<p>  </p> <p>Environmental conditions, like light quality and herbivory, can induce changes in plant physiology. Light quality can be manipulated using LEDs (light emitting diodes) to improve crop quality and yield in horticultural production. The manipulation of light quality has also been utilized in the management of agricultural insect pests. Previous research has provided evidence that changes in light quality can have effects on the growth and chemistry of cannabis crops (<em>Cannabis spp.</em>). Varieties of cannabis are grown for the production of the valued cannabinoids CBD and THC. Pest of cannabis include herbivorous arthropods that reduce hemp yield and quality. Arthropod herbivory can induce chemical and physical changes in plants. This thesis further investigates the role of light quality on both cannabis biology and the crop-pest interaction between cannabis and the cannabis aphid (<em>Phorodon cannabis</em>). In the experiments described herein, the effects of light quality and <em>P. cannabis </em>herbivory on cannabis were assessed by measuring impact on biomass accumulation, yield, and the production of CBD and THC. The effects of light quality on the life history traits of <em>P. cannabis </em>were also measured. Cannabis grown under red-blue light quality saw a reduction in vegetative growth but no reduction in yield. Light treatments had no measured effect on the concentrations of CBD and THC in the cannabis buds. Aphid herbivory decreased bud yield but increased vegetative growth. Aphid herbivory reduced the concentration of both CBD and THC in cannabis bud tissue. Under blue-rich light quality, <em>P. cannabis </em>experienced higher reproductive rates when compared to red-blue and full-spectrum lighting. </p>

<p dir="ltr">Sweetpotato (<i>Ipomoea batatas</i> L.) is a staple crop that provides nutritional benefits to humans globally, but it is subjected to yield loss when competing with weeds, especially during the early stage of establishment. Despite increased organic sweetpotato production in the United States, growers face challenges with limited weed management options and often resort to time-consuming and costly cultivation and hand-weeding. To address this challenge, experiments were developed to determine (1) the effect of sweetpotato cultivar on the critical weed-free period, (2) the effects of in-row plant spacing and cultivar selection on weed suppression and sweetpotato yield, and (3) the impact of buckwheat and silage tarps for row-middle weed control. 1) In 2022, field research was conducted at the Samuel G. Meigs Horticulture Research Farm (Meigs), Lafayette, IN, and at the Southwest Purdue Agricultural Center (SWPAC), Vincennes, IN to estimate the critical weed-free period for ‘Covington’, ‘Murasaki’, and ‘Monaco’ in the Midwest. The experiment was a split-plot design, with weed-free interval treatments as the main plot factor and cultivar as the subplot factor. Weeds were removed by hand and allowed to establish and compete with the crop beginning at 0, 14, 21, 28, 35, or 42 days after transplanting (DAP). As weed-free interval increased from 0 to 42 DAP, predicted total yield increased from 19 kg ha^-1 to 20,540 kg ha^-1for Covington, 3 kg ha^-1 to 11,407 kg ha^-1 for Monaco, and 125 kg ha^-1to 13,460 kg ha^-1for Murasaki at the Lafayette location. A threshold of ≤10% total yield reduction was achieved by maintaining sweetpotatoes weed-free 24 DAP for Covington, 20 DAP for Murasaki, and 33 DAP for Monaco. 2) In 2022 and 2023, studies were conducted at Meigs, Lafayette, IN and SWPAC, Vincennes, IN to evaluate in-row plant spacing and cultivars for weed control and sweetpotato yield. The experiment was a split-split plot design, with in-row spacings of 20, 30, and 40 cm as the main plot factor, weeding frequency (‘critical weed-free period’ and ‘weed free’) as the subplot factor, and sweetpotato cultivar (‘Covington’ and ‘Monaco’) as the sub-subplot factor. However, in 2022, we evaluated only in-row spacing and weeding frequency because of poor establishment of Monaco. In-row spacing had no significant effect on weed densities at 4, 5, and 6 WAP. As in-row spacing increased from 20 to 40 cm, total sweetpotato yield pooled across both locations in 2023 decreased from 30,223 to 21,209 kg ha^-1 for Covington and 24,370 to 20,848 kg ha^-1 for Monaco, however, jumbo yield increased for both cultivars. Findings from this study suggest that an in-row spacing of 20 cm may provide greater yield than the standard spacing, 30 cm, for both Monaco and Covington cultivars and could reduce weed interference through more rapid sweetpotato canopy closure. 3) The experiment was a randomized complete block design, with three row-middle treatments [tarp, buckwheat, and cultivation] and four replicates. Row-middle treatments were established immediately after transplanting ‘Covington’ slips 30 cm apart into raised bed plots consisting of a single row 6 m long and 2 m apart on-center. Buckwheat was planted three weeks after transplanting (WAP) at a rate of 108 kg ha^-1 in row-middle. Row-middles for the tarp treatment were covered for the entire growing season. Weed density at 6 WAP was 184 plants m^-2 for the buckwheat, and 162 plants m^-2 for the cultivation treatments. Total yield was 11,050 kg ha^-1 for the buckwheat, 19,790 kg ha^-1 for the cultivation, and 17,810 kg ha^-1 for the tarping treatments. Tarping effectively suppressed weeds and produced sweetpotato yields comparable to cultivation indicating potential for organic growers. Buckwheat yields were lower than those from tarping and cultivation.</p>

<p>  </p> <p>Plant roots form an intimate relationship with a diversity of soil microorganisms. Some soil-borne microbes cause harmful diseases on crops, but others promote plant growth and enhance host resilience against stressors. Beneficial bacteria have a high potential as a strategy for sustainable agricultural management, many of which have been recognized and commercialized for improving crop growth. Unfortunately, field inoculants of beneficial bacteria often give inconsistent results due to various environmental factors hindering their beneficial properties. Improving crop production utilizing beneficial bacteria requires two approaches: 1) breeding for crops with the enhanced association for beneficial bacteria and 2) improving formulation methods for producing more potent microbial products. To contribute to these goals, we address three critical questions utilizing the tomato root microbiome as a model system. First, we asked how beneficial root-associated bacteria could be efficiently identified. We developed a strategy to select beneficial bacteria from a novel collection of 183 bacterial endophytes isolated from roots of two field-grown tomato species. The results suggest that isolates with similar traits impact plant growth at the same levels, regardless of their taxonomic classification or host origin. Next, we asked whether host genetics contribute to the root microbiome assembly and response to beneficial microbes. An assessment of the root microbiome profile and plant binary interaction experiments suggested the role of host genetics in influencing root recruitment and response to beneficial bacteria. Subsequently, we asked whether root-associated bacteria induce physiological changes in root tissues in the host. We identified two isolates from our bacterial endophyte collection that significantly promoted the growth of tomato genotype H7996 (<em>Solanum lycopersicum</em>). Plant-binary interaction experiments suggested a significant increase of cell wall lignification in the root vasculature starting 96-hour post-inoculation with beneficial bacteria. Additional studies are needed to uncover a possible correlation between the induced vasculature lignification and the growth-promoting effects of the two isolates on H7996. Altogether, our findings highlight the multi-faceted role of root-associated bacteria in promoting plant growth and support the development of crop improvement strategies in optimizing host association with soil bacteria.</p>

No description available.

Department of Ecology and Resource Management / PhDENV / The main aim of the research was to contribute means for converting conventional, high-input production systems to more sustainable ecological systems, thereby improving the sustainability of macadamia production and ultimately contributing to food security. This was achieved by a) investigating the potential use of cover crops and compost to enhance soil quality in macadamia orchards and b) investigating the potential use of use of cover crops and orchard heterogeneity to control stinkbug pests that target macadamia crops. Field experiments were conducted in three phases: phase one tested the potential of six cover crops for crop protection (as trap crops) and simultaneously for soil restoration or fertility enhancement purposes in macadamia orchards. Phase two repeated the trials of phase one (both soil restoration and trap crops) but with modifications to both categories. Soil restoration treatments were conducted with trees which were growing in what appeared to be healthy soils, and then repeated with trees in the same orchard where the topsoil had been degraded (totally removed) by agricultural operations. The third phase repeated the trap crop trials only, but this time on three different study areas (all commercial farms) with the single cover crop which performed the best as a trap crop during phase two. Trials were modified from the first to the last phase to overcome practical implementation problems encountered along the way and to adapt to local conditions experienced in the commercial macadamia farming systems which served as research sites. Diversity of natural orchard vegetation was enhanced in phase three to improve conditions for natural predators as part of the trap crop treatments in the last phase and cover crops were finally first composted and then returned to the root zones of the macadamia trees as part of the soil quality enhancement treatments in the second phase. The results from the trap crop trials shows a significant effect of trap crops combined with increased orchard diversity in reducing unsound kernel percentages caused by stinkbug pests and demonstrate that trap crops combined with an increase in orchard diversity could be utilized in macadamia orchards as a more sustainable alternative to inorganic pesticides against the stinkbug complex. The most notable changes in the soil that took place with soil quality enhancement treatments were the significant increases in soil phosphorous content and pH which resulted not in an improvement in soil quality in terms of these two indicators but revealed an important issue about the use of compost containing animal manure originating from dairies or feedlots. In summary however, it was clear that although not all the soil quality indicators that were employed to assess changes in the soil with compost treatments improved significantly, a holistic consideration of all indicators portrays an overall improvement which was particularly significant in the degraded soil plots where the topsoil had been removed by prior agricultural activities. / NRF

<p dir="ltr">Urban agriculture has grown in popularity in recent decades, due to its ability to provide access to healthy fruits and vegetables in urban zones, as well as its importance in fostering knowledge of agriculture within communities. However, urban agriculture may struggle with unique challenges due to its proximity to urban and industrial activities, such as food safety risks due to toxic heavy metals and metalloids which may be present in urban soils in high concentrations. Heavy metals and metalloids (HM) like arsenic, cadmium, and lead are absorbed by plants from the soil, and may accumulate in the plants’ edible tissues, which are consumed by humans. Carrot (<i>Daucus carota</i> L.), in particular, hyperaccumulates these toxic heavy metals in its edible taproots, leading to food safety risks on urban farms.</p><p dir="ltr">One potential way to help address this challenge is to breed carrot varieties with low uptake of HM. In recent years, researchers have identified lines with high and low uptake in greenhouse trials and single location breeding nurseries. However, to be viable, these lines must consistently vary in HM across sites despite differences in environmental and management factors that can also greatly influence HM bioavailability and uptake. Moreover, screening for differences in HM uptake is time-consuming and expensive, and breeders need new tools to select among segregating breeding populations. By using on-farm participatory research as well as advanced phenotyping technologies, we investigate the viability of breeding carrots for HM uptake and the potential of new tools to advance these efforts in order to mitigate the risks on urban farms.</p><p dir="ltr">In the summers of 2021 and 2022, participatory on-farm trials were conducted to determine the HM risks on Indiana urban farms and to investigate the consistency of differences in HM uptake between carrot breeding lines taken from breeding trials (Chapter 2). Results of these trials indicated that while carrot genotype had an effect, there was still significant variability in carrot uptake of arsenic, cadmium and lead between farm sites and years. Results indicated significant differences between site-years, and carrot HM concentrations that correlated strongly with soil concentrations for that particular element. However, there were some site-years with low soil HM content and other soil factors expected to reduce uptake such as pH and phytoavailable zinc concentrations (such as site-year H), that had high carrot HM content. There were significant differences in carrot cadmium (Cd) and arsenic (As) content between carrot breeding lines. For instance, breeding line 3271 had a high As average concentration but low Cd average concentration, while breeding lines 6220 and 2327 had low As and high Cd concentrations. We identify the possibility of other mediating factors, such as uptake of antagonistic micronutrients, or microbe-assisted HM uptake and amelioration that need further attention.</p><p dir="ltr">In the fall of 2022, a study was conducted to investigate the possibility of using phenotyping technologies such as RGB and hyperspectral imaging to detect Cd stress in carrot and attempt to predict uptake (Chapter 3). RGB (red green blue) is a digital color model in which cameras can capture important visual cues compiled from information about each pixel. Hyperspectral imaging uses cameras to capture wavelengths beyond the visible spectrum, which can detect plant stress indicators like increased anthocyanin content for specific environmental stresses. Results of this trial were useful, with some time points and indices noting differences between carrot lines. For instance, RGB factors hue and fluorescence as well as hyperspectral reflectance plots and vegetative indices swirNDVI and ANTH were the most diagnostic. Breeding lines 6636 and 8503 showed the greatest separation between Cd treated and control carrots in imaging indices. However, further studies will be needed to optimize this approach for breeding programs.</p><p dir="ltr">This research demonstrates that growing carrots on most urban farms in Indiana is safe. The studies also provide further evidence that it will be possible to help lower food safety risks by selecting carrot varieties with low HM uptake, and phenotyping can help to advance these efforts. At the same time, new research to understand how soil factors such as microbiomes influence HM bioavailability and uptake on urban farms are also needed to further reduce potential risks. In the meantime, farmers should continue to test their soil for HM and take appropriate actions to reduce risks such as using raised beds and soil amendments that can bind metals like biochar. Consumers should also continue to wash and peel their carrots before consumption, as well as consume a balanced diet with a diverse set of vegetables and other crops.</p>