Author Correction: New Ca. Liberibacter psyllaurous haplotype resurrected from a 49-year-old specimen of Solanum umbelliferum: a native host of the psyllid vector

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae): life history, relationship to plant diseases, and management strategies

The potato/tomato psyllid,Bactericera cockerelli(Sulc) (Hemiptera: Triozidae) has been a major pest of solanaceous crops for decades. This pest can cause damage to crop plants by direct feeding and, as has been recently discovered, by transmitting the bacterial pathogenCandidatusLiberibacter psyllaurous (a.k.a.Ca.L. solanacearum). Many studies have been conducted to determine the relationship of this pest to plant injury and to develop management strategies to alleviate the damage caused by this pest in a wide variety of solanaceous plants. Studies in the past decade have documented substantial genetic variability in this invasive species, enhanced our rapidly-evolving understanding of the interactions between the insect and the pathogen it carries, and improved our appreciation of the invasive potential of the pest. This review seeks to provide a comprehensive update toB. cockerellilife history, relationship to plant diseases, and the current state of management strategies againstB. cockerelli.

Candidatus Liberibacter psyllaurous. [Distribution map].

A new distribution map is provided for Candidatus Liberibacter psyllaurous Hansen et al. Hosts: potato (Solanum tuberosum), tomato (Solanum lycopersicum), cayenne pepper (Capsicum annuum) and other solanaceous crops. Information is given on the geographical distribution in Europe (Finland), North America (Mexico, USA, Arizona, California, Colorado, Kansas, Nebraska, Nevada, New Mexico, Texas, Wyoming), Central America and Caribbean (Guatemala, Honduras), Oceania (New Zealand). Candidatus Liberibacter psyllaurous is transmitted by the potato phyllid Bactericera cockerelli and the carrot psyllid Trioza apicalis (Hemiptera: Triozidae).

First Report of “Candidatus Liberibacter psyllaurous” (synonym “Ca. L. solanacearum”) Associated with ‘Tomato Vein-Greening’ and ‘Tomato Psyllid Yellows’ Diseases in Commercial Greenhouses in Arizona

During the winter of 2006–2007, plants in commercial tomato greenhouses (GH-1 and GH-2; total 320 acres [129.5 ha]) in Arizona were infested with the potato psyllid Bactericera cockerelli (Sulc) and more than 60% and ~20% of the plants, respectively, exhibited leaf curling, chlorosis, and shortened internodes. In addition, some plants in GH-1 developed an unusual ‘vein-greening’ phenotype. Nucleic acids were isolated from 10 symptomatic and three asymptomatic plants from each greenhouse. PCR primers designed to amplify a phytoplasma-like 16S rDNA (850 bp) yielded the expected size product from GH-1 samples, whereas samples from GH-2 and the asymptomatic samples from both greenhouses did not. Several 16S rDNA PCR products (3 of 60) when cloned and sequenced, surprisingly shared 97% homology with ‘Candidatus Liberibacter asiaticus’ (GenBank No. GQ926917). PCR primers PSY680F 5′-GTTCGGAATAACTGGGCGTA-3′ and PSY1R 5′-CCCATAAGGGCCATGAGGACT-3′, based on the resultant 16S rDNA sequences, were used to amplify a 680-bp fragment from plant DNA extracts and psyllid lysates (1). A robust PCR product (~680 bp) was obtained from 10 of 10 GH-1 plant extracts (GQ926918) and from a GH-1-derived psyllid colony (28 of 35 adults) (GQ926919) and the tomato plants on which they were reared. In contrast, no 680-bp product was obtained from GH-1 asymptomatic plants (0 of 3), GH-2 plants (0 of 10 symptomatic; 0 of 3 asymptomatic), GH-2-derived psyllid colonies (0 of 35 adults), or psyllid colony tomato plants (data not shown). At least three 680-bp amplicons for each sample type were cloned and 8 to 10 inserts were sequenced for each. BLAST analysis revealed that all 680-bp sequences shared 99 to 100% nt identity with the analogous 16SrDNA from “Ca. Liberibacter psyllaurous” (2) and synonym “Ca. L. solanacearum” (3). A second molecular marker was obtained with the 1611F and 480R primers (2) to amplify the 16SrDNA-23S-ITS (980 bp) from >3 plant extracts and psyllid lysates that tested positive for liberibacter. Clustal W alignment of the 16S-23S-ITS sequences from GH-1 original tomato plants and psyllid colony plants (GQ926920) and psyllids (GQ926921) indicated they were 100% identical to each other and BLAST analysis indicated 99 to 100% shared identity with “Ca. L. psyllaurous” (EU812558) (synonym “Ca. L. solanacearum”). Transmission electron microscopy examination of GH-1 and GH-2 psyllids revealed rod and pleomorphic-shaped bacteria (0.5 to 2.0+ μm) at the brain-salivary gland interface in psyllids from the GH-1 liberibacter-positive colony. No such bacteria were observed in GH-2 liberibacter-negative psyllids. These results support an etiological role of a new liberibacter spp. in the development of the ‘vein-greening’ symptom phenotype. In contrast, the GH-2 ‘yellows’ phenotype is reminiscent of ‘psyllid toxicity’ in tomato colonized by B. cockerelli (4). To our knowledge, this is the first report of distinct psyllid-associated diseases in greenhouse tomato in Arizona, one associated with a new ‘Ca. Liberibacter’ spp., manifest as ‘vein-greening’ disease, and the other associated with psyllid feeding, in which liberibacter is undetectable in plants and psyllids, and is manifest as the ‘tomato psyllid yellows’ disease. References: (1) D. R. Frohlich et al. Mol. Ecol. 8:1683, 1999. (2) A. K. Hansen et al. Appl. Environ. Microbiol. 74:5862, 2008. (3) L. W. Liefting et al. Plant Dis. 93:208, 2009. (4) H. J. Pack. Utah Agric. Exp. Stn. Bull. 209, 1929.

First Report of “Candidatus Liberibacter psyllaurous” Associated with Psyllid Yellows of Tomato in Colorado

Greenhouse tomato growers from Fort Lupton, CO contacted the USDA-ARS-USHRL in 2002 regarding plant symptoms resembling “psyllid yellows” associated with Bactericera cockerelli (Sulc) infestations that initially begin as retarded growth, erectness of new growth, chlorosis, and purpling of leaves followed by widespread chlorosis and production of many small, poor-quality fruit (1). Symptoms appeared ≈6 weeks after psyllids were observed and were generally restricted to the top half of the plant. Leaf cuttings from beefsteak tomatoes cv. Quest were immediately placed in RNAlater (Applied Biosystems, Austin, TX). Samples from symptomatic and asymptomatic plants were collected in September and December of 2002. At each date, leaves were sampled from multiple plants and placed in separate RNAlater bottles. September samples exhibited initial “psyllid yellows” symptoms and December samples exhibited severe symptoms. Samples remained at 4°C in RNAlater for 6 years until recent findings suggested that a new species of bacteria, named either “Candidatus Liberibacter psyllaurous” (2) or “Ca. L. solanacearum” (3), may be the causal agent of “psyllid yellows”. The Qiagen (Valencia, CA) DNeasy Plant Kit and recommended protocols were used for four separate DNA isolations from each of the four tomato samples that had previously remained unopened. Five PCR primer pairs designed to amplify three distinct genetic regions within the “Ca L. psyllaurous” rrn operon (16S rRNA, 16S-23S rRNA intergenic region, and 23S rRNA) were used and one primer pair specific to the tomato DNA (18S rRNA gene) that successfully amplified from all samples was used as a positive control. Bacterial primers included one pair designed specifically for 16S rRNA sequences of ‘Ca. L. asiaticus’, ‘americanus’, and ‘africanus’ species (USHRL-CL1) and four sets, Lp-1 through Lp-4, previously described (2) that amplify nonoverlapping regions of the 16S-23S rRNA operon. The USHRL-CL1 primers (USHRL-CL1f: 5′-CTTACCAGCCCTTGACATGTATAGGA-3′, and USHRL-CL1r: 5′-TCCCTATAAAGTACCCAACATCTAGGTAAA-3′) amplify a 195-bp fragment from bp 895 to 1,089 of the ‘Ca. Liberibacter’ sp. 16S rRNA Genbank Accession No. L22532. Only samples from severe symptomatic plants collected in December 2002 yielded amplicons that were purified and sequenced (Genbank: USHRL-CL1, FJ871062; Lp-1, FJ871058; Lp-2, FJ871059; Lp-3, FJ871060; Lp-4, FJ871061). For each bacterial primer pair, the fragment amplified was highly homologous (98 to 100% identity) to “Ca. L. psyllaurous” rRNA gene/intergenic space sequences. The 16S rRNA coding region was identical to two GenBank ‘Ca. Liberibacter’ sp. entries: EU921627 and EU921626 from B. cockerelli samples collected in Dalhart, TX and zebra chip potato samples from Garden City, KS, respectively; however, the whole 2,500 bp amplified and sequenced from our sample contained 11 to 14 polymorphisms when compared to nine “Ca. L. psyllaurous” sequences. Our results clearly indicate that “Ca. L. psyllaurous” isolates were associated with tomato “psyllid yellows” symptoms in Colorado as early as 2002 and significant sequence variation exists within the 16S/23S rRNA intergenic region and 23S rRNA coding region to allow analysis of genetic diversity among “Ca. L. psyllaurous” isolates. References: (1) L. B. Daniels. Ph.D. diss. University of Minnesota, St. Paul, 1954. (2) A. K. Hansen et al. Appl. Environ. Microbiol. 74:5862, 2008. (3) L. W. Liefting et al. Plant Dis. 93:208, 2009.