First Report of Tomato spotted wilt virus Infection of Tomatillo in Georgia.

During the 2000 spring season, tomatillo (Physalis ixocarpa) plants showing chlorotic streaks on leaves were observed in an experimental plot of the University of Georgia's Coastal Plain Experiment Station in Tift County, GA. Leaf samples from 192 plants were collected. These included plants that had chlorotic streaks and those without obvious symptoms. Samples were tested by ELISA using a commercially available Tomato spotted wilt virus (TSWV) detection kit (Agdia Inc., Elkhart, IN). TSWV was found in 10 samples that had chlorotic streaks on leaves, and the remaining plants with no obvious symptoms were negative for TSWV. Infected plants were found in both cultivars, Verde Puebla and Toma Verde. The presence of the virus had no apparent effect on plant size or fruit appearance. TSWV infection of the ELISA-positive samples was further verified by immunocapture reverse transcription-polymerase chain reaction (IC-RT-PCR) (1). The primer pair (5'-ATGTCTAAGGTTAAGCTC-3' and 5' TTAAGCAAGTTCTGTGAG-3') represented the first and last 18 bases of the coding region of the nucleocapsid gene of TSWV, respectively, and produced approximately 800-bp PCR product (1). IC-RT-PCR gave a single DNA band of expected size and no amplification was found in the uninfected control. This is the first report of TSWV on tomatillo in Georgia. Reference: (1) R. K. Jain et al. Plant Dis. 82:900, 1998.

Natural Infestation of Onion Seed by Pantoea ananatis, Causal Agent of Center Rot.

An immunomagnetic separation and polymerase chain reaction (IMS-PCR) assay was used to detect Pantoea ananatis in naturally infested onion seeds. Using species-specific PCR primers and polyclonal antibodies, IMS-PCR consistently demonstrated detection thresholds of 101 to 103 CFU/ml. There was no significant difference between the numbers of CFU recovered from onion seed wash by IMS (after repeated rinses) and by direct plating, indicating that IMS effectively captured P. ananatis cells from heterogeneous bacterial populations. Using IMS-PCR and IMS followed by plating on nutrient agar, P. ananatis was detected in 19.7% of onion seed samples harvested from two onion fields in which center rot developed naturally in 2000. When planted in germination boxes, 53% of the seed samples that tested positive for P. ananatis produced seedlings with symptoms of center rot. There was no significant difference in germination between infested and noninfested seed samples. This is the first report of natural infestation and transmission of P. ananatis in onion seed.

Outbreak of Tomato yellow leaf curl virus (Family Geminiviridae) in Georgia.

Tomato yellow leaf curl virus (TYLCV) of the family Geminiviridae is a serious production constraint to tomato (3). In the southeastern United States the virus has been largely confined to Florida. The disease appeared in the southern most Georgia county (Decatur) in 1998, at an incidence rate of less than 1% (2). During the fall of 1999, tomato plants showing symptoms indicative of TYLCV were observed in commercial fields in Grady, Colquitt, and Lowndes counties and the experimental plots of the Coastal Plain Experiment Station in two locations in Tift County, GA. The 12-acre commercial field in Grady County had a disease incidence of 15%. In Tift County, in both experimental plots (≈5 miles apart), TYLCV incidence ranged from 15 to 20%. Bemisia argentifolii populations in southern Georgia, based on the observed high incidence of silverleaf symptoms in squash and the intensity of adult migrations during August and September, were the highest in more than 5 years. TYLCV infection was verified by polymerase chain reaction (PCR) amplification with degenerate primers (5'-GCC CAC ATY GTC TTY CCN GT-3' and 5' -GGC TTY CTR TAC ATR GG-3') specific to the DNA A component (4). A simplified and faster DNA extraction procedure was used to obtain PCR-ready templates. Leaf tissue was homogenized in 300 µl of extraction buffer (1), followed by one phenol and one chloroform/ isoamyl alcohol (24:1) extraction. The supernatant was purified using a QiaPrep MiniPrep purification kit (Qiagen, Valencia, CA) and was used in PCR amplification. The procedure yielded highly consistent PCR-quality template. The resulting ≈1.3-kb PCR product was cloned in pGEM-T vector (Promega Corp., Madison, WI) and completely sequenced. Sequence comparisons indicated 98% identity with known TYLCV isolates from Spain (GenBank Accession no. AJ223505), the Dominican Republic (GenBank Accession no. AF024715), and Israel (GenBank Accession no. X15656). Using PCR followed by restriction digestion analysis, three symptomatic plants from one field each in Colquitt and Lowndes counties were TYLCV positive. The higher incidence of TYLCV in the Georgia counties of Tift and Grady and its concurrent occurrence in Colquitt and Lowndes counties indicates its rapid spread in the southeastern United States. References:(1) I. B. Dry et al. J. Gen. Virol. 74:147, 1993. (2) M. T. Momol et al. Plant Dis. 83:487, 1999. (3) J. E. Polston et al. Plant Dis. 83:984, 1999. (4) M. R. Rojas et al. Plant Dis. 77:340, 1993.