Number Of Diseased Plants Research Articles

Biocontrol and plant growth promotion by combined Bacillus spp. inoculation affecting pathogen and AMF communities in the wheat rhizosphere at low salt stress conditions.

Applying plant growth-promoting rhizobacteria (PGPR) improves the efficiency of soil-borne disease control and is considered a sustainable practice. However, the effect of PGPR on the fungal community, especially pathogenic fungi and arbuscular mycorrhizal fungi (AMF), remains unclear. In this study, we examined the effects of a compound microbial agent (consisting of Bacillus subtilis HG-15 and Bacillus velezensis JC-K3) on the incidence and yield of wheat under low salt stress, as well as compared the diversity and community composition of the rhizosphere fungal and AMF communities of wheat in the CK (not inoculated bacterial agent) and BIO (inoculated with a bacterial agent) groups. Chlorophyll relative content (SPAD), net photosynthesis rate (Pn), transpiration rate (Tr), leaf water use efficiency (WUE L), grains per spike and wheat yield in the BIO group increased more than in the CK group. The number of diseased plants and disease incidence was observed to be reduced. The relative efficacy reached 79.80%. We classified 1007 fungal operational taxonomic units (OTU) based on Miseq sequencing data: 11 phyla, 173 families, 319 genera, and 521 species. Fifty-four OTUs were classified from the AMF effective sequences, including 1 phylum, 3 families, 3 genera, and 17 species. The inoculation of bacterial agents reduced the relative abundance of pathogen genera such as Gibberella, Fusarium, Cladosporium, and Alternaria in wheat rhizosphere. It increased the relative abundance of AMF species such as Glomus-group-B-Glomus-lamellosu-VTX00193, Glomus-viscosum-VTX00063, and Glomus-Glo2-VTX00280. In addition, pH, EC, exchangeable K, available N, total N, organic matter, and olsen P were the main driving forces for shaping wheat rhizosphere fungi. The pH value was positively correlated with the relative abundance of fungal communities in soil, especially Gibberella, Cladosporium, Fusarium, and Alternaria. In summary, inoculation with Bacillus subtilis HG-15 and Bacillus velezensis JC-K3 affected wheat yield, incidence, rhizosphere soil chemical properties, rhizosphere fungi, and AMF fungal diversity and community. The findings may provide a theoretical foundation and strain support for constructing efficient PGPR-community and clarifying its mechanism of pathogenic bacteria inhibition.

Prevalence and Pathogenicity of the Isolates of Fusarium oxysporum f.sp. lentis in Different lentil Grown Areas of Uttarakhand and Uttar Pradesh

Background: Different lentil-growing regions in India have reported that the lentil wilt poses a serious threat to crop cultivation because it can result in 100 percent crop losses. The fungus Fusarium oxysporum f.sp. lentis is the pathogen responsible for the disease. This infection is carried through the seed and soil. Methods: To understand the current status of the wilt pathogen in the total of twenty-two lentil-growing areas in Uttarakhand and Uttar Pradesh, the present study was conducted over the course of the two consecutive years 2017-18 and 2018-19, to track the incidence and prevalence of the disease. Observations were made on the numbers of diseased plants and number of infected fields to record incidence and prevalence of the lentil wilt, repectively. Moreover, twenty two isolates were collected to examine the different spores, pathogenicity levels and degree of correlation between both of them. Result: The data showed that the pathogen was present in every area at 100 per cent prevalence, with a disease incidence within 6.22-26.25 per cent. Data derived from 100 per cent availability of the pathogen inoculum in all lentil-growing regions over the course of two years predicts the emergence of the wilt disease threat to the crop. The observations indicate that the pathogen’s inoculum level had increased as the incidence of the disease increased during the subsequent crop season. It was also observed that spore size somewhat affects the pathogenicity of the isolates.Therefore the present study was conducted to observe the impact of wilt pathogen on different lentil grown areas and to alarm the farmers about this emerging threat.

The impact of copper oxide and silver nanoparticles on woody plants obtained by in vitro method

The article substantiates the necessity of studying behaviour of copper oxide and silver nanoparticles on forest cultures (downy birch 29-58 (Betula pubescens Ehrh.) and poplar ‘Pyramidal-osokoreviy Kamyshinsky’ (Poplus pyramidalis Roz. x Poplus nigra L.) in in vitro as well as in ‘soil-plant-microbiota’ to ensure stability of forest cultures in forest regeneration. The impact of nanoparticles on shoot regeneration and propagation processes was evaluated by introducing nanoparticles into Woody Plant medium. Differences in the influence of nanoparticles on the life processes of plants depending on their concentration and the stage of clonal micropropagation have been established. The results are demonstrated by a 15-25% reduction in the frequency of infection of poplar and birch explants as well as by an increase in their regenerating potential at the stage of introduction in tissue culture. When the nanoparticle solution is used in the soil substrate, a decrease in the number of diseased plants and an increase in their survival rate of 30% can be observed. The inhibitory effect of silver nanoparticles on some ecological and trophic groups of microorganisms has been established. These results can be used in the application of CuO and Ag nanoparticles in the biotechnology of clonal micropropagation of forest crops.

Spatial autocorrelation study of fatal yellowing in organic oil palm in the eastern Amazon

The oil palm (Elaeis guineensis) is a very important source of vegetable oil worldwide. While oil palm cultivation is not currently economically significant in Brazil, there is immense growth potential for this crop in the Amazon region, with no need for deforestation. Fatal yellowing (FY) is a major phytosanitary barrier to the development of oil palm cultivation in the region. Many plantations have been devastated by FY, but its causes are unknown. The objective of this study was to analyze the spatial autocorrelation of FY in the oil palm crop by applying Moran’s Index (I). The experiment was carried out on a large farm (>8000 ha) in the municipality of Acará, in the state of Pará (Brazil), with 139 plots of oil palm of different genetic materials and ages. The number of diseased plants per plot has been recorded since 2001 and used in the analysis. A positive autocorrelation of disease incidence was calculated based on the observations of the current study. By calculation of the Local Moran’s I it was possible to identify the presence of high-incidence regions in the northeast and the central-west areas of the farm and low-incidence areas in the south and the north and in outlying plots. The approach described in this study was useful in identifying regions with the highest occurrence of FY, and could be useful in the management of this disease.

Spatial-temporal distribution of fatal yellowing in different oil palm genetic materials in eastern amazon

Oil palm (Elaeis guineensis Jacq.) is one of the agricultural crops with the greatest potential for vegetable oil production in Brazil. However, a disease of unknown etiology popularly known as Fatal Yellowin (FY) has caused damage to Brazilian farmers particularly in the eastern region of the Amazon. So, the objective of this study was to evaluate the spatial dependence of FY on three oil palm genotypes, grown for many years in an organic production system in the Amazon region. The study area had 4104 ha, divided into 139 plots. In each plot, the monthly incidence of disease was monitored forming a database. The number of diseased plants per year, number of accumulated diseased plants, number of diseased plants per hectare, growth rate of diseased plants and incidence of accumulated disease were evaluated. The results indicated spatial distribution of the variables adjusted to the gaussian, spherical and exponential models, with predominance of the first model. This increases the purpose that FY is caused by biotic factors. The highest range achieved in the study was 2929 m indicating the susceptibility of the tested genotypes. Some plots close to the river had the highest incidence of the disease on the study, probably associated with higher soil moisture.

Fusarium spp. and inoculum load estimation associated to commercial Agave tequilana offsets at different regional epidemic inductivity levels

<p>Esta investigación tuvo como objetivos identificar la especie(s) de <em>Fusarium</em> asociada(s) a hijuelos comerciales de <em>Agave tequilana</em> y desarrollar una metodología para cuantificar la carga de inóculo en hijuelos provenientes de plantaciones madre de Jalisco con inductividad epidémica diferencial al síndrome marchitez y pudrición seca del cogollo (SMAP). La finalidad fue proporcionar criterios para la certificación de plantaciones madre. La fase de campo se realizó entre marzo-mayo 2018 y 2019 en 21 plantaciones comerciales en 14 municipios de Los Altos, Sur y Valles de Jalisco. Se estimó el número de plantas enfermas (PE) y severidad SMAP (S) en 63 y 200 plantas/plantación mediante App-SIVEA para 2018 y 2019 respectivamente. Se desarrolló y aplicó el método CIFUSAG en 7055 hijuelos y 46 656 colonias fungosas obtenidas de 2364 siembras de lavado basal de la ‘piña’, secciones de tejido interno y macerado total de hijuelo. Unidades formadoras de colonia de <em>Fusarium</em> spp. (Fsp) y hongos totales (HT), purificación, monospóricos, caracterización morfológica y cultural se realizó con los medios Komada, agua-agar, Sabouraud, SNA y Sabouraud, respectivamente, diferenciando 557 aislados. La mayor inductividad epidémica en Los Altos significó moderado Índice de <em>Fusarium</em> [(IF) = (?Fsp) / (?HT)] (0.30 y 0.40) y Fsp (20 y 72UFC) respecto al Sur que tuvo valores más altos (0.69, 0.50; 23, 84UFC, respectivamente) (Tukey p=0.05). Calibre de hijuelo no tuvo influencia en IF y Fsp (p=0.183). IF y Fsp de lavado basal no estuvieron correlacionadas con S de plantas madres (r2 = 0.036 y 0.13), mientras que PE únicamente se correlacionó con Fsp (r2 =0.94). La carga de inóculo obtenida por lavado fue superior al de tejido interno con un total de 17,828 UFC (93%) e IF=0.42. Análisis molecular con el gen EF-1a evidenció asociación de 23 cepas con cuatro complejos filogenéticos: <em>Fusarium</em> <em>oxysporum</em>,<em> F. fujikuro</em>i, <em>F. solani</em> y <em>F. incarnatum-equiseti</em> con identidad superior al 98%. El hijuelo comercial de <em>Agave tequilana</em> constituye un factor de dipersión de al menos cuatro especies de <em>Fusarium</em> spp. en el rango de 3.3±3 y 6.83±4.2 UFC/hijuelo.</p>

Epidemiología regional aplicada a la caracterización inductiva y pronóstico de la mancha gris del agave azul (Cercospora agavicola) en Jalisco, México

<em>Cercospora agavicola</em>, agente causal de la mancha gris del agave azul (<em>Agave tequilana</em>), es un hongo reglamentado bajo control oficial en estados bajo Denominación de Origen del Tequila (DOT). Este trabajo se desarrolló en Jalisco, México, principal región DOT, para determinar la inductividad epidémica espacio-temporal del hongo y desarrollar modelos estocásticos de pronóstico de la mancha gris con el fin de sustentar acciones preventivas regionales. De octubre 2016 a diciembre 2017 se evaluó mensualmente la severidad, incidencia y número de plantas enfermas en 41 parcelas establecidas en plantaciones comerciales de agave de 3-4 años de edad seleccionadas con criterios ponderados de riesgo en Los Altos (20), Valles (11) y Sur (10). La inductividad epidémica regional de<em> C. agavicola</em> fue heterogénea con mayor riesgo para al menos nueve municipios de Los Altos. Sin embargo, bajas tasas epidémicas (0.0008-0.006 unidades semana-1), fuerte restricción de contagio (1-4 plantas), reducido incremento anual de incidencia (0-32 plantas/0.5 ha) y nula captura de esporas evidenciaron la baja aptitud parasítica y epidémica del hongo. Consecuentemente, se encontró limitada capacidad predictiva aun con los mejores modelos generados (R2adj 0.51-0.60). Las horas favorables (HFav) de enero-abril, respecto a la infección, fue consistente entre modelos por lo que puede integrarse como algoritmo preventivo en SIVEA (www.sivea.org.mx). Las pérdidas regionales, bajo los parámetros epidémicos establecidos, se estimaron entre 98.01 MDD y 237 mil dólares americanos. La cercosporina, toxina asociada al género <em>Cercospora,</em> puede estar implicada en el progreso temporal lineal atípico y debe integrarse en futuras investigaciones.

Development of two strains of Fusarium culmorum with a different aggressiveness in the soil and on the roots of barley of two genotypes

Fusarium culmorum can affect plants including cereals or develop saprophytically in the soil. It is unknown whether its saprophytic ability is different in strains with a different aggressiveness. This knowledge could be used for effective breeding of resistant cultivars. Here, we aimed to study the development of two F. culmorum strains with a different aggressiveness in the soil under barley, to compare their saprophytic ability and to reveal the influence, if any, of the host plant on the development of strains in the soil and on the roots. Saprophytic development of the strains was studied on membranes inoculated with macroconidia and placed into non-sterile soil under barley of two genotypes. The fungus was identified on the membranes and on barley roots by indirect immunofluorescent method. Both strains could develop saprophytically. The more aggressive strain (Fc538) showed a lesser saprophytic fitness than the less aggressive strain (Fc885): its mycelial density was lower and the number of chlamydospores was greater. Barley genotypes influenced the development of the fungal strains. Interestingly, conditions for saprophytic development of both strains were more favourable in the soil under barley of the resistant genotype. The more aggressive strain colonized barley of the resistant genotype more actively. Rot symptoms appeared earlier in the barley of the resistant genotype, but the number of diseased plants was greater in the barley of the susceptible genotype. The presence of a saprophytic stage in life cycle should slow down the accumulation of aggressive races in field populations of F. culmorum. Possible interactions between F. culmorum strains and barley plants are discussed.

Spread and yield loss mechanisms of rice stripe disease in rice paddies

Rice stripe disease is an economically important disease of rice caused by the Rice stripe virus (RSV), which is transferred by the small brown planthopper (SBPH). The recent rapid increase in damage to rice crops throughout Japan caused by this disease makes it imperative to develop control methods as soon as possible. To obtain basic data for developing such methods, we studied how the disease causes damage and spreads within paddy fields. Our investigations revealed that diseased plants first appear in mid-June to early July, after which the disease spreads from affected plants to adjacent plants. This suggests that SBPH carrying RSV enter paddy fields, where they infect plants as they move about and lay eggs. Subsequently, hatched viruliferous nymphs infect surrounding plants, thereby spreading the disease. Our analysis of the damage caused by rice stripe disease showed that the earlier the onset of disease, the more extensive the damage caused, and that the disease reduces yield by reducing the number of healthy panicles. This suggests that to reduce damage caused by this disease, it is necessary to ensure the growth of a sufficient number of healthy panicles by controlling the vector insect during the crop’s early growth period. To be most effective, pest control efforts should be timed to target either the first-generation adults that colonize the paddy fields or the second-generation nymphs and adults that cause the rapid increase in the number of diseased plants within a field.

Spatial distribution of cases of fatal yellowing on organic oil palm plantation

This work studied the spatial dispersion of cases of fatal yellowing (FY) in an oil palm plantation in Acará, Pará State, Brazil. Data were collected monthly from two areas, divided in 16 quadrants each, for a 24 month period (2012-2013). In each quadrant, 138 plants were evaluated. The number of diseased plants was counted in twenty planting lines, and the spatial pattern of the disease was analyzed. The following spatial analysis techniques were used: common sequences of “runs”, “doublets” and quadrants. We also determined the levels of disease aggregation in the sectors. Plants with FY had a spatial distribution aggregated in a lower line number when using the “run” analysis than when using the “doublets” method. Aggregation of FY cases was observed in 30% of the evaluated lines. The quadrant analysis confirmed the existence of case aggregation, with vertical and horizontal distribution. The existence of disease forming foci suggests that FY probably has biotic origin. Additional studies are required to confirm this hypothesis.

First report of a ‘Candidatus Phytoplasma phoenicium‘‐related strain (16SrIX‐I) associated with yellowing of Onobrychis viciifolia in Iran

Onobrychis viciifolia (common sainfoin) is a forage legume which enhances biodiversity within agro-ecosystems and is an important forage crop in Iran. During 2014-16, O. viciifolia plants were observed with symptoms of yellowing (Fig. 1), little leaf and reddening of leaflet margins (Fig. 2), witches' broom and dwarfing compared with healthy plants (Fig. 3). The disease, known locally as sainfoin yellowing (SY), was observed in Shalamzar and Shahre Kian locations in Chaharmahal and Bakhtiari province, Iran. In each area, three 1,000 m2 fields were selected randomly and sampled at five points within one square metre on a diagonal transect across each of the fields. The number of diseased plants and the total number of plants in each sampled square metre was determined to calculate the extent of the disease; this being 32% in Shalamzar and 22% in Shahre Kian. To investigate the possible presence of phytoplasmas, total DNA was extracted from samples collected from 16 diseased and five asymptomatic plants in each location. DNA was tested by direct PCR using P1/P7 primers (Deng & Hiruki, 1; Schneider et al., 5), and on these amplicons nested PCR using primers R16mF2/R16mR2 or R16F2n/R16R2 (Gundersen & Lee, 2). Amplicons of the expected size were obtained from all diseased plants, but not from water used as negative control, or from asymptomatic plants. Restriction fragment length polymorphism (RFLP) analyses on R16F2n/R16R2 amplicons using KpnI, AluI, HaeIII, HhaI, HpaII, MseI, RsaI, TaqI and HpaI restriction enzymes showed that all samples had identical restriction profiles, comparable with reference samples of the 16SrIX phytoplasma group (Lee et al., 3) (data not shown). Four samples in total from the two sampling areas were directly sequenced using nested PCR products obtained with P1/P7 and R16mF2/R16mR2. After alignment and assembling, the resulting sequences were trimmed to the R16F2n/R16R2 fragment. Obtained sequences showed 100% identity to each other and one sample from Shalamzar (SSY) was submitted to GenBank (Accession No. KX461906). Sequence comparison by BLAST analysis showed highest sequence identity with phytoplasmas in group 16SrIX (pigeon pea witches' broom). Phylogenetic analysis using the neighbour-joining method (with MEGA software version 6.0) confirmed that the SSY phytoplasma clustered with ‘Candidatus Phytoplasma phoenicium’ (Fig. 4), with 99.4% sequence identity to the reference strain for this phytoplasma (AF515636), and is therefore a ‘Ca. P. phoenicium‘-related strain. Computer-simulated analysis with 17 restriction endonucleases using iPhyClassifier (Zhao et al., 6) showed that the RFLP pattern derived from SSY was not referable to any reported subgroup in 16SrIX group, although the highest similarity was with the 16SrIX-E subgroup (GQ925918), with a similarity coefficient of 0.95. Therefore SSY phytoplasma represents a new subgroup within the 16Sr group IX that was designed as 16SrIX-I. ‘Candidatus P. phoenicium’ is widespread in Iran, and has been reported in GF-677 (Prunus amygdalus × Prunus persica) and Prunus amygdalus in Fars province (Salehi et al., 4). To our knowledge, this is the first report of a phytoplasma associated with O. viciifolia in Iran or worldwide, and indicates that it may serve as phytoplasma reservoir for other agricultural relevant plant species.

<b>Modeling citrus huanglongbing data using a zero-inflated negative binomial distribution

Zero-inflated data from field experiments can be problematic, as these data require the use of specific statistical models during the analysis process. This study utilized the zero-inflated negative binomial (ZINB) model with the log- and logistic-link functions to describe the incidence of plants with Huanglongbing (HLB, caused by Candidatus liberibacter spp.) in commercial citrus orchards in the Northwestern Parana State, Brazil. Each orchard was evaluated at different times. The ZINB model with random effects in both link functions provided the best fit, as the inclusion of these effects accounted for variations between orchards and the numbers of diseased plants. The results of this model show that older plants exhibit a lower probability of acquiring HLB. The application of insecticides on a calendar basis or during new foliage flushes resulted in a three times larger probability of developing HLB compared with applying insecticides only when the vector was detected.

Evaluation of maize/pepper intercropping model in the management of pepper veinal mottle virus, genus Potyvirus, family Potyviridae on cultivated pepper (Capsicum annuum L.) in Nigeria

Three pepper cultivars obtained from National Horticultural Research Institute (NIHORT) Idi-Ishin, Ibadan were intercropped with maize for two planting seasons between March and September in each year. These pepper cultivars were NHV1-D96, and NHV1-E96 and NHV1-F96. A 90-day maturing maize variety (DMSR-1) was used as the intercropping companion plant. The pepper seedlings were raised in a greenhouse. A randomised complete block design was used for this experiment. Each variety was intercropped with maize and replicated three times including the sole plot. The results obtained for each year were not significantly different from each other. There was a significant difference in pepper veinal mottle virus (PVMV) disease incidence and severity at a probability of less than 5% in the treatment used. PVMV disease incidence and severity was relatively higher in the sole pepper crop compared with pepper intercropped with maize. In the three varieties of peppers intercropped with maize, less than 17% disease incidence and 15% disease severity were recorded in all the varieties with a minimum yield of 4 tons per hectare compared with the sole pepper cropping of the same variety that recorded as high as 75% disease incidence and 72% disease severity with a maximum yield of 3.3 tons per hectare. There was a significant negative correlation at probability less than 0.05 between disease incidence, severity and the fruit yield of pepper. Variety NHV1-F96 in the maize intercrop recorded the highest yield of 15.99 tons/ha with a land equivalent ratio of 2.4 tons/ha. The success of the PVMV disease management evaluated in this study was judged by the extent of reduction in number of diseased plants and by an increase in vigor of the cultivated pepper crop, with an increase in fruit yield and quality. This signifies that for devising effective viral disease management for any crop it is important that the vectors of the virus present in the particular area are exactly controlled from having contact with the target plant. The reduction of pest incidence with intercropping of non-host plants should be carefully considered.

Antifungal effects of essential oils from oregano and fennel onSclerotinia sclerotiorum

The antifungal effects of essential oils of oregano (Origanum syriacum var. bevanii) and fennel (Foeniculum vulgare) were evaluated against Sclerotinia sclerotiorum. Effects of the essential oils on morphological structures of hyphae and sclerotia were studied under light and scanning electron microscopes (SEM). Inhibitory effects of volatile and contact phases of the essential oils used were determined on hyphae and sclerotia. Both essential oils have a marked antifungal effect against S. sclerotiorum. Soil amendment with essential oils has significant effect on reducing sclerotial viability. Both essential oils significantly inhibited the fungal growth in soil, thereby increasing the number of surviving tomato seedling by 69.8% and 53.3%, respectively. Light and SEM observations on pathogen hyphae and sclerotia revealed considerable morphological alterations in hyphae and sclerotia. The significant reduction in the mycelial growth and germination of sclerotia would greatly reduce the pathogen inoculum source. This may influence the rate of disease development in soil. Considering the reduction in the number of diseased plants in infested soil amended with essential oils, we concluded that oregano and fennel essential oils could be used as possible bio fungicides alternative to synthetic fungicides against phytopathogenic fungi.

Spatial Analysis Based on Variance of Moving Window Averages

AbstractA new method for analysing spatial patterns was designed based on the variance of moving window averages (VMWA), which can be directly calculated in geographical information systems or a spreadsheet program (e.g. MS Excel). Different types of artificial data were generated to test the method. Regardless of data types, the VMWA method correctly determined the mean cluster sizes. This method was also employed to assess spatial patterns in historical plant disease survey data encompassing both airborne and soilborne diseases. The results obtained using the VMWA method were generally different from those obtained with Lloyd's index of patchiness and beta‐binomial distribution methods, were in partial agreement with the results from spatial analysis by distance indices, and were highly consistent with the results from semivariogram and spatial autocorrelation analysis methods. Results demonstrated that the VMWA method can be applied to many types of data, including binomial diseased or healthy plant counts, incidence, severity, and number of diseased plants or pathogen propagules although directional and edge effects may limit its application.

Pre- and post-plant applications of copper-based compounds to control Erwinia soft rot of calla lilies

Erwinia carotovora subsp. carotovora is a plant pathogen responsible for producing soft rots in many vegetable and floricultural crops, particularly calla lilies, Zantedeschia spp. In this study, the efficacy of various copper-based compounds, such as Phyton-27, Champ 2, fixed copper, and analytical copper, was compared under laboratory and greenhouse conditions. Copper-based compounds suppressed bacterial growth at various cupric ion concentrations in vitro, but the efficacy of some products was reduced by the presence of phosphate ions in fertilizer solutions used in commercial greenhouses. Under greenhouse conditions, the compounds were applied as a preplant or a postplant treatment to tubers of calla lilies. Postplant applications were made either as an overhead drench or through subirrigation, and the applications were carried out at different stages of plant development. Preplant application of Champ 2 or Phyton-27 did not reduce the number of diseased plants compared with the controls. In contrast, postplanting applications of Champ 2 or fixed copper were effective in reducing soft rot; however, these two compounds also reduced overall plant growth. Poor root development and reduced plant growth occurred when these products were applied during the early stages of plant development and when the products were applied overhead rather than through subirrigation.

Effects of habitat fragmentation on choke disease (Epichloë bromicola) in the grass Bromus erectus

Summary The fungal endophyte Epichloë bromicola causes choke disease on Bromus erectus, thereby suppressing maturation of host inflorescences. We conducted a 3‐year field experiment to investigate the effects of small‐scale habitat fragmentation on the occurrence of choke disease in three calcareous grasslands in the Swiss Jura Mountains, where, overall, 4.3% of all flowering tillers had diseased inflorescences. The number of diseased B. erectus plants (presumed genets), the number of tillers with diseased inflorescences, and the number of tillers with healthy inflorescences were counted over 3 years, but healthy tillers could not be allocated to particular genets. Each of 12 blocks contained one large (4.5 × 4.5 m), one medium (1.5 × 1.5 m) and two small (0.5 × 0.5 m) fragments and corresponding control plots. The percentage of tillers in the plots that were infected but did not show disease symptoms (asymptomatic plants) was estimated in the final year of the study using a diagnostic polymerase chain reaction. On average 1.7% of all tillers without disease symptoms were infected. There were significantly more diseased plants in fragment than in control plots, particularly in small fragment plots or in the third year of the study, indicating that disease incidence in the host plant increased after fragmentation if assessed at the level of the genet population. This was probably due both to a switch of genets from the asymptomatic to the symptomatic state and to increased horizontal transmission of the disease in fragments. The increase in the number of flowering tillers with diseased inflorescences was outweighed by that in the number of tillers with healthy inflorescences. Disease incidence was therefore decreased by fragmentation if assessed at the level of the host flowering tiller population. The effect on healthy plants was probably due to beneficial abiotic edge effects following fragmentation. Plot size affected fragmentation response, with the largest increases in small, followed by medium and large fragments. Similarly, the strength of fragmentation responses increased through time over the 3‐year study period. Significant site to site and year to year variation in the number of diseased plants and in the number of tillers with diseased inflorescences suggested that separate experiments with replication within site and year would have yielded a series of interesting but individually different results. Only by repeating the experiments at several sites and over several years was it possible to obtain the general results reported in the previous points.

Response of susceptible, partially resistant and resistant winter wheat cultivars to Blumeria graminis f.sp. tritici – short communication

Response of the susceptible cultivar Kanzler, the partially resistant cultivar Mikon and the resistant cultivar Asta (genes of resistance Pm2, Pm6) to powdery, were tested in two years small plot-experiments. Disease severity was influenced by weather conditions. There were highly significant differences in disease severity, infection type and number of diseased plants between the susceptible cultivar and the cultivars with partial resistance and specific resistance. Smaller differences were between the partially resistant cultivar and the resistant cultivar than between the cultivar with partial resistance and the susceptible cultivar. The most affected leaf was the third leaf from the top in all tested cultivars. Among these cultivars were differences in the highest development of disease in single growth stages.

Leaf rust occurrence in European winter wheat varieties and breeding lines

In 1998 and 1999, 52 winter wheat varieties and breeding lines originated from ten European countries were tested for their reaction to leaf rust, the inoculum was a mixture of races UN3-61SaBa and UN13-77SaBa. Twenty six varieties and lines stayed in the same group (susceptible, moderately susceptible, moderate, moderately resista nt) in both years, with the majority being moderately resistant. Of the Czech varieties Asta, Rexia and VIada stayed in the same group in both years. Some varieties moved from one group in 1998 to another in 1999. Some of the moderately resistant varieties and lines (Hereward, WW2568, P8634, Trakos, WW251 0, Asset, WW2564) showed a hypersensitive reaction (chlorosis, necrosis). There were differences in the number of diseased plants between groups with a different reaction to leaf rust mainly at the beginning of the epidemic

The influence of plant spacing on density-dependent versus frequency-dependent spore transmission of the anther smut Microbotryum violaceum.

The anther smut fungus Microbotryum violaceum is a pollinator-transmitted plant disease. As for other vector-borne diseases, frequency-dependent transmission patterns are predicted, in contrast to the density-dependent transmission of passively spread diseases. Frequency dependence will, however, only arise if vectors compensate for varying plant spacings. To test this assumption, we set up experimental populations of the host plant, Silene latifolia, with varying disease density (number of diseased plants per plot) and frequency (proportion of plants diseased), and three different plant spacings. We measured spore deposition on healthy flowers in these plots on two dates. Spore deposition decreased considerably from the first to the second census, perhaps related to the concomitant decrease in inflorescence sizes of diseased plants. At our first census, spore deposition rates varied with disease frequency, and the effect of frequency depended on plant spacing. While spore deposition was positively frequency dependent at the 1.5-m inter-plant spacing, no effect of disease frequency was found at a spacings of 0.5 m or 3 m. Nor was there an effect of disease density on spore deposition at the first census. At the later census, on the other hand, spore deposition increased almost significantly with increasing disease density (P = 0.08). This difference in deposition pattern together with a significant decrease in spore receipt indicates changes in pollinator spectrum and/or activity. The correlation of spore numbers among flowers within plants, an indication for intra-plant moves by vectors, was significant at 0.5 m and 1.5 m but not at 3 m. Floral traits and sex of individual plants influenced the number of spores they received. On the first census date, spore deposition increased with increasing inflorescence size in female but not in male plants. On the second census date, neither sex nor number of open flowers had an effect on spore receipt. None of the experimental plants became infected, however, probably because of the unusually hot and dry weather.