MOLECULAR CHARACTERIZATION OF RESISTANCE-BREAKING TOMATO SPOTTED WILT VIRUS (TSWV) ISOLATE MEDIUM SEGMENT IN TOMATO

Tomato spotted wilt virus (TSWV) is an economically important disease causing significant yield and quality loss in tomato. The most efficient method of disease control relied on the use of the Sw-5 resistant gene. The new resistance-breaking Tswv isolates have severely infected greenhouses grown tomatoes Eastern Mediterranean area, including Antalya, Turkey. The objective of the study was to identify the cause of the resistance-breaking genetic mutations on the virus genome. The plant materials included resistant Solanum peruvianum PI126944 and four commercial hybrids, and a susceptible control. The six resistance-breaking strains (RBS) of the virus were collected from greenhouse-grown tomato plants throughout Antalya, Turkey. Beginning at the seedling stage, five consecutive inoculations were carried out at five-day intervals, using both the resistant and susceptible genotypes. The Medium segment of the virus includes the cell-to-cell movement protein (NSm) and a precursor of the surface glycoproteins (GN/GC) that were sequenced with different primer combination. The medium segment of the RBS genomes was amplified and 4825 bp sequence aligned and blasted using NCBI database. On-structural movement (NSM) domain of the M segment consistently carried C118Y mutation in all RBS analyzed. The multiple mutations on Gc-Gn domain were not associated with resistance break down. Phylogenetic analysis indicated that RB strain identified in Turkey was closely related to Spanish RB strains. The C118Ymutation overcame the resistance conferred by the Sw-5 gene. Hence, a new resistance source is needed to protect the tomato from new RB strains.