Posts Tagged: citrus
This is a reminder of the complexity of huanglongbing and the bacterial infection it causes. This abstract is from the HLB Conference in Florida last fall.
4.a.5 Symptom variations and molecular markers that illustrate the HLB complexity
Yongping Duan, Marco Pitino, and Cheryl Armstrong
USHRL-ARS-USDA, Fort Pierce, FL 34945, USA
Huanglongbing (HLB) is a devastating bacterial disease of citrus worldwide due to its intracellular and systemic infection. Various HLB symptoms are observed on different species/varieties of citrus plants: from yellow shoots to blotchy mottle on the leaves, from vein yellowing/vein corky to mosaic/green islands similar to zinc deficiency on the leaves, from whitish discoloration to stunted green leaves, etc. These variations of symptoms, which result from a combination of biotic and abiotic stresses, are not only present on individual plants from a variety but also exist on individual branches of an infected plant. Our results indicated that the adaptation of the bacterial populations, such as the dynamics of ‘Candidatus Liberibacter asiaticus' (Las), plays an important role in the induction of various symptoms and that Las mutations as well as the number and recombination events of Las prophages/phages affect this phenomenon. In addition, the selection of the host plants (resistance/tolerance) for the bacterial populations is also critical for symptom expression during disease progression. Based on severity, we divided HLB symptoms into four grades. It is worth noting that the grades of HLB symptom severity show a positive correlation with our newly identified biomarkers from host plants, and that gene expression profiling of different grades of infected leaves rationalized the differentiation based on the dynamics of these biomarkers. Because of these findings, we propose new approaches that allow for rapid selection of variant citrus plants, including bud sports with greater HLB resistance/tolerance.
Non-Technical Summary: Various symptoms of citrus huanglongbing display in different species/varieties of infected citrus plants. These variations of symptoms are not only present on individual plants from a variety, but also exist on individual branches of an infected plant. We have identified some molecular markers from the citrus plants and Las pathogen that illustrate the HLB complexity. Therefore, we propose new approaches that allow for rapid selection of variant citrus plants, including bud sports with greater HLB resistance/tolerance.
Recently, an outbreak of shoot and twig dieback disease of citrus has been occurring in the main citrus growing regions of the Central Valley of California (Fig 1). The causal agents of this disease were identified as species of Colletotrichum, which are well-known pathogens of citrus and other crops causing anthracnose diseases. At this time, it is unclear how wide-spread the disease is in California citrus orchards, but surveys are being conducted to evaluate the spread of this disease in orchards.
The disease was first noticed in 2012 by several growers and nurserymen in various orchards in the Central Valley. Symptoms included leaf chlorosis, crown thinning, gumming on twigs and shoot dieback, and in severe cases, branch dieback of trees (Fig.2). The most characteristic symptoms of this disease are the gum pockets which appear on young shoots either alone or in clusters and the dieback of twigs and shoots (Fig.3). These symptoms were primarily reported from clementine, mandarin, and navel orange varieties. In order to determine the main cause of this disease, field surveys were conducted in several orchards throughout the Central Valley. Isolations from symptomatic plant samples frequently yielded Colletotrichum species.
Field observations indicate that symptoms initially appear during the early summer months and continue to express until the early fall. Trees showing dieback and gumming symptoms characteristic of this disease are usually sporadic within an orchard and generally only a few twigs or shoots are affected within a tree. Morphological and molecular phylogenetic studies allowed the identification of two distinct species of Colletotrichum (Colletotrichum karstii and Colletotrichum gloeosporioides) associated with twig and shoot dieback. Interestingly, these Colletotrichum species were also isolated from cankers in larger branches. Although C. gloeosporioides is known to cause anthracnose on citrus, a post-harvest disease causing fruit decay, it has not been reported to cause shoot dieback of citrus. C. karstii however has not been reported previously from citrus in California and our laboratory is currently conducting field and green house studies to determine the pathogenicity of this species in citrus.
At present, it is unclear how widespread this disease is in California orchards or how many citrus varieties are susceptible to this disease. Pest control advisors are advised to remain alert and monitor citrus trees for the presence of the disease in the Central Valley (particularly clementine, mandarin, and navel varieties) during the early summer months. Continuing research lead by Dr. Akif Eskalen (UC Riverside) in collaboration with Dr. Florent Trouillas (Kearney Agricultural Research and Extension Center), Dr. Greg Douhan (UCCE Farm Advisor Tulare County), and Craig Kallsen (UCCE Farm Advisor in Kern County) is focused on further understanding the biology of the fungal pathogens as well as factors influencing disease expression in order to develop management strategies against this emerging disease.
Shoot dieback symptoms on Clementine
Branch dieback symptoms on Clementine
Gumming symptoms on Clementine
(photos: A. Eskalen)
Funding of the Citrus Research Board is an investment in pertinent research that supports the industry, making the information accessible to all within the industry from pest control advisors to packing houses to farm managers and others within the industry. The goal is to get the research done and then make sure it is used. CRB represents both large and small growers throughout California.
CRB research programs are funded by grower assessments which attract both federal and state funding, funding which represents a third of the total budget. This funding is used to support such projects as, HLB-resistant citrus rootstocks; the development of effective, low-cost HLB early detection technologies to rapidly remove infected trees; improved biocontrol methods for specific insect control like Asian citrus psyllid, as well as others; pre-and post-harvest citrus research to maintain export markets, amongst many other research programs.
The Citrus Research Board also supports the Citrus Clonal Protection Program (CCPP) with the goal of insuring the safe introduction of citrus varieties, disease diagnosis and pathogen elimination of introduced varieties and the maintenance and distribution of introduced varieties. CCPP serves as the primary source of clean, disease-free budwood and new varieties from Florida. This work is a collaboration between the Citrus Nursery Board, the University of California and State and Federal Regulatory agencies. The CCCP has become a major hub of the National Clean Plant Network for Citrus, resulting in the collaboration with 10 citrus centers in nine states and territories with multimillion dollar funding in support of CCCP's operations.
CRB research supports the California Citrus Quality Council (CCQC) with the primary objective of ensuring that California citrus meets domestic and international phytosanitary, food safety, food additive and pesticide residue regulations. CCQC ensures that California citrus growers have access to export markets for their fresh citrus fruit. Exports represent a third of the California citrus grower profits.
CRB-funded research into the California citrus-breeding program has led to the development of the Tango mandarin, along with others. The core breeding program conducts yield trials throughout the state on all varietal types to give growers information on upcoming new varieties and rootstocks. There is ongoing work to incorporate molecular tools to expedite breeding efforts to find plant materials resistant to HLB.
Along with CRB funding for cutting-edge projects for pest and disease control strategies, the CRB-funded CORE IPM Program led by Beth Grafton-Cardwell has responded to citrus grower needs for modifying existing spray schedule to treat Asian citrus psyllid. The program evaluates rotational sprays at appropriate times to avoid pesticide resistance to ACP.
Finally, this CRB-packaged information has been extended to growers through programs, including: The California Citrus Conference, Post-Harvest Conference and Seminar, and Regional Grower Education Seminars. CRB-funded research is compiled in Citrograph Magazine, the only magazine dedicated solely to the California citrus industry.
The California Citrus Research Board (CRB) will be hosting a live Asian citrus psyllid (ACP) fogging. Demonstration will carried out by CRB Researcher, Dr. Spencer Walse.
The demonstration will involve placing ACP throughout t he citrus load in within the bins. Once the tent is sealed the fogger will be turned on (sit for 2 hr) and viles with the ACP will be relocated to show the percent mortality. Previous run of the experiment have been successful.
There will be 2 opportunities to view the demonstration:
Everyone is welcome! Hope to you there!
For more information: Sonia Rios, UCCE Famr Advicor- Riverside/San Diego County
951-683-6491 EXT 224
(Photos were taken at the live demonstration in Riverside County on 4/6/2017)
This is the abstract of a presentation that was made at the recent Huanglongbing Conference held in Orlando, FL. This and other paper abstracts will soon be available at: http://irchlb.org/files/33373ab0-7df3-4117-9.pdf
Spray application of different kaolin formulations on sweet orange plants disrupt the settling and probing behavior of Diaphorina citri
M. Miranda1, O. Zanardi1; H. Volpe1; R. Garcia1; N. Roda2, E. Prado3
1 Fundecitrus, Araraquara, Brazil, 2 Tessenderlo Kerley, Inc./NovaSource, Phoenix, USA, 3 Universidade Federal de Lavras, Lavras, Brazil.
Abstract: The psyllid Diaphorina citri is the vector of the bacteria associated with huanglongbing (HLB), which is the most destructive citrus disease worldwide. Chemical control is the primary tactic against this insect. However, alternative methods are important to achieve a more effective control in an integrated pest management programs. Thus, this research was carried out to assess the influence of different kaolin formulations on the settling and probing behavior of D. citri. In both studies, two wettable powder (WP) kaolin formulations (Tessenderlo Kerley, Inc./NovaSource) were sprayed three times at different concentrations on sweet orange plants. In the experiment to assess the settling behavior, three concentrations (3, 5 and 7% w/v) of both formulations were tested. A non-choice test was performed, where 16 adult psyllids were released in a cage with seedlings of the same treatment, and the number of psyllids/plant at different time intervals was counted. For the probing trial, the electrical penetration graph (EPG) technique was used. Adult psyllids were monitored for 6 h on nursery citrus trees treated with two kaolin formulations at 3 and 5% w/v. The two kaolin formulations have a repellent effect on D. citri, causing an overall reduction of 40% of psyllids settled on treated seedlings compared with untreated control. Moreover, both formulations disrupt D. citri probing behavior, with a significant reduction (60%) in the proportion of psyllids that reach the phloem compared with untreated nursery citrus trees. In general, there were no differences between the kaolin formulations and among the concentrations tested in both experiments (settling and probing). Then, both formulations could be used in an integrated D. citri management program. These findings reinforce the recommendation of kaolin application on young citrus planting as a useful strategy for HLB management, mainly on the edge of the farms.
Photo: ACP Feeding