Healthy Leaf Area Research Articles

The Effects of Rust and Anthracnose on the Photosynthetic Competence of Diseased Bean Leaves

ABSTRACT The effects of rust (caused by Uromyces appendiculatus) and anthracnose (caused by Colletotrichum lindemuthianum) and their interaction on the photosynthetic rates of healthy and diseased bean (Phaseolus vulgaris) leaves were determined by gas-exchange analysis, in plants with each disease, grown under controlled conditions. The equation P(x)/P(0) = (1 - x)() was used to relate relative photosynthetic rate (P(x)/P(0)) to proportional disease severity (x), where beta represents the ratio between virtual and visual lesion. The beta values obtained for rust were near one, indicating that the effect of the pathogen on the remaining green leaf area was minimal. The high values of beta obtained for anthracnose (8.46 and 12.18) indicated that the photosynthesis in the green area beyond the necrotic symptoms of anthracnose was severely impaired. The impact of anthracnose on bean leaf photosynthesis should be considered in assessments of the proportion of healthy tissue in diseased leaves. The accurate assessment of the healthy portion of the leaf could improve the use of concepts such as healthy leaf area duration and healthy leaf area absorption, which are valuable predictors of crop yield. The equation used to analyze the interaction between rust and anthracnose on the same leaf was P(z) = P(0) (1 - x)(x) x (1 - y)(y), where P(z) is the relative photosynthetic rate of any given leaf, P(0) is the maximum relative photosynthetic rate, x is anthracnose severity, y is rust severity, betax is the beta value for anthracnose in the presence of rust, and betay is the beta value for rust in the presence of anthracnose. From the resulting response surface, no interaction of the two diseases was observed. Dark respiration rate increased on diseased leaves compared with control leaves. The remaining green leaf area of leaves with both diseases was not a good source to estimate net photosynthetic rate because the effect of anthracnose extended far beyond the visual lesions, whereas the effect of rust on photosynthesis was essentially limited to the pustule plus halo.

Changes in water relations of Eucalyptus nitens nursery stock during and after lifting and transplanting

Field symptoms of transplanting shock in Eucalyptus nitens open rooted (1/2 + 1/2) transplants suggest water stress. To identify stages in the development of symptoms, changes in water relations were monitored from undisturbed seedlings growing in a commercial nursery through lifting, transplanting into pots and re-establishment of normal water relations. Hydraulic resistance measured as leaf specific resistivity increased with each step in the transplanting process. Resistivity after lifting was double that measured on undisturbed plants in the nursery and subsequently doubled with each of the two successive stages, root trimming and planting out. Resistivity fell after the initial rise, returning to the values recorded in the nursery in two stages. An initial rapid decrease, which was not accompanied by any measurable root growth, was followed by a seven day period without a change in resistivity before a further gradual decrease as root volume increased with new root growth. All water relations measurements were taken on trees which had not suffered any permanent leaf damage as a result of transplanting. For a small group of trees which did suffer damage there was a significant relationship between root volume at planting and the retained healthy leaf area. Before shoot growth had recommenced the final ratio of turgid leaf area to initial root volume was comparable with plants immediately after lifting and before trimming. The results are discussed in terms of the changes in predawn leaf water potential, leaf water potential and the leaf damage or defoliation symptoms occuring in plantations.

Preventative and Curative Applications of Verticillium lecanii for Biological Control of Cucumber Powdery Mildew

The effect of timing of the application of the mycoparasite , Verticillium lecanii, on cucumber powdery mildew , Sphaerotheca fuliginea, was studied in a rooted cucumber leaf bioassay . The mycoparasite was applied at different times before and after mildew inoculation . At near - to maximum humidity ( 95% relative humidity) , early preventative (9 and 5 days before mildew inoculation) and early curative control treatments (2 days after mildew inoculation) gave considerable reduction in mildewed leaf areas , while late curative treatments resulted in greater mildewed leaf area but ultimately a reduced amount of healthy mildewed leaf area ( 20 % ) . Appropriate timing of biocontrol treatment application of V. lecanii is important to achieve good control .

Quantitative Assessment of Lesion Characteristics and Disease Severity Using Digital Image Processing

AbstractThis work describes a dedicated software which detects and characterizes disease lesions on leaves to provide data on the number and type of lesions and the percentage of leaf area diseased (severity). The software, written in C2+, can be used with a standard computer in combination with a colour CCD camera and a frame grabber for image acquisition. The usefulness and adaptability of the software was evaluated using two foliar diseases, Alternaria blight of sunflower and oat leaf rust (Puccinia coronata f.sp. avenae), which differ in symptoms. Using image segmentation and classification techniques, the software discriminated disease symptoms from the healthy leaf area. The number and size of lesions and severity, obtained using the image processing software, were compared with those calculated using a software planimeter or visual assessment. Significant linear relationships between planimeter and the imaging software were obtained for lesion number and severity in oat leaf rust and for severity in sunflower blight. Artefacts, mistakenly classified as blight lesions by the imaging software resulted in an over‐estimation of the number of lesions. Future research is aimed at improving accuracy through better illumination during image capture. A dedicated, compact and portable hardware is currently being developed for field use as a self‐contained device for disease assessment.

Angular Leaf Spot of Phaseolus Beans: Relationships Between Disease, Healthy Leaf Area, and Yield

ABSTRACT Five field experiments were conducted to investigate the relationship between the severity of visible disease (X), area under the disease progress curve (AUDPC), healthy leaf area index on any given day (HLAI), radiation intercepted by healthy leaf area on any given day (HRI), healthy leaf area duration (HAD), total healthy leaf area absorption (HAA), and yield of Phaseolus beans, cultivars Rosinha and Carioca, inoculated with Phaeoisariopsis griseola at several doses. In general, yield was not related to disease severity (X) or AUDPC. In contrast, the highest yields were always related to the highest values of HAD and HAA. The relationship between yield and HAD was linear in each of five trials (29.9 < R(2) < 70.2%, P < 0.001). The relationship between yield and HAA was linear in four of the trials (52.3 < R(2) < 70.3%, P < 0.001) and exponential in one of them (in which the plant canopy was the largest). Singlepoint models using HRI to estimate yield at various times during the crop season were developed. The slope of the yield-HRI relationship proved to be stable (26.8 +/-2.4 g MJ(-1)), regardless of cultivar, locale, planting date, and bean growth stage (from R5 to R8). The yield-HLAI relationship proved to be less consistent. HRI is proposed as a key explanatory variable for a transportable system of disease management; it may be useful in producing precise recommendations at the farm level.

Relationships between defoliation, canopy reflectance and pod yield in the peanut-late leafspot pathosystem

Defoliation of peanut (caused by Cercosporidium personatum), and reflected radiation (800 nm wavelength) of sunlight from peanut canopies, were assessed weekly beginning approximately 60 days after planting. Visual and reflectance assessments obtained with a hand-held, multispectral radiometer continued until one week prior to digging. Critical-point yield-loss models were developed using either percentage defoliation or percentage reflectance values as the independent variable and pod yield (kg ha −1) as the dependent variable. Yield reductions in the four experiments ranged from 52.9 to 79.0%. Based upon coefficients of determination and the standard errors for predicted y-values (yield), the best critical-point models for either assessment method were obtained when peanuts were assessed 2–3 weeks prior to digging. Critical point models using percent reflectance data as the independent variable explained more of the variation in peanut pod yield and had lower standard errors of the y-estimate than critical point models using percent defoliation values as the independent variable. Percent reflectance values explained 96.3–99.3% of the variation in biomass. This study supports the hypothesis that measurements of healthy green leaf area (as estimated by percent reflectance) have a better relationship with pod yield than defoliation based assessments.

A simple non-destructive technique for healthy and diseased leaf area assessment of potato plants

A method for assessing the leaf area of potato plants was based on the number of leaves coinciding with imaginary vertical lines descending from a horizontal grid of points above the plant or crop canopy. Leaves seen through each vertically aligned pair of holes in a perforated double table, covering the midpoint of the exposed area, were counted and moved aside one by one, until the ground was seen. For both green and diseased surfaces the leaf area, or its horizontal component, was calculated as the product of sum of records and the grid cell size. Tested against a destructive method, the technique worked equally well for healthy and diseased leaf area of potato plants infected byPhytophthora infestans. The theoretic estimate of the standard error for a single measurement was derived as the geometric mean of the leaf area and the grid cell size. The method is also suitable forLAI of crop stands.

A simple non-destructive technique for healthy and diseased leaf area assessment of potato plants

A simple non-destructive technique for healthy and diseased leaf area assessment of potato plants

Relationships Among Late Leafspot, Healthy Leaf Area Duration, Canopy Reflectance, and Pod Yield of Peanut

Experiments were conducted to investigate the relationships among disease severity, canopy reflectance, healthy leaf area duration, and pod yield of peanut. For Florunner, a cultivar susceptible to late leafspot (caused by Cercosporidium personatum), pod yield in 1988 and 1989 decreased as the duration of healthy leaf area (HAD) decreased. Several levels of cumulative stress from disease (estimated by the HAD) were obtained by periodic sprays of four rates of the fungicide chlorothalonil. Canopy reflectance at 800 nm decreased as disease severity and defoliation increased during the season. Regression of reflectance against green leaf area gave coefficients of determination (R2) of 0.77 in 1988 and 0.95 in 1989 for Florunner and 0.87 in 1989 for Southern Runner. The pod yield of Florunner was reasonably predicted from HAD for all treatments except the untreated control. The prediction model was developed earlier by averaging the loss of pods that accompanied a delay in harvest of 78 crops of Florunner. The original model was then modified with a scaling factor for maturity of the crop at harvest. The yields predicted from HAD with the newly scaled model were within 11% of the actual yield of Florunner in 1988 and 1989. The yield predicted with the model for Southern Runner, a cultivar known to produce more foliage and to partition proportionately less photosynthate to the pods than Florunner, was overestimated by an average of 18%. Modification of the model parameters to account for the lower partitioning of photosynthate for Southern Runner brought the average predicted pod yields within 6% of the actual yields. The HAD-yield relationship may be used to estimate the relative, radiation-use efficiency of a peanut cultivar.

Growth, Development, Yield, and Seed Quality of Florunner Peanut Affected by Late Leaf Spot1

Abstract Late leaf spot, induced by Cercosporidium personatum (Berk. &amp; Curt.) Deighton, causes serious yield losses of peanut (Arachis hypogaea L.) in the southeastern United States. A two-year study was conducted to observe progress of late leaf spot and to evaluate subsequent effects of late leaf spot on accumulation of dry matter, leaf area index (LAI), and pod production of Florunner peanut in fungicide-treated and non-treated plots. Disease severity, which is an expression of both disease-induced defoliation and necrotic leaf area, was used as an indicator of disease progression in the field. The leaf dry weight, LAI, and the dry weight of the total biomass were significantly different at 93 days after planting (DAP) in 1986, and at 78 DAP in 1987 between fungicide-treated and non-treated plots. Late leaf spot reduced the potential yield (harvested and dropped pods) of Florunner peanut by 37% in 1986 and 46% in 1987. In non-treated plots, the abscission of pods was initiated later but progressed faster in 1986 than in 1987. The predictions of pod yield with the measures of healthy leaf area duration (HAD) and healthy area absorption (HAA) were adequate for fungicide-treated plots where pod losses were minimal. However, HAD and HAA were inadequate for predicting pod yield of a peanut crop severely infected by late leaf spot, primarily because this predictive approach does not account for losses of dropped pods.

Ratio Between Virtual and Visual Lesion Size as a Measure to Describe Reduction in Leaf Photosynthesis of Rice Due to Leaf Blast

The effect of Pyricularia oryzae, the causal organism of blast in rice, on net photosynthetic rate of rice leaves was measured in the field and in a greenhouse experiment. Leaf blast reduced photosynthesis not only through a reduction in green leaf area, but also through an effect on photosynthesis of the remaining green leaf tissue. A function was derived to relate the net photosynthetic rate of diseased leaf area (P x ) to the photosynthesis of comparable healthy leaf area (P o ) and disease severity (x): P x =P o (1-x) β (...)

Yield Loss in Sweet Corn in Response to Defoliation or Infection by Exserohilum turcicum

Abstract Net CO2 assimilation was reduced in sites of infection by Exserohilum turcicum in leaves of Seneca 60 sweet corn before lesions appeared. In leaf tissue adjacent to infected areas, there was an early small increase in CO2 assimilation followed by a gradual decline to nearly 0 net CO2 exchange by 7 days after inoculation. Translocation of photosynthates in to disease lesions from healthy tissue distal to the lesions was observed within 1 h after exposure of 1.2–cm2 areas of the leaf blade to 14CO2. No translocation from lesions to healthy leaf tissue was observed. The effects of defoliation at specific leaf positions on yield of sweet corn plants were accurately simulated by a model in which yield is expressed as a function of healthy leaf area absorption of incident insolation. Removal of leaves from the bottom third of the plants caused no yield loss, whereas removal of leaves above the ear caused significant losses. The model underes, timated the yield loss caused by infection by E. turcicum by approximately 22 %. The observed effects of infection by E. turcicum on photosynthetic efficiency in leaf tissue adjacent to lesions and on translocation of photosynthates into lesion from distal parts of the leaf show that the effect of northern leaf blight on yield is greater than can be accounted for by the direct loss of healthy leaf area through necrosis within disease lesions.

Detection and Measurement of Plant Disease Gradients in Peanut with a Multispectral Radiometer

Percent reflectance values, when used as the independent variable, explained 94.6-96.5% of the variation in peanut rust disease severity along rust gradients. Reflectance of sunlight from peanut canopies at 800 nm provided a rapid and objective measurement of disease intensity and the amount of green leaf area contributing to pod yield. Recording percent reflectance offers a means to quantify the benefits obtained from disease control tactics aimed at protecting and maintaining healthy green leaf area from the effects of plant pathogens

A study of natural populations of the celery leaf‐miner, Philophylla heraclei L. (Diptera, Tephritidae) II. Importance of changes of mines for larval populations

SummaryThe leaf‐mining larvae of the celery fly, P. heraclei, have the ability to leave their primary mine to bore a secondary mine in another leaflet or leaf. This phenomenon is always numerically significant under natural conditions (depending on the plots and the years, 38 to 97% of the larvae observed made such a change), although it is not an obligatory behavior.The distribution of the secondary mines on the leaflets and on the leaves varies with the importance of the migrations, with the total unoccupied and healthy leaf area and with the relative position of different leaves on the plant. These migrations are due to the insufficiency of healthy food available for the larvae: either because the quantity of parenchyma offered by a leaflet is too small for a larva, or because there is intraspecific competition following multiple egg‐layings on the same leaflet, or because there is a deterioration of the quality of the parenchyma, particularly following the development of celery leaf‐spot.The possibility for the larvae of P. heraclei to bore secondary mines appears to be an extremely important factor in the population dynamics of this species. This permits the reduction of the negative effects of intraspecific competition and celery leaf‐spot, and permits the colonization by the larvae of young leaves not used by the females at the time of egg‐laying.