Leaf Spot Infection Research Articles

Differentially expressed gene transcripts in wheat and barley leaves upon leaf spot infection

A cDNA library was created on the basis of transcripts that were generated during the process of infection of wheat and barley with Pyrenophora tritici-repentis or P. teres. Due to the time course of infection assays, the leaves were collected at various intervals after inoculation until 100 h after inoculation. We compared the temporal development of the two pathogens, as well as the effect of varieties of the same crop species, and differences among isolates of a single pathogen. The appressoria and vesicular structures developed more rapidly in barley varieties inoculated by P. teres than in wheat varieties inoculated by P. tritici-repentis. The lower level of susceptibility of the wheat variety Globus and the barley variety Heris to P. tritici-repentis and P. teres, respectively, was apparent from 12 h after infection. Information on changes in expression profiles during pathogenesis and on the clones that could be functionally assigned to the known gene sequences is presented. Out of the 360 transcript derived fragments (TDFs) produced in the barley-P. teres pathosystem in our trials, 62% were specific to the plant-pathogen interaction. In the wheat-P. tritici-repentis pathosystem 291 TDFs occurred, 63% were specific to the plant-pathogen interaction.

First Report of Bipolaris peregianensis Causing Leaf Spot of Cynodon dactylon in China.

Cynodon dactylon is widely cultivated as a sod crop in warm climates worldwide. In early September 2009, heavy leaf spot infection was observed on C. dactylon from Zhengzhou, Henan, China. Early symptoms appeared as small, elliptical, pale brown lesions on the leaves. Lesions later expanded to 5 to 10 mm long and 1 to 2 mm wide, becoming brown to dark brown. A fungus was consistently isolated from leaf spots on potato dextrose agar (PDA), but with poor sporulation. Morphological characteristics were observed from single-conidium cultures on tap water agar + wheat straw (TWA+W) after 5 to 7 days. Conidiophores were light to medium brown, cylindrical, solitary or clustered, unbranched, usually with basal cells enlarged, and 94.5 to 147.0 × 4.0 to 9.0 μm. Conidia were fusoid, strongly curved, end cells broadly hemiellipsoidal, brown, 58.5 to 84.5 × 13.5 to 18.5 μm, with 6 to 10 septa. These morphological characteristics are similar to those of Bipolaris peregianensis (2). The identity of our fungus was confirmed to be B. peregianensis by DNA sequencing of the internal transcribed spacer (ITS) region (GenBank Accession No. JQ316121), which was 99% homologous to those of other B. peregianensis isolates (= Cochliobolus peregianensis; Accession Nos AF071328 and AF158111) (1). Koch's postulates were performed with the leaves of three pots of C. dactylon. Leaves were sprayed with 1 × 105 conidia/ml of B. peregianensis; an equal number of leaves in the pots of the same plant sprayed with sterile distilled water served as the control. All test plants were covered with plastic bags for 24 h to maintain high relative humidity at 23 to 25°C. After 7 days, more than 50% of inoculated leaves showed symptoms identical to those observed in natural condition, whereas controls remained symptom free. Reisolation of the fungus from lesions on inoculated leaves confirmed that the causal agent was B. peregianensis. To our knowledge, this is the first report of leaf spots caused by B. peregianensis on C. dactylon in China. The disease cycle and the control strategies in the regions are being further studied.

The chrysanthemum × Artemisia vulgaris intergeneric hybrid has better rooting ability and higher resistance to alternaria leaf spot than its chrysanthemum parent

The rooting ability and resistance to alternaria root spot of the chrysanthemum ( Chrysanthemum grandiflorum (Ramat.) Kitamura) variety ‘Zhongshanjingui’, the mugwort ( Artemisia vulgaris L.) variety ‘Variegata’ and ten independent ‘Zhongshanjingui’ × ‘Variegata’ intergeneric hybrids were compared. Although the rooting ability of the hybrid cuttings was not as high as those taken from mugwort itself, it was higher than that of chrysanthemum with respect to the rate of initiation of both adventitious and lateral roots. By 15 d after cutting, the hybrids produced a mean of ∼22 adventitious roots per cutting (mean length 23.4 mm), whereas ‘Zhongshanjingui’ produced only ∼14 (14.5 mm). The ability of the cuttings to recover from dehydration also differed: hybrid cuttings were able to form ∼9 lateral roots per adventitious root, while those from ‘Zhongshanjingui’ could form only 4.1. ‘Zhongshanjingui’ was susceptible to alternaria leaf spot infection, the hybrid was moderately resistant and ‘Variegata’ was highly resistant. An assay based on essential oils extracted from the leaf showed that both the hybrid and ‘Variegata’ leaves possessed more antifungal activity than extracts from ‘Zhongshanjingui’ leaf.

Predicting favorable conditions for early leaf spot of peanut using output from the Weather Research and Forecasting (WRF) model

Early leaf spot of peanut (Arachis hypogaea L.), a disease caused by Cercospora arachidicola S. Hori, is responsible for an annual crop loss of several million dollars in the southeastern United States alone. The development of early leaf spot on peanut and subsequent spread of the spores of C. arachidicola relies on favorable weather conditions. Accurate spatio-temporal weather information is crucial for monitoring the progression of favorable conditions and determining the potential threat of the disease. Therefore, the development of a prediction model for mitigating the risk of early leaf spot in peanut production is important. The specific objective of this study was to demonstrate the application of the high-resolution Weather Research and Forecasting (WRF) model for management of early leaf spot in peanut. We coupled high-resolution weather output of the WRF, i.e. relative humidity and temperature, with the Oklahoma peanut leaf spot advisory model in predicting favorable conditions for early leaf spot infection over Georgia in 2007. Results showed a more favorable infection condition in the southeastern coastline of Georgia where the infection threshold were met sooner compared to the southwestern and central part of Georgia where the disease risk was lower. A newly introduced infection threat index indicates that the leaf spot threat threshold was met sooner at Alma, GA, compared to Tifton and Cordele, GA. The short-term prediction of weather parameters and their use in the management of peanut diseases is a viable and promising technique, which could help growers make accurate management decisions, and lower disease impact through optimum timing of fungicide applications.

Genotype × environment interaction for yield and reaction to leaf spot infections in groundnut in semiarid West Africa

Capitalizing on the yield potential in available groundnut germplasm, and high stability of kernel yield are important requirements for groundnut producers in semiarid environments. Forty-seven groundnut genotypes were evaluated from 2003 to 2005 at 4 locations representative of the Guinea and Sudan savanna ecologies in Ghana. The objectives were to assess genotypic differences in reaction to early and late leaf spot infections under natural field conditions, assess the extent of genotype × environment (G × E) interaction for kernel yield, and determine the relationship between yield potential and yield stability. Genotypes differed significantly in their reaction to leaf spot infections indicated by the area under disease progress curve (AUDPC). Genotypic AUDPC was negatively correlated with maturity period (P < 0.01), with kernel yield (P < 0.05) at each of the 3 locations in the Guinea savanna ecology but not in the Sudan savanna ecology and with each of four stability parameters (P < 0.05). High or low yielding genotypes were grouped based on Dunnett’s test at P < 0.10. High yielding groups had significantly low AUDPC, high biomass, high partitioning of dry matter for kernel growth, and were later in maturity compared to low yielding genotypes. Significant G × E interaction effect for kernel yield was dominated mainly by the lack of correlation among environments variance (76–78%) relative to the heterogeneity of genotypic variance component (22–24%). Stability of yield assessed through the among-environment variance, Wricke’s ecovalence, and Finlay-Wilkinson regression coefficient revealed that genotypes in the higher yielding group were relatively unstable compared to the low yielding group. Indicated by the Kataoka’s index of yield reliability, however, relatively unstable genotypes in the high yielding group are expected to be more productive even under assumptions of high risk aversion (P = 0.75–0.95) compared to the more stable, low yielding genotypes. The findings indicate that deploying these recently developed germplasm in semiarid regions in West Africa provides a better match to farmers’ risk-averse strategies compared with the use of existing earlier maturing cultivars.

Influence of variety and intra-row spacing on &lt;i&gt;Cercospora&lt;/i&gt; leafspot disease of groundnut in Bauchi, Nigeria

Cercospora leafspot infection was analyzed for ten diverse groundnut varieties sown at two intra-row spacings during 1998 and 1999 rainy seasons at Bauchi, Nigeria. Significantly (P Cercospora leafspot were obtained at 50x30cm intra-row spacing. Spacing of 50x20cm however encouraged development of the disease. Late maturing and spreading types were resistant to Cercospora leafspot,compared to erect and early maturing types which are susceptible. Progress of Cercospora leafspot on groundnut was influenced by higher rainfall, relative humidity and low temperatures. Global Journal of Agricultural Sciences Vol. 4(2) 2005: 177-182

Evaluation of parental banana varieties and new hybrids regarding potential yield and resistance to Sigatoka and nematode in India

Introduction . Banana and plantains rank fourth among the most important food crops of the world, and India holds the position of the largest producer. A study was undertaken to evaluate the potential yield of new synthetic banana hybrids based on bunch weight and fruit quality. It also assessed the nematode damage, Sigatoka leaf spot disease and parthenocarpy stability. Materials and methods . Thirteen new hybrids and eleven parental bananas of dessert type were used and evaluated in the first vegetative generation. Plant growth parameters, viz., pseudostem height and girth, number of leaves, and suckers per plant were measured at the flowering stage and the damage of roots by nematode and intensity of the Sigatoka leaf spot disease were assessed at the harvest stage. The content of total soluble solids, and reducing, non-reducing and total sugars in the fruit was estimated. Results . All the hybrids exhibited parthenocarpy and there was no reversion from parthenocarpy to non-parthenocarpy. The plant height and girth and the leaf number varied among the hybrids significantly. The maximum bunch weight was recorded for H-212 (ABB) which showed a regular suckering habit, very high content of total soluble solids and reducing sugars, and more leaves without leaf spot infection than the other hybrids; moreover, H-212 is a female sterile dessert-type banana and it is tolerant to nematode and resistant to Sigatoka. The reproduction factor of Radopholus similis on H-211 (AA), H-213 (ABB) and H-02-01 (AA) was significantly lower than on H-203 (AA), H-209 (ABB) and H-205 (AA). Conclusions . Our studies distinguished one triploid ABB hybrid H-212 with high yield and fruit quality, and no sanitary problems; it can be released for commercial cultivation to banana growers.

Severity of Alternaria Leaf Spot and Seed Infection by Alternaria sesami (Kawamura) Mohanty and Behera, as Affected by Plant Age of Sesame (Sesamum indicum L.)

Severity of Alternaria Leaf Spot and Seed Infection by Alternaria sesami (Kawamura) Mohanty and Behera, as Affected by Plant Age of Sesame (Sesamum indicum L.)

Severity of Alternaria Leaf Spot and Seed Infection by Alternaria sesami (Kawamura) Mohanty and Behera, as Affected by Plant Age of Sesame (Sesamum indicum L.)

AbstractAlternaria leaf spot incited by Alternaria sesami, was monitored to determine the effect of plant age on disease severity and seed infection by A. sesami in plots containing sesame accession SPS SIK 110 plants of five different ages. The increase in percentage leaf area blighted and percentage defoliation fit the Gompertz model more closely than the logistic model. Rates of increase in blighted leaf area and defoliation, and areas under disease curves (AUDPC) varied among the five different plant ages. Plant ages with larger AUDPCs generally had faster rates of disease progress. Plants inoculated at 8 and 12 weeks of age were most susceptible to the disease and those inoculated at 4 weeks exhibited the least susceptibility. Seed infection was determined by the oat‐meal agar plate method and the infection was highest in plants infected at 8 and 10 weeks of age and least in plants infected at 4, 6 and 12 weeks of age.

Diagnosis of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in the UK

Summary.Light leaf spot lesions were generally first observed as light green areas on leaves of UK winter oilseed rape crops in January or February and later became brittle and bleached. Elongated lesions, which were brown with indistinct edges, developed on stems in the spring and summer, when lesions were also observed on flower buds, pedicels and pods. Development of diagnostic white pustules (spore masses of Pyrenopeziza brassicae, which erupt through surfaces of infected tissues) for confirmation of light leaf spot infection on symptomless plants or plants with indistinct or ambiguous symptoms in the autumn, winter or spring was enhanced by incubating plants in polyethylene bags. In experiments with artificially inoculated plants, glasshouse‐grown plants exposed in infected crops and plants sampled from crops, white pustules developed at all incubation temperatures from 2oC to 20oC on infected leaves of different cultivars. The period of incubation required before the appearance of pustules decreased as the time that had already elapsed since the initial infection increased. The longest periods of incubation were required at the lowest temperatures (2oC or 5oC) but leaves senesced and abscised from plants most quickly at the highest temperatures (15oC or 20oC), suggesting that the optimal incubation temperature was between 10oC and 15oC.

Genetic analyses of grey leaf spot infection of maize in a single location 12 × 12 diallel

The inheritance of resistance to grey leaf spot of maize (Zea mays L.), caused by Cercospora zeae-maydis, was studied using a 12 × 12 diallel cross. Information on the heterotic performance of the inbred lines enabled identification of patterns of transmission of resistance to susceptible genotypes. The study confirmed that an accurate evaluation of heterotic patterns for grey leaf spot requires an assessment of both the inbred lines and all the single crosses among them. Resistance of the tested maize genotypes to grey leaf spot can be expressed in terms of an additive-dominance model, with dominance almost complete. As the incidence of this fungus reached epidemic proportions only after physiological maturity, yield was not adversely affected by grey leaf spot. Genotypic correlations between grey leaf spot ratings, yield and kernel quality traits suggested that certain of the tested genotypes displayed sink-induced susceptibility to the disease. Hayman's (1954) variance-covariance graphical technique co...

Genetic Resistance, Fungicide Protection and Variety Approval Policies for Controlling Yield Losses from Cercospora Leaf Spot Infections

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Plant infection and yield loss associated with cercospora leaf spots of groundnut (Arachis hypogaeaL.) in Sierra Leone

Abstract Infection and yield loss induced by groundnut leaf spots were determined with benomyl during the 1989 and 1990 crop seasons under natural disease pressure in the field in Sierra Leone. Weather conditions in both years were highly favourable to leaf spot infection and development. In 1989 benomyl, applied at weekly intervals and at the rate of 0.15 kg a.i. ha−1 for a total of 10 applications, effectively controlled leaf spots and increased both pod and haulm yields by 85%. An estimated potential pod yield loss of 46% was recorded, indicating the importance of the diseases as major constraints to groundnut production in Sierra Leone. In 1990, however, a higher level of leaf spots severity was observed causing extensive damage of the foliage. Benomyl, applied at bi‐weekly intervals and at the rate of 0.225 kg a.i. ha−1 for a total of five applications failed to effectively control the diseases, increasing pod yield by only 27%.

The effect of propiconazole on leaf spot infection and seed yield of velvet grass

The effect of propiconazole on leaf spot infection and seed yield of velvet grass

SIMULATION OF THE TEMPORAL SPREAD OF LEAFSPOT AND THE EFFECT ON PEANUT GROWTH

Leafspot is a fungal disease which occurs frequently in peanut and can cause almost complete defoliation if left untreated. The plant/disease interactions are complex, and it is difficult to predict the effect of altering one component in the system, such as timing of fungicide applications. The objective of this research was to develop a subroutine for the growth model PEANUT to enable the prediction of early leafspot development over a growing season and to predict leafspot's effect on peanut growth. A FORTRAN subroutine was developed for PEANUT which simulated early leafspot progression based on daily spore production, average daily temperature, and the area of healthy leaf tissue. Lesion initiation was calculated using a modified logistic equation, with the latent periods distributed normally in time as a function of ambient temperature. The predicted percent leafspot infection and percent defoliation agreed well with both the calibration and validation data. Total leaf mass, stem mass, and pod mass were also predicted well by the simulation model for 1988, the only year growth data for peanuts subjected to leafspot were available. More data are needed to validate the PEANUT/LFST model during years when yield losses occur due to leafspot. The leafspot subroutine developed in this study expands the ability of the growth and development model PEANUT to predict growth and yield under diseased conditions. In addition, the disease simulator can be used to improve the efficiency of breeding programs in selection for resistance to early leafspot. The next step in model development is to include the effects of fungicide on the spread of leafspot, and to use the model for investigating fungicide control strategies.

Recurrent selection progress in a population derived from an interspecific peanut cross

Two cycles of recurrent selection for yield were previously conducted using a population of Arachis hypogaea L.-like tetraploid hybrid derivatives selected from among the progeny of a cross between A. hypogaea and A. cardenasii Krap. et Greg. nom. nud., a diploid species with resistance to late leafspot (Cercosporidium personatum (Burk. and Curt.) Deighton). Using the 10 highest yielding parents from each of the above cycles of recurrent selection, a study was conducted for 12 morphological traits and susceptibility to leafspot infection in a replicated test at a single location. The two parents used to initiate the interspecific hybrid population (PI 261942-3 and A. cardenasii) as well as two adapted cultivars (Florigiant and NC 7) were included as checks. The objectives of the study were to determine the amount of genetic variation remaining in the population after two cycles of recurrent selection in order to predict whether further progress from selection could be expected and determine the potential for utilizing wild species for the improvement of quantitative traits in peanut. The results indicate that significant levels of genetic variation remain in the population after two cycles of recurrent selection for all traits measured, including several components of yield and leafspot resistance. This suggests that continued progress in population improvement from further cycles of selection should be possible while enhancing the genetic diversity of cultivated peanut germplasm.

Survival of Alternaria brassicae and Alternaria brassicicola on crop debris of oilseed rape and cabbage

Summary Alternaria brassicae and A. brassicicola lesions present on infected leaves of oilseed rape and cabbage placed outdoors on soil produced viable spores for as long as leaf tissues remained intact. For oilseed rape this was up to 8 wk and for cabbage up to 12 wk. On leaves exposed in November and January spore concentrations decreased with time but on leaves exposed between April and June spore concentrations increased up to 9‐fold in the first 4–6 wk and then declined. On stem sections of seed plants of oilseed rape and cabbage similarly placed on the soil, the fungi produced viable spores for up to 23 wk with spore concentrations increasing up to 11‐fold in the first 6–8 wk after harvest. These results indicate that infected debris of brassica crops remaining on the ground after harvest may provide a source of dark leaf spot infection which may be implicated in the spread of the disease within and between crops.

Quantitative Genetic Variation for Resistance to Leaf Spot (Ramularia tulasnei) in California Strawberries

Abstract Strawberry (Fragaria × ananassa Duch.) seedlings from biparental crosses were planted in two trials at Watsonville, Calif. Sept. 1985 and 1986. The 1985 trial was scored on three dates and the 1986 trial on four dates for leaf spot (Ramularia tulasnei) infection. Individual seedlings were assigned a value of 0 to 5 on each date, with 0 indicating no infection and 5 indicating very severe infection. Average infection scores were lowest for the earliest scoring dates in both years (0.93 and 0.38) and maximum at late scoring dates (2.83 and 1.49). Narrow-sense heritabilities for infection scores estimated using partial diallel analyses were 0.07 and 0.03 for the earliest scoring dates in the two trials and were 0.24 and 0.28 for the latest dates. Early season estimates of broad-sense heritabilities were calculated as 0.13 and 0.03, whereas estimates based on later scorings ranged from 0.32 to 0.52. The low heritabilities for early scoring dates result from incomplete and uneven infection, indicating that selection under field conditions will be most effective under conditions of very high infection. The moderate heritabilities and predicted gains estimated for high-infection conditions suggest considerable opportunity for improvement of leaf spot resistance by recurrent breeding and selection using available quantitative genetic variation.

Observations on the epidemiology of Leptosphaeria macutans stem canker in winter oilseed rape

SUMMARYThe main source of Leptosphaeria maculans (Desm.) Ces. &amp; de Not. infection on winter oilseed rape in Cambridgeshire was stubble debris from the previous season. Heavy leaf spot infection of seedlings near unploughed oilseed rape stubble resulted in complete crop loss. The fungus actively colonised stubble debris after harvest and perithecia were formed predominantly on tissues colonised during this period. Ascospores were detected throughout the year, mainly from October to April. The degree of leaf spot infection in the autumn was correlated with stem canker infection at the end of flowering and with severe stem lesions at harvest. The incidence of leaf spot infection was greater in the spring than in the autumn, particularly during the period of extension growth and early flowering. Stem canker infections were first seen in March and continued to develop up to and after harvest.

I. Pathogenic variation in fungi and bacteria and mycorrhizal compatibility: Variation in Pseudomonas morsprunorum and the selection of cherry cultivars resistant to bacterial canker

ABSTRACTDuring 1971 and 1972 leaf spot infection caused by Pseudomonas morsprunorum was far more severe on the cv. Roundel than on the normally more susceptible cv. Napoleon, and Roundel supported higher leaf surface populations of the pathogen. This unprecedented reversal in the established field performance of the two cultivars was associated with the presence on the trees of a colony variant (race 2) of P. morsprunorum that differed from the forms of the organism previously described (race 1) in physiological, pathological and phage sensitivity characteristics. In inoculation experiments race 2 isolates showed some specificity for Roundel and race 1 isolates for Napoleon. This difference was reflected in the distribution of the races on trees of the two cultivars growing in experimental plots and commercial orchards. Similar interactions between race and host genotype were observed amongst progeny from breeding programmes and material originally selected for resistance to bacterial canker after inoculation with race 1 proved susceptible to race 2.Three distinct groups of isolates with the colony characteristics of race 2 have been identified and one of these has affinities with Pseudomonas syringae. Group 1 isolates, corresponding to P. morsprunorum and comprising non‐fluorescent forms, were the most virulent in pathogenicity tests and accounted for the majority of race 2 infections in the field.