Search

The relationship between initial population densities (Pi) of Meloidogyne hapla on growth of three rose rootstocks (Rosa corymbifera ‘Laxa’, R. multiflora and R. canina ‘Inermis’) and nematode population development was studied. Each plant species was inoculated with ranges of nematode densities of 0, 0.062, 0.125, 0.25, 0.50, 1, 2, 4, 8, 16, 32, 64 and 128 second-stage juvenile/g soil and were allowed to grow for 9 weeks. Seinhorst yield model math formula was fitted to total fresh biomass data of the rootstocks. The tolerance limits (T) were 0.04, 0.09 and 0.01 J2/g soil and the minimum yield (m) 0.65, 0.47 and 0.43 for R. corymbifera ‘Laxa’, R. multiflora and R. canina ‘Inermis’, respectively. The reproductive factor (Pf/Pi) was highest at low initial nematode densities for all rootstocks and then decreased to below maintenance level with increasing initial population densities. Root gall severity consistently increased with initial nematode population density. Furthermore, number of root galling showed a strong positive relationship with final nematode population per gram root fresh weight. The relation between Pi and Pf was also fitted to the Seinhorst population model (Pf = (M*Pi)/Pi + M/a). Rosa multiflora supported the population of M. hapla to a maximum population density (M) of 27.53 J2/g soil with an estimated average maximum multiplication rate (a) of 24.39. For R. corymbifera ‘Laxa’ and R. canina, the maximum multiplication rate was 4.34 and 3.62 and the maximum population density 6.08 and 4.78 J2/g dry soil, respectively. Hence, it was demonstrated that all three rootstocks were susceptible to even low initial nematode densities and therefore are considered good hosts for M. hapla

Fusarium graminearum is a devastating fungal pathogen that causes significant yield and quality losses in cereals. We utilized a diversity set of barley (140 genotypes) to explore vital resistance alleles against this aggressive pathogen. The resistance assessment was carried out on spikes and leaves via artificial inoculations under control conditions. The phenotypic data was subjected to genome-wide association analysis using a genetic map based on DArT and SNP markers. This analysis revealed eleven and nine marker trait associations for leaf disease scoring (LDS) and spike disease scoring (SDS), respectively. The strongest QTL for LDS was found on chromosome 1H where a minor allele of wild origin decreased disease symptoms by 78%. The major QTL allele for SDS was linked with marker locus SCRI_RS174710 on chromosome 5H. In addition, four favorable epistatic interactions effects were found in decreasing disease symptoms. Overall, three QTL were common for LDS and SDS, which indicates a partial genetic relatedness of these resistances in barley. The QTL alleles for LDS and SDS will help to establish organ specific resistances in cultivated barley.

Near-range and remote sensing techniques have demonstrated a high potential in detecting diseases and in monitoring crop stands for sub-areas with infected plants. The occurrence of plant diseases depends on specific environmental and epidemiological factors; diseases, therefore, often have a patchy distribution in the field. This review outlines recent insights in the use of non-invasive optical sensors for the detection, identification and quantification of plant diseases on different scales. Most promising sensor types are thermography, chlorophyll fluorescence and hyperspectral sensors. For the detection and monitoring of plant disease, imaging systems are preferable to non-imaging systems. Differences and key benefits of these techniques are outlined. To utilise the full potential of these highly sophisticated, innovative technologies and high dimensional, complex data for precision crop protection, a multi-disciplinary approach—including plant pathology, engineering, and informatics—is required. Besides precision crop protection, plant phenotyping for resistance breeding or fungicide screening can be optimized by these innovative technologies.

In Germany, maize is one of the most important agriculture commodities, a major component in animal feed as well as an essential substrate producing biogas. Maize ear rot poses a major impact worldwide as it is caused by several Fusarium spp., most of which have the ability to produce mycotoxins. Despite of the expansion of the maize acreage in recent years, limited information is available concerning the incidence of Fusarium ear rot in Germany. Therefore, in a two-year survey maize crops were sampled in the major maizeproducing areas in Germany to establish the severity of Fusarium ear rot and the biodiversity of Fusarium species. In 2006, the frequency of kernels infected by Fusarium spp. ranged from 0.7 % to 99.7 %; the average incidence was 32.4 %. Thirteen Fusarium species were isolated from maize kernels, with F. verticillioides, F. graminearum and F. proliferatum being the predominant species. In 2007, the highest incidence of Fusarium ear rot was 64 %; the mean level of infection was 21.7 %. F. graminearum was by far the most frequent species isolated from all sampled fields in 2007. In addition, F. crookwellense, F. subglutinans and F. avenaceum were also frequently isolated. In particular, the fumonisin-producing species F. verticillioides an F. proliferatum were less frequent than in 2006. The year-to-year variability in the frequency of Fusarium species and in the overall infection rate may be explained by significant differences in temperature and precipitation during the growth periods.

Fusarium Head Blight (FHB) is one the most important diseases in small grain cereals and often is caused by a complex of Fusarium species. Some of these species are able to produce one or several mycotoxins. The spatial distribution of the disease and associated mycotoxins was examined in this study. Results were mapped and analysed with a geographic information system (GIS). Correlations between the incidence of the deoxynivalenol (DON) producing Fusarium species and DON contamination of kernels were rather weak. The level of DON contamination seemed to be less influenced by the frequency of DON producing Fusarium species than by other factors.

Adhesion to the host surface is the first step for successful plant pathogen development and has been reported to be associated with both passive and active processes. For conidia of Venturia inaequalis, which depend on leaf wetness for germination, this process has not yet been described. Conidia of V. inaequalis adhered to wet hydrophobic surfaces immediately after contact to the surface, hours before initiation of germination. Attachment of nongerminated conidia was much better on hydrophobic surfaces, such as apple leaves and polystyrene, than on hydrophilic glass. Conidia released adhesive material localized in a droplet named spore tip glue (STG) at the spore apex which interacted with a contact surface only when water was present. Histochemical investigations indicated the presence of proteins and carbohydrates in STG, lectin labeling the presence of β-galactose and N-acetylglucosaminyl residues. Transmission electron microscopy revealed two phases in the STG at the tip of dry mature conidia; as STG was present on the outer side of the intact fungal cell wall its formation should be associated with the secretion of glue through pores of the conidial wall. Surface-active substances affected the adhesion of conidia to hydrophobic surfaces stressing the importance of hydrophobic interactions. The use of protein biosynthesis inhibitors did not affect adhesion of conidia indicating that the adhesive material was preformed. It is concluded that the coincidence of STG, contact to a hydrophobic surface, and free water are essential for the adhesion of V. inaequalis conidia.

Disease progress of downy mildew on cucumber leaves, caused by the obligate biotrophic pathogen Pseudoperonospora cubensis, was shown to be associated with various changes in transpiration depending on the stage of pathogenesis. Spatial and temporal changes in the transpiration rate of infected and noninfected cucumber leaves were visualized by digital infrared thermography in combination with measurements of gas exchange as well as microscopic observations of pathogen growth within plant tissue and stomatal aperture during pathogenesis. Transpiration of cucumber leaf tissue was correlated to leaf temperature in a negative linear manner (r = -0.762, P < 0.001, n = 18). Leaf areas colonized by Pseudoperonospora cubensis exhibited a presymptomatic decrease in leaf tem perature up to 0.8°C lower than noninfected tissue due to abnormal stomata opening. The appearance of chlorosis was associated with a cooling effect caused by the loss of integrity of cell membranes leading to a larger amount of apoplastic water in infected tissue. Increased water loss from damaged cells and the inability of infected plant tissue to regulate stomatal opening promoted cell death and desiccation of dying tissue. Ultimately, the lack of natural cooling from necrotic tissue was associated with an increase in leaf temperature. These changes in leaf temperature during downy mildew development resulted in a considerable heterogeneity in temperature distribution of infected leaves. The maximum temperature difference within a thermogram of cucumber leaves allowed the discrimination between healthy and infected leaves before visible symptoms appeared.

It is well accepted that agricultural production must be increased considerably in the foreseeable future to meet the food and feed demands of a rising human population and increasing livestock production. Crop protection plays a key role in safeguarding crop productivity against competition from weeds, animal pests, pathogens and viruses. The loss potential of these pest groups and the actual losses—i.e. losses despite the present crop protection practices—have been estimated for wheat, rice, maize, barley, potatoes, soybeans, sugar beet and cotton for the period 1996–1998 on a regional basis for 17 regions. Among crops the loss potential of pests worldwide varied from less than 50% (on barley) to more than 80% (on sugar beet and cotton). Actual losses are estimated at 26–30% for sugar beet, barley, soybean, wheat and cotton, and 35%, 39% and 40% for maize, potatoes and rice, respectively. Overall, weeds had the highest loss potential (32%) with animal pests and pathogens being less important (18% and 15%, respectively). Although viruses cause serious problems in potatoes and sugar beets in some areas, worldwide losses due to viruses averaged 6–7% on these crops and

Dans les conditions agricoles et climatiques specifiques du Rheinland (DE), 48 essais au champ sur trois ans ont demontre la possibilite d'appliquer la strategie fongicide basee sur un seuil d'intervention du IPM Wheat Model. Les donnees sous-jacentes pour les seuils d'intervention et le dosage de fongicides appliques sont decrits. Les agents pathogenes des cereales concernes, surtout Mycosphaerella graminicola et Puccinia recondita, ont ete controles dans les premiers stades du developpement de l'epidemie en utilisant des doses reduites de fongicides. Le IPM Wheat Model donne une lutte de grande efficacite, en terme d'incidence et de severite de la maladie, aussi bien en cas de faible ou de forte pression de la maladie. Les niveaux de rendement consecutifs a la reduction effective des maladies etaient presque les memes que ceux de la modalite sans maladie. L'augmentation totale du rendement variait entre 15 et 30% avec une moyenne globale d'environ 20%, et a donc permis un benefice financier de 50-100 EUR ha - 1 lors des annees considerees.

The efficacy of Metarhizium anisopliae in combination with sublethal concentrations of oils and potassium-oleate for biological control of whiteflies was tested under controlled conditions. Three commercial products (Biola ® , Naturen ® , Neudosan ® ) and five experimental formulations of plant oils were tested. The efficacy of M. anisopliae against Trialeurodes vaporariorum and Bemisia tabaci without additives was about 50%. At 1/20 of their recommended dosages, all compounds tested significantly increased the efficacy of M. anisopliae for the control of T. vaporariorum , with the formulated sunflower oil Biola ® giving the highest synergistic effect, reaching nearly 100% control. Not only was the level of control increased but also the speed of action was improved, resulting in a higher reliability of control. Three of seven additives showed no effects on the viability of conidia on the leaf surface, whereas the formulations of the other oils and oleates reduced the longevity of spor...

Fifteen wheat varieties commercially grown in Kenya were tested for their susceptibility to head blight and mycotoxin accumulation after inoculation with Fusarium graminearum in pot experiments. The strains of the pathogen used had been isolated from wheat collected in different growing areas of Kenya. Head blight susceptibility was assessed as the percentage of spikelets bleached and area under disease progress curve; kernel colonization by fungal mycelium was determined as ergosterol content. All varieties were found to be moderately to highly susceptible. However, the varieties differed in head blight susceptibility (29–68% of spikelets bleached; mean 54%), fungal colonization (67–187 μg/g ergosterol content; mean 111 μg/g) and the resulting mycotoxin contamination [deoxynivalenol (DON) 5–31 μg/g; mean 13.5 μg/g]. Grain weight reductions due to head blight ranged from 23 to 57% (mean 44%). The varieties could be therefore divided into partially resistant and highly susceptible genotypes. The kernels of highly susceptible varieties had higher mycotoxin and ergosterol contents. However, the kernels of some varieties contained more fungal mycelium (ergosterol) without the corresponding high amounts of DON, suggesting that they possess some resistance to DON accumulation. Less susceptible varieties showed resistance to fungal spread, as indicated by a slow disease development and lower content of fungal biomass.

Details of our long-term research programme concerning the epidemiology of Fusarium spp. and mycotoxin production are summarized. Evaluation of the occurrence of Fusarium spp., mainly on winter wheat (Triticum aestivum), was carried out by investigating Fusarium infection and mycotoxin contamination. Two to 15% of grains were infested during 1995–1998 at three climatologically differing localities of the Rhineland, Germany. Disease progress was accelerated by rainfall during the flowering season. The species most frequently isolated were Fusarium avenaceum, F. poae, F. culmorum and F. graminearum. The mean deoxynivalenol (DON) content varied from 19μgkg−1 (1995) to 310μgkg−1 (1998) and was not always correlated with disease severity. Organic farming systems showed lower rates of infection with ear blight and lower mycotoxin contamination than conventional farming systems.

Actual and potential crop losses of eight major food and cash crops have been estimated by evaluating data from literature and field experiments. Total losses were calculated from yield reductions due to pathogens, animal pests and weeds on a regional, continental and global level. Since 1965, worldwide production of most crops has increased considerably. Simultaneously, crop losses in wheat, potatoes, barley and rice increased by 4 to 10 percent, in maize, soybean, cotton and coffee losses remained unchanged or slightly decreased. The efficacy of crop protection practices was calculated as the percentage of potential losses prevented by control. The efficacy is highest in cotton (55 percent), it reaches only 34 to 38 percent in the food crops rice, wheat and maize. The variability among cropping areas is high: In Western Europe, 61 percent of potential crop losses is prevented, in North America and Oceania 44, in all other regions 38 percent. Due to the small share of Western Europe in worldwide production of 8 percent, the efficacy of actual crop protection worldwide is only 40 percent. In view of population growth and rising food demand crop production has to be increased substantially. As potential loss rates often increase with attainable yields high productivity largely depends on effective crop protection management. Scenarios for the production of food crops by the year 2025 in developed and in developing countries are given. Recent and future developments in crop protection can contribute to establish sustainability in agriculture and to preserve natural resources. However, although effective control methods have been developed for most biotic yield constraints, the use of crop protection products is regulated by economic considerations rather than by food demand.

Meloidogyne hapla is one of the most damaging plant-parasitic nematodes in temperate regions. This nematode has a wide host range with more than 500 plant taxa including roses. In Ethiopia, rose production has developed over the past 10 years to the second most important export market after coffee. Considering the high damage potential of M. hapla, infestation of roses in Ethiopia with this nematode could result in major economic losses. Therefore, awareness of this nematode species is extremely important. During two surveys conducted in August 2011 and April 2012, M. hapla was detected in soil samples from six out of nine rose producing farms located in the districts of Ziway, Holleta, Sebeta, and Menagesha. At infested farms, rose plants appeared stunted and less productive and often showed symptoms of chlorosis and wilting. Identification was based on morphological and morphometrical characters of females, males, and second-stage juveniles, which were all within the range of variability known for this species (4). Shape of juvenile stylet knobs, shape of male head, and perennial pattern of the females with characteristic punctuations between the anus and tail terminus were also typical for M. hapla. The morphological identification was confirmed by sequence analysis of the D2-D3 expansion segment of the 28S rDNA gene following amplification with the primers D2A (5′-ACAAGTACCGTGAGGGAAAGTT-3′) and D3B (5′-TCGGAAGGAACCAGCTACTA-3′) (1). PCR products were purified and sequenced at the Macrogene sequencing facility service (Amsterdam, The Netherlands). Sequences were deposited in GenBank (KJ645427 to 33). The sequences were compared with previously published sequences in NCBI database and showed 96 to 100% sequence similarity with M. hapla accession nos. GQ130139, DQ328685, KF430798, and DQ145641. Unfortunately, comparison of sequences did not provide further information about the origin of this Ethiopian population, if it is native to Ethiopia or was imported with infected plant material. To the best of our knowledge, this is the first record of M. hapla occurring in Ethiopia. M. hapla is known as a serious pest of roses in colder climate regions. In Africa, it was previously reported from Tanzania (3) and South Africa (2). Thus, it appears that this species has now become also established in Ethiopia at higher altitudes (1,400 to 2,100 m above sea level) within the urban hinterland of Addis Ababa. References: (1) Baldwin et al. Mol. Phy. Evol. 8:248, 1887. (2) J. H. O'Bannon. Institute Agri. Res. 29, 1975. (3) E. Onkendi and L. N. Moleleki. Eur. J. Pl. Pathol. 136:1, 2013. (4) A. G. Whitehead. Trans. Zool. Soc. Lon.31:263, 1968.

Near-range and remote sensing techniques are excellent alternatives to destructive methods for measuring beneficial effects of fungicides on plant physiology. Different noninvasive sensors and imaging techniques have been used and compared to measure the effects of three fungicidal compounds (bixafen, fluoxastrobin and prothioconazole) on wheat (Triticum aestivum L.) physiology under disease-free conditions in the greenhouse. Depending on the fungicidal treatment, changes in green leaf area and yield parameters were observed. Chlorophyll fluorescence of leaves was useful for measuring differences in the effective quantum yield of PSII. Reflectance measurements of wheat leaves were highly sensitive to changes in plant vitality. The spectral vegetation indices were useful for determining the differences among treatments in terms of leaf senescence, pigments and water content. The analysis of ear and leaf surface temperature was reliable for detecting effects of fungicides on plant senescence. Using nondestructive sensors, it was possible to assess a delay in senescence of wheat due to fungicide application. Furthermore, it was deduced that sensors and imaging methods are useful tools to estimate the effects of fungicides on wheat physiology. Physiological parameters measured by the sensors were actually more sensitive than yield parameters to assess the effect caused by fungicide application on wheat physiology.