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ARS Home Research Annual Report on Science Accomplishments FY 2021





- Advancing Human Nutrition Research
- Advancing Sustainable Aquaculture Production
- Advancing Sustainable Livestock Production
- Combating AMR
- Combating Citrus Greening
- Controlling Insect Pests
- Developing New Crop Varieties
- Expanding Public Access to Agricultural Information
- Improving Pasture and Rangeland Management
- Improving Rural Economies
- Monitoring and Mitigating Plant Disease
- Optimizing Agricultural Management to Mitigate Climate
- Optimizing Water Use Management
- Protecting Animal Health Disease Detection
- Protecting Human and Animal Health
- Protecting Pollinator Health
- Reducing Labor and Advancing Precision Agriculture
- Safeguarding the Food Supply

**Combating Citrus Greening Disease** DOWNLOAD TWO-PAGER PDF  **ARS combats citrus greening disease through disease detection, prevention, and mitigation research. In 2021, the California Department of Food and Agriculture (CDFA) confirmed 2,510 trees in 5 counties were infected, including the county where the ARS Citrus Germplasm Collection is located.**This is an increase in infected trees reported from the past 2 years. The Citrus Research and Field Trial(CRAFT) program is in its third year supporting citrus replant efforts across all citrus-growing regions ofFlorida. Nearly 5,000 acres of new citrus planting are part of CRAFT research projects. The following ARSadvancements in 2021 highlight ongoing citrus greening response efforts. **Biotechnology improves early detection of citrus greening bacteria.**Early detection and rapidresponse are the keys to mitigating citrus greening. Pennsylvania State University and ARS researchers inFort Pierce, Florida, have used cutting-edge CRISPR/Cas technology to develop a diagnostic test thatcould enable early diagnosis of citrus greening, orhuanglongbing (HLB). The new assay can detectthe presence of the disease's causal agent—thebacteriumCandidatusLiberibacter asiaticus (CLas)—ata sensitivity level 100 to 1,000 times greater than thecommonly used qPCR diagnostic test. The new assaycalled DETECTR, or DNA endonuclease-targetedCRISPR trans reporter, is compatible with currenttechnology and holds promise for providing a rapid andeconomical test for citrus greening in the field. **A parasitoid used to control pests transmits citrus greening.**Parasitoids are frequently used in biologicalcontrol and integrated pest management strategies allover the world. ARS researchers in Fort Pierce, Florida,demonstrated for the first time a risk posed by thesecontrol agents. Deployment of parasitoids has beenpromoted as a means of suppressing Asian citruspsyllid (ACP), a pest that transmits citrus greeningdisease , or HLB, in citrus orchards. However, whilecontrolling ACP, the parasitoidTamarixia radiatacan inadvertently vector the HLB pathogen CLas. This diminishesTamarixia radiata’sbiological controlefficiency, particularly in orchards where CLas-infected and uninfected asymptomatic citrus trees coexist.This finding presents a new and significant caution to the strategy of implementing biological control usingparasitic wasps. **Two for one: new technology detects two citrus pathogens in one test.**Citrus greening is managedin California by intensive surveys and immediate eradication. Detecting citrus greening is complicated bythe presence of citrus stubborn disease, which is caused by a different pathogen than the citrus greeningpathogen. However, trees infected with either pathogen exhibit symptoms that are similar, resulting inmisidentification and complicating citrus greening control and eradication efforts. ARS researchersin Parlier, California, developed two different PCR tests that can rapidly differentiate between the twopathogens populations. These methods provide clear quantitation of pathogens, which is critical whenthere are only low concentrations of target DNA and is critically important in regulatory programs involvingmandatory eradication. **There are more insect pests in citrus orchards in China than previously known.**Citrus is animportant commercial crop throughout the world and citrus pests severely limit production and economicreturns. Scientists in the ARS-associated laboratory in Beijing, China, conducted surveys of citrus pestsin China, which is one of the centers of origin of citrus. Collected insects from citrus orchards in Chinaunderwent DNA analysis and were grouped as either pests or beneficials. Results showed that thenumber of pests is much higher than has been documented in literature. The data generated in this studyprovide a valuable resource for research in a broad range of areas, such as citrus pest management andmonitoring programs. A swallowtail butterfly sits on top of a flower. Keres, Preston. A Swallowtail butterfly visits Goldpetal Farms in Chaptico, Md., July 17, 2021. USDA Photo. https://flic.kr/p/2mc1ouQ


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