A survey of 238 golf courses in 10 states of the western United States found root-knot nematodes (Meloidogyne spp.) in 60% of the putting greens sampled. Sequence and phylogenetic analyses of 18S rRNA, D2-D3 of 28S rRNA, internal transcribed spacer-rRNA, and mitochondrial DNA gene sequences were used to identify specimens from 110 golf courses. The most common species, Meloidogyne naasi, was found in 58 golf courses distributed from Southern California to Washington in the coastal or cooler areas of those states. In the warmer regions of the Southwest, M. marylandi was recovered from 38 golf courses and M. graminis from 11 golf courses. This constitutes the first report of M. marylandi in Arizona, California, Hawaii, Nevada, and Utah, and the first report of M. graminis in Arizona, Hawaii, and Nevada. Two golf courses in Washington were infested with M. minor, the first record of this nematode in the Western Hemisphere. Columbia root-knot nematode, M. chitwoodi, was found in a single golf course in California. Polymerase chain reaction restriction fragment length polymorphism of the intergenic region between the cytochrome oxidase and 16S rRNA genes in the mitochondrial genome with restriction enzyme SspI was able to distinguish populations of M. graminis from M. marylandi, providing a fast and inexpensive method for future diagnosis of these nematodes from turf.

Field experiments were conducted at Marianna, FL in 2006 and Tifton, GA in 2006 and 2007 to compare new peanut (Arachis hypogaea) cultivars to the moderately resistant cv. Georgia Green and the highly resistant cv. AP-3 for field resistance to Tomato spotted wilt virus (TSWV), genus Tospovirus, and to determine the effects of in-furrow application of phorate insecticide and use of twin-row versus single-row patterns on incidence of spotted wilt in these cultivars. Cvs. Georgia Green, AP-3, Georgia-03L, Georgia-01R, Florida-07, McCloud, and York were evaluated in all five experiments, and Tifguard was added in experiments at Tifton. All cultivars except McCloud had lower incidence of spotted wilt than Georgia Green in all experiments. McCloud was intermediate in resistance to TSWV and had lower incidence of spotted wilt than Georgia Green in four of five experiments. Use of the twin-row pattern also reduced incidence of spotted wilt in McCloud in both years. On Georgia Green, phorate reduced incidence of spotted wilt in 2007 and twin-row pattern reduced incidence in both years. Phorate had no effect on spotted wilt in AP-3, Georgia-03L, McCloud, Georgia-01R, or Tifguard in either year. Twin-row pattern reduced either final incidence or area under the disease progress curve in all cultivars in at least 1 year of the study. All of these new cultivars should reduce the risk of losses to spotted wilt compared with Georgia Green. In highly resistant cultivars, especially AP-3, York, and Tifguard, use of phorate insecticide or twin-row pattern may not be necessary, and may not provide noticeable benefit in reduction of spotted wilt or increased yield.

In April 2006, sweet onions (Allium cepa) that were grown in Wayne County, GA displayed symptoms typical of either center rot caused by Pantoea ananatis or a foliar blight caused by Iris yellow spot virus (IYSV). After samples tested negative for IYSV by enzyme-linked immunosorbent assay and polymerase chain reaction, isolations were made from basal areas of leaves of infected plants where healthy and diseased tissues converged. All samples yielded yellow colonies on trypticase soy broth agar (TSBA) that were nonfluorescent when transferred to King's medium B. Four strains were characterized and tentatively identified as a Pantoea sp. by yellow pigmentation of colonies, oxidative and fermentative use of glucose, and lack of oxidase. However, the inability to produce indole from tryptophan, negative ice-nucleation activity, ability to reduce nitrate to nitrite, and the presence of phenylalanine deaminase were characteristics more typical of P. agglomerans than P. ananatis. Furthermore, all test strains utilized cellobiose, raffinose, lactose, gelatin, melibiose, and malonate. The identity of the bacterium was confirmed as P. agglomerans by BIOLOG (Hayward, CA). In addition, the 16S gene was amplified using universal primers (forward 5′-AGTTTGATCCTGGCTCAG-3′ and reverse 5′-TACCTTGTTACGACTTCGTCCCA-3′ (1) and sequenced. A BLAST search of the sequence against the NIH GenBank nucleotide library also confirmed the identity of the onion pathogen as P. agglomerans (97% identity) by having 8 of the top 10 bacteria providing significant alignments identified as P. agglomerans. The remaining two matches were uncultured bacteria from environmental samples. To confirm pathogenicity, two onion plants for each of the four test strains were inoculated with a turbid, aqueous bacterial suspension (~1 × 108 CFU ml-1) or sterile water in the lab (n = 8) and the field (n = 8). In addition, two plants each were inoculated with P. ananatis as a positive control and with a water blank and a nonpathogenic strain of P. agglomerans from peach (Png 86-2) as negative controls. All test strains of P. agglomerans produced severe blighting and withering of onion leaves in 4 days, while the water control and Png 86-2 were negative. Results were the same for both lab and field trials. Bacteria recovered from the plants infected with the test strains demonstrated the same characteristics of P. agglomerans as described above. Although P. agglomerans was originally reported as a pathogen of onion in South Africa (2), to the best of our knowledge, this is the first report of P. agglomerans causing a disease of onions in the United States. The long-term impact on the onion industry at this time is unknown. However, considering the close relationship of this organism with P. ananatis and the similarity of disease symptoms with those caused by center rot, there is potential that this bacterium could become established in the onion-growing area of Georgia and become part of a center rot ‘complex’. References: (1) T. De Baere et al. J. Clin. Microbiol. 42:4393, 2004. (2) M. J. Hattingh and D. F. Walters. Plant Dis. 65:615, 1981.

No abstract

Nischwitz, C, Skantar, A., Handoo, Z. A., Huit, M. N., Schmitt, M. E., and McClure, M. A. 2013. Occurrence of Meloidogyne fallax in North America, and molecular characterization of M. fallax and M. minor from U.S. golf course greens. Plant Dis. 97:1424-1430.Several species of root-knot nematodes {Meloidogyne spp.) are known to have significant presence on turfgrass in golf course greens, particularly in the western United States. Nematodes isolated from a golf course in King County, WA were identified as Meloidogyne minor based on analysis of the large ribosomal subunit (LSU 28S D2-D3 expansion segment), the internal transcribed spacers 1 and 2 (ITS rDNA), the intergenic spacer region 2 (IGS2), and the nuclear proteincoding gene Hsp90. Sequence-characterized amplified region (SCAR) primers that were originally designed to be specific for M. fallax were found to cross-react with M. minor. A population from Califomia was determined to be M. fallax based on juvenile tail morphology and analysis of the ribosomal markers and Hsp90, comprising tlie first report of this species in North America. Using trees based on Hsp90 genomic alignments, the phylogenetic relationships of these populations and known root-knot nematode species were congruent with previous trees based on ribosomal genes. Resolution of M. fallax and M. chitwoodi using Hsp90 was equivalent to species separation obtained with 28S or 18S rDNA alignments. The strengths and weaknesses of ribosomal and Hsp90 markers, and the use of SCAR polymerase chain reaction as diagnostic tools are discussed.

No abstract

Iris yellow spot virus (IYSV) was first observed in sweet onions in Georgia (USA) in 2003 in the Vidalia region. The virus had been reported in the onion‐growing regions in western USA several years before being detected in Georgia in the east. Although symptoms were observed on onions in Peru several years earlier, the presence of IYSV was not confirmed in Peru until after the virus was detected in Georgia. We characterized nine isolates of IYSV recovered from sweet onions in both Georgia (four isolates) and Peru (five isolates) by sequencing the nucleocapsid (N) gene and compared those sequences with sequences available in GenBank. Sequence divergence between IYSV isolates from Georgia and Peru was low with 1.1%, and comparisons with IYSV isolates from other regions showed divergence of up to 11.4%. Bootstrap analysis indicated with a high degree of confidence that the Georgia and Peruvian isolates fell into the same clade and were different from known isolates from western USA that fell into sister clades. The high degree of similarity between Georgia and Peruvian isolates suggests that gene flow occurred from Peru into Georgia.

Wheat mosaic virus (WMoV) (syn. High Plains virus) causes chlorotic streaks and mosaic on corn foliage, and it stunts ear development. In 2016 and 2017, plants in a sweet corn crop in northern Utah developed chlorotic streaking on leaves, and the plants remained stunted throughout the growing season but did not die after emergence. Symptoms ranged from bright yellow to nearly white streaks in stunted plants to faint chlorosis in plants that grew to normal height but only developed one ear or no ears. The symptoms resembled those caused by WMoV. Imaging using an unmanned aerial vehicle with a near-infrared camera showed that infected plants were scattered randomly across the field, a pattern often observed with seed-transmitted pathogen. All five symptomatic plants tested positive for WMoV. To confirm that no other virus was present, two samples of symptomatic plants were sent to a commercial laboratory, where they were screened for 11 viruses. They only tested positive for WMoV. In greenhouse grow-out tests, 83% of the seed germinated, and six plants developed symptoms in the first 5 weeks after emergence. The symptomatic seedlings were tested for WMoV, confirming infection. This study confirmed WMoV can be seed transmitted under field conditions.