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Disease Pressure (disease + pressure)
Selected AbstractsDowny mildew (Plasmopara viticola) epidemics on grapevine under climate changeGLOBAL CHANGE BIOLOGY, Issue 7 2006SALINARI FRANCESCA Abstract As climate is a key agro-ecosystem driving force, climate change could have a severe impact on agriculture. Many assessments have been carried out to date on the possible effects of climate change (temperature, precipitation and carbon dioxide concentration changes) on plant physiology. At present however, likely effects on plant pathogens have not been investigated deeply. The aim of this work was to simulate future scenarios of downy mildew (Plasmopara viticola) epidemics on grape under climate change, by combining a disease model to output from two general circulation models (GCMs). Model runs corresponding to the SRES-A2 emissions scenario, characterized by high projections of both population and greenhouse gas emissions from present to 2100, were chosen in order to investigate impacts of worst-case scenarios, among those currently available from IPCC. Three future decades were simulated (2030, 2050, 2080), using as baseline historical series of meteorological data collected from 1955 to 2001 in Acqui Terme, an important grape-growing area in the north-west of Italy. Both GCMs predicted increase of temperature and decrease of precipitation in this region. The simulations obtained by combining the disease model to the two GCM outputs predicted an increase of the disease pressure in each decade: more severe epidemics were a direct consequence of more favourable temperature conditions during the months of May and June. These negative effects of increasing temperatures more than counterbalanced the effects of precipitation reductions, which alone would have diminished disease pressure. Results suggested that, as adaptation response to future climate change, more attention would have to be paid in the management of early downy mildew infections; two more fungicide sprays were necessary under the most negative climate scenario, compared with present management regimes. At the same time, increased knowledge on the effects of climate change on host,pathogen interactions will be necessary to improve current predictions. [source] Variety-specific Epidemiology of Cercospora beticola Sacc. and Consequences for Threshold-based Timing of Fungicide Application in Sugar BeetJOURNAL OF PHYTOPATHOLOGY, Issue 4 2010Ulrike Kaiser Abstract In Central Europe, fungicides to control leaf spot disease in sugar beet caused by Cercospora beticola are applied based on thresholds of disease incidence (DI, per cent of infected plants). As variety-specific fungicide application was not analyzed to date, the epidemiology of C. beticola and its effect on white sugar yield (WSY) in varieties with different susceptibility were investigated at seven sites in Germany and Austria in 2004 and 2005. All varieties reached the summary thresholds 5 / 15 / 45% DI in all environments. Fitting a logistic growth curve to DI revealed significant differences among varieties. At high disease pressure, susceptible varieties reached a considerably higher disease severity (DS, per cent of infected leaf area) at harvest and a larger area under disease progress curve (AUDPC) than resistant varieties. Fitting a logistic growth curve to DS showed an increasing differentiation among varieties with time. The growth rate estimated based on the logistic growth curve was the only variable that performed equally well in differentiating varieties under low and high disease pressure. With increasing disease pressure, varieties differed considerably in WSY, but differences between susceptible and resistant varieties were significant only in some environments. The disease-loss relation between AUDPC and relative WSY was variety-specific. Resistant varieties had an approximately identical WSY with and without infection and compensated for negative infection effects even at higher AUDPC. Therefore, at high disease pressure, resistant varieties had a higher relative yield compared to susceptible ones. However, our results indicate that there is no need to develop variety-specific thresholds, but resistant varieties reach the established thresholds later than susceptible ones. Consequently, the time of fungicide application can be delayed in resistant varieties. This will help to reduce the use of fungicides to the bare essentials as requested for the integrated crop protection management. [source] Rapid Screening Method of Cassava Cultivars for Resistance to Colletotrichum gloeosporioides f.sp. manihotisJOURNAL OF PHYTOPATHOLOGY, Issue 1 2002C. N. FOKUNANG An in vitro method for assessing cassava anthracnose disease (CAD) resistance was developed as a preliminary screen to a CAD-resistant breeding programme. Potato dextrose agar (PDA) media was amended by extracts from the stem cortex of 10 cassava cultivars (30001; 30572, 30211, 88/02549, 88/00695, 88/01336, 91/00344, 91/00313, 91/00684 and 91/00475), and assayed for efficacy of inhibition of the growth of Colletotrichum gloeosporioides f. sp. manihotis isolates (05FCN, 10FCN, 12FCN, and 18FCN). Morphological and physiological data indicated that there was a significant difference (P , 0.05), in mycelial growth, spore germination and sporulation among the four isolates on PDA amended with cassava stem extracts. Extracts from cassava cultivars 30211, 91/00684 and 91/00313 showed higher inhibition of germ tube development, mycelial growth and sporulation of the fungal isolates, whereas cultivars 88/02549 and 88/01336 showed the least inhibition. The 10 cultivars were further tested in both greenhouse and field conditions, under disease pressure for two planting seasons, to corroborate resistance to the fungus as observed in vitro. Greenhouse and field trials with the 10 cassava cultivars showed a significant difference (P , 0.05) in CAD resistance. Cultivars 88/02549 and 88/01336 were highly CAD-susceptible, as shown in the in vitro assays and confirmed in the greenhouse and field tests. The other eight cultivars were either resistant (30211, 91/00684), or moderately resistant (30572, 88/00695, 91/00475, 91/00344, 30001 and 91/00313) to CAD. The study shows that an in vitro screening assay of cassava for resistance to CAD could serve as a convenient preliminary screening technique to discriminate CAD-resistant from CAD-susceptible cassava cultivars. The in vitro screening method considerably reduces time and labour in comparison with the current screening techniques of cassava, which involve field planting, inoculation and evaluation. [source] Potential for effective marker-assisted selection of three quantitative trait loci conferring adult plant resistance to powdery mildew in elite wheat breeding populationsPLANT BREEDING, Issue 5 2006D. M. Tucker Abstract Three quantitative trait loci (QTL) associated with adult plant resistance (APR) to powdery mildew (Blumeria graminis) in wheat (Triticum aestivum) cultivar ,Massey' were mapped in a previous study. The three QTL were located on chromosomes 2A, 2B and 1B, and explained 50% of the total phenotypic variation. A 293 recombinant inbred line (RIL) breeding population (UJ) derived from the cross of ,USG 3209', a derivative of ,Massey', and ,Jaypee' was used to evaluate the potential effectiveness of marker-assisted selection (MAS) for APR. Powdery mildew severities of the 293 UJ RILs were evaluated in 2002 (F5 : 6) and 2003 (F6 : 7) under natural disease pressure in the field. The 293 RILs were also evaluated for disease severity in a 2004 (F7 : 8) greenhouse experiment using a composite of five different isolates of B. graminis. Selection of RILs possessing the QTL on chromosome 2A, and to a lesser extent, the one on chromosome 1B was effective in identifying powdery mildew resistance in both greenhouse and field experiments. Overall, selecting RILs with QTL on chromosomes 2A and 2B was most successful in identifying highly resistant RILs, which had mean mildew severities of 4.4% and 3.2% in 2002 and 2003 field experiments, respectively. Breeders implementing MAS programs for APR to powdery mildew via selection of RILs containing the two QTL on chromosomes 2A and 2B likely will obtain RILs having high levels of resistance in the field, however combining all three QTL may ensure greater durability. [source] A model of the effect of fungicides on disease-induced yield loss, for use in wheat disease management decision support systemsANNALS OF APPLIED BIOLOGY, Issue 1 2007A. Milne Abstract A model of the effect of foliar-applied fungicides on disease-induced yield loss is described, parameterised and tested. The effects of fungicides on epidemics of Septoria tritici (leaf blotch), Puccinia striiformis (yellow rust), Blumeria graminis f.sp. tritici (powdery mildew) and Puccinia triticina (brown rust) on winter wheat were simulated using dose,response curve parameters. Where two or more active substances were applied together, their joint action was estimated using an additive dose model where the active substances had the same mode of action or a multiplicative survival model where the modes of action differed. By coupling the model with models of wheat canopy growth and foliar disease published previously, it was possible to estimate disease-induced yield loss for a prescribed fungicide programme. The difference in green canopy area and, hence, interception of photosynthetically active radiation between simulated undiseased and diseased (but treated) crop canopies was used to estimate yield loss. The model was tested against data from field experiments across a range of sites, seasons and wheat cultivars and was shown to predict the observed disease-induced yield loss with sufficient accuracy to support fungicide treatment decisions. A simple method of accounting for uncertainty in the predictions of yield loss is described. Fungicide product, dose and spray timing combinations selected using the coupled models responded appropriately to disease pressure and cultivar disease resistance. [source] Evaluation of fungal antagonists for grey mould management in early growth of pot rosesANNALS OF APPLIED BIOLOGY, Issue 1 2004D S YOHALEM Summary Several filamentous fungi can reduce disease incidence and suppress sporulation of Botrytis cinerea during early establishment and vegetative growth of pot roses. Two isolates of Ulocladium atrum were the most successful of those fungi tested, were consistently more effective than the fungicide, iprodione and not different from each other. Tween 80, added as a dispersant, had no effect on the efficacy of U. atrum. An isolate of Clonostachys rosea also gave better disease control than iprodione, although not to the levels given by isolates of U. atrum, nor was its behaviour consistent across experiments. Another isolate of C. rosea performed well in one trial, had no discernible effect in a second and was excluded from the third due to poor inoculum quality. Commercial Trichoderma harzianum preparations (Trichodex and Supresivit) failed to reduce disease incidence under the high disease pressure of these experiments, but did reduce sporulation of the pathogen relative to untreated controls. [source] Relationship between incidence and severity of cashew gummosis in semiarid north-eastern BrazilPLANT PATHOLOGY, Issue 3 2004J. E. Cardoso The incidence,severity relationship for cashew gummosis, caused by Lasiodiplodia theobromae, was studied to determine the feasibility of using disease incidence to estimate indirectly disease severity in order to establish the potential damage caused by this disease in semiarid north-eastern Brazil. Epidemics were monitored in two cashew orchards, from 1995 to 1998 in an experimental field composed of 28 dwarf clones, and from 2000 to 2002 in a commercial orchard of a single clone. The two sites were located 10 km from each other. Logarithmic transformation achieved the best linear adjustment of incidence and severity data as determined by coefficients of determination for place, age and pooled data. A very high correlation between incidence and severity was found in both fields, with different disease pressures, different cashew genotypes, different ages and at several epidemic stages. Thus, the easily assessed gummosis incidence could be used to estimate gummosis severity levels. [source] | ||||||||||