|Mallik, I -|
|Gudmestad, N -|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 6, 2009
Publication Date: August 1, 2009
Citation: Crosslin, J., Mallik, I., Gudmestad, N.C. 2009. First report of tomato spotted wilt virus causing potato tuber necrosis in Texas. Plant Disease. 93(8):845. Interpretive Summary: In the summer of 2008, potato tubers originating from Texas were observed to have large surface lesions and internal discolorations. The symptoms suggested that a virus might be the cause. The samples were tested for several viruses that are known to cause tuber symptoms and the only virus identified was tomato spotted wilt virus (TSWV). The sequence of the coat protein gene of the Texas potato isolate was mostly closely related to an isolate found on Eastern black nightshade in Colorado. TSWV has been reported on potatoes in North Carolina and in other parts of the world including Australia, where it is a major problem. However, this is the first report of TSWV causing tuber symptoms on potatoes in Texas.
Technical Abstract: In the summer of 2008, potato tubers (cv FL1867, FL2053, and FL1922) from commercial fields near Dalhart, Texas were observed with distinct external erumpent rings and severe internal discolorations including blotches, spots, and dry, cork-like tissue. The presence of rings suggested the possible involvement of one or more viruses. Nucleic acid from symptomatic tuber samples received in WA (FL1867 and FL1922) tested positive for Tomato spotted wilt virus (TSWV) by RT-PCR with primers TSWV 1 and 2. Similarly, tubers (FL1867 and FL2053) received in ND tested positive for TSWV with forward (S1983) and reverse (S2767) primers of Tsompana et al. The 777 bp TSWV 1/2 and 803 bp S1983/S2767 amplicons were cloned and three clones of each were sequenced. Analysis of the consensus sequences and BLAST comparisons confirmed the WA and ND sequences were indeed TSWV in origin and were each 98-99% identical to the corresponding coat protein region of a number of TSWV isolates and most closely related to an isolate detected in Eastern black nightshade from Colorado (GenBank AY777475). The deduced amino acid sequences of the 777 bp capsid protein open reading frame differed from AY777475 at only two residues from each of the WA and ND sequences. The WA and ND derived sequences were deposited with GenBank as accessions FJ882069 and FJ882070, respectively. Eight of the symptomatic tubers tested negative for Tobacco rattle virus, Alfalfa mosaic virus, and the necrotic strains of Potato virus Y by RT-PCR. Mechanical transmission tests were conducted by grinding symptomatic tuber tissue (FL1867 or FL1922) in ten volumes of 30 mM potassium phosphate buffer, pH 8.0, containing 10 mM sodium diethyldithiocarbamate and 10 mM sodium thioglycollate and rub-inoculated onto Carborundum-dusted leaves of Samsun NN tobacco. Approximately 10 days after inoculation, chlorotic-necrotic rings were present on the inoculated leaves and circular necrotic lesions developed on upper leaves. Dark stem lesions were also present on inoculated tobacco and the upper leaves eventually (3 weeks) developed severe, spreading lesions on the upper leaves. Tissue from the symptomatic tobacco tested positive for TSWV by RT-PCR (primers TSWV 1/2) and also with a TSWV-specific Immunostick (Agdia, Inc.). TSWV has been reported on field grown potatoes in North Carolina and has been reported on potatoes in Australia and in other parts of the world. To the authors’ knowledge, this is the first report associating TSWV with tuber necrosis on potatoes in Texas.