Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2009
Publication Date: 10/1/2009
Citation: McKenzie, C.L., Shatters, Jr., R.G. 2009. First report of "Candidatus Liberibacter psyllaurous" associated with psyllid yellows of tomato in Colorado. Plant Disease 93(10):1074. Interpretive Summary: In the fall of 2002, a hydroponic tomato grower from Sunblest Farms, Fort Luptin, CO contacted USDA-ARS-USHRL regarding plant symptoms associated with potato/tomato psyllid infestations recurring with yearly migrations. Psyllid yellows symptoms in tomato initially begin as retarded growth, erectness of new growth, chlorosis, and purpling of the leaves followed by malformation and distortion of foliage, widespread chlorosis, growth at a standstill for weeks to months, stimulated flower bloom and production of numerous and small poor quality fruit. Usually plant symptoms began to appear about six weeks after the first psyllids arrived in the greenhouses and symptoms were restricted to the top half of the plant with the plants reaching about 10 feet in length. Beef steak tomatoes cv Quest samples with symptoms were shipped to us overnight. These samples were stored at 4'C for six years until recent findings suggested that a new species of bacteria, Candidatus Liberibacter psyllaurous or Candidatus Liberibacter solanacearum (these species appear to be synonymous; however, debate over species names continues and we have chosen to use the psyllaurous species name for this report) may be the causal agent of tomato psyllids yellows. We recently confirmed that the tomato samples contained Ca. Liberibacter psyllaurous. Our results indicated that Ca. L. psyllauraous isolates have been associated with tomato psyllid yellows symptoms in Colorado as far back as 2002.
Technical Abstract: In the fall of 2002, a hydroponic tomato grower from Luptin, CO sent plant samples from tomato plants exhibiting psyllid yellows to USDA-ARS-USHRL to be analyzed. DNA was isolated from the tomato samples using the Qiagen plant DNeasy kit and recommended protocols (Qiagen, Valencia, CA) and five separate primer pairs were used to amplify fragments of three distinct genetic regions within the Ca L. psyllaurous genome (16S rRNA, 16S-232S rRNA intergenic region, and the 23S rRNA sequences). Primer pairs included one pair designed specifically for C. Liberibacter 16S rRNA sequences from asiaticus, americanus and africanus species (in-house primer set named USHRL-CL1) and four primer pairs, Lp-1 through Lp-4, previously described (2). The PCR fragments were purified and sequenced (genbank IDs are as follows: USHRL-CL1, FJ871062; Lp-1, FJ871058; Lp-2, FJ871059; Lp-3, FJ871060; Lp-4, FJ871061). For each primer pair, the fragment amplified was highly similar to (98 to 100 percent identical) the associated Ca L. psyllaurous rRNA sequences. This sequence could not be amplified from asymptomatic tomato samples either provided at the time or asymptomatic tomato grown in 2008 in our research greenhouses. Interestingly, the 16S rRNA sequence was identical to two Genbank entries: EU921627 and EU921626. The EU921627 sequence was amplified from genomic DNA of B. cockerelli collected in Dalhart, TX and that of EU921626 was amplified from zebra chip symptomatic potato from Garden City, KS. Only the genomic sequences encoding the 16S rRNA was present for these two entries; however, comparison of the intergenic and 23S rRNA coding region was done to other USA and New Zealand isolates. The Colorado psyllid yellows sequence we present contained from 11 to 14 polymorphisms when compared to all Ca. L. psyllaurous sequences reported to date. Our results clearly indicate: 1) That Ca. L. psyllauraous isolates are associated with tomato psyllid yellows symptoms in Colorado as far back as 2002; and, 2) Significant sequence variation exists within the 16S/23S rRNA intergenic region and the 23S rRNA coding region to allow analysis of genetic diversity among Ca. L. psyllaurous/solanacearum isolates to be characterized.