Varieties of Lantana camara (lantana) have been introduced into many countries of the world as ornamental plants and have become invasive weeds in many countries including South Africa. In South Africa, it mostly invades the sub-tropical eastern and northern range. Mechanical and chemical control options are expensive and ineffective. A biocontrol programme was initiated in South Africa in 1961. To date, 22 insect species, and a fungus have been introduced, of these 10, and the fungus have established. Three indigenous lepidopteran species and an exotic generalist pest mealybug are also associated with the weed. The variable success of some of the agents released on L. camara worldwide has been ascribed to a few factors. One important aspect is the large range of varieties encountered in the field. It is therefore essential to be able to predict the possible establishment and impact of agents on many varieties. Laboratory trials on five of the established agents showed clear varietal preferences. In the field, most of the biocontrol agents had limited geographic ranges, linked to altitudinal conditions, as higher populations were recorded at low lying warm summer rainfall areas. A pink and orange flower corolla lobe and throat colour combination and plants with few to medium leaf hairs were most abundant in South Africa. Most of the agent species had individual preferences towards different flower colour combinations, as the agents built up different population levels on varieties in the field, within the suitable geographic region for the insect species. Eight agents preferred smooth leaved varieties, while three preferred hairy leaves, and three had no specific preference to leaf hairiness. Varietal preferences thus did play a significant role in agent populations and accompanied impact achieved in the field. New candidate agents need to be proven specific under quarantine conditions and the results extrapolated to predict specificity in the field, while avoiding potential non-target effects. Many authors have questioned the validity of laboratory host specificity trials. The conventional wisdom is that insects portray a far wider host range in the laboratory than what they would do in the field. In other words, laboratory studies measure the physiological host range of an agent and are conservative and usually don’t reflect the ecological host range of agents in the field. To avoid unnecessary rejections of biocontrol agents, this study has made a retrospective study of the host specificity of agents established in the field. Their laboratory and field host ranges were compared and it was found that virtually all the agents reflect similar or less non-target effects in the field than predicted during multiple choice trials. Of the 14 agents, only one introduced species, Teleonemia scrupulosa, and the indigenous species, Hypena laceratalis and Aristea onychote were able to sustain populations on non-target species in the field in the absence of L. camara. Insect populations on non-target species were much reduced compared to that on L. camara. Furthermore non-target effects were only recorded on plant species closely related to the target weed. The multiple choice trials therefore predict field non-target effects accurately. Predictions of non-target effects of candidate agents can therefore be accurately predicted by laboratory studies, in terms of species likely to be affected and to what extent. One field that need further study though is the impact of non-target effects, especially on Lippia species by L. camara biocontrol agents.

An autecological study of the heterosporous fern Azolla filiculoides Lamarck and its endosymbiotic blue-green alga Anabaena azollae Strasburger, based on a combination of field and laboratory studies, is presented. The taxonomy, morphology and anatomy of the fern-alga association were studied as well as nutritional and physiological aspects of the symbiosis. These studies have defined the habitat and nutritional requirements of the fern and have provided new insights into its reproductive biology, nitrogen metabolism and the nature of the association between the fern and alga. In the catchment area of the Hendrik Verwoerd Dam the availability of suitably sheltered habitat limits the distribution of A. filiculoides while the availability of nutrients, in particular calcium, phosphorus and iron, limits the growth of the fern. The multilayered mats formed by A. filiculoides are essential for spore production, cause dramatic changes in the hydrochemistry of the underlying waters and confer a great competitive advantage on the plant. Methods for the isolation of the fern and algal components of the symbiosis have been developed but recombination of the individual organisms to reform the symbiosis was unsuccessful. The development of the fern is closely linked to that of the alga and the association is maintained throughout the life cycle of the fern. Because of its specific habitat and nutritional requirements, A. filiculoides is unlikely to colonize the open waters of the Hendrik Verwoerd Dam.

The objectives of this project were to measure changes in frequency of occurrence of submerged macrophytes over the first two growing seasons following stocking with triploid grass carp at two fish per acre and to measure differences in macrophyte biomass between areas excluded from herbivory and adjacent control sites after 16 months following establishment of exclosures. The project also seeks to measure concentrations of fluridone following the herbicide treatment, and to compare two methods of aquatic vegetation sampling.

Fall-planted forage radish (Raphanus sativus L. longipinnatus) cover crops have shown successful weed suppression and recycling of fall-captured nutrients. This research evaluated the nutrient cycling and weed suppressive benefits of forage radish cover crop mixtures to develop an integrated system for no-till sweet corn (Zea mays L. var rugosa) production that improves crop yield and soil health. Treatments included forage radish (FR), oats (Avena sativa L.) and forage radish (OFR), a mixture of peas (Pisum sativum subsp arvense L.), oats and forage radish (POFR), and no cover crop control (NCC). Subplots were assigned to nitrogen fertilizer treatments to evaluate N sufficiency and timing: 0 kg N ha-1 as the control, 28 kg N ha-1 at side-dress, and 56 kg N ha-1 with application split between planting and side-dress. Results indicated that POFR and OFR provided improved N cycling and sweet corn yield compared with FR and NCC. Early season N from decomposing cover crop residue was sufficient to eliminate the need for N fertilizer at sweet corn planting, thereby reducing input costs and risks of environmental pollution.

<p></p>Comprehensive information of breeding germplasm is a necessity to develop effective strategies for accelerated breeding. I characterized Purdue University soft red winter wheat breeding population that was subjectof intensive germplasm introduction and introgression from exotic germplasm. Using genotyping-by-sequences (GBS) approach, I developed ~15,000 single nucleotide polymorphisms (SNPs) and studied extent of linkage disequilibrium (LD)and hidden population structure in the population.The extent of LD and its decay varied among chromosomes with chromosomes 2B and 7D showing the most extended islands of high-LDandslow rates of decay. Four sub-populations, two with North American origin and two with Australian and Chinese origins, were identified. Genome-wide scans for signatures of selection using FSTand hapFLK identified 13 genomic regions under selection, of which six loci (<i>LT, Ppd-B1, Fr-A2, Vrn-A1, Vrn-B1, Vrn3</i>) were associated with environmental adaptation and two loci were associated with disease resistance genes (<i>Sr36 </i>and <i>Fhb1</i>).<br><p></p><div><br></div><div>The population was evaluated for agronomic performance in field conditions across two years in two locations. Genome-wide association studies identified major loci controlling yield and yield related traits. For days to heading and plant height, large effects loci were identified on chromosome 6A and 7B. For test weight, number of spikes per square meter, and number of kernels per square meter, large effect loci were identified on chromosomes 1A, 4B, and 5A, respectively. However, for grain yield<i> per se</i>, no major loci were detected. A combination of selection for other large effect loci for yield components and genomic prediction could be a promising approach for yield improvement.<br></div><div><br></div><div>In addition, the population was evaluated for FHB resistance under misted FHB nurseries inoculated with scabby corn across 2017-18 (Y1) and 2018-19 (Y2) seasons at Purdue Agronomy Farm, West Lafayette,in randomized incomplete block designs. Phenotypic data included disease incidence (INC), disease severity (SEV), <i>Fusarium</i> damaged kernels (FDK), FHB index (FHBdx), and deoxynivalenol concentration (DON). Twenty-five loci were identified at -<i>log</i>P ≥ 4.0 to be associated with five FHB-related traits. Of these 25, eighteen explained more than 1% of the phenotypic variations. A major QTL on chromosome 2Bi.e., Q2B.1 that explained 36% of variation in FDK was also associated with INC, FHBdx, and DON. The marker-trait associations that explained more than 5% phenotypic variation were identified on chromosomes 1A, 2B, 3B, 5A, 7A, 7B,and 7D. To investigate the applicability of other QTL with less signal intensity, the threshold criterion was lowered to -<i>log</i>P ≥ 3.0, which resulted in the identification of 67 unique regions for all traits. This study showed that the FHB-related traits have significant correlations with the number of favorable alleles at these loci, suggesting their utility in improving FHB resistance in this population by marker-assisted selection.The genotype and phenotype data produced in this study will be valuable to train genomic prediction models and study the optimal design of genomic selection training sets. This study laid foundation for the design and breeding decisions to increase the efficiency of pyramiding strategies and achieving transgressive segregation for economically important traits such as yield and FHB resistance.<br></div>

Food insecurity and nutrition are two of the biggest challenges facing our society. Urban agriculture can help address these challenges, though lack of awareness about opportunities for engagement and degraded soils are two barriers that could prevent people from realizing the benefits that these operations can provide. Soils in urban areas are often highly degraded due to development activities and lack the structure and microbial life needed to sustain healthy, productive plants. Many lifelong habits such as healthy eating and engagement in community gardening are best established during young adulthood. Graduate school is a particularly unique time period, as many students are living on their own for the first time with modest incomes and some have young families that are particularly vulnerable to food insecurity. Consequently, the first objective of this project was to identify which barriers, if any, Purdue graduate students face when purchasing and consuming fresh produce and participating in local urban agriculture initiatives as Purdue’s campus and much of the surrounding area are characterized as food deserts by the USDA. We also sought to determine how the COVID-19 pandemic influenced food access and motivations for healthy eating and community garden engagement. To answer these questions, we distributed a voluntary 33 question online Qualtrics® survey to all Purdue graduate students via mass email blast. Results indicate that many Purdue graduate students face individual and structural barriers to accessing fresh fruits and vegetables. International respondents, in particular, were particularly vulnerable to structural barriers. Not having access to a personal vehicle appears to be the primary predictor of who was most vulnerable, especially during the pandemic. Results also indicate that students are interested in participating in local urban agriculture initiatives, but most are unaware of their existence. Students indicated that e-mails were the best method for increasing awareness and engagement. The second objective of this study was to determine whether leaf mold compost could improve the health and productivity of degraded urban soils. In addition, we aimed to determine whether the leaf compost could better support a beneficial microbial inoculant to further enhance crop productivity, as well as the extent to which plant genotype moderates these beneficial plant-soil-microbial relationships. To answer these questions, leaf compost was obtained from a local grower and applied to experimental plots at the Purdue University Farm. Two tomato varieties, Wisconsin 55 and Corbarino, were inoculated with Trichoderma harzianum T-22 or a sterile water control, and transplanted into the field trials. 15 Survival following transplanting, vigor, disease ratings and the yield and quality of tomato fruit were quantified over the course of two growing seasons. Results indicated that several measures of soil health were significantly increased in compost-amended soils and the health and productivity of tomato plants greatly improved. The microbial inoculant dramatically reduced transplant stress, especially in Wisconsin 55. Other more subtle differences among the tomato varieties indicated that urban agriculture systems could be improved through varietal selection. These studies highlight the fact that graduate students are not immune to food insecurity and proper nutrition and they are interested in connecting with urban agriculture initiatives to address these challenges. Pairing of the two groups could prove to be a successful mutualistic symbiosis as graduate students provide the enthusiasm and manpower that urban gardens need while urban gardens offer access to low-cost fresh produce that many graduate students desire. Leaf mold compost can aid in these initiatives by providing a cost-effective approach to improve the health and productivity of urban soils and crops, while at the same time providing further benefits such as reduced accumulation of valuable carbon sources in municipal landfills. Results like these provide stark evidence that agriculture, particularly urban agriculture, can continue to improve access to nutritious foods through green initiatives and innovations.

L’objectif de cette thèse est de proposer une démarche pour identifier des plantes de service (Pds) utilisables en couverture vivante pour contrôler les adventices en bananeraie. Nous avons d’abord quantifié les effets de compétition réciproque entre le bananier et une couverture contrôlée par fauchage pour Brachiaria decumbens et Cynodon dactylon. Ces couverts ont eu des effets dépressifs sur la nutrition azotée du bananier et la productivité en premier cycle, le second cycle n’étant pas affecté. Dans un deuxième temps nous avons caractérisé au champ, en plantes isolées, la croissance en biomasse de huit légumineuses candidates sous différentes intensités lumineuses. En conditions lumineuses non limitantes, chaque espèce répondait à une dynamique exponentielle, définie par la biomasse 14 jours après semis et le taux de croissance relative (RGR). En conditions d’ombrage limitant, le RGR est réduit et le rapport surface foliaire sur biomasse aérienne croît. Ces réponses permettent de définir quatre stratégies d’adaptation à l’ombrage et d’identifier les Pds adaptées sous bananeraie. Pour trois de ces espèces, sur la base de la réponse de l’efficience photosynthétique, nous proposons un modèle de croissance en fonction de la ressource lumineuse. En peuplement, en présence d’adventices, aucune espèce évaluée n’a pu contrôler les grandes graminées, Stylosanthes guianensis et Centrosema pascuorum ont cependant réduit la biomasse des autres adventices de 60%. En bananeraie, les deux espèces évaluées ont exercé un contrôle sur les adventices mais ont réduit la productivité du premier cycle. Pour autant, ces résultats sont encourageants pour l’utilisation de Pds en bananeraie à des fins de contrôle des adventices. / The objective of this PhD thesis was to provide an approach to identify suitable cover crops (Pds) for weed control use in banana plantations. Firstly, we quantified the reciprocal effects between the banana crop and a grass cover controlled by mowing, for Brachiaria decumbens or Cynodon dactylon. These cover crops have had similar depressive effects on the nitrogen nutrition and on the productivity of the first cycle, but not afterward during the second cycle. Second step, we carried out a field characterization of eight legume cover crops, on isolated plants, under a range of light intensity. In non-limited light growth conditions, the biomass growth corresponded to an exponential dynamic, mathematically defined for each species by the biomass 14 days after sowing, and the relative growth rate (RGR). When affected by the shade, the RGR was reduced and the ratio between Leaf area and aerial plant biomass increased. We defined four adaptive strategies of the cover crops to the shade, what constitute criteria guidelines for cover crop use in banana cropping systems. For three of these species, on the basis of the response of the radiation use efficiency, we are proposing a plant growth model without any limiting factor other than light resource. In stands with the presence of weeds, neither of this cover crops was able to control the tall gramineous, but Stylosanthes guianensis and Centrosema pascuorum reduced the biomass of other weeds by 60%. Finally, in banana plantations, the two evaluated species provided a control of the weeds but reduced the productivity of the first cycle. Our results are comforting for the use of cover crops in banana plantation as a mean for weed control.

No description available.

<p>The management of gray mold, caused by the fungus <em>Botrytis cinerea</em>, on ornamental plants relies heavily on fungicide applications. To improve fungicide efficacy, the manipulation of nozzle type, spray volume, and pressure influence droplet size (µm) and density (droplets/cm2) on the leaf’s surface. However, leaf wettability dictates how well the application droplets adhere and spread across the surface. When leaf surfaces are waxy (hydrophobic) or hairy (tomentose), droplets fail to adhere, impacting fungicide sorption.</p> <p>The goal of this research was to evaluate how the interaction of droplet density and leaf wettability impact the efficacy of chemical and biological fungicides against <em>Botrytis cinerea</em>. Leaf surfaces vary between species, within species, leaf age, and leaf sides (abaxial or adaxial). Hydrophobic leaf surfaces influence fungicide efficacy by reducing fungicide droplet spread compared to the wettable and hydrophilic leaf surfaces. The presence of trichomes on the leaf surface can inhibit droplets from reaching the surface.</p> <p>To quantify droplet density, a fine and coarse spray of fungicide treatments was applied with a yellow fluorescent dye. After application, <em>Begonia</em> x <em>hybrida</em> ‘Dragon wing’ leaves were placed on black, blackout curtains below a blacklight. Images were analyzed by ImageJ, using an image processing method. The number of lesions, disease incidence, were counted to observe fungicide efficacy. Results show there was no interaction between the actual droplet density within treatments applied with fine and coarse sprays. However, the interaction between spray type (fine and coarse) and treatments can have a significant effect on disease incidence. Disease incidence was significantly different between the systemic and contact fungicides for fine and coarse sprays. However, the systemic fungicide treatment had the highest disease incidence compared to the contact fungicide.</p> <p>To assess leaf wettability impact on fungicide efficacy, five <em>Begonia </em>species (<em>B. scharffii, B. erythrophylla, B. </em>x<em> hybrida ‘</em>Dragon Wing’<em>, B. epipsila, and B. goldingiana</em>) were used based on their observed leaf surface type. A contact angle goniometer was used to take pictures of a droplet on <em>Begonia</em> leaf surfaces. The quantification of the leaf surface took place by using the ImageJ program ‘Drop-Snake’ within the plugin ‘Drop Analysis’. The number of lesions, an indicator of disease incidence, were counted to observe fungicide efficacy. Results showed the contact angles were different between the <em>Begonia</em> species. There was a significant interaction between the <em>Begonia</em> species and treatments, where <em>Begonia</em> ‘hairy’ and ‘waxy’ leaf surfaces can influence fungicide efficacy. However, there was no significance for the interaction between <em>Begonia</em> species’ contact angles and treatments.</p> <p>These studies advance our understanding of how droplet density and leaf surfaces influence fungicide efficacy, thus improving our ability to manage <em>Botrytis</em> for diverse ornamental plants. </p>

Weed control is an integral part of a successful overall production strategy in row- cropping systems and has the potential to reduce or eliminate yield losses that negatively affect profitability. Timely and correctly selected herbicide applications are the major keys for effective weed control in a majority of instances. However, there are negative factors that contribute to ineffectiveness and weed escape issues that currently lack viable options for management. Sparsely populated late-season weeds that emerge after lay-by herbicide applications and weeds that have become tolerant and resistant to traditional herbicide chemistries are of greatest concern. Historically, these weeds would have been pulled or chopped by hand or removed by cultivation, but with current production strategies built around conservation tillage and herbicide management practices, blanket disturbance of the soil through plowing is not a viable option. There is an immediate need for site-specific weed management to address these weed escapes while minimizing soil disturbance that reduces residual herbicide efficacy and lessens moisture losses that negatively effects the growing crop