Volatiles that signal the presence of flush may be important components in scent lures. Flushing shoots are essential for ACP reproduction. Signature odors might include cuticular hydrocarbons, ammonia, methanol, and carbon dioxide, all of which are emitted during leaf expansion. These compounds may synergize ACP response to terpenes emitted by foliar scent glands. Sesquiterpenes may be important signal compounds. These terpenes are prevalent in the aromas of ‘super hosts’ but most are commercially unobtainable; little is known about their effect on psyllid attraction. A better understanding of these factors could lead to the development of scent lures that are consistently effective in a variety of application situations. Better monitoring tools would especially be useful where ACP population densities are low or for tracking psyllid movement patterns. Citrus groves receiving nutritional sprays to manage HLB were compared with groves in the same areas receiving conventional fertilization treatments.In 2009–2012, HLB fruit were sorted into symptomatic and asymptomatic , while later , no distinction was made between symptomatic and asymptomatic HLB fruit. Fruit were washed and juiced using JBT extractors and finishers, then pasteurized following industry standards. Sensory tests were performed with trained and untrained panelists. In 2009–2010, differences between juice from healthy and HLBa fruit were minimal, and only perceived by trained panelists. Juice from HLBs was off-flavored, bitter, sour, with some metallic, tingling, and umami taste. These descriptors were mostly used for early season Hamlin,macetas 5 litros while the effect of HLB on Valencia juice flavor was minimal. Nutritional treatments had no consistent effects on juice flavor over the 5-year duration of the study.
Difference-from-control tests showed improvements due to nutritional treatments on Hamlin in January 2012, December 2012, and January 2013, i.e., panelists could not detect differences between juice from healthy and HLB fruit. Trained panelists found more differences between juice from healthy and HLB fruit than between juice from different nutritional treatments, except for one Hamlin nutritional juice in December 2012. Blends made with 75:25, 50:50, and 25:75 ratio of healthy and HLB Hamlin juice were also tested. Trained panelists classified the 75:25 blend with healthy juice, and 25:75 with HLB juice, confirming previous blending studies, while the flavor of the 50:50 blend varied with harvest. In conclusion, no management practice in the field was able to alleviate the effect of HLB on juice flavor. However, much of the off-flavor depended on the season and levels of sugars, acids, and other components in the juice. The Asian citrus psyllid was detected in California in October 2008 and has invaded most of the citrus grown in southern California. Huanglongbing was detected in Los Angeles County in 2012 and poses a significant threat to California’s ~$2 billion citrus industry. Establishment of ACP and HLB can cause huge economic loss and it is important to slow the spread of the HLB pathogen. At present, this can best be achieved by controlling the size and spread of psyllid population through integrated management strategies. A series of lab trials were conducted to evaluate the residual efficacy of various conventional and organic chemicals for ACP control and for selection of chemicals that were least toxic to natural enemies like Tamarixia radiata. The most persistent organic insecticide tested was Entrust + oil and to a lesser extent Trilogy. Among four pyrethroids, Danitol was most effective and persistent, while Mustang was weaker when tested with adult ACP. However, when toxicity was tested with adult Tamarixia, both the organic and conventional pesticides were not as toxic as they were to ACP adults. In a separate study, a field trial was conducted to test the efficacy of organic insecticides against ACP nymphs. Among the materials tested, Entrust + oil provided better control in comparison to two other products.
Future plans include further trials under lab and field conditions to evaluate products for ACP control that are least toxic to natural enemies.The Asian citrus psyllid vectors pathogens that cause Huanglongbing or citrus greening disease. Management of ACP is critical in all habitats including organic citrus for area-wide suppression of HLB. Mature citrus trees in Florida go through dormancy in winter producing little or no new growth required for ACP to develop and reproduce. Targeting overwintering ACP adults with sprays of broad-spectrum insecticides has been shown to provide significant reduction into growing season and opportunity for biological control and selective insecticides. This tactic is adopted area-wide in Florida and Texas and also used in California. However, organic farmers struggle with management of ACP and HLB because they cannot use synthetic insecticides. Consequently, we have initiated development of ACP control programs testing use of organic insecticides and release of Tamarixia radiata also suitable for conventional citrus and urban habitats. We evaluated dormant winter sprays of an organic insecticide, Pyganic applied in November, December, and January compared to a single spray of the synthetic pyrethroid Danitol in January against ACP in Valencia and Hamlin oranges. Pyganic was applied either alone, with horticultural mineral oil , or soybean oil at 2% volume by volume. Significant effects of Pyganic plus either oil lasted for 1–2 weeks after November and December applications. Pyganic + HMO and Danitol maintained ACP at or below 0.1 adults per tap sample for 4–5 weeks, and significant suppression lasted 2 months after the January application. Monthly applications of Pyganic with HMO appear to be a reasonable option for organic growers to suppress overwintering ACP. Organic programs evaluating promising insecticides alone or altered with oils or other surfactants are being evaluated parallel to a conventional program. Tamarixia radiata are also being released for integration in these programs. Findings and implications for ACP management will be discussed. Tolerance, or resistance, to citrus Huanglongbing will be important as a long-term solution for this disease. In a field trial conducted with over 1000 plants belonging to different genera in the sub-family Aurantioideae, we observed field tolerance in many Australian citrus relatives. To confirm these results in a controlled greenhouse setting, we have exposed 140 plants to Candidatus Liberibacter asiaticus via psyllid feeding under no-choice conditions for a period of 2 weeks.
We have maintained these seedlings under greenhouse conditions and conducted detailed analysis on the presence of the pathogen and level of tolerance observed in various plants after exposure to the pathogen. We have analyzed the samples using qPCR and droplet digital PCR to estimate the bacterial titer in accessions that were either susceptible, tolerant, or resistant in field studies. To confirm the presence or absence of the pathogen in plants with questionable qPCR results, ddPCR analysis was conducted targeting multiple genomic regions of Candidatus Liberibacter asiaticus. Since these experiments are conducted using open pollinated seeds where the pollen parent is not known, we have also conducted about 2000 pollinations using Microcitrus, Eremocitrus, pummelo, and mandarin as both seed and pollen parents. The targeted crosses were also conducted with known HLB tolerant cultivars of mandarins like Temple tangor and Fallglo mandarin. Citrus greening, also known as Huanglongbing , is a devastating disease on Citrus plants and is caused by the yet unculturable bacterial Candidatus liberibacter spp. This gram-negative bacterium is limited to vascular tissue and mainly accumulates in the symplasm of autotrophic organs. In addition, the accurate quantification of viable bacteria is necessary to assess the status of potentially-infected trees as well as to test any possible control strategies. A number of methods have been broadly described to quantify total bacteria content; which includes the detection of both live and dead bacteria as well as the different bacterial pathovars. In the present work,macetas de 30 litros an improved detection method, based on PCR is described, which employs new designed primers. Real-time PCR was also employed to test the sensitivity of the method, which was able to detect 10 copies per genome in tree-infected trees. In addition, Droplet Digital PCR was also developed to detect two copies per plant genome, which is the highest sensitivity reached in current protocols. The accuracy of the tested techniques will allow assessing the feasibility of possible controlling methods of this devastating disease. Researchers have been exploring more effective ways to control the Asian Citrus Psyllid , the only known insect vector of the phloem-limited bacterium “Candidatus Liberibacter sp.” responsible for Citrus Greening or Huanglongbing disease. Research results are reported on the use of a crowd sourcing challenge-based strategy to identify gene targets in the ACP that can function as interdiction points to control the insect using an oral uptake RNA interference strategy. This challenge was sponsored and developed by the Florida citrus industry and posted on the web through Innocentive, Inc. Interested participants were allowed to submit suggested targets with justifications for orally administered dsRNAs that would be hypothesized to induce mortality by RNAi. Of the sequences submitted, a committee of experts selected 43 for an oral uptake bio-assay performed using an artificial diet screen to identify those that induced mortality. Subsequently, a citrus phloem-limited virus vector was used to engineer citrus to produce candidate dsRNAs in the phloem. When ACP fed on these plants, there was much greater ACP mortality than was observed by artificial diet delivery, in some cases producing 100% adult ACP mortality in detached-leaf bioassays.
RNA Seq analysis shows that resulting ACP transcriptome changes were attributable to genes functionally linked to the gene targeted by RNAi. New methods are needed to control the spread of the citrus greening pathogen, Candidatus Liberibacter asiaticus , by the Asian Citrus Psyllid . This collaborative project funded by the California Citrus Research Board is focused on discovery of protein-protein interactions involved in Huanglongbing transmission. During transmission of CLas within the ACP, interactions between the vector and host regulate how the pathogen moves through the insect, replicates, and is transmitted into a plant. In this study, Protein Interaction Reporter technology has been used to characterize protein interactions between CLas and ACP. The PIR strategy was developed by the Bruce Lab and uses novel crosslinker molecules which covalently link interacting proteins. Mass spectrometric analysis of PIR cross-linked peptides provides information on the relative proximity and orientation of surface exposed lysine residues in cross-linked protein complexes. The Bruce and Cilia labs have previously successfully applied PIR technology to study interactions with an aphid-transmitted virus. Percoll density gradient centrifugation has been applied to purify enriched populations of CLas cells from infected ACP. Using this method, intact CLas cells retaining interactions with ACP tissues are recovered. Infected psyllids were homogenized in a non-denaturing buffer, and the concentrated lysate was applied to a Percoll gradient. Centrifugation resulted in two distinct bands in the Percoll gradient—these fractions were recovered, the cells were washed, and qPCR was used to quantitate the amount of CLas cells present. The PIR cross-linker was used to capture protein interactions in the enriched CLas sample, and the cross-linked peptides were subjected to mass spectrometry analysis. Given the challenges of working with this non-culturable pathogen, this Percoll method for CLas enrichment has a range of potential applications, including the use of purified CLas cells as immunogen for antibody production.Huanglongbing is the most serious recent threat to the US citrus industry. Several studies have indicated that Poncirus is resistant to HLB, but the Poncirus genes for HLB resistance are to be identified and characterized. The Ctv locus in Poncirus confers durable broad-spectrum resistance to citrus tristeza virus , a virus that is phloem-limited like CLas, has been identified and sequenced. We compared the genomic organization of the Ctv region to the corresponding regions from three susceptible citrus species and analyzed the genes, particularly the resistance genes within the locus, in an attempt to gain perspective of the to-be-identified HLB resistance gene in Poncirus. Copy number and localization of R-genes at the Ctv and ctv regions vary considerably from species to species; R-genes have been on faster paces of sequence change than surrounding genes. Dramatic structural rearrangements have occurred, resulting in an expansion of ~60 kb at the Ctv region over the ctv region. While the center of the Ctv region is packed with a rich and diverse group of retrotransposable elements , the ctv regions are free of REs. Pondering these phenomena at Ctv, it is intriguing to speculate the likely structure and evolution of the Poncirus genomic regions harboring HLB resistance genes.Huanglongbing is the most devastating disease of citrus.