Field Isolates of Tomato spotted wilt virus Overcoming Resistance in Pepper and Their Spread to Other Hosts in Italy

Abstract

Isolates of Tomato spotted wilt virus (TSWV) severely and systemically infecting commercial pepper cultivars with resistance introgressed from Capsicum chinense PI152225 were found in Albenga (northwestern Italy) in July 2000. Experimentally, these resistance-breaking (RB) isolates overcame the resistance in C. chinense PI152225, but they produced infection in other hosts similarly to non-RB isolates from the same area. The RB isolates were indistinguishable from TSWV by serology and electron microscopy, and they were efficiently transmitted by Frankliniella occidentalis. Such isolates were recovered on the same farm in tomato, pepper, and artichoke 2 and 12 months later, suggesting natural spread from the resistant plants and survival. The RB isolates survived in experimental mixed infections with a non-RB isolate in susceptible pepper and C. chinense, but cross-protection in pepper acted against them. Commercial TSWV-resistant pepper but not resistant tomato cultivars from different companies were susceptible to these RB isolates after mechanical inoculation. Similar isolates were not detected among TSWV samples collected from 1993 to 2000 in the area. The management of TSWV and thrips using resistant pepper cultivars is discussed.

Field isolates ofTomato spotted wilt virusovercoming resistance in capsicum in Australia

“…The strain described here is similar in several respects to the Tsw-virulent strain reported from Italy (Roggero et al 2002). Both are virulent towards the Tsw gene only and infect a wide range of Capsicum genotypes carrying this gene.…”

“…Both strains are transmitted by F. occidentalis and have caused high disease levels in capsicum crops with the Tsw gene grown in glasshouses. Although there are several reports on the ability of TSWV isolates to overcome resistance in capsicum lines following manual inoculation, the only reported instances of serious field infection of Tsw genotypes are from Italy (Roggero et al 2001(Roggero et al , 2002, Spain (Margaria et al 2004) and Australia (this work). Although Tsw-virulent isolates detected following serial manual inoculation of TSWV-resistant genotypes may compete effectively in field situations, it is also likely that some will be defective, having lost the envelope and associated glycoproteins during successive mechanical transfers, thus reducing or preventing transmission by thrips (Moury et al 1997;Sin et al 2005) All capsicum cultivars tested for resistance to TSWV were susceptible to the Tsw-virulent strain, indicating that a common source of resistance, the Tsw gene, was present in all and the cultivars' genetic background had little, if any, influence on the expression of the resistance gene.…”

“…CNPH 275) (Black et al 1991;Moury et al 1997;Boiteux and de Avila 1994;Boiteux et al 1993;Boiteux 1995). Commercially available cultivars with this resistance are now grown in several countries including Australia (Roggero et al 2002;Persley et al 2006). The most widely used resistance source in tomato is the Sw-5 gene, derived from L. peruvianum and expressed as a hypersensitive reaction (Stevens et al 1992).…”

“…The most widely used resistance source in tomato is the Sw-5 gene, derived from L. peruvianum and expressed as a hypersensitive reaction (Stevens et al 1992). Field isolates virulent towards the Tsw gene have been found in Louisiana (Hobbs et al 1994), Brazil (Boiteux and Nagata 1992), Italy (Roggero et al 2002) and Spain (Margaria et al 2004). Several workers have generated isolates able to overcome the Tsw gene and cause systemic infection following sap inoculation of resistant lines and serial passage of selected isolates (Moury et al 1997;Thomas-Carroll and Jones 2003).…”

Phylogenetic analysis of Tomato spotted wilt virus (TSWV) NSs protein demonstrates the isolated emergence of resistance-breaking strains in pepper

“…The application of pepper cultivars bearing Tsw resistance gene triggered the rapid emergence of new RB isolates few years after introducing these resistant Capsicum cultivars. First, reports on resistance breakdown by newly emerged TSWV RB strains were published from the Mediterranean pepper-producing regions, such as Italy and Spain [5][6][7]. Then the appearance of RB isolates was detected in other continents and countries, such as Australia and Hawaii [8,9].…”