Floriculture, a flourishing industry since the end of 1990s, is a source of livelihood for thousands of people in Ethiopia. Investment into the sector has been promoted with the objective of creating employment opportunities, foreign exchange earnings and links to the international market. Flowers are now among major export commodities along-side other agricultural products such as coffee and oil seeds. The sector’s contribution as a source of employment is considerable in terms of poverty reduction as poverty is a deep rooted problem in Ethiopia. However, there are challenges related to employment conditions and environmental externalities. This thesis examines into the problems of environmental protection and regulatory frameworks regarding the floriculture industry. It provides analysis on factors that affect the effective implementation of regulatory frameworks. The thesis addresses the main environmental challenges associated with flower production. The main analysis is that in Ethiopia the problem basically lies with excessive application of pesticides and fertilisers; the impact eventually extends to affecting water and soil quality. Concerns about excessive utilization of surface and ground water are also addressed. With case studies of two freshwater lakes, the thesis demonstrates how establishment of floriculture companies adjacent to lakes compromise water quality and quantity, and affects aquatic life. Focusing on each environmental problem, the thesis provides analysis on existing regulatory frameworks and identifies lack of effective implementation as the root of the problem leading to environmental degradation. The country’s level of development has been a restricting factor to channel resources necessary to employ expertise and infrastructure. At the same time, there are tendencies of prioritizing economic development, through attracting investment, than environmental protection driven by the belief that strict regulation obstructs investment. The thesis also highlights that absence of effective and adequate regulatory framework has been a challenge to the objectives of investment promotion in Ethiopia and the right to improved living standard and to sustainable development guaranteed in the Constitution. The thesis suggests that strict monitoring and inspection of flower production process is needed, and the primary response to regulate environmental impacts must rest on the government. It identifies a number of intervention areas, including strengthening pesticide registration and control system, putting in place water use and discharge permit systems, requiring Environmental Impact Assessment reports and supporting companies to implement sustainable flower production methods. Promoting good agricultural production methods, private environmental standards and certification schemes can play role in improving environmental standards. However, compliance expenses can restrict industry wide implementation of the standards. The analysis offered in the thesis provides an evaluation of the main challenges facing the Ethiopian flower industry at a time of increasing volatility in the market. This is the first legal analysis of the environmental impact of flower industry in Ethiopia.

The diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), is the most important global pest of Brassica crops. It is now prevalent wherever Brassicas are grown and costs the agricultural industry US$ 4-5 billion annually. Traditionally, DBM is controlled by the use of insecticide only applications which has led to wide spread insecticide resistance in DBM populations. As insecticide only control strategies are not viable in the long term, it is the opinion of many experts that integrated pest management (IPM) is the way forward for DBM control. A component of the IPM system which holds great potential is entomopathogenic fungi (EPF). Despite their promise, EPF are not currently routinely used by growers to control DBM. This is mainly because the efficacy of EPF biopesticides tends to vary from one application to the next. The aim of this project was to study interactions between EPF and other elements of the IPM system to understand and address sources of variability. Temperature is the most important determinant of EPF growth, virulence and DBM development. However, there are considerable knowledge gaps when it comes to understanding the effect of temperature on these processes. This is mainly because of the left-skewed nature of the physiological response to temperature. We assessed the suitability of five non-linear models to describe these interactions and found Briere-1 to be the most appropriate model. Cardinal temperatures taken from it were used to develop a day-degree (DD) model which could accurately predict the virulence of EPF against DBM at fluctuating, “field realistic”, temperatures. In an IPM system, EPF would be applied with synthetic insecticides. Consequently, it is important to know how co-application of these products would affect the survival of groups of DBM larvae. After applying low-concentrations of various insecticides with EPF we found there to be negligible evidence of antagonism, indicating the insecticides and EPF are compatible for use within an IPM system. Finally, the effect of the age structure of the DBM larval population on efficacy of EPF biopesticides was investigated. We found that, because larvae slough off conidia during ecdysis, time between treatment of EPF and moult had a significant effect on larval mortality. It is hoped that this study will improve growers’ confidence in EPF biopesticides, and expedite their use within IPM systems to control DBM.

Pesticides are vital for controlling agricultural pests and increasing crop yields; however, they can have detrimental effects on the environment and human health. Regulatory laboratory studies need to be carried out to assess the risks of a pesticide before it can be produced and sold. These regulatory studies tend to poorly predict pesticide fate and degradation in the field, likely due to specified test conditions not accurately representing the environment. This thesis focuses on the potential for adding greater environmental realism to regulatory-type tests, using the fungicide isopyrazam in OECD 308- and 309-type studies. Regulatory tests are carried out under dark conditions. Microcosm studies were conducted in the presence of non-UV light to minimise photolysis, yet include phototrophic transformation; there was significantly more biodegradation in illuminated microcosms compared to those carried out in the dark, in which there was little degradation. The effect was more pronounced in water-sediment microcosms compared to water-only microcosms, as the sediment provided a platform for phototrophic biofilm development. Regulatory tests do not consider temporal variation in the microbial composition of environmental inoculum. Experiments carried out over two years showed that the outcome of tests, in terms of both degradation and mineralisation, were variable with inocula collected at different time periods from the same river location. Regulatory tests are also carried out statically. Recirculating microflume experiments showed that flowing water increased dissipation compared to static systems, regardless of light treatment. This suggests regulatory tests are not properly representing flowing aquatic systems, e.g. rivers. Lastly, regulatory tests are carried out on a small scale. Although there was little effect on pesticide decline in different sized microcosms, in the larger microflumes, dissipation occurred even under dark conditions. A number of Operational Taxonomic Units were specific to the microflumes suggesting that, on a larger scale, there was a wider variety of microorganisms that better reflected the environment. This work provides evidence for potential modifications to regulatory tests and insight into non-standard tests that industry could include in regulatory submissions.

Plants - including commercially important crops - are exposed to numerous pathogens often resulting in significant loss of yield. Understanding the underlying mechanisms of pathogen recognition and defence strategies is key in successfully ensuring food security. Research on plant-pathogen interactions has mainly focused on the gene networks after pathogen perception as well the identification of resistance genes. Latest research suggests that chromatin remodelling, including nucleosome displacement and DNA or histone-modifying enzymes are important in plant immunity. This thesis focuses on chromatin remodelling as the mechanism by which plants mount an effective immune response. The thesis also investigates the role of histone acetylation as one of several chromatin remodelling mechanisms. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) are two classes of histone modifying enzymes that antagonistically govern the acetylation levels of histones in gene promoters and gene bodies ultimately affecting gene expression. HAG1 was identified as an important positive regulator of plant immunity in the interaction with Pst DC3000. A proteomic approach allowed the identification of TOPLESS family members as HAG1 interactors. Considering that chromatin remodelling is an important aspect of plant immunity, it was hypothesised that pathogens have evolved mechanisms to interfere with such processes. To this end, this thesis will present a comprehensive approach towards identifying Pst DC3000 Type-III effectors with the ability to interfere with chromatin remodelling. HopO1-1 was initially identified as an effector with chromatin binding properties, however, further experiments pointed more strongly towards this effector’s involvement in processes such as translation and photosynthesis. Overall, this thesis contributes towards a better understanding of the roles of histone acetylation and HAG1 histone acetyltransferase in plant immunity and sheds light into which Pst DC3000 effectors could be potentially involved in chromatin remodelling processes.

Growers of field vegetable crops are under increasing pressure to reduce their reliance on synthetic chemical pesticides and increase their use of alternative pest management tools, including biological control agents. In this project, experiments have been conducted to investigate insect pathogenic fungi as control agents of the cabbage aphid on horticultural brassicas. These fungi contribute to the natural regulation of aphid populations, but they can also be mass-produced and applied to crops by growers as “biopesticides.” Field experiments were carried out over two seasons to investigate the association between the population dynamics of cabbage aphids, insect pathogenic fungi, and other natural enemies. This has been backed up by laboratory experiments on one particular fungus, Pandora neoaphidis, which causes natural epizootics in cabbage aphid populations, and which has not been studied against this pest in detail before. Research has focused in particular on developing laboratory methods for characterizing fungal virulence, and on the effect of temperature on fungal infectivity as a key environmental variable affecting Pandora outbreaks. Finally, the susceptibility of cabbage aphid to infection by commercially available fungal biopesticides has been compared against aphid susceptibility to Pandora neoaphidis.

Integrated Postharvest Management of Anthracnose in Dragon Fruits Using Plant Extracts The study was conducted to develop an environmentally, biodegradable, non-toxic and sustainable bio-fungicide using the formulation where each plant crude extract (ginger, turmeric and “dukung anak”) at different concentrations were incorporated separately with 10% gum Arabic (GA). The formulation was assessed against a wide range of parameters such as disease incidence (DI) and severity (DS) as well as postharvest quality (physicochemical and nutritional) on dragon fruits during storage at 11±20C, 80% RH for up to 28 days. Additionally, the study also investigated a diagnostic tool, thus Loop-mediated isothermal amplification (LAMP), for early detection of anthracnose in dragon fruits caused by Colletotrichum gloeosporioides Penz during postharvest storage. Prior to the formulation, the antifungal effect of each plant extract alone was evaluated in vitro (against C. gloeosporioides ) at concentrations (2.5 mg/ml, 5 mg/ml, 7.5 mg/ml and 10 mg/ml) and in vivo (on the fruits to control anthracnose) at concentration (5 mg/ml, 10 mg/ml and 15 mg/ml). In vitro antifungal activity of plants extracts alone showed that all plant extracts showed significant antifungal activity against C. gloeosporioides that causes anthracnose in dragon fruit. This was evident in inhibition of mycelial growth and conidial germination, which translated to morphological damage such as distortion and shrivelling in the fungal hyphae during scanning electron microscopy (SEM) studies result. Ginger crude extracts at 10 mg/ml showed a promising result in terms of suppressing mycelial growth (88.48%) and conidial germination (87.5%) which was comparable to commercial fungicide (Mancozeb) at 2 mg/ml (80.45%). In the in vivo study, where dragon fruits were coated (treated) with only plant extracts by dipping, fruits treated at 15 mg/ml irrespective of the crude extracts experienced severe disease incidence due to phytotoxicity. However, DI and DS was significantly low in dukung anak-treated fruits irrespective of the concentration used. Postharvest anthracnose caused by C. gloeosporioides and its severity was signficantly low in dukung anak-treated fruits at 10 mg/ml which was not different in fruits treated with 10 mg/ml of turmeric crude extracts after 28 days of cold storage. The antifungal activity was due to the presence of bioactive compounds gingerol, curcumin and some alkaloids in ginger, turmeric and dukung anak which resulted in electrolye leakage from fungal cell wall contributing to direct control of anthracnose. Whiles dukung anak extract controlled anthracnose and its severity at 10 mg/ml, DI was more pronounced in ginger-treated fruits even at 5 mg/ml due to phytotoxicity. Overall, disease incidence was highest especially at 15 mg/ml irrespective of plant extract used. Additionally, the external appearance of treated fruits at 10 mg/ml and 15 mg/ml of extracts alone (irrespective of the type of plant used) negatively affected customers appeal and preference due to compromised original smell and colour of the fruit. To overcome this problem, a formulation compromised of each plant crude extracts especially at higher concentrations (10 mg/ml and 15 mg/ml) and at a lower concentration (5 mg/ml) were incorporated with 10%GA to develop a alternative non-chemical approach that can enhance the efficacy of each plant extract against anthracnose whilst improving other postharvest quality of fruits. Fruits treated with a composite coating of 10%GA+10 mg/ml turmeric crude extracts significantly reduced anthracnose and its severity by about 94% compared to controls. This was not different in fruits treated with 10%GA+15 mg/ml ginger extract after 28 days of storage. For a rapid detection of postharvest anthracnose caused by C. gloeosporioides, LAMP, a diagnostic tool showed that composite coating of 10%GA+5 mg/ml of turmeric markedly reduced the amount of fungal DNA isolated from infested fruits compared to controls. A clear indication that Lamp can be used for detection of anthracnose during postharvest storage. Generally, respiration rate and ethylene production were significantly lower in fruits coated with 10%GA plus either 10mg/ml or 5 mg/ml of ginger crude extracts even though it was markedly low in fruits coated with 10%GA+10 mg/ml of the either turmeric or dukung anak crude extracts. In this study, fruit treated coated with 10%GA+10 mg/ml of any crude extracts especially turmeric crude extract showed the greatest firmness, reduced water loss, delayed colour development, lowered the levels of TSS and maintained a high TA after 21 to 28 days of storage. Furthermore, an composite coating of 10%GA+10 mg/ml of turmeric crude extract helped to maintain higher total antioxidant and nutritional activity in dragon fruits due to the presence of high ascorbic acid content and total phenolic compounds. Similarly, sensory evaluation results proved the effectiveness of 10%GA+10 mg/ml of turmeric crude extract composite coating by maintaining the overall quality of dragon fruits. These findings suggest that 10%GA+10 mg/ml of turmeric crude extracts can be used for extending the storage life of dragon fruits for up to 28 days. Additionally, this study proposes LAMP as a promising diagnostic tool for early detection of postharvest anthracnose in dragon fruits and other tropical fruits during regular checks in transits (sea transports) or at packing houses. By doing so, the onset of postharvest anthracnose could be detected and immediate steps taken to control the disease.

The modification of floral characteristics will be beneficial in improving the efficiency of hybrid seed production and the breeding of more climate resilient varieties in bread wheat (Triticum aestivum). Methods for phenotyping floral traits were initially tested using small genotype panels under controlled conditions and in field trials. Low-tech phenotyping methods appropriate for use by breeders and researchers were developed and demonstrated to be accurate. A panel of 111 genotypes was subsequently assessed in field trials using these methods. A high level of genotypic variation was observed for anther extrusion, anther length and anthesis duration/pattern and phenotypes were found to be stable across trials. Using this phenotypic data set, floral trait marker-trait associations (MTAs) were detected by association mapping and additional anther extrusion quantitative trait loci (QTLs) have been detected by linkage mapping in a bi-parental population. The phenotypic effects of candidate loci co-localizing with MTAs and QTLs were investigated using TILLING mutants and modifications to floral characteristics have been observed in some mutant lines. The utilization of phenotyping and genomic resources described in the present study is discussed and areas of future research have been identified.

Take-all, caused by the soil-borne ascomycete fungus Gaeumannomyces graminis var. tritici, (Ggt), is a root disease that devastates wheat production worldwide. Current control measures consist of partially effective chemical seed dressings and cultural methods such as crop rotation. There is currently no genetic control of the disease. The first aim of this PhD project was to characterise a range of diploid and hexaploid wheat germplasm that possess a promising level of take-all resistance under field conditions. Both above and below ground phenotyping was carried out and soil moisture probes were used to evaluate upper root function for a range of hexaploid varieties. A diploid Triticum monococcum MDR037 (S) X MDR046 (R) mapping population was screened and revealed a good spread in susceptibility to take-all across two field seasons. The population has subsequently been genotyped and genetic analyses will be carried out to explore the genetic basis of resistance. Phialophora fungal species, belonging to the genus Gaeumannomyces, colonise wheat roots but do not destroy the vascular tissue and have previously been found to suppress take-all disease. In the second approach to control Ggt, winter wheat varieties on the AHDB Recommended List (RL) were screened for their ability to build-up natural populations of Phialophora fungi in the field. Differences were revealed in their potential to build-up Phialophora spp. under a first wheat crop. A Phialophora isolate collection was gathered and draft genomes were sequenced, assembled and annotated for the three Phialophora spp. found in UK soils. Preliminary analysis suggests that considerable polymorphism may exist between homologous genes found in all three species. These findings provide a novel contribution to the potential of these two differing control mechanisms against take-all disease.

With the world population estimated to be nine billion by 2050, the need to exploit plant genetic diversity in order to increase and diversify global food supply, and minimise the over-reliance for food on a few staple crops is of the utmost importance to address food security challenges. Bambara groundnut (Vigna subterranea (L) Verdc.), is an underutilised legume indigenous to Africa, rich in carbohydrates, with reasonable amounts of protein. It is known to be drought tolerant, able to grow on marginal lands where other major crops cannot with minimal rainfall ( < 700 mm) and no chemical inputs. The present study aimed to investigate and evaluate transcriptomic changes in two bambara groundnut genotypes; DipC and TN (Tiga Nicuru), derived from landraces, in response to drought stress using microarray XSpecies and next generation RNA sequencing approaches by utilising data, resources and approaches derived from major crops and model plants. Crop improvement for abiotic stress tolerance and increasing/stabilising yield have been difficult to achieve due to the complex nature of these stresses, and the genotype x environment interaction (GxE). Using bambara groundnut as an exemplar species this study also highlights how a number of recent technologies and approaches used for major crop research, can be translated for use in the research of minor crops for a better understanding of the genetics governing drought traits. To investigate the drought tolerance of bambara groundnut, microarray XSpecies and next generation RNA sequencing (RNA-seq) analysis was completed on leaf tissue from DipC and TN under drought and control (irrigation) conditions at different developmental stages (vegetative, reproductive and pod development). This is the first drought experiment reported in bambara groundnut employing the RNA-seq approach. Both investigation of mild (microarray XSpecies) and relatively severe (RNA-seq) drought stress for the DipC and TN genotypes, adapted to similar environmental conditions, provided initial evidence that the two genotypes used different sets of genes to achieve drought response traits (including; ABA synthesis, hormone signaling, osmotic adjustment, accumulation of antioxidants, lignin synthesis, down-regulation of photosynthesis related genes, carbohydrate metabolism, cell-wall modification and transporters). Hence, both genotypes may have adapted in different ways to enable them to grow in the semi-arid conditions, suggesting that there may be more than a single way to achieve resilience in the face of drought stress. The key enzymes involved in metabolic pathways, such as carbohydrate metabolism, redox homeostasis, lipid metabolism, photosynthesis, generation of precursor metabolites/energy, and cell wall component biogenesis were affected by drought stress in both genotypes. XSpecies microarray experiment identified several differentially expressed genes (DEG) in each genotype and the four potential drought candidate genes (PAL1, Beta-fructofuranosidase, COMT, UBC-2) identified were validated utilising quantitative reverse transcriptase PCR (qRT-PCR). In addition, both drought experiments (mild and severe) also showed that the two genotypes expressed a number of genes of what are classically considered to be ‘drought-response’ genes even under the control condition. These results suggest that high expression of drought-response genes even under control conditions in both genotypes may lead to greater root growth and other avoidance traits which prime the plant for future dry periods, hence preparing for drought conditions. Morphological differences and the rapid reduction in photosynthesis, stomatal conductance and transpiration observed in both genotypes under drought stress provides a platform to link these physiological data with gene expression data. The observed physiological responses (i.e reduction in stomatal conductance and photosynthesis) under drought stress were backed up by high expression of genes related to stomatal closure via ABA signaling and down-regulation of photosynthesis-associated genes. A selection of genes chosen from microarray XSpecies and RNA-seq experiments were further used to identify their approximate chromosomal location in bambara groundnut using a cross-species approach. A total of 4 genes (HOX, AUX_IAA, acid phosphatase and dehydrin) were found to be near or within the confidence intervals of the QTLs underlying two drought traits (stomatal density/leaf area and CID). The initial results suggest that some of the locations of genes identified in XSpecies microarray and RNA-seq experiments could underlie QTL involved in controlling drought traits in bambara groundnut. These data provide the basis for drought trait improvement in bambara groundnut, which will facilitate functional genomics studies. Analysis of this dataset have suggested that both genotypes are primed to respond to drought stress and have adapted in different ways to achieve drought tolerance. This will help in understanding the mechanisms underlying the ability of crops to produce viable yields under drought conditions. Future work should verify whether the identified genes are associated with the trait of interest.

Disease tolerance is defined as the ability to maintain grain yield in the presence of disease and could be a potential defence mechanism to be incorporated into breeding programmes. It is an attractive goal, as disease tolerance has the potential to be a broad-spectrum, durable defence mechanism while exerting little selection pressure on pathogen populations. Relatively little is known about how disease tolerance is conferred, but most of the hypotheses suggest resource capture and resource-use traits such as large green canopy area, increased light extinction coefficient and a high source to sink balance. Disease tolerance in current wheat genotypes is generally associated with low yield potential, and for disease tolerance to be incorporated into commercial breeding it is important to determine whether this link can be disassociated. In this study, an attempt was made to identify physiological traits conferring disease tolerance to Septoria tritici blotch (STB) in winter wheat. Wheat genotypes contrasting in disease tolerance were selected for in-depth phenotyping of selected physiological traits to determine their association with disease tolerance. A number of publications have attempted to link disease tolerance to physiological traits in wheat, based on their yield loss to disease symptom relationship. However, in this study it was proposed that variation in non-symptomatic disease could influence the appearance of disease tolerance which has not previously been investigated. The ratio of in-leaf pathogen biomass to visual disease symptoms was studied in both controlled-environment experiments and in field experiments to determine whether a high in-leaf pathogen biomass was associated with disease tolerance. Two field experiments were conducted during the field seasons 2011/12 and 2013/14 at Teagasc Oak Park, Carlow, Ireland and ADAS Rosemaund, Herefordshire, UK, respectively. A field experiment was also conducted in 2012/13 at Teagasc Oak Park, but due to dry conditions and little disease presence this field experiment was excluded from nearly all experimental analyses. In each experiment, there were two fungicide treatments, non-target disease control and full disease control. In order to increase genetic variability, 38 selected lines from a L14 x Rialto doubled-haploid (DH) mapping population developed by the International Maize and Wheat Improvement Centre (CIMMYT) were screened alongside 10 UK-adapted reference genotypes for contrasting disease tolerance in 2012. Tolerance was quantified as yield loss per unit of green lamina area index (GLAI) loss to disease. L14 is a CIMMYT spring wheat large-ear phenotype advanced line and Rialto is a UK winter wheat which has high radiation-use efficiency and stem soluble carbohydrate. The DH lines displayed an increased range of disease tolerance compared to the UK-adapted reference genotypes. Selected genotypes were subjected to in-depth phenotyping for an extended range of physiological traits in 2014 to identify traits associated with increased disease tolerance. The traits measured included pre- and post- anthesis radiation interception, light extinction coefficient at anthesis, pre- and post anthesis radiation-use efficiency and stem water soluble carbohydrate accumulation at ear emergence + 7 days. In general, there was a wide range of physiological traits displaying weak associations with disease tolerance. The main traits associated with disease tolerance were related to large and/or maintained source capacity in the presence of disease, such as increased GLAI at anthesis and increased post-anthesis light interception. There was also a general association with low grain yield in the absence of disease and decreased harvest index. Increased disease tolerance was associated with high source capacity and low sink capacity, and there was an association between a high source to sink balance, measured as increased Healthy Area Duration (HAD) per grain, and disease tolerance. The impact of genotype variation on the amount of non-symptomatic disease to visual disease expression was investigated in controlled-environment (CE) experiments. In-leaf Zymoseptoria tritici fungal biomass (pathogen load) was quantified by a Real Time qPCR assay targeting the β-tubulin gene (Accession no. AY547264) and compared to visual disease expression. In the first CE experiment, two wheat genotypes were exposed to increasing concentrations of Z. tritici inoculum. There were differences in rates of pathogen development and pathogen presence between inoculum concentrations in both visual disease symptoms and pathogen loads. In the following CE experiment, a wider range of genotypes exposed to a high inoculum level were shown to differ significantly in the relationship between visual disease symptoms and pathogen loads. In order to determine the impact of genotype variation on the visual disease symptoms to pathogen load ratio, flag leaves of genotypes screened for in-field disease tolerance in 2012 and 2014 were analysed. Large variations in the disease symptoms to pathogen load ratio were identified, which has not previously been shown in wheat experiments. An attempt was made to relate the visual symptoms – pathogen load ratio to non-lesion green area loss as a measure of a potential metabolic cost of increased pathogen pressure, but no such relationship was found. An increased pathogen load per unit visual symptoms did not account for larger yield losses than predicted for a given disease level and there was no direct relationship between symptom expression - pathogen load ratios and disease tolerance. The consistency of high/low displays of disease tolerance calculated by different disease measures was investigated using three different ways of measuring disease; HAD, area under disease progress curve (AUDPC) and pathogen DNA quantified by qPCR. In general, the two measures of pathogen presence (AUDPC and pathogen load) tended to quantify disease tolerance similarly, while the HAD-based tolerance contrasted. There were also differences in which traits were associated with disease tolerance for the different methods of calculating tolerance; the calculations based on AUDPC and pathogen DNA tended to associate a decreased source capacity to disease tolerance while the HAD-based tolerance indicated an association with increased source capacity. All methods, however, indicated that a low yield potential was associated with disease tolerance. In conclusion, there was a large range of disease tolerance found in the field experiments compared to previous investigations. The HAD-based disease tolerance seems to be mainly related to a large source capacity and a low sink capacity. However, the genotype ratings of high/low disease tolerance and associated physiological traits seem to vary according to the method of calculating tolerance. There were large differences in the ratio of visual symptoms-pathogen load between genotypes; even though this did not have a direct impact on disease tolerance or yield loss it could potentially be associated with increased metabolic costs.