Infectious fungal diseases pose a substantial threat to susceptible plant species, causing host declines, limiting host populations’ community role, and threatening the sustainability of natural ecosystems. Evaluating disease severity and progression is essential for understanding the impacts of these diseases, and this information could provide insights into developing future interventions. On Roan Mountain, Tennessee, native monocot Veratrum viride (Röhl.), was recently discovered to be infected with a fungal pathogen, Pseudocercosporella sublineolata (Thüm. U. Braun.), a Veratrum-specific leaf spot disease. To understand the prevalence and impacts of this disease, a demographic and disease severity study was performed. We hypothesized that P. sublineolata infection was associated with the decline of leaves and the premature seasonal senescence of V. viride plants, and that the increase in the number of leaf spots over the growing season was associated with the decline in plant health. To test these hypotheses, twenty plants from two different populations on Roan Mountain were systematically selected and tagged for a total of forty plants. From June through September 2021, demographic characteristics (plant height, number of leaves, and whether the plant flowered), and disease data (plant health, number of leaf spots, diameter of spots, and whether spots harbored P. sublineolata spores) were recorded over seven visits. To diagnose the disease, leaf spot samples were collected, slides were prepared and examined for spores at 100/200X magnification. We confirmed the diagnosis of P. sublineolata infection based on the conidia’s shape, size, and number of cells. The relationship between P. sublineolata and plant senescence was strengthened because the samples had abundant conidia that were present as pure isolates rather than a mixture of other potential microbial pathogens. All plants in the study declined progressively throughout the growing season, and they senesced earlier than expected, i.e., before the first frost. This early season decline likely limits reserves stored in the overwintering bulb and inhibits seed maturation, thereby posing a threat to the viability of these V. viride populations on Roan Mountain.

Alzheimer’s disease (AD) progressively impairs cognitive and functional abilities. Research on pharmacological treatment of AD is shifting to earlier forms of the disease, including preclinical stages. However, assessment methods traditionally used in clinical research may be inappropriate for these populations. The Alzheimer Disease Assessment Scale-cognitive (ADAS-cog), a commonly used cognitive battery in AD research, is most sensitive in the moderate range of cognitive impairment. It focuses on immediate recall and recognition aspects of memory rather than retention and delayed recall. As clinical trials for dementia continue to focus on prodromal stages of AD, instruments need to be retooled to focus on cognitive abilities more prone to change in the earliest stages of the disease. One such domain is delayed recall, which is differentially sensitive to decline in the earliest stages of AD. A supplemental delayed recall subtest for the ADAS-cog is commonly implemented, but we do not know precisely where along the spectrum of cognitive dysfunction this subtest yields incremental information beyond what is gained from the standard ADAS-cog. An item response theory (IRT) approach can analyze this in a psychometrically rigorous way. This study’s aims are twofold: (1) to examine where along the AD spectrum the delayed recall subtest yields optimal information about cognitive dysfunction, and (2) to determine if adding delayed recall to the ADAS-cog can improve prediction of functional outcomes, specifically patients’ ability to complete basic and instrumental activities of daily living. Results revealed differential functioning of ADAS-cog subtests across the dimension of cognitive impairment. The delayed recall subtest provided optimal information and increased the ADAS-cog’s measurement precision in the relatively mild range of cognitive dysfunction. Moreover, the addition of delayed recall to the ADAS- cog, consistent with my hypothesis, increased covariation with instrumental but not basic activities of daily living. These findings provide evidence that the delayed recall subtest slightly improves the ADAS-cog’s ability to capture information about cognitive impairment in the mild range of severity and thereby improves prediction of instrumental functional deficits.

Submitted by (lucia.rodrigues@ufrpe.br) on 2017-02-21T14:43:15Z No. of bitstreams: 1 Domingos Eduardo Guimaraes tavares de Andrade.pdf: 1134828 bytes, checksum: b275aaaed4ce9ad14aa4a28ddd01f571 (MD5) / Made available in DSpace on 2017-02-21T14:43:15Z (GMT). No. of bitstreams: 1 Domingos Eduardo Guimaraes tavares de Andrade.pdf: 1134828 bytes, checksum: b275aaaed4ce9ad14aa4a28ddd01f571 (MD5) Previous issue date: 2004-03-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This study aimed to verify the frequency of fungi associated to melon (Cucumis melo L.) roots with collapse symptoms and their correlation with physical, chemical and microbiologic characteristics of soils. It also aimed to analyze the influence of inoculum densities and strains of Monosporascus cannonballus on the melon collapse, evaluating suitable methods to quantify disease. Melon plants with collapse symptoms and soil samples were collected from 10 producing areas, located in the counties of Mossoró and Baraúna (State of Rio Grande do Norte) and Quixeré (State of Ceará). The isolation frequency (FI) of fungi was obtained for each area, while the soil samples were analyzed in relation to physical, chemical and microbiologic characteristics. Monosporascus cannonballus inoculum densities of 0.1, 0.5, 1, 5, 10, 25 and 50 cfu/g of soil were essayed for collapse severity (SD), plant length (CP), shoot fresh biomass (BFPA) and root fresh biomass (BFR), shoot dry biomass (BSPA) and root dry biomass (PSR), areas of first and second true leaves (A1FD and A2FD), accumulated leaf area (AFA), total volume of plant (VTP), total fresh biomass of plant (BFTP) and total dry biomass of plant (BSTP). In the variability essay were utilized 44 strains of M. cannonballus with inoculum density of 10 cfu/g of soil. In the FI survey, high prevalences were verified for Fusarium solani and Macrophomina phaseolina (100%), while lower values were verified for Rhizoctonia solani (40%), M. cannonballus (30%) and Sclerotium rolfsii (30%). Fusarium solani and M. phaseolina presented similar FI, ranging from 1.6 to 60.0%, while M. cannonballus showed FI from 0.0 to 71.1%, R. solani from 0.0 to 18.0% and S. rolfsii from 0.0 to 13.3%. The FI of F. solani and M. cannonballus were respectively higher in melon type Orange (57.1%) and Cantaloupe (40.9%), as well as in areas with one or two years (45.4%) andwith more than five years (48.2%) of cropping. The FI of F. solani and M. cannonballus were inversely correlated (r = -0.79), and were influenced by the amount of Bacillus spp. in the soil (r = -0.71 and 0.80, respectively). The FI of M. phaseolina correlated with phosphorus level (r = 0.68), the FI of R. solani with flocculation degree (r = 0.67), field capacity (r = -0.81), pH (r = -0.75), aluminum level (r = 0.85) and total acidity (r = 0.69). The FI of S. rolfsii correlated with the permanent wilting point (r = -0.78) and soil available water (r = 0.75). The progress curves of SD, CP, A1FD, A2FD and AFA, related to inoculum densities, were adjusted by non-linear logistic model. Low inoculum densities (0.1, 0.5 and 1 cfu/g of soil) produced high levels of SD, ranging from 15.6 to 53.1%. Densities from 20 to 50 cfu/g of soil did not substantially increase SD. In the essay with different M. cannonballus strains, the analyzed variables propitiated formation of threesimilarity groups and evidenced strain variability within and among areas. High coefficients of correlation and determination confirmed the fit of SD with A1FD, A2FD and AFA in two essays demonstrating potential use to quantify the melon collapse. / Este estudo teve como objetivos determinar a freqüência de fungos associados às raízes de meloeiro (Cucumis melo L.) com sintomas de colapso, relacionando-a com as características físicas, químicas e microbiológicas dos solos, e verificar a influência de densidades de inóculo e isolados de Monosporascus cannonballus sobre o colapso do meloeiro, avaliando metodologias adequadas para a quantificação da doença. Meloeiros com sintomas de colapso e amostras de solos foram coletados em 10 áreas produtoras, localizadas nos municípios de Mossoró e Baraúna (RN) e Quixeré (CE). A freqüência de isolamento (FI) de fungos foi obtida para cada área, enquanto as amostras de solo foram analisadas quanto às características físicas, químicas e microbiológicas. No ensaio de densidades de inóculo de M. cannonballus foram utilizadas as densidades de 0,1; 0,5; 1; 5; 10; 25 e 50 ufc/g de solo, avaliando-se a severidade do colapso (SD), comprimentoda planta (CP), biomassa fresca da parte aérea (BFPA) e da raiz (BFR), biomassa seca da parte aérea (BSPA) e da raiz (BSR), áreas da 1ª e 2ª folhas definitivas (A1FD e A2FD), área foliar acumulada (AFA), volume total da planta (VTP), biomassa fresca total (BFTP) e biomassa seca total da planta (BSTP). No ensaio de variabilidade foram utilizados 44 isolados de M. cannonballus, na densidade de inóculo de 10 ufc/g de solo. No levantamento da FI, prevalências elevadas (100%) foram constatadas para Fusarium solani e Macrophomina phaseolina, enquanto valores menores foram verificados para Rhizoctonia solani (40%), M. cannonballus (30%) e Sclerotium rolfsii (30%). Fusarium solani e M. phaseolina apresentaram FI similares, variando de 1,6 a 60,0%, enquanto M. cannonballus apresentou FI de 0,0 a 71,1%, R. solani de 0,0 a 18% e S. rolfsii de 0,0 a13,3%. As FI de F. solani e M. cannonballus foram respectivamente superiores em meloeiros dos tipos Orange (57,1%) e Cantaloupe (40,9%), assim como em áreas com um ou dois anos (45,4%) e com mais de cinco anos (48,2%) de cultivo. As FI de F. solani e M. cannonballus correlacionaram-se inversamente entre si (r = -0,79), sendo estas influenciadas pela quantidade de Bacillus spp. presente no solo (r = -0,71 e 0,80, respectivamente). A FI de M. phaseolina correlacionou-se com o teor de fósforo (r = 0,68), a FI de R. solani com o grau de floculação (r = 0,67), capacidade de campo (r = -0,81), pH (r = -0,75), teor de alumínio (r = 0,85) e acidez total (r = 0,69), enquanto a FI de S. rolfsii correlacionou-se com o ponto de murcha permanente (r = -0,78) e a água disponível no solo (r = 0,75). As curvas de progresso da SD, CP, A1FD, A2FD e AFA, em função das densidades de inóculo, foram ajustadas pelo modelo não-linear logístico dose-resposta. Baixas densidades de inóculo (0,1; 0,5 e 1 ufc/g de solo) produziram elevados níveis deSD, que variaram de 15,6 a 53,1%. Densidades entre 20 e 50 ufc/g de solo não aumentaram substancialmente a SD. No ensaio com diferentes isolados de M. cannonballus, o conjunto das variáveis analisadas propiciou a separação de três grupos de similaridade, ficando evidente a variabilidade dos isolados dentro de uma mesma área e entre áreas. Elevados coeficientes de correlação e determinação confirmaram o ajuste da SD com A1FD, A2FD e AFA nos dois ensaios, demonstrando o potencial de utilização destas variáveis para quantificar o colapso do meloeiro.

Le dessèchement précoce du tournesol résulte d'une infection de bas de tige par Phoma macdonaldii qui provoque une nécrose encerclante et un rétrécissement du diamètre du collet. Cette attaque entraine une sénescence foliaire brutale occasionnant des pertes dommageables pour la culture. Des contaminations artificielles par des spores ou du mycélium de P. macdonaldii ont permis de reproduire artificiellement des pieds secs et confortent l'implication de ce champignon dans ce syndrome. Dans un contexte où la protection chimique et la résistance variétale sont limitées, la maîtrise de P. macdonaldii par le contrôle cultural pourrait constituer une alternative efficace. Des essais au champ et en serre menés de 2006 à 2009 à l'INRA et au Cetiom ont permis de mettre en évidence l'importance de la conduite de culture du tournesol sur la fréquence et la gravité du dessèchement précoce et de mieux comprendre l'étiologie de ce syndrome. Une alimentation azotée importante, un peuplement dense et à un régime hydrique limitant en post floraison forment trois facteurs particulièrement favorables au développement du syndrome de desséchement précoce attribué à P. macdonaldii. L'alimentation azotée, au travers de la fertilisation, est le principal facteur favorisant la maladie ; le régime hydrique limitant et la densité de peuplement amplifient la maladie. Le faible diamètre de bas de tige (sous de fortes densités) associé à la prolifération du champignon dans le xylème (azote), occasionnerait une réduction de la conductance hydraulique par obstruction des vaisseaux. Amplifiée lorsque la disponibilité en eau du sol est limitante, cet arrêt de la transpiration se traduit par une sénescence anticipée de 40 jours par rapport à la maturité physiologique de peuplement sains. / Sunflower premature ripening results from an infection by Phoma macdonaldii causing lesions girdling the stem base and narrowing the diameter of the collar. This attack induces a sudden leaf senescence damaging for the culture. Artificial inoculations with spores or mycelium of P. macdonaldii aimed to reproduce the disease and confirm the involvement of this fungus in this syndrome. In a context where chemical protection and plant resistance are limited, control of P. macdonaldii by cultural control could be an effective alternative. Field and greenhouse trials conducted from 2006 to 2009 at INRA and Cetiom showed the importance of sunflower crop management on the frequency and severity of early drying, and better understand the etiology of this syndrome. A significant nitrogen supply, a dense population and a limited water regime postflowering are particularly conducive to premature ripening. Nitrogen supply is the main factor favoring the disease; limited water regime and density amplify the disease. The small stem base diameter (under high densities) associated with the proliferation of the fungus in the xylem (nitrogen), may reduce hydraulic conductance by vessel blockage. Amplified when soil water availability is limiting, this stop of the transpiration leads to early senescence 40 days before physiological maturity of healthy plants.

Alternaria spot, caused by Alternaria tenuis, is an important disease of cladodes of the prickly pear cactus (Nopalea cochenillifera) in Brazil. There are no standard methods for assessment of the disease, so a standard area diagram set (SAD) was developed based on disease severity encompassing 2, 4, 7, 12, 22 and 40% of the cladode area spotted. SAD was validated by 10 raters, who analysed 50 cladodes with a range of disease severity, without and with SAD as an assessment aid. The accuracy, precision, reproducibility and repeatability of the estimates with and without the scale were determined using simple linear regression analysis. Without SAD the accuracy and precision of raters estimates were poor, with significantly constant and systematic bias, and determination coefficients (R2) ranging from 0.56 to 0.78. When raters employed SAD, significant reductions were observed in both constant and systematic bias, with R2 ranging from 0.91 to 0.96. In fact, raters achieved the highest repeatability (mean R2 = 0.95) and reproducibility (R2 0.80 in all cases) of estimates when using SAD. The proposed SAD set is suitable for assessment of Alternaria spot of prickly pear cladodes and improves the accuracy and precision of assessments. / A mancha de alternária, causada por Alternaria tenuis, foi detectada em cladódios de palma forrageira miúda (Nopalea cochenillífera) no Brasil em 2001 e, desde então, os relatos de sua ocorrência é conseqüente defoliação de palmas no campo se tornou constante. Devido à inexistência de métodos padronizados para quantificação desta doença desenvolveu-se uma escala diagramática com os seguintes níveis de área lesionada: 2, 4, 7, 12 ,22 e 40%. A validação da escala foi realizada por 10 avaliadores que estimaram a severidade da mancha de alternaria em 50 imagens de cladódios com diferentes níveis de intensidade da doença. A validação se deu em três etapas: i. sem o uso da escala; e ii. Primeira avaliação com a escala; e iii. Segunda avaliação com a escala. O intervalo entre etapas foi de 15 dias. A acurácia, precisão, reprodutibilidade e repetibilidade das estimativas foram avaliadas por meio de análise de regressão linear simples entre a severidade real e a estimada, com e sem auxílio da escala. A escala confeccionada foi de fácil utilização e proporcionou melhoria significativa nas estimativas de severidade, possibilitando bons níveis de acurácia e excelentes níveis de precisão, reprodutibilidade e repetibilidade, podendo ser utilizada em levantamentos de campo, estudos epidemiológicos e comparação de medidas de controle da doença.

Chronic diseases are a significant cause of illness and mortality in the United States. Hereditary predisposition to chronic diseases is a useful indicator for identifying people at risk for disease development. An ideal tool for determining this predisposition is the CDC, NIH, and AAFP recommended third-degree family health history (FHH). The aim of this quantitative, cross-sectional study, based on the theoretical frameworks of social constructivism and the health belief model, was to assess the possible influence between the completed third-degree FHH and the participant's perception of disease risk. Two-hundred seventy-three participants were recruited from health care facilities and from the general population using convenience sampling. Bivariate and multivariate tests were applied to analyze the obtained data. Binary regression indicated a statistically significant association between the presence of heart disease, stroke, breast cancer, ovarian/cervical cancer, prostate cancer, colon cancer, and diabetes, and the perception of risk for the particular disease as noted in the FHH. A familial history of stroke appeared to be the strongest predictor of perception of disease risk. Moreover, increasing age, particularly within the age range of 40 to 57, was associated with increasing levels of perception of disease risk for heart disease, stroke, and prostate cancer. Individuals from the general population significantly indicated higher-than-average risk for colon cancer compared to those from health care facilities. Social change implication of this study may be the widespread implementation of a familial health history questionnaire that leads to an impactful, higher degree of disease risk awareness, prompting preventive action on the part of the individual, and leading to improved individual and population health.

Proportional loss models commonly used in disease surveys are based on the assumption that per cent yield loss is the same in all crops, regardless of their yield potential. Estimates of regional crop loss may be inaccurate if the relationship between disease and yield loss is affected by crop yield potential. The importance of crop yield potential in disease: yield loss modelling was investigated and models for more accurate regional crop loss estimates were developed, taking crop yield potential into account. Two spring sown barley (cv. Triumph) experiments were conducted in 1987/88 and 1988/89 in Canterbury, New Zealand, to study the effect of crop yield potential on the relationship between disease and yield loss. Crop yield potentials of 323 to 806gDM/m² were generated in seven crops by varying nitrogen and water inputs, sowing date (mid-spring and early-summer) and season. Leaf rust (Puccinia hordei Otth) epidemics of different severity were generated by applying fungicides at different times, frequencies and rates to control the natural epidemics. Disease was measured as per cent disease severity (%DS), green leaf area, radiation interception and near-infrared radiation (NIR) reflectance from crop canopies. Yield was measured as total and grain dry weight. Epidemics were severe in the fully diseased plots from GS 34 and 46 to maturity in the late and early sown crops respectively. Disease reduced grain yield by 50 to 63% in 1987/88 and 24 to 38% in 1988/89 in the fully diseased plots. Disease: yield loss models were derived by regression analysis for each crop in 1987/88. Single point, multiple point and area under curve models were derived from %DS and GLAI variables, and proportional (%) and actual (gDM/m²) grain yield. The effect of yield potential was determined by comparing regression equation coefficients for each crop with crop yield potential. An area under green leaf area index curve (AUGLAIC): actual yield model was best suited to determining the effect of yield potential on yield loss. This model was selected because AUGLAIC summarised the effect of disease on plant growth over the season and actual yield represented the crop yield potential in the absence of disease and the response of actual yield to disease. Crop yield potential did not affect actual yield loss caused by leaf rust. Disease measured as AUGLAIC explained most of the variation in yield (R²adj=0.93) for all crops in both years. Assessment of GLAI is not suitable for estimation of regional crop loss because of the requirement for a rapid and low cost method. Reflectance of NIR from the crop canopy was investigated as an alternative to GLAI measurements. Reflectance was correlated significantly (P<0.001) with GLAI (r=0.66 to 0.89) and green area index (r=0.76 to 0.92). Reflectance measured at grain-filling (GS 85-87) explained most (R²adj=0.94) of the variation in yield for all crops in both years. The relationship between AUGLAIC and yield was validated with data from independent diseased and healthy barley crops. The AUGLAIC: yield model described the effects of disease on yield accurately but overestimated yield by 49 to 108% in the healthy crops. Models based on accumulated PAR (photosynthetically active radiation) intercepted by green leaves explained the observed deviations in yield of these crops from the AUGLAIC: yield model. Accumulated PAR models accounted for differences in incident radiation, canopy structure, radiation interception by green leaves, radiation use efficiency and harvest index which are important in determining dry matter production and grain yield. Accumulated PAR models described the effects of disease on crop growth which were not represented by GLAI alone. Variation in crop yield potential at the regional scale is important in disease: yield loss modelling and can be accounted for by using either separate equations for each yield potential crop or crop category, robust models, inclusion of a form function for yield potential or choice of disease and yield variables which integrate yield potential.

Zielsetzung Die Konsensempfehlungen zur Begutachtung der Berufskrankheiten Nr. 2108 und Nr. 2110 (bandscheibenbedingte Erkrankungen der Lendenwirbelsäule) setzen bei der häufigsten Fallkonstellation, der sog. B2-Konstellation, voraus, dass mindestens eines von 3 Zusatzkriterien erfüllt ist. Zwei dieser Zusatzkriterien werden in der vorliegenden Sonderauswertung der Deutschen Wirbelsäulenstudie (DWS) empirisch überprüft. Methoden Untersucht wurden die einwirkungsabhängigen Zusatzkriterien „besonders intensive Belastung“ (2. Zusatzkriterium) und „Belastungsspitzen“ (3. Zusatzkriterium). Mittels logistischer Regressionsanalyse wurden für Alter und Studienzentrum adjustierte Odds-Ratios (als Schätzer des relativen Bandscheiben-Erkrankungsrisikos) mit 95 %-Konfidenzintervallen (95 % KI) berechnet. Es wurden jeweils im gleichen Regressionsmodell Odds-Ratios für die Erfüllung und für die fehlende Erfüllung eines Zusatzkriteriums ermittelt. Grundsätzlich ist ein Kriterium dann zur Unterscheidung zwischen beruflich verursachten und nicht beruflich verursachten bandscheibenbedingten Erkrankungen geeignet, wenn die Risikoschätzer bei Erfüllung des jeweiligen Kriteriums deutlich höher liegen als bei fehlender Erfüllung des Kriteriums. Bei den Belastungsspitzen wurde die Höhe der mit Hebe- oder Tragevorgängen verbundenen Druckkräfte in der Lendenwirbelsäule (LWS) variiert, ab der das Kriterium der Belastungsspitzen als erfüllt angesehen wurde; ferner wurde die Zahl der Schichten variiert, in denen das Kriterium der Belastungsspitzen erfüllt sein musste. Alle Berechnungen wurden getrennt für Männer und Frauen für die Dosismodelle „Original-MDD“ und „BSG-Modell“ durchgeführt. Ergebnisse Bei Vorliegen einer „besonders intensiven Belastung“ finden sich keine höheren bandscheibenbezogenen Erkrankungsrisiken als bei fehlendem Vorliegen dieses Zusatzkriteriums. Als „best estimate“ kann von der Erfüllung des Zusatzkriteriums „Belastungsspitzen“ dann ausgegangen werden, wenn beim BSG-Modell in mindestens 600 Schichten des gesamten Berufslebens Tagesdosen von mindestens 2,0 kNh (Kilonewton-Stunden = 1000 Newton-Stunden) pro Schicht bei Männern bzw. mindestens 0,5 kNh bei Frauen durch Belastungsspitzen (Druckkraft ≥ 6,0 kN bei Männern, ≥ 4,5 kN bei Frauen) erreicht werden. Schlussfolgerung Die Sonderauswertung der Deutschen Wirbelsäulenstudie kann keine Bestätigung des 2. Zusatzkriteriums der B2-Konstellation „besonders intensive Belastung“ erbringen. Das 3. Zusatzkriterium „Belastungsspitzen“ wird hingegen grundsätzlich bestätigt – es sollte über mindestens 600 Arbeitsschichten erfüllt sein, um als Positivkriterium für die Anerkennung einer bandscheibenbedingten Berufskrankheit fungieren zu können.

Studies were conducted on three field trials of wheat cv. Kopara to investigate the lack of compensation by later determined components of yield because of early disease constraints. The investigation was based on the hypothesis that early disease reduces root development and thus causes the plants to be water constrained at later growth stages when soil water deficits usually occur. The reduced root development and soil water deficits may reduce the ability of the plant to compensate for reductions in early determined components. The hypothesis was tested by the application of irrigation to alleviate water stress. In a disease free crop, the possible phytotonic effects of the fungicides benomyl and triadimefon on wheat were investigated. These fungicides had no phytotonic effects on shoot, root growth, or yield under the prevailing conditions. The effect of disease on root development was analysed by root length measurements. Disease present in the crop at any stage of growth affected root development. Root development in the upper zones of the soil profile was reduced more by disease compared to those zones below 35 cm. A full disease epidemic reduced root development more than an early or late disease epidemic. The early and late disease epidemics had similar effects on root length. Alleviation of early disease constraints enabled greater development of roots to offset any earlier reductions. Soil water deficits increased root development in the lower zones of the nil disease plants. The presence of adequate soil water from irrigation reduced the requirement for further root growth in all treatments. In the 1981-1982 field trial a full disease epidemic reduced yield by 14% whereas an early disease epidemic reduced yield by 7%. The reduction in yield was attributed to a lower grain number. With irrigation the yield reduction in the full disease plants was 12% whereas in the early disease plants the reduction was only 2.4%. This indicated that plants affected by the early disease epidemic were water constrained. In this study, the results suggested that, for conditions prevailing in Canterbury, the supply of water at later growth stages increased grain weight in plants which were subject to early disease epidemics. This suggests that reduced root development caused by early disease and soil water deficits may prevent compensation by grain weight. Water use was similar in all disease treatments. After irrigation the irrigated plants of all treatments used more water. Disease affected water use in relation to yield production however, and was better expressed by water use efficiency. Water use efficiency was reduced in the full disease plants. A stepwise regression analysis suggested that water use efficiency was affected directly by disease at later growth stages, and indirectly via an effect on total green leaf area at early growth stages. This study partially proves the hypothesis that reductions in root development caused by an early disease epidemic may constrain the plants at later growth stages when water deficits usually occur. It was shown that the reduction in root development caused by disease could be counteracted by irrigation. In this respect, water served as a tool to study the effect of disease constraints on the yield of wheat. A knowledge of cereal crop physiology, root growth and function is used to explain and discuss the observations made in this research programme. The results are discussed in relation to the way in which disease affects yield through its effect on root development. The possible reasons for the continued effects of disease even after the control of disease at later growth stages are discussed. The economic use of fungicides and water in diseased crops are also outlined. Suggestions for future studies on disease-yield loss relationships are provided. The repetition of these experiments in different sites and climatic regions could provide information which may be incorporated in disease-yield loss simulation models. This could then be used to predict root development and water requirements of diseased plants, and provide a basis for economic use of fungicides and water, and for better disease management programmes.