Location: Soil Dynamics Research
2023 Annual Report
Objectives
The new research will initially focus on managing the cotton leaf roll dwarf virus (CLRDV), also known as “cotton blue disease.” The project will have the following objectives:
1. Identify alternative (other than cotton) plant hosts for CLRDV which may contribute to its spread within cropping systems in the US cotton belt.
2. Understand seasonal population dynamics of insect vectors responsible for the spread of CLRDV within the landscape and their interactions with disease- or insect-tolerant germplasm.
3. Identify agronomic practices and management strategies for diverse germplasm for reducing risk of virus spread, disease expression, and yield loss caused by CLRDV.
Approach
The funds will be used to study the key epidemiological factors responsible for spread of cotton leaf roll dwarf virus (CLRDV) in cotton. Research will be undertaken on crop management to investigate production practices that minimize crop susceptibility to the disease, which include cultivar selection, crop health inputs, rotation, and cover crop selection as well as establish the relationship between symptom onset, host growth stage, and losses in lint yield and quality. Key epidemiological mechanisms for both the virus and the vector will be identified. On the cotton production landscape, aphid vector host selection along with dispersal and colonization patterns will be studied. This will allow strategies to be tested for alternative and sustainable management practices. It will build on the current field knowledge and strengthen the tools necessary to mitigate yield impacts at the grower level. Laboratory, field and controlled environment experiments will be utilized to build on the current knowledge to better understand the impact that winter crop production and common management practices have on virus and vector epidemiology. In addition, germplasm response to the virus in terms of symptomology and genotypic response will be addressed in order to identify resistance to either the vector or the virus providing a GxExM approach to this research.
Progress Report
This is the final report for this project. New project currently going through research review.
In Fiscal Year (FY) 2023, collaborations continue between NSDL and Auburn University to identify management strategies to minimize risk of cotton leaf roll dwarf virus (CLRDV). This is the final year of the current ARS in-house National Program (NP) 216 project. This project was a new project that was not previously reviewed. Funding for this project was received during the middle of the previous NP 216 project cycle (2018 – 2023), but significant activities and achievements are as follows. A series of projects focused on developing a season long integrated management plan are ongoing. These strategies pertain to specific questions designed to address interactions between CLRDV and plant health, fertility requirements, herbicide injury, and other biotic stresses, while also quantifying on-farm incidence. Results from agronomic management studies show that traditionally recommended control strategies like cotton stalk destruction are ineffective at controlling CLRDV. These results also showed a significant difference in disease incidence based on mid- vs. late-season sampling periods, indicating the amount of late-season disease spread. Results from aphid management studies showed that insecticide treatments were ineffective at reducing disease incidence. Studies were conducted to identify reservoir weed hosts. An infectious clone with fluorescent dye was developed to visualize virus movement in the plant which showed how slow the virus moves within the plant and explains the long latency period. cDNA clones were developed to observe how plants respond to CLRDV infection. Protocols were developed to allow variant detection and monitoring. High throughput sequencing was conducted to identify viromes in infected cotton and aphid vectors to determine potential interactions affecting symptomology. Results from a sentinel plant and pan trapping study showed that aphids can transmit CLRDV for up to 18 weeks (April to November), even when the known vector (cotton aphid) is present at low populations. This suggests there may be other species capable of transmitting the virus. Results from a sentinel plot study showed incidence was higher in late planted cotton than early planted cotton. Results from a study monitoring titers through time along with photosynthetic parameters showed virus titers present a typical “multiple bell-shape” infection pattern and, regardless of symptom appearance, a reduction in photosynthetic parameters occur in infected plants. Funds received have been allocated to enhance research infrastructure (e.g., field and laboratory equipment) capability associated with viral disease work in cotton for NSDL and collaborators at Auburn University to facilitate future research in this area. In addition, a search was conducted, and a candidate was hired for the vacant Entomologist position in the project with an anticipated start date of August 2023.
Accomplishments
1. Aphis gossypii proven to transmit cotton leafroll dwarf virus (CLRDV). In 2017, a new variant of cotton leafroll dwarf virus (CLRDV-AL) was discovered in cotton fields and reported to be infested with aphids and whiteflies in southern Alabama. Whitefly populations were abnormally high that year, which lead to confusion by growers and consultants as to which insect was vectoring the virus. Poleroviruses have traditionally been reported to be vectored by aphids, until recently when two new poleroviruses were reported to be transmitted by whiteflies. Therefore, ARS researchers in Auburn, Alabama, in collaboration with researchers at Auburn University, designed a study to determine if aphids or whiteflies transmit CLRDV to cotton. Their results showed CLRDV-AL was transmissible by winged and wingless cotton aphids, but not by whiteflies. These findings emphasize the importance of screening insect vectors for the transmission of new plant viruses in order to correctly identify the vector(s) and provide growers and stakeholders with appropriate information to make informed management decisions.
2. Prospective alternate hosts of an emerging polerovirus in cotton landscapes in the southeastern United States. Identifying alternate hosts that can act as virus inoculum sources and vector reservoirs in the landscape is critical to understanding virus epidemics. Cotton leafroll dwarf virus (CLRDV), a serious pathogen in cotton production, is transmitted by the cotton/melon aphid, but the role of alternate hosts in CLRDV establishment is not clear. As a result, ARS researchers in Auburn, Alabama, in collaboration with researchers at the University of Georgia and Auburn University, examined fourteen common plant species in the landscape including crops, weeds, and ornamentals (hollyhock, marshmallow, country mallow, abutilon, arrowleaf sida, okra, hibiscus, squash, chickpea, evening primrose, henbit, palmer amaranth, and teaweed) that also included an experimental host to determine their potential as alternate hosts of CLRDV via aphid transmission assays. CLRDV was detected following inoculation in hibiscus, okra, N. benthamiana (the experimental host), palmer amaranth, and teaweed but not in the others. CLRDV accumulation was highest in the experimental host compared with cotton and other hosts. However, aphids feeding on CLRDV-infected teaweed, hibiscus, and okra alone were able to acquire CLRDV and back-transmit it to non-infected cotton seedlings. This study demonstrated that plant hosts in the agricultural landscape can serve as CLRDV inoculum sources and as aphid reservoirs that may contribute to reoccurring CLRDV epidemics in the southeastern US. Correctly identifying potential hosts and/or aphid reservoirs for CLRDV will be critical to developing future CLRDV control strategies.
3. Cotton leaf roll dwarf virus (CLRDV) transmissible to cotton by cotton aphids, but not cowpea and green peach aphids. In order to understand what insect species are capable of transmission and how effectively they could transmit CLRDV, different aphid species were examined across various metrics to estimate their vector/transmission capabilities. Metrics included how quickly a species can acquire the virus (acquisition access period, AAP), how quickly they transmit the virus (inoculation access period, IAP), and how long they can retain and transmit the virus (retention time). ARS researchers in Auburn, Alabama, in collorboration with researchers at Auburn University, tested these metrics on the cotton aphid, cowpea aphid, and green peach aphid with respect to CLRDV transmission. Wingless and winged morphs of the cotton aphid acquired CLRDV in 30 min and 24 h, inoculated CLRDV in 45 and 15 min, and retained CLRDV for 15 and 23 d, respectively. The other two aphid species did not acquire CLRDV from or transmit CLRDV to cotton. As a result, control strategies that concentrate virus transmission can focus on the cotton aphid as the primary CLRDV vector.
4. First report of tomato yellow leaf curl virus (TYLCV) infecting upland cotton in Alabama, USA. In previous TYLCV research, cotton is commonly used as a non-host. ARS researchers in Auburn, Alabama, in collaboration with researchers at Auburn University, screened cotton samples for TYLCV and other begomoviruses in 2018 because of high whitefly numbers observed that year, while simultaneously screening for cotton leaf roll dwarf virus (CLRDV). Results showed five out of 200 (5/200) cotton samples tested positive for TYLCV. Further confirmation of TYLCV in cotton was achieved by agroinoculating cotton seedlings with the virus. These results showed 2/18 inoculated cotton plants tested positive for TYLCV. Whitefly transmission of TYLCV to cotton was confirmed using a leaf-disc bioassay and confirmed in (9/20) cotton leaf discs. No obvious begomovirus symptoms were observed on cotton plants in the field or laboratory. Although these results show it is possible for TYLCV to infect cotton, TYLCV infection of cotton does not appear to be of economic importance. However, improving our understanding of any viruses that can infect cotton or interact with other viruses, such as CLRDV, is critical to develop future mitigation strategies.
Review Publications
Pandey, S., Bag, S., Roberts, P., Conner, K., Balkcom, K.S., Price, A.J., Jacobson, A.L., Srinivasan, R. 2022. Prospective alternate hosts of an emerging polerovirus in cotton landscapes in the southeastern United States. Viruses. 14(10):2249. https://doi.org/10.3390/v14102249.
Heilsnis, B., Mahas, J., Conner, K., Pandey, S., Clark, W., Koebernick, J., Srinivasan, R., Martin, K., Jacobson, A. 2023. Characterizing the vector competence of Aphis gossypii, Myzus persicae and Aphis craccivora (Hemiptera: Aphididae) to transmit cotton leafroll dwarf virus to cotton in the United States. Journal of Economic Entomology. 116(3):719-725. https://doi.org/10.1093/jee/toad080.
Mclaughlin, A., Heilsnis, B., Koebernick, J., Conner, K., Jacobson, A. 2023. First report of tomato yellow leaf curl virus infecting upland cotton (Gossypium hirsutum) 2 in Alabama, USA. Plant Disease. 106(11):2773-3007. https://doi.org/10.1094/PDIS-09-20-2041-PDN.
Heilsnis, B., Mclaughlin, A., Conner, K., Koebernick, J., Jacobson, A. 2023. Vector competency of aphis gossypii and bemisia tabaci to transmit cotton leafroll dwarf virus. Journal of Cotton Science. 26(1):23-30.
