Many plant viruses affecting crops are dependent upon vectors for transmission. The behavior of these vectors in turn can be affected by the host plant's response to virus infection. This project continues investigations into the effects of virus infections on the principal vectors of two important viruses, Potato leaf roll virus (PLRV) and Barley yellow dwarf virus (BYDV-PAV), affecting potato and wheat respectively. Prior work has shown that volatile cues from infected plants affect aphid behavior with implications for plant-to-plant movement of the virus. In this project, we will address a long-term goal to develop an understanding of the role of virus-induced changes in plants in the spread of PLRV and BYDV and to apply this understanding to reduce the impact of the diseases they cause. The specific objectives are: 1. Assess behavioral responses of aphids to plants at various stages of the disease progression using three pathosystems as models (PLRV- Potato-GPA; BYDV-Wheat-BCOA). 2. Assess if PLRV infection affects virus titer, VIV production, and the resulting distribution of GPA within the plant. 3. Examine effects of VIV on among plant movement by aphids and spread of virus in both pathosystems. 4. Compare responses of viruliferous and nonviruliferous aphids to virus-infected and non-infected plants. Expected outcomes include a research community better informed about the roles of plant cues in spread of important disease causing viruses in crops. This will direct efforts to improve management of aphid-vectored viruses by manipulating their behavior through various means, including plant breeding. Vector management will remain central in efforts to limit virus impacts on key economic and staple crops in the USA and worldwide. Methods based on sound understanding of the biology of these systems are needed and can result from this project.
OBJECTIVES: Elucidate the effects of virus-induced changes in potato and wheat plants on the spread of Potato leaf roll virus (PLRV) and Barley yellow dwarf virus (BYDV) by their aphid vectors.
1. Assess behavioral responses of aphids to plants at various stages of the disease progression using two pathosystems as models (PLRV-Potato-GPA; BYDV-Wheat-BCOA).
2. Determine whether virus titer, VIV production, and the resulting distribution of aphids vary within the infected plant in the PLRV-Potato-GPA pathosystem.
3. Examine effects of VIV on among plant movement by aphids and spread of virus using two pathosystems as models (PLRV-Potato-GPA; BYDV-Wheat-BCOA).
4. Compare behavioral responses of viruliferous and nonviruliferous aphids in the two pathosystems (PLRV-Potato-GPA; BYDV-Wheat-BCOA).
Outputs anticipated are the experiments to be conducted to meet objectives 1 - 4, presentations to appropriate industry personnel and to the scientific community, identification of cues influence aphid vectors suitable for applied research aimed to limit virus spread or manage virus disease, two Ph.D. graduates trained at the interface of entomology and plant virology.
General procedures: Two pathosystems will be studied: wheat-Rhopalosiphum padi-BYDV and potato-Myzus persicae-PLRV. Wheat studies will use variety Lambert and transgenic virus-resistant lines derived from Lambert. Potato studies will use Russet Burbank. For testing, plants will be inoculated with respective viruses using viruliferous aphids. Bioassays will determine responses of aphids to infected and sham-inoculated (infested with virus-free aphids) under various conditions. When required volatiles from infected plants will be measured and quantified by trapping and analysis with gas chromatography-mass spectrometry. Virus titer in plant tissues will be determined as needed using an ELISA procedure.
Objective 1 - choice tests will determine aphid preference for infected vs virus-free plants at various stages of infection. The ages of the plants and time since infection will be varied to mimic various conditions that can occur in the field. When preferences are observed, the role of volatiles in conditioning these preferences will be assessed with chemical analysis and appropriate bioassays that isolate volatile cues from other cues.
Objective 2 - Plants from each system that are maximally different from controls in their effects on aphids will be examined for effects of infection on aphid distribution within the infected and virus-free plants. These data will be compared with virus distribution within the plant.
Objective 3 - Aphid movements and virus spread in 2-plant or multi-plant arrays of plants that include infected and healthy plants will be conducted to ascertain the importance of volatiles from infected plants in this process. This will be examined in each system by disrupting the volatile signals. In wheat, transgenic plants that do not strongly induce will be used. In potato and line with overexpression of enzymes in volatile metabolism will be used. The bioassays will include those with winged and wingless aphids and, if indicated using field mesocosms to seek confirmation of patterns obtained in the laboratory. Objective 4 - Viruliferous aphids will be compared with virus-free aphids for responses to virus-infection-induced changes in host plants.