Progress 03/01/16 to 02/29/20
Outputs
Target Audience:Farmers, Extension staff, agronomists, other agricultural professionals, entomologists Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?A PhD student on the project, Wadih Ghanem, was trained in QIIME2 for quantitativeanalysis of soil microbiomes with Greg Caporaso and Nicholas Bokulich at Northern Arizona University. Student also received training and background in phylogenetic methods. How have the results been disseminated to communities of interest?Two oral presentations at international conferences in 2019: Kaplan, I. Plant-mediated changes to the soil microbiome affecting aboveground herbivory. Section: Multitrophic & Network Ecology. Gordon Research Conference on Plant-Herbivore Interactions (Advancing Plant-Herbivore Interactions Through Complementary Approaches and the Blurring of Disciplinary Boundaries), Ventura, CA (March 2019) Ghanem, W., and I. Kaplan. Exploiting soil legacy effects as a tool for crop and pest management in high tunnels. Entomological Society of America, St. Louis, MO (Nov 2019) What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
During our 2017 and 2018 field seasons, we tested the influence of plant phylogenetic diversity on pests of striped cucumber beetle, Acalymma vittatum, and we have reported on our results in previous annual reports. During the growing season of 2019, we pursued two additional objectives that grew out of this previous work. First, because we hypothesized that our 2018 results may be driven by the response of beetles to odors released by plants, we tested whether phylogenetically distantly related plant species could alter attraction to a preferred host plant species. To establish a baseline of preference, we compared the behavioral response of female A. vittatum to zucchini (Cucurbita pepo) and maize (Zea mays), two distantly related plant species (they shared a common ancestor 376.5 million years ago). We expected that A. vittatum would be attracted to zucchini because they are a pest on this plant species, and they are not a pest on maize. Using a y-tube olfactometer choice assay, we presented female beetles a choice between the odors of individual plants of these two species. Unexpectedly, beetles significantly preferred maize over zucchini (X2 = 5.5, P < 0.05). Building on our field results from 2018, we next tested whether beetles would prefer the odor from a mixture of zucchini and corn (one plant of corn and one of zucchini) versus a monoculture of zucchini (two plants of zucchini). Based on our field experiment from 2018, we expected that beetles would prefer the monoculture. Unexpectedly, beetles significantly preferred the odor from the mixture of corn and zucchini (X2 = 5.8, P < 0.05). To determine whether beetles were responding to different volumes of odor rather than specific odors (perhaps corn was just making more odor), we tested whether beetles preferred odors from two corn plants to odor of two zucchini plants. In this case, beetles preferred the odor of two zucchini over the odor from two corn plants (X2 = 5.5, P < 0.05). These results are confusing and do not align well with our field results. We expect to continue more assays in future work to understand what they really mean. Second, following up on some interesting results from 2018, we characterized the suite of parasites and parasitoids that attack established A. vittatum. In 2018, we unexpectedly found nematodes in adult A. vittatum beetles. Entomopathogenic nematodes had only been reported from this pest species in 1925 so we were surprised to find them and wanted to better characterize their occurrence. During evaluations for nematodes, we found other parasite species and are working on characterizing the whole parasite/parasitoid community. Out of 1265 beetles collected in 2019, 387 were parasitized (30.6%; 134 female beetles, 253 males, 2 unknown) and at least two parasite species infected 14 females and 34 males. Nematodes were the most abundant parasites and we found them in 244 beetles (~19% of collected beetles, 60% of beetles infested with any parasites/parasitoids). We encountered the remaining parasitic species in the following abundances: Celatoria setosa (Coquillett) (Diptera: Tachinidae) larvae in 78 beetles (~5.5% and 20%), Centistes diabroticae (Gahan) (Hymenoptera: Braconidae) larvae in 47 beetles (~3.5% and 12%), Cn. diabroticae eggs in 22 beetles (~2% and 6%), and Gregarinasina (a gregarine protist) in 50 beetles (~4% and 13%). Among parasitized beetles, about 35% were female and 65% were male, and parasitized females were significantly larger than parasitized males. Males and females had equivalent numbers of parasitic organisms per beetle, and elytron length was not a significant predictor of the number of parasitic organisms per beetle host. Additional comparisons between each common parasitic organism and the beetle sex of hosts revealed only that Cn. diabroticae larvae were more abundant in males. Molecular identification based on 18S rRNA revealed the nematodes to be Howardula spp, with the closest known species being Howardula phyllotretae (28 samples; % ID range 96.9% to 97.6%; GenBank accession # JX291137; D. Denver, personal communication). This indicates the nematodes from A. vittatum could be an undescribed species or a known species whose molecular information is not in a database. In addition to the above work on how phylogenetically dissimilar plants in polyculture affect colonization of cucumber beetles and other pest or beneficial arthropods in a spatial/interplanting context, we also completed our experimental work evaluating how taxonomic relatedness affects the success of rotations for tomato using a plant-soil feedback framework. The initial greenhouse study guiding this part of the project was published in 2018 in Journal of Applied Ecology and during 2019 we finalized analysis of the corresponding two-year field experiment (2017-18), which is now in press at Evolutionary Applications. Both studies were featured in the below blog and press release, respectively: https://appliedecologistsblog.com/2018/06/14/crop-rotations-called-into-question/ https://nau.edu/nau-research/crop-yield/ We tested 35 species of crops and weeds varying in their relatedness to tomato (Solanum lycopersicum). We used community profiling of the bacteria and fungi to determine the extent to which soil microbes contribute to phenotypic differences in crop growth. PCR amplicon libraries targeting the 16S rRNA encoding gene present in metagenomic DNA were produced using a barcoded primer set adapted for the Illumina HiSeq2000 and MiSeq. DNA sequence data were then generated using Illumina paired-end sequencing at the Environmental Sample Preparation and Sequencing Facility (ESPSF) at Argonne National Laboratory. Genomic DNA was also amplified using an internal transcribed spacer (ITS) barcoded primer set, adapted for the Illumina HiSeq2000 and MiSeq. Sequence data were processed and analyzed using the plugin-based microbiome bioinformatics framework QIIME 2. Overall, tomato yield was lower in soil previously cultivated with tomato; yet, past the species level there was no effect of phylogenetic distance on crop performance. Tomatoes growing in self (tomato) plots had 15.3% lower yield than tomatoes growing in non-self (i.e., all other nontomato plant species) plots (p < .001). However, neither genus (p = .724) nor family (p = .996) had any predictive explanatory power on tomato growth. In fact, yield was nearly identical when comparing across these broader taxonomic groups. Similarly, tomato yield was the same in fallow control plots compared with any of the treatments receiving plants (p = .643). Soil microbial communities, on the other hand, were compositionally more similar between close plant relatives. Random forest regression predicted log10 phylogenetic distance to tomato with moderate accuracy (R2 = .52), primarily driven by bacteria in the genusSphingobium. Random forest classifiers, using the combined bacterial and fungal community, could accurately predict the previous plant species grown in each soil plot 27.6% of the time, a nearly 10-fold improvement over the baseline accuracy rate of 2.8% (the accuracy rate that would be achieved by assigning all samples to the most common class). The predictive features are primarily bacterial and include several Sphingobium species that are most abundant in soils previously planted with Solanaceae, indicating that this group of bacteria is enriched by that plant family. Interestingly, different Sphingobium species are associated with two different clusters of Solanaceae, separating Solanum and Capsicum sp. from other Solanaceae regardless of domestication status (crop versus weed), suggesting genus-specific associations among Solanaceae and Sphingobium groups. These data indicate that, beyond avoiding conspecifics, evolutionary history contributes little to understanding plant-soil feedbacks in agricultural fields; however, microbial legacies can be predicted by species identity and relatedness.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
I Kaplan, NA Bokulich, JG Caporaso, LS Enders, W Ghanem, KS Ingerslew. 2020. Phylogenetic farming: Can evolutionary history predict crop rotation via the soil microbiome? Evolutionary Applications
https://doi.org/10.1111/eva.12956
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Progress 03/01/18 to 02/28/19
Outputs
Target Audience:Farmers, Extension staff, agronomists, other agricultural professionals, entomologists. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?We have shared our results with entomologists at the Joint Annual Meeting of the Entomological Society of America and Entomological Society of Canada, the Department of Entomology at Penn State University, and the Gordon Conference for plant-herbivore interactions. Below are the oral presentations: Coco, A., I. Kaplan, J. F. Tooker. The noisy buffet: How crop phylogenetic relatedness affects insect abundance. Joint Annual Meeting of the Entomological Society of America and Entomological Society of Canada, Vancouver, BC, Canada, 13 November 2018 Coco, A., Masters Thesis Defense. The influence of crop phylodiversity on insect pests of squash and their natural enemies. Department of Entomology, The Pennsylvania University. 10 May 2019 Kaplan, I., and K. Ingerslew. Phylogenetic farming: Can evolutionary history inform crop rotation? Symposium: How Crop Diversification across Space and Time Influences Herbivory. Joint Annual Meeting of the Entomological Society of America and Entomological Society of Canada, Vancouver, BC, Canada, 13 November 2018 Kaplan, I. Plant-mediated changes to the soil microbiome affecting aboveground herbivory. Plant-Herbivore Interaction Gordon Research Conference, Ventura, California, 1 March 2019 What do you plan to do during the next reporting period to accomplish the goals?In the final year of the project, we will conduct greenhouse experiments to understand if visual or chemical cues are involved in the influence of associational resistance on SCB that we detected with our field experiment. We will also share our research with the agricultural community and complete development of the online tool that we have designed to help farmers layout their farms with phylogenetic diversity in mind.
Impacts
What was accomplished under these goals?
During 2018, we established at Penn State's research farm in central PA the second year of our field experiment to understand the influence of phylogenetic relatedness of neighboring crop species on insect pests and natural enemies. We explored the influence of phylogenetic distance on associational resistance to insect communities, using butternut squash (Cucurbita moschata) as a focal crop species and surrounded it with four rows of crops of different evolutionary divergence times relative to butternut squash. The divergence times and plant species were: Cucurbitaceae: Cucurbita pepo (butternut squash), 0 mya; Cucurbita pepo (zucchini), 32 mya; Citrullus lanatus (watermelon), 147 mya; Solanaceae: Capsicum annuum (sweet pepper), 238.3 mya; Asteraceae: Helianthus annuus (sunflower), 238.3 mya; Poaceae: Zea mays (sweet corn) and Avena sativa (common oats), 376.5 mya. We established 40 plots, which contained five rows. The central row contained butternut squash while the four surrounding rows contained one of the plant species listed above as well as a blank control (i.e., four empty rows surrounding the center row of squash) and butternut squash monoculture (i.e., five rows of butternut squash). Distance between rows was 1.5 m between rows and 6 m between plots. We quantified herbivore populations on squash foliage and flowers, and the amount of insect damage received by squash plants in each plot. We gathered data using scouting, sticky traps, pitfall traps, and dissections of cucumber beetles to find parasites. We scouted the central row of squash weekly and used the other methods every other week or monthly. Generally we found that phylogenetic relatedness of neighboring plant species had an inconsistent effect on abundance of herbivorous insects and others (predators, parasitoids, pollinators, detritivores). In 2018, striped cucumber beetles (SCB) were most abundant, followed by squash bugs, western corn rootworm (WCR), and spotted cucumber beetle (SPCB). Insect abundances in June and July were not significantly affected by divergence time. Later in the field season, a pattern emerged that was consistent with our phylogenetic diversity-based hypothesis, and it appeared to be mostly driven by SCB abundance, which decreased as divergence time increased on August 6 and August 28 (6-Aug, F1 = 46.71, P = <0.0001, R-squared = 58.60%, 28-Aug; χ21 = 5.67, P = 0.017, R-squared = 8.29%). Abundance of all herbivorous insects responded negatively to phylodiversity strongest on August 6 (F1 = 36.85, P = <0.0001, R-squared = 52.75%), followed by August 28 (χ25 = 40.96, P = <0.0001, R-squared adj = 33.87). Abundance of squash beetles in flowers in August was weakly influenced by increasing phylodiversity. When measured using sticky cards, herbivorous insects were again negatively influenced by increasing phylogenetic diversity; the species on stick cards whose abundances were consistent with this pattern were SCB, thrips, and tarnished plant bug. Neither bees in squash flowers nor natural enemies collected on sticky cards or pitfall traps were influenced by the phylogenetic diversity of the neighboring plants of the central row of squash. Thus far we conclude that plant phylogenetic diversity can be a predictor of herbivorous insect abundance for our focal crop, butternut squash. Phylodiversity, therefore, appears to play an inconsistent role structuring herbivorous insect communities, and is likely to have influenced the apparency of neighboring plants, which is derived from interactions of their chemical and visual cues. At Purdue, in 2018 we completed the second year of a two-year study designed to evaluate the role of phylogenetic diversity in crop rotations.Because we aimed to measure tomato responses to soil legacy effects from year 1 species treatments, we grew tomatoes throughout the entire field with seedlings transplanted in the exact location where the previous year's plants grew. Some of the previous year species were persistent in reestablishing from rhizomes (e.g., thistle, horsenettle, some grasses); these plants were repeatedly pulled by hand as needed to avoid competing with tomato. On June 1, we transplanted 1,216 tomato seedlings (var RG 611) into the field (i.e., 304 plots x 4 plants per plot). During transplant, we collected soil from each plot for microbial and nutrient analyses to quantify the soil legacy from year 1 treatments. To do so, we sampled from the top 3 inch profile of the soil layer at each of the four locations in a plot where plants previously grew; then we combined these samples, creating a single ca. 350 g soil sample per plot. Sterile nitrile gloves were used to avoid microbial contamination between plots. In the field we temporarily stored samples in plastic ziplock bags in a cooler, before placing them in a -20°C freezer in the lab until analysis. After manually homogenizing samples, a 2 g subsample was isolated for microbial analysis (see below sections). The remainder was sent to the University of Connecticut Soil Nutrient Analysis Laboratory (Storrs, Connecticut) where they were analyzed for plant available calcium, magnesium, phosphorus, potassium, sulfur, iron, manganese, copper, zinc, aluminum and boron using a modified Morgan extractant. Tomato harvest began August 22 when green fruits began ripening and lasted for two weeks. Blocks were harvested sequentially to avoid temporal effects on yield that may impact interpretation of treatments. Each plant was cut at its base, fruits were removed, and we separately measured vegetative biomass and total fruit yield per plant. Currently, we are working with bioinformatics specialists at Northern Arizona University to interpret the effects of phylogenetic diversity on soil microbes and tomato yield using the program QIIME.
Publications
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Progress 03/01/17 to 02/28/18
Outputs
Target Audience:Entomologists; faculty, graduate students, undergraduate students, postdoctoral scientists and other professionals in academia, government, and industry Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?We have given the following posters and oral presentations at scientific conferences during the past year on this project: Coco, A., I. Kaplan, and J. Tooker. Does phylogenetic relatedness affect associational resistance? A test with vegetable crops. Annual Meeting of the Entomological Society of America, Denver, CO, November 2017 Ingerslew, K., and I. Kaplan. Can phylogenetic relatedness predict the strength of plant-soil feedbacks and inform crop rotation? Symposium: Interdisciplinary Approaches to IPM. Annual Meeting of the Entomological Society of America, Denver, CO, November 2017 Kaplan, I., and K. Ingerslew. Phylogenetic farming: Can evolutionary history inform crop and insect management? 16th International Symposium on Insect-Plant Relationships, Tours, France, July 2017 Ingerslew, K.S., and I. Kaplan. Does the magnitude of plant-soil feedbacks correlate with phylogenetic relatedness? Symposium: Plant-Insect Interactions in the Face of a Changing Climate. Annual Meeting of the North Central Branch of the Entomological Society of America, Indianapolis, IN, June 2017 What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
During the past year we made progress in three areas. First, developing a grower survey tool to learn about the factors driving the spatial and temporal components of crop placement on diversified vegetable farms. The online survey has a series of questions such as... What factors most strongly influence the location of different crop species on your farm? Answer options: soil type, irrigation, timing of management (including planting, harvesting or weeding), topography (hills, slopes, drainage, etc), order within a rotation, other What factors most strongly influence the sequence of your crop rotation? Answer options: soil nutrients, weed control, timing of planting/harvesting, bed preparation, relatedness of previous crop species, availability of farming equipment, economy: yield benefits vs costs, N/A, I do not practice crop rotation To date, the survey was advertised on the Vegetable Gazette through PSU Extension: https://extension.psu.edu/we-need-your-feedback-on-veggie-rotations-and-field-layouts?j=205951&sfmc_sub=25426665&l=159_HTML&u=3973931&mid=7234940&jb=2 And the survey tool is now openly available as a google docs website: https://docs.google.com/forms/d/1UJRcbOsdCPUCYtv1ybrtKHv-W4luft992YGVzok6OiU/viewform?edit_requested=true Currently, Penn State is developing a new website that will include the existing survey but also add a mapping program for growers to spatially map out their farm with different crops. Second, the team at Penn State started their first year of experimental work testing the effects of phylogenetic diversity on insect pests in neighboring crops (e.g., spatial impacts). This work is led by Co-PD, John Tooker, and conducted by a M.S. student his lab, Angela Coco. In the summer of 2017, a field experiment was conducted at the Russell E. Larson Agricultural Research Center at Rock Springs, PA. Treatments included four divergence periods from butternut squash, as the focal crop, replicated five times per crop, each having butternut squash (Cucurbita moschata) as the center row. Additional treatments (same replication): a butternut monoculture and a "blank" treatment with a center row of butternut surrounded by 4 empty rows. Divergence periods were: 32-147, 213.9, 238.3, and 376.5 my. The corresponding crop species for these four divergence periods were as follows... divergence 1: Cucurbita pepo, Citrullus lanatus; divergence 2: Phaseolus vulgaris, Pisum sativum; divergence 3: Capsicum annuum, Helianthus annuus; divergence 4: Avena sativa, Zea mays. Plot sizes were 6 x 11.5 m with 50 plots, 3 ft between rows, 4 ft between plots, and 10 ft alleys. Data were collected from 8 August to 20 September 2017. This was much later than planned due to unexpected flooding and crop damage by groundhogs. Collection techniques included scouting foliage and flowers, pitfall traps and sticky traps in center rows and row 5 for each plot. Overall, we found that insect pests (including striped cucumber beetles, squash bugs, and aphids combined) tended to decrease with increasing intercrop divergence from butternut squash. In a zero -inflated Poisson test, divergence periods 2 and 3 were significantly different than divergence period 0 (p<0.005). Predators showed the opposite pattern with significantly higher activity densities in divergence periods 1-4 compared with divergence period 0. Last, the team at Purdue, led by PD Ian Kaplan and his postdoctoral associate Kathryn Ingerslew, began experimental work testing the effects of phylogenetic diversity on crop rotations. We tested 36 plants commonly encountered on diversified vegetable farms, including 22 crops and 14 weeds that vary along a spectrum of relatedness to tomato. We also tested whether soil conditioning affects the performance of an aboveground insect pest, the tobacco hornworm Manduca sexta. In November 2016, soil was collected from Throckmorton Purdue Agricultural Center in Lafayette, Indiana from a field that was out of crop production for five years, but previously used for corn and soybean. We used this soil to create ten pot replicates for each plant species (i.e., 360 total pots), arranged in a randomized complete block design. At the conclusion of an eight-week soil conditioning period, the above- and belowground biomass were harvested for each plant. Also, soil samples from four random pot replicates in each plant species treatment were collected and the soil microbial community was characterized using phospholipid fatty acid (PLFA) analysis. Excess soil was collected from all pots and used to begin the feedback phase of the study. To do so, we used the 36 experimentally conditioned soils as inoculum to evaluate tomato growth and pest resistance. Conditioned soil from each pot replicate was used to fill two cone-tainers (diameter 3 cm, height 12.4 cm), each of which received three tomato seeds (var. Better Boy). Within each replicate, one plant was used to measure tomato growth, while the other was used to assess hornworm Manduca sexta (L.) (Lepidoptera: Sphingidae) performance. Overall, phylogenetic relatedness did not predict plant-soil feedback effects on tomato biomass or hornworm performance; rather, impacts of soil conditioning were highly species- or family-specific. For example, tomatoes growing in soil previously containing plants in the Asteraceae family were notably resistant to caterpillar feeding. There was also a disconnect between which plant species caused negative feedbacks on tomatoes vs. hornworms (e.g., thistle Cirsium discolor soil had strong negative effects on herbivory but no impact on plant growth). Hence, negative feedbacks on hornworms are likely due to enhanced defence instead of simply reducing leaf availability. These data demonstrate that, despite being widely recommended by agronomists in most cropping systems, phylogenetic relatedness is a poor predictor for the success of crop pairings in rotation, especially in tomato. Better understanding of species-specific effects of soil conditioning will lend insight into how polycultures can be better designed to optimize crop growth while reducing susceptibility to insect pests, which is particularly useful on diversified farms that cultivate a variety of crop species. In the summer of 2017, we also began the first year of a two-year field experiment that was aimed to mirror the aforementioned greenhouse experiment. To do so, we created 8 replicated blocks of four-plant plots using the same 36 conditioning treatments, resulting in 288 total plots. These species treatments were cultivated in 2017 in the field at the Meigs-Throckmorton Purdue Agricultural Center. In the fall these plants were removed and in 2018 we will cultivate tomato throughout the field to determine how rotation crop identity and relatedness affect tomato yield and pest resistance.
Publications
- Type:
Journal Articles
Status:
Accepted
Year Published:
2018
Citation:
Ingerslew, K., and I. Kaplan. 2018. Distantly related crops are not better rotation partners for tomato. Journal of Applied Ecology, in press
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Progress 03/01/16 to 02/28/17
Outputs
Target Audience:Farmers, cropping system planners, and integrated pest managers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?A postdoctoral scientist, Kathryn Ingerslew, working on the project gained training in phylogenetic methods for creating cladograms across broad plant groupings using the program Phylomatic and R. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
We began the project this year with the Purdue team hiring a postdoctoral scientist, Dr. Kathryn Ingerslew, and the Penn State team hiring a graduate student, Angela Coco. The Penn State team is beginning their work on spatial aspects of phylogenetic diversity on insect pests in vegetable crops. We initiated a greenhouse experiment to test how evolutionary divergence influences associational resistance. The experiment is ongoing and involves tomato, Solanum lycopersicum and its herbivore, Manduca sexta. The experiment includes four volatile treatments: an untreated tomato plant, a tomato plant dosed with tomato volatiles, a tomato plant dosed with non-tomato volatiles, or a tomato plant dosed with solvent alone. We are using eight "non-tomato plants" from each of the four major divergence periods to determine how evolutionary relatedness influences the apparency of plants to herbivores: plants that diverged from tomato: 8-29 million years ago, 112-206 mya, 233-239 mya, or > 376 mya. We predict that plants more distantly related to tomato will increase associational resistance, decreasing the number of eggs laid. We also begun a field experiment testing the same hypothesis. The experiment is in a field 270 x 200ft with 10 treatments (5 replicates of each) and is testing the influence that various adjacent plant species have on herbivore damage to cucumber, Cucumis sativus. The eight plant species we are using vary in their evolutionary divergence periods relative to cucumber. Again, we expect that plants more distantly related to cucumber will increase associational resistance, decreasing amount of damage that plants receive. The Purdue team is focusing on temporal components of phylogenetic diversity, examining how relatedness affects crop rotations or weeds via their soil legacy. This work includes an examination of effects on the focal crop, tomato, growth and susceptibility to insect pests (caterpillars, Manduca sexta, and aphids, Myzus persicae). These experiments relate to Objective 1 of the project. The temporal experiment was conducted in a greenhouse on the Purdue campus. We collected soil from an agricultural field in Lafayette, Indiana (TPAC, Throckmorton Purdue Agricultural Center) that was cultivated with clover for the past several year. This soil was filtered using a mesh sieve to exclude large rocks or other debris. The soil was then mixed 50:50 with sterilized sand and placed in 4 in pots where it was conditioned for 10 weeks with each of 36 species of common crops and agricultural weeds (n=8-12 pot replicates per species). After the conditioning period, the soil from the rhizosphere zone was collected and used as starter inoculum combined with a 50% sterilized growing mix (field soil + sand). Above- and below-ground biomass was measured for all conditioning plants to use as a covariate. This soil was placed in conetainers and tomato seeds were germinated in the soil. After six weeks of growth, half of all replicates received 3 second instar hornworm larvae who were caged onto plants and allowed to feed for one week, after which caterpillars were collected and weighed. Control uninfested plants were then harvested and we recorded shoot and root fresh weights. Additionally, we used PLFA (phospholipid fatty acid) to analyze the microbial community from each of the soil types. Initial data from our experiment indicate that phylogenetic relatedness does not significantly predict the strength of the soil feedback on tomato growth or pest performance. The difference between crop and weed was also non-significant. However, family- and species-specific effects were apparent. For example, plants in the Cucurbitaceae had the strongest negative impact on tomato, whereas plants in the Asteraceae led to the biggest reduction in pest growth. Interestingly, the composition of the soil microbial community predicted the strength of plant-soil feedbacks. Using a PCA (principal coordinates analysis) we found a relationship between the first PCA factor and total tomato biomass. Currently we are preparing the same plant species treatments for conditioning field soil using the same treatments over a two-year period. Also, for Objective 2 of the project we began constructing a grower survey that integrates understanding of both spatial and temporal design aspects. This survey was co-developed by Purdue and Penn State and was evaluated by non-project personnel at both institutions for completeness and accuracy. Following field trials, both universities will begin using this survey to compare their outcomes with on-farm grower practices.
Publications
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