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Leaf Spot Disease (leaf + spot_disease)
Selected AbstractsVariety-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] Infection of Blackcurrant Leaves by Drepanopeziza ribis in Relation to Weather Conditions and Leaf PositionJOURNAL OF PHYTOPATHOLOGY, Issue 5 2009Xiang Ming Xu Abstract Drepanopeziza ribis causes the leaf spot disease of blackcurrant (Ribes nigrum) and may lead to severe premature leaf-fall. Artificial inoculation studies were carried out to investigate infection of leaves by D. ribis conidia in relation to environmental conditions and leaf position (age) on cvs. Baldwin and Ben Hope in April and July 2007. All leaves on a number of selected extension shoots on potted three-year old plants were inoculated with conidia and then incubated under different conditions: 10, 17.5 and 25°C each with five wet periods (4, 8, 12, 24 and 30 h). Number of infected leaves was determined. The two cultivars differed significantly in their susceptibility to conidial infection: cv. Baldwin was much more susceptible than cv. Ben Hope. Older leaves on extension shoots were more susceptible to conidial infection than younger leaves. Increasing length of wetness duration led to increasing incidence of leaves infected, particularly when inoculated in July. However, the effects of temperature were inconclusive and generally very small in comparison with other factors. Field epidemics were monitored over three years (2005,07). Field data confirmed the main findings from controlled inoculation studies: severe disease was associated with very wet conditions and older leaves. Furthermore, they also suggested that significant disease increase only occurred from late July onwards. [source] Bipolaris sorokiniana, a cereal pathogen of global concern: cytological and molecular approaches towards better control,MOLECULAR PLANT PATHOLOGY, Issue 4 2002Jagdish Kumar Summary Bipolaris sorokiniana (teleomorph Cochliobolus sativus ) is the causal agent of common root rot, leaf spot disease, seedling blight, head blight, and black point of wheat and barley. The fungus is one of the most serious foliar disease constraints for both crops in warmer growing areas and causes significant yield losses. High temperature and high relative humidity favour the outbreak of the disease, in particular in South Asia's intensive ,irrigated wheat,rice' production systems. In this article, we review the taxonomy and worldwide distribution, as well as strategies to counteract the disease as an emerging threat to cereal production systems. We also review the current understanding of the cytological and molecular aspects of the interaction of the fungus with its cereal hosts, which makes B. sorokiniana a model organism for studying plant defence responses to hemibiotrophic pathogens. The contrasting roles of cell death and H 2O2 generation in plant defence during biotrophic and necrotrophic fungal growth phases are discussed. [source] Effect of a nonhost-selective toxin from Alternaria alternata on chloroplast-electron transfer activity in Eupatorium adenophorumPLANT PATHOLOGY, Issue 5 2005S. Chen AAC-toxin, a putative nonhost-selective phytotoxin, was obtained from Alternaria alternata causing a brown leaf spot disease of Crofton weed (Eupatorium adenophorum). The effect of AAC-toxin on the electron transfer reaction of chloroplasts showed that the activity of photosystem II, but not photosystem I, was completely inhibited by the toxin. AAC-toxin affected the following chlorophyll fluorescence parameters: coefficient of photochemical quenching (qP), the half-time value of fluorescence rise, and the O,J,I,P fluorescence induction kinetics curve, but not the ratio values of Fv/Fm (the quantum yield of photosystem II) and the half-time value of fluorescence quenching. It was concluded that the toxin inhibited electron transfer from QA to QB (primary and secondary quinine acceptors of photosystem II) in photosystem II by competing with QB for the binding site in D1 protein on the thylakoid membrane. [source] Analysis of leaf appearance, leaf death and phoma leaf spot, caused by Leptosphaeria maculans, on oilseed rape (Brassica napus) cultivarsANNALS OF APPLIED BIOLOGY, Issue 1 2010S.J. Powers Development of phoma leaf spot (caused by Leptosphaeria maculans) on winter oilseed rape (canola, Brassica napus) was assessed in two experiments at Rothamsted in successive years (2003,04 and 2004,05 growing seasons). Both experiments compared oilseed rape cultivars Eurol, Darmor, Canberra and Lipton, which differ in their resistance to L. maculans. Data were analysed to describe disease development in terms of increasing numbers of leaves affected over thermal time from sowing. The cultivars showed similar patterns of leaf spot development in the 2003,04 experiment when inoculum concentration was relatively low (up to 133 ascospores m,3 air), Darmor developing 5.3 diseased leaves per plant by 5 May 2004, Canberra 6.6, Eurol 6.8 and Lipton 7.5. Inoculum concentration was up to sevenfold greater in 2004,05, with Eurol and Darmor developing 2.4 diseased leaves per plant by 16 February 2005, whereas Lipton and Canberra developed 2.8 and 3.0 diseased leaves, respectively. Based on three defined periods of crop development, a piece-wise linear statistical model was applied to the progress of the leaf spot disease (cumulative diseased leaves) in relation to appearance (,birth') and death of leaves for individual plants of each cultivar. Estimates of the thermal time from sowing until appearance of the first leaf or death of the first leaf, the rate of increase in number of diseased leaves and the area under the disease progress line (AUDPL) for the first time period were made. In 2004,05, Canberra (1025 leaves ×°C days) and Lipton (879) had greater AUDPL values than Eurol (427) and Darmor (598). For Darmor and Lipton, the severity of leaf spotting could be related to the severity of stem canker at harvest. Eurol had less leaf spotting but severe stem canker, whereas Canberra had more leaf spotting but less severe canker. [source] | ||||||||||