for TSWV. All the hybrids carrying the Sw5 gene could not be infected with the wild type strain p105, with the exception of 4 plants of F1 UGX 9233, whereas the isolate T992 infected systemically every individual plant from all the F1 hybrids tested. The CV Marmande was infected systemically by both p105 and T992 isolate. This series of inoculation in controlled environment showed that strain T992 of TSWV is indeed a resistance breaking strain. Previous work analysed the population of TSWV present in Apulia region and suggested the possible presence of resistance breaking strain on tomato (Finetti-Sialer et al., 2002): we cloned and sequenced parts of the S and M genomic segments of the T992 isolate and the two sequences of the two fragments were deposited in the Genebank with the accession numbers AY848922 and AY848921 respectively. The sequences were compared to others present in the database: when using the 560 bp fragment corresponding to the Nsm region the same fragment resulted most closely related (99%) to the SAN-1 isolate (AY124966) described from the Apulia region in a precedent work (Finetti Sialer et al., 2002); when using the 780 bp N fragment it resulted more closely related (99.6% identity at the nucleotide level) to the LE98-527 strain from Bulgaria (Heinze et al., 2001). The T992 isolate is an A-like isolate according to the MaeI restriction pattern used for a classification previously suggested for TSWV Apulian isolates (Finetti-Sialer et al., 2002).
First report in Italy of a resistance-breaking strain of tomato spotted wilt virus infecting tomato cultivars carrying the Sw5 resistance gene.
CIUFFO M;M M;GALLITELLI D;TURINA;
2005
Abstract
During summer 2004 samples of a processing tomato variety carrying the Sw5 resistance gene to TSWV were collected from plants with suspected TSWV infection grown in open field condition in Mesagne (BR), Apulia (southern Italy). Leaf extracts from each sample were tested with lateral flow and/or ELISA (Roggero et al. 2002) for the presence of TSWV, INSV, CMV, TMV, PVY. Samples were also observed with the electron microscope and inoculated mechanically onto a set of test plants including some commercial F1 hybrids carrying the Sw5 resistance gene. Only TSWV was detected in all the samples. One of the TSWV isolates, called T992, was further investigated for its capability of overcoming the resistance provided by the presence of the Sw5 gene. It was used to mechanically inoculate 20 individual plants for each commercial tomato F1 hybrid carrying the Sw5 gene (Donald, York, Rovente, Valiente, Hermes, UGX 9233, Diaz, ISI 19343, Es 5302, Scipio, Herdon) with the appropriate control cultivar without the Sw5 gene (Cultivar Marmande). A different set of plants of the same hybrids was mechanically inoculated with strain p105, a wild type strain of TSWV previously characterized (Roggero et al., 2002). Tomato plantlets were inoculated at the 4-5 true leaf stage, and systemic infection was tested 20 days post inoculation through an ELISA specific for TSWV. All the hybrids carrying the Sw5 gene could not be infected with the wild type strain p105, with the exception of 4 plants of F1 UGX 9233, whereas the isolate T992 infected systemically every individual plant from all the F1 hybrids tested. The CV Marmande was infected systemically by both p105 and T992 isolate. This series of inoculation in controlled environment showed that strain T992 of TSWV is indeed a resistance breaking strain. Previous work analysed the population of TSWV present in Apulia region and suggested the possible presence of resistance breaking strain on tomato (Finetti-Sialer et al., 2002): we cloned and sequenced parts of the S and M genomic segments of the T992 isolate and the two sequences of the two fragments were deposited in the Genebank with the accession numbers AY848922 and AY848921 respectively. The sequences were compared to others present in the database: when using the 560 bp fragment corresponding to the Nsm region the same fragment resulted most closely related (99%) to the SAN-1 isolate (AY124966) described from the Apulia region in a precedent work (Finetti Sialer et al., 2002); when using the 780 bp N fragment it resulted more closely related (99.6% identity at the nucleotide level) to the LE98-527 strain from Bulgaria (Heinze et al., 2001). The T992 isolate is an A-like isolate according to the MaeI restriction pattern used for a classification previously suggested for TSWV Apulian isolates (Finetti-Sialer et al., 2002).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
