“Candidatus Liberibacter solanacearum” Titer Over Time in Bactericera cockerelli (Hemiptera: Triozidae) after Acquisition from Infected Potato and Tomato Plants Author(s): Venkatesan G. Sengoda , Jeremy L. Buchman , Donald C. Henne , Hanu R. Pappu , and Joseph E. Munyaneza Source: Journal of Economic Entomology, 106(5):1964-1972. 2013. Published By: Entomological Society of America URL: http://www.bioone.org/doi/full/10.1603/EC13129 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. ARTHROPODS IN RELATION TO PLANT DISEASE “Candidatus Liberibacter solanacearum” Titer Over Time in Bactericera cockerelli (Hemiptera: Triozidae) After Acquisition From Infected Potato and Tomato Plants VENKATESAN G. SENGODA,1 JEREMY L. BUCHMAN,1 DONALD C. HENNE,2 HANU R. PAPPU,3 1,4 AND JOSEPH E. MUNYANEZA J. Econ. Entomol. 106(5): 1964Ð1972 (2013); DOI: http://dx.doi.org/10.1603/EC13129 ABSTRACT The potato psyllid, Bactericera cockerelli (Sˇulc) (Hemiptera: Triozidae) is a serious pest of potato and other solanaceous crops. B. cockerelli has been associated with the bacterium “Candidatus Liberibacter solanacearum” (Lso), the causal agent of zebra chip, a new and economically important disease of potato in the United States, Mexico, Central America, and New Zealand. The biology of liberibacter transmission to potato and other host plants by the potato psyllid is largely unknown. The current study determined Lso acquisition by adult psyllids following different acquisition access periods (AAP) on potato and tomato, quantiÞed Lso titer over time in postacquisition psyllids, determined Lso-acquisition rate in psyllids at each AAP on each source of inoculum, and determined inßuence of host plant Lso titer on Lso acquisition rates and postacquisition titer in psyllids over time. Results showed that Lso detection rates and titer increased over time in psyllids following AAPs of 8, 24, and 72 h on tomato and potato and Lso titer was highest when psyllids acquired Lso from tomato versus potato. Lso titer ranged from 200- to 400-fold higher in tomato leaves, petioles, and stems than those of potato. The increase of Lso titer in the insects reached a plateau after an average of 15 d following 24 and 72 h AAP on potato or tomato. At this 15-d plateau, Lso titer in postacquisition psyllids was comparable with that of infective psyllids from the Lso-infected laboratory colony. Lso-acquisition rate in psyllids fed on potato and tomato increased up to 5 and 20, 15 and 35, 35 and 75, and 80 and 100%, respectively, when the insects were allowed access to plants for 4, 8, 24, and 72 h, respectively. KEY WORDS potato psyllid, Liberibacter, potato, tomato, acquisition access period The potato psyllid, Bactericera cockerelli (Sˇulc) other cultivated solanaceous crops in the Americas (Hemiptera: Triozidae), is a serious pest of potato, (Munyaneza 2012). In Europe, Lso severely affects tomato, pepper, and other solanaceous crops (Pletsch carrot crops, where it is transmitted to carrot by the 1947, Wallis 1955, Munyaneza 2013, Munyaneza and psyllids Trioza apicalis (Fo¨rster) and Bactericera trigo- Henne 2013). Historically, B. cockerelli has caused nica Hodkinson (Munyaneza et al. 2010a,b, 2012a,b; severe outbreaks of “psyllid yellows disease” in the AlfaroÐFerna´ndez et al. 2012a,b). western United States (Pletsch 1947, Wallis 1955). Little is known about the biology and mechanisms Recently, B. cockerelli has been associated with the of Lso transmission to potato and other solanaceous bacterium “Candidatus Liberibacter solanacearum” host plants by the potato psyllid (Hansen et al. 2008; (Lso). This bacterium species is the putative causal Buchman et al. 2011a,b; Munyaneza 2012). Informa- agent of zebra chip (ZC), an economically important tion is lacking on the mode of transmission (i.e., prop- disease of potato in the United States, Mexico, Central agative, circulative, persistence, etc.) of Lso by B. America, and New Zealand. Lso also severely damages cockerelli and its latency period within the insect. Development of effective management strategies for The use of trade, Þrm, or corporation names in this publication is Lso and its insect vectors will not be realized until for information and convenience of the reader. Such use does not constitute an ofÞcial endorsement or approval by the United States their interactions and transmission biology are better Department of Agriculture or the Agricultural Research Service of understood. The objectives of this research were to: 1) any product or service to the exclusion of others that may be suitable. determine Lso acquisition by adult potato psyllids USDA is an equal opportunity provider and employer. following different acquisition access periods (AAP) 1 USDAÐARS, Yakima Agricultural Research Laboratory, 5230 Kon- nowac Pass Road, Wapato, WA 98951. on potato and tomato plants, 2) quantify Lso titer over 2 Texas A&M University, Department of Entomology, Subtropical time in postacquisition potato psyllids, 3) determine Pest Management Laboratory, Weslaco, TX 78596. Lso-acquisition rate in adult potato psyllids at each 3 Department of Plant Pathology, Washington State University, Pullman, WA 99164. AAP on each source of inoculum plant, and 4) deter- 4 Corresponding author, e-mail: [email protected]. mine inßuence of Lso titer in the host plants on the October 2013 SENGODA ET AL.: POSTACQUISITION LIBERIBACTER TITER IN B. cockerelli 1965 bacterium acquisition rate in the psyllids and its post- of insects on this host plant. Thus, it was concluded acquisition titer over time. that sweet potato was not suitable as a host to Lso. However, sweet potato was later used to maintain potato psyllids following Lso-acquisition experiments Materials and Methods and monitor Lso titer in the insects over time as de- Source of Insects. Lso-free and -infected potato scribed below. psyllid colonies were established in the laboratory at Lso Acquisition Experiments. Psyllids were allowed the United States Department of AgricultureÐAgricul- to feed on the potato or tomato inoculum plants and tural Research Service (USDAÐARS) facility at acquire Lso during selected AAP. The experiments Wapato, WA, using psyllids originally collected from were conducted in a greenhouse maintained at 24Ð a commercial potato Þeld near Dalhart, TX, in 2007. 28ЊC, 50% RH, and a photoperiod of 16:8 (L:D) h. Five The colonies were maintained at 29ЊC, 50% relative Lso-infected potato and tomato plants (2 mo old) each humidity (RH), and a photoperiod of 16:8 (L:D) h on were kept in two separate small dome cages (1462W potato plants in a controlled environment room for BugDorm-2 rearing cage, white, dimension of 24 by 24 several generations. Insects from the colonies were by 24Љ, BioQuip Products, Rancho Dominguez, CA). tested monthly using conventional polymerase chain Approximately, 2,000 Lso-free psyllid adults were re- reaction (PCR) as described below to estimate Lso leased into each of two cages containing Lso-infected infection rate. Before the current study, the Lso in- potato or tomato plants. After insect release into the fection rate in the adult psyllids was 100% (a sample cages, groups of 400 psyllids were collected from each of 25 individual psyllids was tested). cage using an insect aspirator after 1, 4, 8, 24, and 72 h Sources of Plants Materials. Potato (Solanum tu- AAP and transferred to separate cages containing berosum), tomato (Solanum lycopersicum), and sweet sweet potato plants. In each AAP treatment, samples potato (Ipomea batatas) plants were used in the study. of 10 psyllids each were collected from sweet potato CertiÞed disease-free potato mini-tubers of variety plants immediately, and at 2, 4, 6, 9, 12, 15, 17, and 20 d Atlantic used in the study were obtained from CSS after transfer to sweet potato. Because it takes about Farms Inc. (Colorado City, CO). Tomato seeds (va- 3 wk for potato psyllids to complete a life cycle, insect riety Early Girl) were purchased from Ed Hume collections were not continued beyond 20 d to avoid Seeds, Inc. (Puyallup, WA). Sweet potato (variety mixing original Lso-exposed psyllids with the new White Delight) plants were established in the green- progeny emerging adults. Insects were frozen in liquid house from stem cutting. The plants were grown in the nitrogen and then stored at Ϫ40ЊC pending later test- greenhouse at the USDAÐARS Wapato facility in 1⁄2-L ing by real-time PCR to quantify Lso titer in each pots (Kord Products, Toronto, Ontario, Canada). The insect. Lso titer in the sweet potato-reared insects plant growth media consisted of a mixture of 86% sand, were compared with those of infective psyllids col- 13.4% peat moss, 0.5% Apex time release fertilizer (J. R. lected from laboratory-maintained Lso-psyllid colo- Simplot Co., Lathrop, CA), and 0.1% Micromax mi- nies. To conÞrm that psyllids from the laboratory col- cronutrients (Scotts Co., Marysville, OH). onies could transmit Lso to potato, 10 Lso-free potato Source of Lso Inoculum. To generate a source of plants were each exposed to a single potato psyllid for Lso inoculum for pathogen acquisition experiments, 24 h, after which insects were removed from the plants potato, tomato, and sweet potato plants were inocu- with an aspirator.