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1.
Effects of inoculum concentration, wetness duration and plant age on the development of tomato early blight were evaluated in relation to host susceptibility under controlled environmental conditions. The main effect of early blight was premature defoliation, which was linearly related to the percentage of leaf area showing symptoms. As ln(inoculum concentration, conidia mL−1) increased from 6·2 to 11·5, the percentages of leaf area affected and of defoliation increased linearly. Four h of leaf wetness after inoculation were sufficient to initiate the disease on plants of hybrid Skala RZ but not on those of cv. Rio Rojo, for which at least 6 h leaf wetness were needed. As wetness duration increased up to 24 h, there was an increase in the percentage leaf area showing symptoms and in the percentage of defoliation, but thereafter there was no significant increase in either parameter. Tomato plants were susceptible to Alternaria solani at all growth stages, but susceptibility increased as plants matured. There were no significant differences in susceptibility between tomato cultivars and hybrids.  相似文献   

2.
ABSTRACT Three field experiments were conducted in 1997, 1998, and 1999 to investigate the effects of angular leaf spot and rust, separately or combined, on host growth and yield of individual bean plants (Phaseolus vulgaris). In each experiment, three treatments were established by inoculating cv. Carioca with Phaeoisariopsis griseola, Uromyces appendiculatus, or with both pathogens. An additional control treatment was not inoculated, but was sprayed with a fungicide. In the 1997 and 1999 experiments, angular leaf spot reached higher disease levels than rust, whereas in 1998, rust was more severe than angular leaf spot. Host growth, expressed as healthy leaf area duration (HAD), and yield were the highest in 1997 and lowest in 1998. In each experiment, the treatments did not differ significantly to the area under leaf area progress curve, HAD, and healthy leaf area absorption (HAA). All inoculated treatments had significantly more severe disease and less yield than the control treatment. Based on the analysis of 60 plants in each experiment, yield was not related to the areas under disease progress curve for either or both diseases. In 1997 and 1999, yield was related to HAD (R(2) = 0.57 and 0.43) and HAA(R(2) = 0.60 and 0.55). Based on the combined analysis of all 36 plots, angular leaf spot reduced the leaf area because of defoliation, whereas rust did not affect the leaf area. Rust reduced yield more than four times that of angular leaf spot, although the decrease in photosynthesis to angular leaf spot was twice that of rust.  相似文献   

3.
Monocyclic components (development rate during the incubation period or latent period, lesion density, lesion size and disease severity) of rust ( Uromyces appendiculatus ) and of angular leaf spot ( Phaeoisariopsis griseola ) in two bean ( Phaseolus vulgaris ) cultivars (Rosinha G-2 and Carioca), pre-infected or not with bean line pattern mosaic virus (BLPMV), were determined. Trials were conducted at temperatures in the range from 9 to 27°C for rust and from 12 to 30°C for angular leaf spot. Regardless of viral pre-infection, the effect of temperature on the four monocyclic components followed an optimum curve and could be described by a generalized beta function. Generally, angular leaf spot was favoured by higher temperatures with an optimum for disease severity between 24.2 and 28.3°C compared with 15.9–18.5°C for rust. Pre-infection with BLPMV did not change the shape of the optimum curves for all components, but significantly reduced lesion density and disease severity on both cultivars. The development rates during incubation and latent periods for both fungal diseases were not affected by BLPMV. Pre-infection with virus did not alter the ranking of cultivars with respect to resistance to both fungal diseases.  相似文献   

4.
A preparation of Trichoderma harzianum was sprayed on cucumber plants in greenhouses in order to control fruit and stem grey mould. Up to 90% control was achieved by the biocontrol agent (0·5–1·0 g/l) which in most experiments under commercial conditions was as effective as the dicarboximide fungicides iprodione or vinclozolin (0·5 g/l each) alone or alternated with diethofencarb + carbendazim (0·25 g/l each). However, in one experiment disease incidence in Trichoderma -treated plots did not differ significantly from the control. A mixture of T. harzianum with a dicarboximide fungicide resulted in up to 96% control of grey mould. In this case control was always significant ( P =0·05) but improvement of control compared with each treatment alone was not significant ( P =0·05). The alternation of sprays with the biocontrol preparation and with a dicarboximide fungicide was tested in three out of the five experiments and was found to be effective, thus enabling a reduction in the use of chemical sprays. Populations of T. harzianum were on a level of 3 × 105-8 × 105 c.f.u. per leaf and ten times lower on one fruit. They remained high after the second and third sprays. Conditions favouring the ability of T. harzianum to control grey mould were temperatures above 20°C and relative humidity between 80 and 97%.  相似文献   

5.
The pattern of Cylindrocladium pteridis adhesion, germination and penetration in eucalypt leaves was assessed using scanning electron microscopy. The effects of inoculum concentration, leaf wetness period, plant age and branch position of cylindrocladium leaf blight and defoliation severity were assessed in greenhouse studies using two Eucalyptus grandis × E. urophylla hybrid clones. Penetration occurred through stomata, and there was no difference in the number of penetrations between young and old leaves. Percentage leaf area with lesions and defoliation increased with the increase in inoculum concentration (1 × 102 to 105 conidia mL−1), duration of leaf wetness period (6 to 48 h) and plant age (60 to 180 days). Branch position in plants also significantly affected the percentage leaf area with lesions and defoliation, the latter variable being significantly higher at the stem base. The highest values of lesion area were also observed on leaves at the stem base in both clones. The Pearson correlation between defoliation and leaf area with lesions was significant in all experiments ( r  > 0·9) indicating a high association between these two variables.  相似文献   

6.
Unifoliate leaves of 9-day-old green bean, Phaseolus vulgaris cv. Redlands Pioneer, were inoculated with 104 conidia/ml Colletotrichum lindemuthianum , causing local lesions, or sprayed with 20 μg 2, 6-dichloro-isonicotinic acid/ml formulated by Ciba-Geigy Ltd as CGA 41396. At various times afterwards (7–16 days), first, second or third trifoliate leaves of these plants were challenge-inoculated with 105 conidia/ml C. lindemuthianum or with the rust pathogen, Uromyces appendiculatus. The numbers of anthracnose lesions or rust uredinia resulting from challenge-inoculation were reduced to similar extents by both pre-treatments compared with control plants. Halo blight, caused by Pseudomonas syringae pv. phaseolicola , was reduced in first trifoliates following treatment of unifoliate leaves 6 days earlier with CGA 41396. Induced resistance to root-infecting pathogens was not observed when stems of either 14- or 16-day-old plants were inoculated with mycelial plugs of Fusarium solani f. sp. phaseoli , or when 11- and 15-day-old plants were inoculated with Rhizoctonia sp., Treatment with CGA 41396 did not protect seedlings when they were transplanted into a mix containing the Fusarium sp. 1 day later.  相似文献   

7.
Lopes DB  Berger RD 《Phytopathology》2001,91(2):212-220
ABSTRACT The effects of rust (caused by Uromyces appendiculatus) and anthracnose (caused by Colletotrichum lindemuthianum) and their interaction on the photosynthetic rates of healthy and diseased bean (Phaseolus vulgaris) leaves were determined by gas-exchange analysis, in plants with each disease, grown under controlled conditions. The equation P(x)/P(0) = (1 - x)() was used to relate relative photosynthetic rate (P(x)/P(0)) to proportional disease severity (x), where beta represents the ratio between virtual and visual lesion. The beta values obtained for rust were near one, indicating that the effect of the pathogen on the remaining green leaf area was minimal. The high values of beta obtained for anthracnose (8.46 and 12.18) indicated that the photosynthesis in the green area beyond the necrotic symptoms of anthracnose was severely impaired. The impact of anthracnose on bean leaf photosynthesis should be considered in assessments of the proportion of healthy tissue in diseased leaves. The accurate assessment of the healthy portion of the leaf could improve the use of concepts such as healthy leaf area duration and healthy leaf area absorption, which are valuable predictors of crop yield. The equation used to analyze the interaction between rust and anthracnose on the same leaf was P(z) = P(0) (1 - x)(x) x (1 - y)(y), where P(z) is the relative photosynthetic rate of any given leaf, P(0) is the maximum relative photosynthetic rate, x is anthracnose severity, y is rust severity, betax is the beta value for anthracnose in the presence of rust, and betay is the beta value for rust in the presence of anthracnose. From the resulting response surface, no interaction of the two diseases was observed. Dark respiration rate increased on diseased leaves compared with control leaves. The remaining green leaf area of leaves with both diseases was not a good source to estimate net photosynthetic rate because the effect of anthracnose extended far beyond the visual lesions, whereas the effect of rust on photosynthesis was essentially limited to the pustule plus halo.  相似文献   

8.
A total of 119 isolates of Rhizoctonia were collected from stem canker lesions, stolon and root lesions, hymenia on stems, or from black scurf on tubers of potato plants ( Solanum tuberosum ) in Finland (latitudes 60–67°N). All isolates except three belonged to anastomosis group 3 (AG-3) of R. solani , as determined by phylogenetic analysis of the internal transcribed spacer sequences (ITS1 and ITS2) of ribosomal RNA (rRNA) genes. Sensitivity of the 119 isolates to the fungicide flutolanil was tested in vitro (EC50 values 0·14–0·75  µ g active ingredient mL−1). The isolates also varied considerably in growth rate (5·1–14·8 mm day−1). The severity of disease caused by 99 isolates was determined based on the proportion of potato sprouts affected by lesions, discoloration or death, which was c . 1–60%. Only two isolates that were able to cause severe symptoms showed particularly low sensitivity to the fungicide and rapid growth rate. One isolate each of anastomosis groups AG-2-1 and AG-5 and an unknown, binucleate Rhizoctonia sp. were detected. The AG-5 isolate and the binucleate isolate caused mild symptoms on potato sprouts, whereas the AG-2-1 isolate was not pathogenic. Taken together, AG-3 of R. solani was the predominant causal agent of the stem canker and black scurf diseases of potato in Finland and showed considerable variability in disease severity, fungicide sensitivity and growth rate in vitro .  相似文献   

9.
Bean rust, caused by Uramyces appendiculatus, is one of the major diseases in dry and snap bean production world-wide. Numerous advancements in disease management have been made to reduce rust losses. Host resistance is an important component of rust management. However, durability of disease resistance has often been short due to the use of single genes for resistance interacting with extremely high virulence diversity of the bean rust fungus. The challenge to increase durability of resistance has led to strategies such as gene pyramiding of race-specific resistance, selection and use of partial resistance, and investigation and discovery of leaf morphological features that may slow the rust epidemic. Germplasm with multiple sources of rust resistance has been developed in specific bean seed classes and released for public and commercial use in intensive production systems such as those in the United States. However, progress to develop rust resistant germplasm for the subsistence agriculture of Latin America and Africa where intercropping and mixed cultivars dominate the production system has been slow. Incorporation of high yielding, disease-resistant components as partial replacement in farmer's mixtures has the potential to reduce severity in the crop and increase yield in the presence of rust. This strategy would not erode the genetic diversity that is historically known to enhance resistance durability and for many years has given stability in production in the subsistent agriculture systems.  相似文献   

10.
Throughout the development of plants, certain biotic and abiotic phenomena can occur which reduce not only the photosynthetic area, but also the growth, depending on the stage of plant development. Responses by plants to defoliation depend on species, the timing of agricultural practices and the intensity level of defoliation. An experiment was carried out in Tunja, Colombia under greenhouse conditions, in order to evaluate the tolerance of faba bean plants (Vicia faba) to partial defoliation. Every week material was removed along each newly emerged leaflet to simulate 50% defoliation. Another group was grown with the entire leaf area to function as a control. As a result of partial defoliation, the specific leaf area, absolute growth rate, relative growth rate and total biomass were reduced, but the leaf weight ratio was increased. In addition, the pattern of dry matter partitioning was altered so that the amount of biomass accumulated was reduced in the roots, but increased in the leaves. Additionally, the partially defoliated plants showed the ability to partly restore the removed leaf area. In this way it could be inferred that the plants of Vicia faba present a moderate capacity to tolerate early defoliation during the vegetative phase.  相似文献   

11.
Reaction to inoculation with powdery mildew caused by Sphaerotheca fuliginea was observed on leaf discs and young plants of eleven representatives of seven edible cultivar groups of Cucurbita pepo. Disease intensity (i.e. number of infections per leaf) was highly correlated ( r 2=0·863, P <0·0001) with spore yield per leaf. Spore yield per leaf and frequency of sporulation on leaf disks were moderately ( r 2=0·505), but significantly correlated ( P <0·01), suggesting that frequency of sporulation can be used for initial screening against susceptibility in a breeding programme. Spore yield per leaf and spore yield per artificially inoculated leaf disc were highly correlated ( r 2=0·87, P <0·0001); this suggests that counting of spores on leaf discs, a laborious but accurate procedure, could be used on the remaining plants as a second step in selection for resistance of the variation in the response of edible C. pepo to the pathogen, 85·8% was attributed to differences between the edible groups and only 14·2% to individual cultivars within a group. Cultivars of the cocozelle and vegetable marrow groups were the most susceptible, whereas relatively resistant cultivars were found in the scallop and straightneck groups.  相似文献   

12.
The population of Phytophthora infestans in Brazil consists of two clonal lineages, US-1 associated with tomatoes and BR-1 associated with potatoes. To assess whether host specificity in these lineages resulted from differences in aggressiveness to potato and tomato, six aggressiveness-related epidemiological components – infection frequency (IF), incubation period (IP), latent period (LP), lesion area (LA), lesion expansion rate (LER) and sporulation at several lesion ages (SSLA) – were measured on detached leaflets of late blight-susceptible potato and tomato plants. Infection frequency of US-1 was similar on potato and tomato leaflets, but IF of BR-1 was somewhat reduced on tomato. Incubation period was longer on both hosts with US-1, although this apparent lineage affect was not significant. Overall there was no host effect on IP. On potato, BR-1 had a shorter LP (110·3 h) and a larger LA (6·5 cm2) than US-1 (LP = 162·0 h; LA = 2·8 cm2). The highest LER resulted when isolates of BR-1 (0·121 cm2 h−1) and US-1 (0·053 cm2 h−1) were inoculated on potato and tomato leaflets, respectively. The highest values of the area under the sporulation capacity curve (AUSC) were obtained for isolates of US-1 inoculated on tomato leaflets (6146) and for isolates of BR-1 on potato leaflets (3775). In general, higher values of LA, LER, SSLA and AUSC, and shorter values of LP were measured when isolates of a clonal lineage were inoculated on their original host than with the opposite combinations. There is evidence that there are quantitative differences in aggressiveness components between isolates of US-1 and BR-1 clonal lineages that probably contribute to host specificity of P. infestans populations in Brazil.  相似文献   

13.
The production of ascochitine by seven isolates of Ascochyta fabae accounted for the toxicity of culture filtrates of the fungus to cells isolated from leaves of Vicia faba. The LD50 value for cells from cultivars that were susceptible, tolerant or resistant to the fungus was similar i.e. 3·0 × 10−5 m , 3·8 × 10−5 m and 2·9 × 10−5 M, respectively. Ascochitine affected neither the germination of seeds nor the growth of mature plants at 5·17 × 10−4 m but caused necrosis and wilting of plant cuttings at 2·5 × 10−4 m and 5·10−4 m . There was no association between virulence of 16 isolates of A. fabae for three cultivars of V.faba and the production of ascochitine in vitro. One isolate produced no ascochitine in vitro and yet was the most virulent for two of three cultivars. The toxin could not be extracted from infected plants.  相似文献   

14.
Powdery mildew and leaf rust caused large yield losses in spring barley grown near Christchurch, New-Zealand, in two seasons. Disease present during early growth stages was as damaging to yield as disease late in the season. Moderate leaf rust severities after anthesis were most damaging when combined with earlier mildew epidemics. Later growth did not compensate for reduced yield potential induced by early infection. This was attributed, at least in part, to an effect on leaf size, and therefore on green leaf area, at later growth stages. There was a closer relationship, by regression analysis, of yield to green leaf area than to disease severity in three cultivars.
The three cultivars. which differed in yield potential and disease resistance, were not equally sensitive to disease. It is proposed that high yielding cultivars may be the most sensitive to yield constraint by disease.  相似文献   

15.
The epidemiology of the Neotropical rust caused by Puccinia psidii in the Indian Myrtaceae Syzygium jambos (rose apple) was investigated in central Brazil. Disease severities recorded during a 12-month period were fitted by a Fourier curve with three cyclic components or harmonics. The first, second and third harmonics accounted for 49·6, 25·9, and 1·5% of total disease measured, respectively. A highly significant linear correlation was observed between the first harmonic and the accumulated number of days having at least 6 h wetness, or a minimum of 90% relative humidity, combined with temperatures that ranged from 18 to 20°C. No significant correlation was observed between the second and third harmonics and the weather variables evaluated. Rose apple trees showed a flush of growth with new susceptible host tissue during the evaluation period, with two major outbreaks of rust of variable intensity. Host growth was fitted by a Fourier curve with two significant harmonics. The first and second harmonics accounted for 37·5 and 22·1% of total host growth measured, respectively. A highly significant negative linear correlation was observed between the first harmonic and daily maximum and minimum temperatures, rainfall, and duration of the light period. Inoculum availability was not a limiting factor for disease progress since urediniospores were present during most of the period studied. A major peak in numbers of rust spores followed the main peak of disease severity. Thus, rust epidemics on rose apple in central Brazil were shown to depend on the duration of leaf wetness in the dark, and also on night-time temperatures during that same wetness period. This study is the first example of a periodical analysis of an epidemic in a perennial crop.  相似文献   

16.
A virus was isolated in Italy from Tamus communis in which it caused symptoms of red mosaic and leaf distortion. The virus, for which the name tamus red mosaic virus (TRMV) is suggested, was differentiated from other potexviruses or possible potexviruses on the basis of host range, particle properties and serology. In crude preparations, TRMV had elongated particles of modal length 550–560 nm and diameter of 13 nm. TRMV was easily purified from Chenopodium quinoa and had a buoyant density of 1·34 g/cm3 in CsCl and 1·27 g/cm-3 in Cs2SO4. An antiserum to TRMV was obtained with a titre of 1/1024 in slide precipitin tests. TRMV was related to, but distinct from, tamus latent virus, a potexvirus isolated from Tamus communis in the UK, and more distantly related to potato virus X, cactus virus X and commelina virus X. Polyacrylamide gel electrophoresis (PAGE) indicated that the virus particles contained a single protein species of estimated molecular weight 25·2 kDa. Enzymatic digestions, agarose gel electrophoresis and infectivity of the isolated nucleic acid indicated that the virus has a single major molecule of single-stranded positive-sense RNA of estimated molecular weight 2120 kDa ( ca. 6·4 kb).  相似文献   

17.

Vegetables in the tropics are grown continuously throughout the year due to the favorable climate. Unfortunately, leafy vegetables are often damaged because of slugs and snails. These mollusks and other herbivores cause different levels of defoliation to plants which can significantly impact their growth, production, and quality of the harvested product. A study was carried out in order to artificially simulate the effect of a loss in foliar area caused by these pests. The impact of severe artificial defoliation in spinach plants (Spinacia oleracea) was evaluated in Tunja, Colombia. Under greenhouse conditions and after transplanting, the plants had 75% of their leaf area removed. This procedure was repeated weekly on newly emerging leaves while a control group of plants was left intact. 71 days after transplanting, the plants were harvested, and the leaf area and dry weight of the plants were measured with which some allometric variables were calculated to express growth. Variables such as the number of leaves, plant height, total dry weight, relative growth ratio, leaf weight ratio (LWR), and root to shoot ratio (R:S) were unaffected by defoliation while leaf area, leaf area ratio (LAR), and specific leaf area (SLA) were reduced with the partial removal of the leaf area. The partial defoliation resulted in an increased partial biomass of the leaves. These results suggest that spinach plants have a moderate tolerance to partial defoliation.

  相似文献   

18.
Over a period of 3 years, five agronomically distinct crops of winter wheat were grown in plots in which straw (1 kg m−2), manure (4 kg m−2) or nothing were incorporated into the soil. Plant establishment and height, but not leaf area per tiller, were lower in straw-treated plots. Fertilizer regimes differed between years. Soil and leaf nitrogen were recorded; there was no obvious link between N and any disease or soil amendment. The numbers of leaf layers scorable for disease were similar in all treatments. At the end of the season, plants from straw-treated plots had consistently reduced septoria tritici blotch (caused by Mycosphaerella graminicola ), powdery mildew [caused by Erysiphe ( Blumeria ) graminis ], brown rust (caused by Puccinia recondita ) and foot rot (caused by Fusarium spp.). Early on, M. graminicola was worse in straw-treated plots. In manure-treated plots, P. recondita was reduced but effects on other diseases were inconsistent and slight. A fungicide, chlorothalonil, was applied in one crop; its effects did not interact with those of other treatments. Mycosphaerella graminicola was not suppressed by straw in outdoor pot experiments. Late in the season, straw-treated plants had significantly higher leaf silica ( P  < 0·01). In a glasshouse experiment, plants supplied with silicon had less E. graminis infection ( P  < 0·001) and higher leaf silica, but effects on M. graminicola were inconsistent. A prior inoculation of M. graminicola primed plant defences against a subsequent attack of E. graminis , but only in the presence of adequate Si. It is postulated that straw acts in the field by increasing Si availability.  相似文献   

19.
Soybean rust is caused by an obligate parasite (Phakopsora pachyrhizi) which has spread in Brazil in each new season since 2001 and, despite the efforts to control the disease, losses have occurred every year. Its control demands several tactics amongst which chemical control with fungicides is the main method and remains indispensable. Control strategies such as the use of cultivars with partial resistance are desirable, but are not yet commercially available. The present study analyzed the existing differences in the reactions of short, medium and long cycle soybean cultivars against Asian rust and their responses to fungicide sprays. The experiment was conducted at Uberlandia-MG, Brazil, under field conditions from December 2007 to May 2008, in the Syngenta Seeds Experimental Station. The high pressure of the disease in the experiment simulated the natural pressure that the disease often reaches in Brazil. The studied variables were: visual severity (percentage of infected leaf area), percentage defoliation and productivity (kg ha−1). Disease severity was expressed as AUDPC (area under disease progress curve). Variance analysis and comparison of means by the Tukey test (5% significance) were done for all variables studied. Significant differences were observed between cultivar effects and chemical control programs. The results obtained here indicate that the cultivars M-Soy 8199RR and Emgopa 315RR were less susceptible to disease, and that a control program termed “monitoring” (in which the appearance of new pustules of the pathogen were monitored to make the decision at each fungicide spray) was the most effective.  相似文献   

20.
The relationship between severity of blackleg, or phoma stem canker ( Leptosphaeria maculans/L. biglobosa ), and subsequent primary inoculum production on oilseed rape ( Brassica napus ) stubble was investigated at two sites in France over 3 years. The quantity of primary inoculum produced in the following year increased with canker severity, from 1·9 to 10·8 pseudothecia cm−2 on stubble with the least and most severe cankers, respectively. Stubble incubated at Le Rheu (cooler, more rain) had 1·7 times more pseudothecia than stubble incubated at Grignon. Stubble collected at Grignon had 2·7 times more pseudothecia than that collected at Le Rheu. The use of Darmor, a cultivar with a good level of quantitative resistance, reduced the severity of canker in the field, but not the subsequent inoculum production for stubble of the same canker severity class. At both sites, maturation of pseudothecia occurred after 63–75 days of incubation and increased with canker severity with a mean of 0·5 and 3% mature pseudothecia appearing per favourable day, on stubble with the least and most severe cankers, respectively. A simplified procedure for pseudothecial quantification proved satisfactory: for all three observers, most (91–96%) of the fructifications counted as pseudothecia were real pseudothecia. Only a few (4–14%) of the fructifications considered as non-pseudothecia were in fact pseudothecia of L. maculans . The total area occupied by pseudothecia, which was simpler and faster to evaluate, was correlated (coefficient of determination, R 2 = 71%) with the number of counted pseudothecia. The results presented here make it possible to forecast the quantity of available primary inoculum for a given disease severity.  相似文献   

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