Progress report for GW21-222
Project Information
Globodera pallida, the pale cyst nematode (PCN) is a quarantined pest of potato in Idaho. With the potential to cause up to 80% yield loss and to remain in the soil for 20 to 30 years, it poses a major threat to the Idaho potato industry. Growers with infested fields are losing profit because they can no longer plant potato until PCN is deemed fully eradicated and they undergo the extensive deregulation process. This proposal seeks to investigate the efficacy of trap crops and crop rotation as sustainable management strategies for use in eradication efforts. Trap crops must be nonhosts that stimulate PCN hatch but prevent development and reproduction. Previous research has identified litchi tomato and quinoa as crops with PCN trap crop potential. Goals of the project include evaluating the impact and feasibility of litchi tomato and quinoa on populations of PCN over time in both greenhouse and Idaho field conditions. Three-year crop rotations with this trap crops and partially resistant potato variety 'Innovator' are being assessed. Findings are being presented to agricultural stakeholders through various presentations and a published newsletter. If litchi tomato and quinoa are successful in significantly reducing PCN populations in the field, they can be recommended to growers with PCN-infested acreage. Quinoa has the added benefit of providing a valuable yield when used in rotation. Ultimately, this project would ideally establish more sustainable strategies for use in an integrated management approach to the eradication of the pale cyst nematode.
Objectives:
- Determine the effect of the quinoa variety ‘Kailey’ and litchi tomato on pale cyst nematode (PCN) populations in both greenhouse and Idaho field conditions.
- Compare the effect of quinoa to that of litchi tomato as trap crops for the pale cyst nematode through evaluating post-treatment hatching effect, viability of eggs, and reproduction on potato.
- Evaluate efficacy of three-year field rotations with resistant potato ‘Innovator’ and litchi tomato on PCN populations under Idaho field conditions.
- Present findings to potato producers and other stakeholders at the annual Idaho Potato Conference and publish a newsletter on implications of the results in eradication of the pale cyst nematode.
Hickman_WSARE updated project timeline
Funding Start: 8/1/21, Funding End: 7/31/23
*Funding will support the next 2 years of research
Research Objectives 1 & 2: Litchi Tomato vs Quinoa as Trap Crops Field Trial
| Maintain 2nd field trial | Aug – Sept 2021 |
| Terminate 2nd field trial at 12 weeks, microplots to cold room for 8 weeks minimum | Sept 2021 |
| Perform evaluations of cyst bag samples collected at 6-weeks and 12-weeks | Sept – Nov 2021 |
| Plant bioassay and grow 12 weeks |
Jan – Apr 2022 |
| Terminate bioassay, dry soil/root samples for cyst extraction | April – May 2022 |
| Extract cysts from soil/root samples, conduct evaluations of recovered cyst bags | May – Sept 2022 |
Research Objectives 1 & 2: Litchi Tomato vs Quinoa as Trap Crops Greenhouse Trial
| Terminate greenhouse trial 1 bioassay, dry soil/root samples for extraction | Oct 2021 |
| Extract cysts. Perform evaluations on recovered cyst bags | Oct – Dec 2021 |
| Plant trial 2, grow for 12 weeks | Jan – Apr 2022 |
| Terminate. Pots into the cold room for 8-week dormancy period. Perform evaluations on the 12-week cyst bag samples | Apr – Jun 2022 |
| Remove pots from cold room, plant bioassay with potato and grow 12 weeks | Jun – Oct 2022 |
| Terminate, dry soil/root samples for cyst extraction. Extract cysts. Conduct evaluations of recovered cyst bags | Oct 2022 – Jan 2023 |
Research Objective 3: Investigation of Crop Rotations for PCN Reduction Over Time
| Maintain trial 1 (year 2) and trial 2 (year 1) in field | Aug– Sept 2021 |
| Terminate trial 1 (year 2) and trial 2 (year 1). Trial 1 (year 2) microplots go to the cold room at U of I. Trial 2 (year 1) microplots go to storage facility. Minimum 8-week cold period. | Sept 2021 |
| Conduct evaluations on end of season cyst bag samples | Oct – Dec 2021 |
| Plant trial 1 (year 3) bioassay with Russet Burbank in greenhouse and grow for 12 weeks. Conduct evaluations on beginning season cyst bag samples. | Jan – May 2022 |
| Plant trial 2 (year 2) in the field for 12 weeks. Conduct evaluations for beginning season cyst bag samples. Extract cysts from trial 1 (year 3) bioassay and conduct evaluations on recovered cyst bags. | May – Sept 2022 |
| Terminate trial 2 (year 2), store microplots in cold room at U of I for 8 weeks. Conduct evaluations on end of season cyst bag samples. | Sept – Dec 2022 |
| Plant trial 2 (year 3) bioassay potato and grow for 12 weeks. Conduct evaluations on beginning season cyst bag samples. | Jan – May 2023 |
| Dry and extract cysts from trial 2 (year 3) bioassay. Conduct evaluations on recovered cyst bags. | May – Jul 2023 |
Objective 4: Outreach & Education
| Present at IAPP meeting | Nov 2021 |
| Present at Idaho Potato Conference | Jan 2022 |
| Present at IAPP meeting | Nov 2022 |
| Present at Idaho Potato Conference | Jan 2023 |
| Publish newsletter on trap crops and crop rotation for PCN eradication | Jul 2023 |
Cooperators
- - Producer
- (Researcher)
- (Researcher)
Research
Research Objectives:
- Determine the effect of the quinoa variety ‘Kailey’ and litchi tomato on pale cyst nematode (PCN) populations in both greenhouse and Idaho field conditions.
- Compare the effect of quinoa to that of litchi tomato as trap crops for the pale cyst nematode through evaluating post-treatment hatching effect, viability of eggs, and reproduction on potato.
- Evaluate efficacy of three-year field rotations with resistant potato ‘Innovator’ and litchi tomato on PCN populations under Idaho field conditions.
Objectives 1 & 2 Approach: Litchi Tomato vs Quinoa as PCN Trap Crops
Greenhouse Trials
The impact of quinoa and litchi tomato on PCN populations is being assessed in both greenhouse and field trials. In the greenhouse trials, 12 repetitions of quinoa, litchi tomato, barley, and Russet Burbank were grown in a randomized complete block design in 6-inch clay pots inoculated with PCN at a starting rate of 8 eggs per gram of soil. Barley is a known nonhost of PCN with no hatching stimulatory effect that served as a negative control. Russet Burbank is a susceptible potato that served as a positive control. Standard protocols were followed to contain PCN in which the soil was inoculated using cysts contained within 1-in2 mesh cyst bags. Soil was a 2:1 mix of sand to soil sterilized by autoclave. Russet Burbank was grown from disease-free 4-week-old tissue cultures. Barley was grown from seed. Litchi tomato and quinoa were planted as 4-week-old transplants. Plants were grown for 12 weeks while receiving standard amounts of water and fertilizer. At 12 weeks, one cyst bag per pot was sampled to determine egg counts, percent viable eggs, and percent hatch stimulated by potato root diffusate. Egg counts were conducted by breaking open a cyst and using microscopy to count all eggs still containing a juvenile nematode. In order to determine percentage of viability, eggs were stained with a fluorescent dye and later washed. Any eggs that retained the dye have a disrupted membrane and were considered no longer viable. Hatch was determined by applying potato root diffusate to a known number of eggs. Potato root diffusate contains a hatching stimulus so that after eggs were incubated over a 2-week period, percentage of hatched eggs was determined by counting the number of hatched juveniles. Plants were terminated at 12 weeks and pots were be stored in a cold room for 8 weeks to simulate a dormancy period.
After 8 weeks in the cold room, pots were planted with susceptible or resistant potato 4-week-old tissue cultures. Six repetitions were planted with Innovator, a potato variety with partial PCN resistance, and six repetitions were be planted with Russet Burbank as the susceptible variety. After 12 weeks of growth in greenhouse conditions, the experiment will be terminated. Soil and root samples will be dried to undergo extraction. An elutriator will be used to extract PCN cysts from the soil and root samples. Cysts will be counted and average egg counts per sample were calculated in order to determine the reproduction factor. Remaining cysts in the recovered cyst bags will be evaluated for egg counts, percent viable eggs, and percent hatch stimulated by potato root diffusate. The greenhouse trial is being repeated twice.
Field Trials:
The field trials are being conducted at a field site located in a PCN-infested field near Idaho Falls. Field trials were contained within microplots to avoid further infestation of field soil with PCN. Microplots consisted of two 5-gallon buckets. The upper bucket was filled with soil and contained holes at the bottom so that excess water could drain through. A lower bucket collected water and soil that drained. During field maintenance trips, the water collected in the lower buckets of the microplots was drained through a filter that collected any escaped cysts. Microplots were infested with mesh cyst bags attached to stakes at a starting infestation rate of 4.3 eggs per gram of soil in hopes of attaining a rate of 2.5 eggs per gram of soil in pre-bioassay control plots. The treatments consisted of quinoa, litchi tomato, and barley as a negative control. There were 12 replications for each treatment and setup was a randomized complete block design. The barley and quinoa were grown from seed while 4-week-old litchi tomato seedlings were transplanted. There were 6 plants per microplot and the soil surface was be covered by layers of mesh and landscape fabric to contain any escaped cysts. Microplots were embedded in the field with 3-ft spacing. Treatments were planted in May and grown for 12 weeks receiving water as needed and fertilizer biweekly. Field maintenance occurred every two weeks in which microplots were inspected and weeded, and water collected in the lower bucket was emptied through a filter. A cyst bag was sampled from each plot at 6-weeks and at 12-weeks to evaluate egg counts, percent viable eggs, and percent hatch stimulated by potato root diffusate. After 12-weeks, plants were terminated and microplots were sealed with lids and brought back to the University of Idaho to be placed in a cold room for 8 weeks to simulate a dormancy period. After 8-weeks, a bioassay with susceptible or resistant potato was planted. Six repetitions were planted with partially resistant variety Innovator while six repetitions were planted with the susceptible variety Russet Burbank. Following 12 weeks of growth in greenhouse conditions, soil and root samples were dried to undergo cyst extraction in the elutriator. Cyst counts and average egg counts were used to determine the reproduction factor. Recovered cyst bags were evaluated for egg counts, percent viable eggs, and percent hatch stimulated by potato root diffusate. This field trial is being repeated three times due to abnormally high temperatures during the second trial in June 2021 which may have impacted the cysts.
The impact of quinoa and litchi tomato are being assessed based on remaining total egg counts, percentage of remaining eggs still viable, and percentage of viable eggs that hatch in comparison to the controls before and after the bioassay with potato. PCN reproduction after treatment with quinoa or litchi tomato is also being evaluated. All data are being analyzed with a SAS analysis of variance for randomized complete block design. Means separation is being used to compare the effects of litchi tomato and quinoa on PCN populations.
Objective 3 Approach: Investigation of Crop Rotations for Reduction of PCN Over Time
The three-year crop rotations are being assessed as field trials. As with the field trials described for Objectives 1 and 2, this field trial is also taking place within microplots at the PCN-infested field site near Idaho Falls. Microplots were inoculated with cyst bags at an initial rate of 7.5 eggs per gram of soil. Sampling cyst bags were included so that there are enough for sampling at the beginning and end of each growing season. These samples were evaluated for egg counts, percent viable eggs, and percent hatch stimulated by potato root diffusate so that the impact of the rotation can be tracked over time. In addition, a 250-cc soil sample approximately 6 inches below the soil line were taken from each microplot at the end of both the first and second years to undergo PCN cyst extraction. This soil sample allowed us to detect reproduction occurring during the rotation.
The field trial was planted in May and set up in a randomized complete block design. The first year consisted of 15 repetitions of litchi tomato and 15 repetitions of the partially resistant potato variety ‘Innovator’. Litchi tomato served as a trap crop to cause PCN hatch but prevented development so it would reduce PCN populations. ‘Innovator’ is a partially resistant variety meaning it allowed some reproduction of PCN and added to the soil infestation level. Litchi tomato and ‘Innovator’ were transplanted as 4-week-old seedlings. There were 6 plants per plot. These plants grew for 12 weeks before termination. Microplots were stored in a storage unit until the following May. In year 2, each of the original groups of 15 repetitions had 5 repetitions planted as ‘Innovator’, 5 repetitions planted as litchi tomato, and 5 repetitions planted as barley. Barley once again was a nonhost that did not stimulate PCN hatch. These plants were grown in field conditions for 12 weeks. At 12 weeks, plants were terminated and microplot buckets were sealed with a lid and placed into storage for winter. Microplots were returned to the field in May for year 3 in rotation. In year 3, all repetitions were planted with the susceptible potato variety ‘Russet Burbank’. Following 12-weeks of growth, the recovered cyst bags will be analyzed for egg counts, percentage of viable eggs, and percentage of hatch with potato root diffusate. In addition, soil and root samples will be dried for PCN cyst extraction in the elutriator. Any extracted cysts will be counted and have egg counts conducted to calculate the reproduction factor after the 3-year rotation. This rotation field trial is being repeated twice.
The three-year rotations will be evaluated based on the reduction viable eggs in the recovered cyst bags over time. At the end of the rotation, the overall impact on PCN infestation level can be assessed. All data are being analyzed using analyses of variance and least squares means separation conducted in SAS. Based on these results, the rotation most effective in reducing PCN populations can be further investigated as a possible strategy for growers.
Litchi Tomato Compared to Quinoa as PCN Trap Crops
Trap crops for the pale cyst nematode (PCN) in Idaho must be nonhosts that stimulate hatch of the nematode so that it hatches but is unable to develop and reproduce. Litchi tomato is known to be a successful PCN trap crop because when followed by susceptible potato, it can cause up to 99% reduction in PCN reproduction (Dandurand & Knudsen, 2016). There is evidence that quinoa is a nonhost that causes hatch of PCN (Franco et al., 1999). However, prior to this study, quinoa had yet to be evaluated as a PCN trap crop in Idaho. In order to assess the potential of quinoa as a trap crop in Idaho field conditions and to compare its efficacy to litchi tomato, a field experiment including litchi tomato, quinoa, and the nonhost barley was set up and inoculated with PCN in microplots in the field. At the end of the growing season, a cyst bag was retrieved from each plot. Cysts were broken open in order to enumerate remaining encysted eggs, determine percent viability of these eggs, and to calculate percent hatch of remaining eggs after application of potato root exudates. As expected, the results showed barley to have the greatest number of remaining encysted eggs and highest hatch because it is a nonhost that did not stimulate hatch of the nematode (Table 1). Remaining eggs and hatch were significantly lower after quinoa, but hatch and egg count was lowest after the litchi tomato (Table 1). Compared to the control, quinoa reduced eggs by 43% while litchi tomato reduced eggs by 62%. Litchi tomato also significantly reduced viability (Table 1). There is evidence that litchi tomato has toxicity to the nematode in addition to causing hatch. Next, susceptible or resistant potato was grown in microplots to determine PCN reproduction following the nonhosts quinoa, litchi tomato, and barley. Cysts were extracted from the microplot soil. As expected, the nonhost barley which is not a PCN trap crop followed by susceptible potato had the highest PCN reproduction with an average of 868 cysts (Table 2). Reproduction on susceptible potato after planting quinoa was significantly lower than with the barley with an average of 515 cysts (Table 2). Litchi tomato followed by susceptible potato was significantly lower than the quinoa but statistically the same as barley and quinoa followed by resistant potato (Table 2). This shows the value of a resistant potato in rotation. However, litchi tomato followed by resistant potato was significantly lowest with zero PCN reproduction (Table 2). The second trial of this experiment has completed the bioassay with potato and is being extracted to determine PCN reproduction. A third trial in the field is also underway. Should results be similar to the first trial, it will reveal quinoa's potential as a PCN trap crop. Although quinoa is not as effective as litchi tomato in reducing PCN, it does reduce populations more so than a nonhost control and is even more effective if followed by a resistant potato.
Table 1. Litchi Tomato vs quinoa field trial 1 end of season cyst evaluations.
|
Field Treatment |
Average Eggs/Cyst |
Average % Hatch |
Average % Egg Viability |
|
Barley |
120.33 a |
14.34% a |
53.68% a |
|
Quinoa |
69.42 b |
9.65% b |
45.53% a |
|
Litchi Tomato |
45.52 c |
3.20% c |
24.33% b |
*Significant differences indicated by different letters beside means.
Table 2. Litchi tomato vs quinoa field trial 1 reproduction on susceptible or resistant potato.
|
Field Treatment |
Bioassay Cultivar |
Average Cysts Per Plot |
|
Barley |
Susceptible Potato |
868.25 ± 27.95 a |
|
Quinoa |
Susceptible Potato |
515.58 ± 22.04 b |
|
Litchi Tomato |
Susceptible Potato |
27.12 ± 3.56 cd |
|
Barley |
Resistant Potato |
25.22 ± 4.09 cd |
|
Quinoa |
Resistant Potato |
53.52 ± 5.50 c |
|
Litchi Tomato |
Resistant Potato |
0 d |
*Significant differences indicated by different letters beside means.
Evaluation of Crop Rotations to Reduce PCN Over Time
The impact of three-year crop rotations on potato cyst nematode is being evaluated in Idaho field conditions. In year 1, microplots were grown with either litchi tomato or resistant potato 'Innovator'. Innovator is a European variety with moderate PCN resistance that serves as a model for a resistant russet variety that may one day be developed for Idaho. Cysts were evaluated for remaining encysted eggs, egg viability, and egg hatch when potato exudates are applied at the end of the growing seasons. In the first year for both trials, we see that cysts treated with litchi tomato and resistant potato have statistically the same average remaining encysted eggs and percent egg hatch (Table 3; Table 4). However, litchi tomato significantly reduced egg viability compared to the resistant potato (Table 3; Table 4). This was expected because litchi tomato has additional toxicity to the nematode. Samples of approximately 500 cc of soil were also taken at the end of the first growing season to assess reproduction of PCN. Litchi tomato is a nonhost and as expected had no reproduction in both trials (Table 5). Innovator is not fully resistant to PCN and thus can have low reproduction, which we saw based on the soil sampling after year 1 of trial 2 where two of the plots with resistant potato each had 1 extracted cyst. Although this reproduction on resistant potato is low, it reveals that rotations with the nonhost trap crop litchi tomato may be more effective in reducing PCN populations over time.
In year 2, plots received litchi tomato, resistant potato 'Innovator', or the nonhost barley. Cysts were sampled and evaluated at the beginning of year 2 and end of year 2. Based on remaining encysted eggs in these samples, we can see that PCN is greatly reduced in all treatments because initial population reduction was so great after year 1 (Figure 1). Ultimately, we will see the impact of these rotations after year 3, in which all plots are planted with susceptible potato. Soil will be extracted to determine final reproduction of PCN. It is expected that plots that had only resistant potato will have greater reproduction than those receiving litchi tomato. Soil samples at the end of year 2 revealed low but significant reproduction in the Innovator to Innovator plots compared to the other treatments (Table 6). Trial 1 year 3 and Trial 2 year 2 are currently in the field.
Table 3. Crop rotation trial 1 end of year 1 cyst evaluations.
|
Year 1 Treatment |
Average Eggs/Cyst |
Average % Hatch |
Average % Egg Viability |
|
Litchi Tomato |
99.20 |
4.14% |
61.69% b |
|
Innovator |
102.58 |
5.48% |
88.80% a |
*Significant differences indicated by different letters beside means.
Table 4. Crop rotation trial 2 end of year 1 cyst evaluations.
|
Year 1 Treatment |
Average Eggs/Cyst |
Average % Hatch |
Average % Viability |
|
Litchi Tomato |
72.77 |
6.97% |
55.48% b |
|
Innovator |
65.81 |
4.27% |
89.56% a |
*Significant differences indicated by different letters beside means.
Table 5. Crop rotation trial 1 end of year 1 reproduction based on soil sampling.
|
Y1 Treatment |
Average Cysts |
|
Litchi Tomato |
0 |
|
Innovator |
0 |
Figure 1. Crop rotation average viable eggs in rotation over time. Average viable eggs were calculated at the beginning and end of each growing season for the first 2 years in rotation based on average egg counts and egg viability of recovered cysts.
Table 6. Crop rotation trial 1 end of year 2 reproduction based on soil sampling.
|
Y1 Treatment |
Y2 Treatment |
Average Cysts |
|
Litchi Tomato |
Barley |
0 b |
|
Litchi Tomato |
Innovator |
0 b |
|
Litchi Tomato |
Litchi Tomato |
0 b |
|
Innovator |
Barley |
0.4 b |
|
Innovator |
Innovator |
1.0 a |
|
Innovator |
Litchi Tomato |
0 b |
*Significant differences indicated by different letters beside means.
Literature Cited:
Dandurand, L. M., and Knudsen, G. R. 2016. Effect of the trap crop Solanum sisymbriifolium and two biocontrol fungi on reproduction of the potato cyst nematode, Globodera pallida. Annals of Applied Biology 169:180-189.
Franco, J., Main, G., & Oros, R. (1999). Investigation-Research: Trap Crops as a Component for the Integrated Management of Globodera spp.(Potato Cyst Nematodes) in Bolivia. Nematropica: 51-60.
Research Outcomes
Education and Outreach
Participation Summary:
In year 1 of this project, data was insufficient to present to agricultural professionals and stakeholders. In the upcoming year, a presentation will be given at the Society of Nematology annual meeting in September. The findings and progress of this project will also be presented to stakeholders and growers at the Idaho Association of Plant Protection annual meeting in November. The SARE survey will be distributed at this meeting as well. In the future, I hope to also present or hold a workshop at the annual 2023 Idaho Potato conference. At the end of this project, a newsletter will be created to distribute to growers and other stakeholders. We also hope to publish the study in a scientific journal.