Location: Emerging Pests and Pathogens Research
Project Number: 8062-22000-023-009-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2022
End Date: Jul 31, 2024
Objective:
Host resistance is the most effective and environmentally-sound method for combating nematode and viral diseases in potatoes. Our previous studies identified fifteen wild potato clones of the U.S. Potato Genebank collection that were shown to have novel resistance to Ro2 and G. pallida. It is necessary to further confirm the novel resistance of these wild potato clones and evaluate whether these clones may also offer novel resistance to potato spindle tuber viroid (PSTVd) and other pospiviroids. Use of nematophagous fungi as biological control agents or nematicidal compounds derived from fungi or wild potato species as targeted biopesticides shows great promise for environmentally sustainable solutions for controlling nematodes. Collections of entomopathogenic fungi at USDA-ARS in Ithaca contain taxa known to be effective against other cyst nematodes that will be tested for toxicity to and control of potato cyst nematodes (PCN).
Objectives for this agreement:
1) Test wild potato clones for resistance to pospiviroids;
2) Retest the same potato clones for resistance against Ro2 and G. pallida;
3) Test potential nematicidal properties of root exudates derived from candidate wild potato clones on (PCN), and
4) Test fungi with known activity against other cyst nematodes and those isolated from PCN for activity against PCN.
Approach:
1) Test wild potato clones for resistance to pospiviroids. The cooperator's lab will evaluate about twenty wild potato clones for resistance to PSTVd and tomato chlorotic dwarf viroid (TCDVd). These clones will be subjected to testing for their response to TCDVd and PSTVd after mechanical inoculation. Inoculated plants will be observed weekly and symptoms will be photographed throughout the growth season until tuber harvest (for clones that can tuberize). Tubers will be observed and photographed at harvest and 1 month after harvest following storage at room temperature, and the yield for each plant will be collected. Two tubers per plant will be randomly selected for the second season grow-out experiment. In this experiment, daughter tubers will be planted in 1-gallon pots after sprouting, and the development of potato plants will be observed for symptom development and tuber yield and quality data will be collected at harvest and 1-month after storage. Potato foliar samples will be collected weekly post-inoculation (season 1) or post-emergence (season 2) and subjected to RT-PCR testing for TCDVd and PSTVd using established protocols.
2) Retest the same wild potato clones for resistance against Ro2 and G. pallida. PCN resistance evaluation will be conducted in the ARS lab (for Ro2 evaluation) and in the cooperator's lab at University of Idaho (for G. pallida evaluation). Standard pot assay will be conducted. Once plants are established, they will be inoculated with nematode eggs and grown for 3-4 months. Each clone will have 4 replicates and Desiree (PCN susceptible), Brodie (Ro2 resistant), and Innovator (G. pallida resistant) will be included as controls. Nematode cysts will be extracted and counted to determine PCN resistance.
3) Test potential nematicidal properties of root exudates derived from candidate wild potato clones on PCN. Studies have shown that roots of some wild potato species release biologically active compounds that are toxic to nematodes. Root exudates will be collected from candidate clones and tested on their effects on PCN hatch, mobility, and infectivity using bioassays as established in ARS and Cooperator labs
4) Testing fungi with known activity against other cyst nematodes for activity against PCN. In-vitro bioassays to test parasitism and toxicity towards PCN will be performed using fungi confirmed to have high bioactivity against other cyst nematode, including those in genera Pochonia, Purpureocilliaum, and Ilyonectria as well as with novel fungi we isolate for this project from PCN cysts. Parasitism assays will measure percent colonization of PCN eggs by these fungi using microscopy, while toxicity assays will expose PCN to fermentation filtrates from these fungi to measure direct toxicity (survival) of PCN juveniles and inhibition of egg-hatch. For promising candidate isolates, we will conduct growth chamber screens using established methods but with an additional fungal treatment applied to evaluate their ability to control density and reproduction of PCN on potato plants.
