Necrotic Leaf Area Research Articles

Studies on the epidemiology of the tar spot disease complex of maize in Mexico

During the period 1986–1988 field studies were conducted on the epidemiology of the tar spot disease complex (TDC) of maize (Zea mays) caused by Phyllachora maydis, Monographella maydis and Coniothyrium phyllachorae. Under field conditions we found that P. maydis symptoms always appeared first, followed by symptoms of either M. maydis or C. phyllachorae. M. maydis causes leaf necrosis and has the most devastating effect. The primary symptoms covered about 12% of the leaf area below the ear leaf, whereas the total necrotic leaf area amounted to 30–60%, here considered as a secondary effect. Maximum TDC severity occurred during the winter season of 1988, which was characterized by a temperature range of 17–22°C, a mean RH >75%, and > 7h of leaf wetness per night. The highest numbers of windborne ascospores of P. maydis were trapped at an RH > 85% and at temperatures of 17 to 23°C in the winter of 1987 and 1988, although large numbers were also caught at temperatures of >23°C and RH <70%. Spore release was strongly influenced by light conditions and followed a similar diurnal curve throughout three seasons, reaching a maximum at 17.00–21.00 hours. The spread off. maydis within the field was very homogeneous. The incubation period of P. maydis was 12 to 15 days, and most of the ascospores were released within 3 weeks after formation of the ascostromata. M. maydis inoculum in plant debris was reduced by 90% within 3 to 4 months.

Biosynthesis and metabolism of abscisic acid in tomato leaves infected withBotrytis cinerea

Two virulent strains ofBotrytis cinerea Pers., one of them (Bc 6) producing abscisic acid (ABA) via 1′,4′-trans-diol-ABA in defined liquid culture, and a second strain (Bc 9) without the ability to form ABA or its fungal precursor, and two near-isogenic lines of tomato were used to study the biosynthesis and metabolism of ABA in infected isolated leaves. The tomato plants used wereLycopersicon esculentum Mill. cv. Ailsa Craig (wild type) and the ABA-deficient mutantflacca. The level of 1′,4′-trans-diol-ABA increased in Ailsa Craig andflacca leaves in a similar pattern to about 4 μg·(gDW)−1 after conidiospore infection with Bc 6, but not after infection with Bc 9. Pulse-feeding experiments showed that [214-C]-1′,4′-trans-diol-ABA was metabolised to ABA and to further plant metabolites of ABA (phaseic acid, dihydrophaseic acid and polar compounds) in both uninfected and infected leaves. Following infection, the turnover of 1′,4′-trans-diol-ABA was reduced. The level of endogenous ABA in leaves infected with the ABA-producing strain Bc 6 rose more than tenfold in Ailsa Craig and twofold inflacca, respectively. Infection of Ailsa Craig leaves with Bc 9 caused a fivefold increase in ABA, and no increase of ABA inflacca. It is concluded that at least four processes control the level of ABA in wild-type tomato leaves infected withBotrytis cinerea: stimulation of fungal ABA biosynthesis by the host; release of ABA or its precursor by the fungus; stimulation of biosynthesis of plant ABA by the fungus; inhibition of its metabolism by the fungus. Application of ABA together with fungal spores to tomato leaves caused a faster development of necrotic leaf area than spore inoculation only.

Response of Phaseolus vulgaris L. to differing ozone regimes having identical total exposure

Abstract Protocols were designed to test for differences in response of plants to ozone treatments having equal total exposure (concentration × time) but different exposure profiles Kidney beans ( Phaseolus vulgaris L., cv. California Dark Red) were exposed to ozone in controlled fumigation chambers within a greenhouse Four different ozone exposure profiles were used, each having the same total cumulative exposure (SUM00) and the same 7, 12 and 24 h seasonal means. The three exposure profiles which incorporated peak concentrations more severely impacted response parameters compared to a steady-state profile which did not exceed the National Ambient Air Quality Standard. Significant differences were found in percent necrotic leaf area, number of pods and top dry weight between exposure profiles. In additional analyses, the response parameters were regressed against seasonal cumulative ozone concentrations raised to powers of 0.33 and from 0.5 to 4 in steps of 0.5 in order to increase effective weighting of the higher concentrations. Total dry weight and leaf necrosis were best fit with the sum of the squared concentrations ( n = 2) while number of pods was best fit by the summed concentrations to the 3.5 power ( n = 3.5). These analyses suggest the peak ozone concentrations are important in determining plant response.

Genotype-specific differences in chilling tolerance of maize in relation to chilling-induced changes in water status and abscisic acid accumulation.

Four inbred maize lines differing in chilling tolerance were used to study changes in water status and abscisic acid (ABA) levels before, during and after a chilling period. Seedlings were raised in fertilized soil at 24/22°C (day/night), 70% relative humidity. and a 12-h photoperiod with 200 μmol m-2 s-1 from fluorescent tubes. At an age of 2 weeks the plants were conditioned at 14/12°C for 4 days and then chilled for 5 days at 5/3°C. The other conditions (relative humidity, quantum flux, photoperiod) were unchanged. After the chilling period the plants were transferred to the original conditions for recovery. The third leaves were used to study changes in leaf necrosis, ion efflux, transpiration, water status and ABA accumulation. Pronounced differences in chilling tolerance between the 4 lines as estimated by necrotic leaf areas, ion efflux and whole plant survival were observed. Conditioning significantly increased tolerance against chilling at 5/3°C in all genotypes. The genotypes with low chilling tolerance had lower water and osmotic potentials than the more tolerant genotypes during a chilling period at 5/3°C. These differences were related to higher transpiration rates and lower diffusive resistance values of the more susceptible lines. During chilling stress at 5/3°C ABA levels were quadrupled. Only a small rise was measurable during conditioning at 14/12°C. However, conditioning enhanced the rise of ABA during subsequent chilling. ABA accumulation in the two lines with a higher chilling tolerance was triggered at a higher leaf water potential and reached higher levels than in the less tolerant lines. We conclude that chilling tolerance in maize is related to the ability for fast and pronounced formation of ABA as a protective agent against chilling injury.

Leaflet and Canopy Photosynthesis of Peanut Affected by Late Leaf Spot

AbstractLate leaf spot, induced by Cercosporidium personatum (Berk. & Curt.) Deighton, is the most important foliar disease affecting peanut (Arachis hypogaea L.) in Florida and neighboring states. The disease first occurs as necrotic lesions on peanut leaflets and subsequently induces leaflet abscission. Field experiments were conducted to study the effects of late leaf spot on leaflet and canopy photosynthesis. Fully expanded leaflets at the tip of the main stem were tagged and leaflet photosynthesis was measured during the subsequent weeks with a portable photosynthesis system. Leaflet photosynthesis was reduced linearly with the increase in the percentage of necrotic leaf area. Reduction in light utilization due only to necrotic leaf area did not explain completely the reduction in leaflet photosynthesis. Regression analysis suggested that 15% necrotic leaf area contributed to a 65% reduction in the photosynthesis of infected leaflets. It appears that there was an effect on leaflet photosynthesis due to host cells invaded or affected by the pathogen. A chamber made of aluminum frame covered with mylar film was used to estimate canopy photosynthesis over a land area of 0.56 m2. At the canopy level, the effect of reduction in leaflet photosynthesis was negligible compared to the effect of disease‐induced defoliation. The decrease in leaf area index was the major component involved in the reduction of canopy photosynthesis because of the effect of late leaf spot. Canopy photosynthesis was inversely proportional to total disease severity, which is an expression of both defoliation and necrotic area.

A Field Disease Evaluation Method for Selecting Wheats Resistant to Mycosphaerella graminicola

AbstractReliable and efficient methods of selection are important for improving disease resistance. Three methods of field assessment of the Septoria tritici blotch disease, caused by Mycosphaerella graminicola (Fückel) Schroeter, were compared to identify the most reliable for selecting resistant wheats, Triticum aestivttm L. Nine cultivars which differed in disease reaction to plant height and maturity, and their progenies from several generations were used. The methods consisted of scoring chlorotic and necrotic leaf area covered with pycnidia on the flag leaf and the leaf below the flag leaf (flag leaf‐1) as percent of the total leaf area, on a plant‐basis, and the percent necrosis visually estimated on a plot‐basis. Plot data were greatly influenced by environmental changes leading to inconsistent genetic results. The flag leaf and flag leaf‐1 methods provided the most precise consistent results. The use of the flag leaf‐1 method is suggested for selection.

Virulence Patterns of Geographically Differing Isolates ofPyrenophora tritici-repentisand Sources of Resistance in Wheat

Nineteen single-conidiospore isolates of Pyrenophora tritici-repentis were isolated from leaf samples of wheat collected from Brazil, Germany, India, and Nepal, and one ascospore isolate was obtained from the United States for a virulence analysis study. Eight wheat cultivars were inoculated with a conidial suspension from each isolate, and percent necrotic leaf area was measured 5-6 days later using video image analysis. A highly significant interaction was found between cultivars of wheat and isolates of P. tritici-repentis. Cluster analysis of the data indicated only a moderate variation in virulence among the isolates of P. tritici- repentis (.)

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

Abstract Late leaf spot, induced by Cercosporidium personatum (Berk. & 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.

Peanut Breeding for Leafspot Resistance in Wide and Narrow Intrarow Spacings1

Abstract Sixteen peanut (Arachis hypogaea L.) genotypes were grown without the use of fungicides for two years in two planting arrangements, one an intrarow spacing typically used in commercial production (5 cm between plants) and the other typically used in breeding selection plots (30 cm between plants). At 10-day intervals throughout each growing season the proportion of necrotic leaf area caused by leafspots (Cercospora arachidicola Hori and Cercosporidium personatum (Berk. & Curt.) Deighton), leafspot disease rating (0-9), and stage of vegetative growth (v stage) were assessed. Leafspot disease ratings of genotypes spaced 30-cm apart were significantly correlated with the ratings of genotypes in 5-cm spacing. There was no interaction between genotypes and spacing. Percentage necrotic area in 30-cm and 5-cm plantings was significantly correlated. However, large experimental error and complex interactions among spacings, genotypes, and time of observation lessened the value of this method of disease assessment. While the correlation of v stage in the two spacings was highly significant, differences among genotypes were not consistent.

Simulated Transit Vibration and Silver Thiosulfate Applications Affect Ethylene Production and Leaf Abscission of Begonia and Schefflera

Abstract Vibrations of 0.02 gravitational force (g) at 4.1 cycles per second (cps) were applied to Begonia ‘Medora’ and Schefflera arboricola (Hayata) Merrill during 6 days of simulated transit. Vibration caused leaf abscission, necrotic leaf areas, and severed stem tips. Silver thiosulfate (STS), applied as a previbration foliar spray (0, 0.28, 0.56, 1.12, mM silver), increased leaf abscission of begonias but not scheffleras during simulated transit. Ethylene emanation from stem tips of both species increased as STS concentration increased. Ethylene emanation from stem tips was not affected by vibration. During 4 weeks of simulated retail holding, STS decreased begonia leaf abscission.

Determination of leaf heat resistance: comparative investigation of chlorophyll fluorescence changes and tissue necrosis methods.

Heat tolerance limits for a variety of vascular plant leaves were determined both with the conventional post-culture necrosis method and by measurements of the heat-induced increase in chlorophyll fluorescence (F-T curves). The reliability of the fluorescence test was improved with the addition of far-red background light which counteracts dark reduction of the Photosystem II acceptor pool by heat-stimulated endogenous electron donors. This was of particular importance in the case of xeromorphic leaves in which the diffusion barrier for oxygen is high. A satisfactory correlation was found between T L50, the temperature at which a 30 min exposure results in 50% necrotic leaf area following post culture, and the critical temperature, T c ,the temperature at which the dark fluorescence level begins to increase during slow heating of a leaf sample at a rate of 0.7 K min-1, in the fluorescence test. The correlation can be described by a linear function, T L50=1.12 T c -5.37,with a correlation coefficient, r=0.87. Maximal deviation of the regression line from the line T L50=T c was 1.2 K, with 22 determinations for leaves with widely varying heat tolerance limits. This shows that heat-induced fluorescence changes within the thylakoid membrane may be connected with the irreversible leaf tissue damage which occurs following prolonged exposure to high temperature. On the basis of the heat dosage equation of Lepeschkin, a more general expression can be obtained which allows calculation of the accumulated heat dosage under the experimental conditions of the standard fluorescence test (slow heating, 0.7 K min-1). Such calculations reveal that for a given species the 'fraction of critical dosage' begins to increase, i.e. accumulating heat reaches an injurious level, at a temperature which approximately coincides both with T L50, obtained with the necrosis method, and with T c ,the critical temperature derived from the fluorescence test. Hence, the increase in fraction of critical dosage and the rise in chlorophyll fluorescence seem to concur. It is concluded that the fluorescence assay provides a rapid and reliable means of determining the heat tolerance limit of leaf tissue.

The effect of wind gusts on leaf growth and foliar water relations of aspen.

Potted plants of various trees and shrubs (clones), exposed in the dividing strip and along the border of a motorway, showed an inhibition of leaf growth and a faster development of necrotic leaf areas, when suffering from water deficiency. In greenhouse experiments with potted aspen exposed to periodic artificial wind gusts, wind velocities of 6 m/s were sufficient to inhibit leaf growth by 50%. Therefore it is suggested that repeated strong shaking of plants grown near a motorway, caused by traffic wind, might be responsible for this inhibition. Measurements of water relations did not show obvious changes when aspen trees with [Formula: see text]-month old leaves were treated with wind gusts, but when plants were continously treated with wind (6 m/s) significant increases in stomatal diffusive resistances and transpiration rates were found as well as a significant decrease in water potential. Aspens with young leaves, exposed to the same treatment, showed a rising of stomatal diffusive resistance in the beginning, but after about [Formula: see text] h diffusive resistances suddenly decreased. Subsequently after a 2 to 3-h wind treatment intercostal necrosis appeared over the whole leaf surface.

Enzymatisch - analytische Untersuchungen zum Adenosinphosphatgehalt SO2-begaster Erbsen

Abstract An enzymatic method has been elaborated to measure the concentration of the purine nucleotides AMP, ADP and ATP in green plant material. The influence of SO2 fumigation (0,3 ppm/m3) on the concentration of these nucleotides has been investigated. As compared to the control the concentration of AMP, ADP and ATP is increased by 40% in the fumigated peas. After ten days of treatment the concentration of the nucleotides decreases slowly in the fumigated seedlings and drops far below that of the control when necrotic leaf areas appear. The molar ratio of AMP: ADP: ATP remains constant in fumigated and unfumigated plants over a period of three weeks of culture. Consequently also the energy charge [ADP+2ATP/Z(AMP+ADP+ATP)] doesn't change. The value of the energy charge is 0,69 and indicates a slightly anabolic situation of the metabolism throughout the time of investigation. Therefore the energy charge is an insufficient criterion to be used as indicator of SO2 effects on plant metabolism.