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1.
Diaporthe helianthi the causal agent of sunflower (Helianthus annuus) stem canker, causes significant reductions in yield and oil content in most sunflower-growing areas. With the aim of enhancing host resistance, we selected in vitro sunflower calli against culture filtrates of two pathogen isolates (7/96 and 101/96). This technique may be an effective and rapid tool to discriminate the most virulent D. helianthi isolate and to screen for host resistance in the early stage of a breeding programme. Further investigation on the mechanisms involved in defence pathways showed no induction of salicylic acid and pathogenesis-related proteins in calli, indicating that the host resistance is not associated with Systemic Acquired Resistance but probably other biochemical mechanisms.  相似文献   

2.
V. Rossi  S. Giosu 《EPPO Bulletin》2003,33(3):389-396
A system dynamic model for epidemics of Blumeria graminis (powdery mildew) on wheat was elaborated, based on the interaction between stages of the disease cycle, weather conditions and host characteristics. The model simulates the progress of disease severity, expressed as a percentage of powdered leaf area, on individual leaves, with a time step of one day, as a result of two processes: the growth of fungal colonies already present on the leaves and the appearance of new colonies. By means of mathematical equations, air temperature, vapour pressure deficit, rainfall and wind are used to calculate incubation, latency and sporulation periods, the growth of pathogen colonies, infection and spore survival. Effects of host susceptibility to infection, and of leaf position within the plant canopy, are also included. Model validation was carried out by comparing model outputs with the dynamics of epidemics observed on winter wheat grown at several locations in northern Italy (1991–98). Simulations were performed using meteorological data measured in standard meteorological stations. As there was good agreement between model outputs and actual disease severity, the model can be considered a satisfactory simulator of the effect of environmental conditions on the progress of powdery mildew epidemics.  相似文献   

3.
Pseudomonas syringae pv. actinidiae (Psa) was identified as the causal agent of severe epidemics of bacterial canker on Actinidia chinensis (yellow kiwifruit) in central Italy occurring during 2008–9. A total of 101 strains were obtained from infected leaves, twigs, branches and trunks of cvs Hort16A, Jin Tao and CK3. Outbreaks were also found on A. deliciosa cv. Hayward. A representative set of 21 strains were compared with other Psa strains isolated from previous outbreaks in Japan and Italy as well as with P. s. pv. syringae strains obtained from A. chinensis and with strains of genomospecies 8. Repetitive‐sequence PCR (rep‐PCR) typing using BOX and ERIC primer sets revealed that all Psa strains obtained during 2008–9 showed the same fingerprinting profile. This profile, however, was different from those of strains previously isolated in Japan and Italy. Multilocus sequence typing (MLST) of gapA, gltA, gyrB and rpoD revealed a higher genetic variability among the strains than rep‐PCR, with some of them showing the same sequence pattern although isolated from different areas, cultivars and years. None of the recently obtained strains possessed genes coding for phaseolotoxin or coronatine, and all had an effector protein, namely hopA1, differentiating them from the strains causing past outbreaks in Japan and Italy. All isolates were inhibited in vitro by copper‐based compounds, antibiotics, geraniol, citronellol and by a chitin‐based organic compound. The recent epidemics found in central Italy on yellow kiwifruit appear to have been caused by a different Psa population than those previously recorded in Japan, South Korea and Italy.  相似文献   

4.
Epidemics of Peronospora parasitica are strongly affected by temperature and air moisture, and the interaction of these factors. Because a significant percentage of radish plants are grown in greenhouses, it may be possible to influence epidemics by altering the greenhouse climate. The objective of this study was to test the hypothesis that epidemics of P. parasitica can be modelled by the effects of air temperature and moisture in the greenhouse. Such a model could then be used to analyse greenhouse climate control strategies with regard to managing downy mildew. Five radish crops were grown under greenhouse conditions with set-points for heating and ventilation intended to obtain favourable conditions for disease development during the first part of the growing cycle. Subsequent to this first phase, unfavourable conditions were set until harvest. Disease incidence was measured once a week until the radishes reached marketable size. In addition, experiments were carried out in growth chambers in which inoculated plants were subjected to air temperatures between 8 and 27°C, and disease incidence and sporulation intensity were measured. Data from these two experiments were then used to estimate model parameters. In this model, the interactions of air temperature (T) and water vapour saturation deficit (SD) were adequately described by a multiplicative relationship. The simulated epidemics by the fitted model were highly correlated with the observed epidemics (r = 0.91, R 2 = 0.83, n = 29). Parameter estimates indicated that T of ca. 20°C and SD < 0.03 hPa resulted in the highest rates of disease development and that the rate was zero when SD > 2.0 hPa. Both experimental data and simulations showed that epidemics of P. parasitica can be effectively controlled by managing the greenhouse climate.  相似文献   

5.
A laboratory feeding test was conducted on queenless micro‐colonies of three bumblebee workers (Bombus terrestris L) to study the effects of low doses of imidacloprid on pollen and syrup consumption, worker survival, brood size and larval development. Two doses were used: D1 = 10 µg AI kg−1 in syrup and 6 µg AI kg−1 in pollen; D2 was 2.5 times higher in syrup and 2.7 higher in pollen. During 85 days 27, 30 and 29 micro‐colonies were reared for control, D1 and D2 treatments respectively. Food consumption was not affected by either dose. During the 5‐day pre‐oviposition period the mean insecticide intake was 4.8 ng per day per worker in treatment D2. Both doses slightly but significantly affected worker survival rate by 10% during the first month, without any dose‐effect relationship. Brood production was significantly reduced in D1 treatment and larval ejection by workers was significantly lower in D1 and D2 than in control. No significant effect of D1 and D2 treatments on the duration of larval development was revealed. No residue could be detected in workers still alive after 85 days. It was concluded that the survival rate and reproductive capacity of B terrestris was not likely to be affected by prolonged ingestion of nectar produced by sunflower after seed‐dressing treatment with imidacloprid (Gaucho), since honey or pollen collected by honeybees foraging treated sunflower never revealed concentrations of imidacloprid higher than 10 µg kg−1. © 2000 Society of Chemical Industry  相似文献   

6.
Sunflower (Helianthus annuus L.) is an important oilseed crop in South Africa, and is grown in rotation with maize in some parts of North West, Limpopo, Free State, Mpumalanga and Gauteng provinces. Alternaria leaf blight is currently one of the major potential disease threats of sunflower and is capable of causing yield losses in all production regions. Alternaria helianthi was reported as the main cause of Alternaria leaf blight of sunflower in South Africa; however small-spored Alternaria species have been consistently isolated from leaf blight symptoms during recent surveys. The aim of this study was to use morphological and molecular techniques to identify the causal agent(s) of Alternaria blight isolated from South African sunflower production areas. Alternaria helianthi was not recovered from any of the sunflower lesions or seeds, with only Alternaria alternata retrieved from the symptomatic tissue. Molecular identification based on a combined phylogenetic dataset using the partial internal transcribed spacer regions, RNA polymerase second largest subunit, glyceraldehyde-3-phosphate dehydrogenase, translation elongation factor and Alternaria allergen gene regions was done to support the morphological identification based on the three-dimensional sporulation patterns of Alternaria. Furthermore, this study aimed at evaluating the pathogenicity of the recovered Alternaria isolates and their potential as causal agents of Alternaria leaf blight of sunflower. Pathogenicity tests showed that all the Alternaria alternata isolates tested were capable of causing Alternaria leaf blight of sunflower as seen in the field. This is the first report of A. alternata causing leaf blight of sunflower in South Africa.  相似文献   

7.
During the winter season, Sclerotinia sclerotiorum infects the stem bases of greenhouse‐grown sweet basil plants and, in severe epidemics, it may also infect the shoots. Sclerotia of S. sclerotiorum, and the ascospores that are released from the apothecia that form on them, serve as the inoculum for white mould epidemics. This research aimed to identify cropping parameters associated with lower incidence of white mould in a survey of the main basil‐growing region in Israel, and study cultural methods that might suppress the disease. The survey revealed that this mould, in the main growing area in Israel, has one cycle of infection. Factors associated with increased moisture in the greenhouse were found to be associated with increased levels of the disease. The use of a lower planting density reduced the incidence of white mould in semi‐commercial experimental plots, as well as the severity of the disease on shoots infected by S. sclerotiorum after harvest, in comparison to the commonly used higher planting density, with no negative effect on yield. Mulching the beds with polyethylene effectively reduced disease, and a combination of polyethylene mulch and increased plant spacing reduced disease severity on cut shoots in a synergistic manner. In conclusion, cultural control methods reduced disease incidence under field conditions and severity of the disease on cut shoots.  相似文献   

8.
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9.
Postbloom fruit drop (PFD) is an important citrus disease that causes up to 100% yield losses during years in which conditions are favourable for the occurrence of epidemics. The conidia of Colletotrichum acutatum and C. gloeosporioides, causal agents of PFD, are predominantly dispersed by rain splash. At the beginning of epidemics, the distribution of diseased plants is random and the disease progress rate is very high, which is unusual for pathogens spread by rain splash. As the pathogen produces abundant conidia on diseased petals, pollinating insects may contribute to disease dispersal. This study investigated honeybees (Apis mellifera) as dispersal agents of C. acutatum and C. gloeosporioides among citrus plants. Two experiments were carried out in a screenhouse in which citrus plants were protected (or not) in insect‐proof cages. The source of inoculum was placed on one side of the screenhouse, and a honeybee hive was placed on the opposite side. All uncaged plants showed symptoms of the disease, and none of the caged plants exhibited PFD symptoms. The monomolecular model showed a good fit to disease progress in both experiments. Conidium‐like structures of Colletotrichum spp. were identified attached to the bodies of the honeybees by scanning electron microscopy. These results have revealed that honeybees disperse Colletotrichum among citrus plants.  相似文献   

10.
Olive anthracnose, caused by strains or populations of Glomerella cingulata (anamorph Colletotrichum gloeosporioides) pathogenic for olive, was introduced into southern Italy before or during the 2nd World War presumably from Albania or Greece. In the following 20 years, severe outbreaks of fruit rot and dieback of twigs and branches were recorded in several areas of Puglia, Calabria, Sicilia and Sardegna. After the 1970s, the epidemics gradually regressed. At present, the disease is restricted to certain humid areas of southern Italy. Factors associated with this regression are discussed, including a supposed change in virulence of the fungus, possibly as a consequence of mixing of the introduced strains infecting olive trees with local, less pathogenic populations of G. cingulata. The first results of a comparison of olive isolates with isolates of the pathogen from citrus and Annona muricata in Calabria suggest that the population from olive is relatively homogeneous and can be distinguished from the population infecting other hosts by a number of morphological, pathogenic and biochemical characteristics.  相似文献   

11.
Tomato chlorosis virus (ToCV), a member of the genus Crinivirus (family Closteroviridae), has been present in Spain since at least 1997, causing annual epidemics of yellowing in protected tomato crops. In 1999, sweet pepper plants exhibiting stunting and symptoms of interveinal yellowing and mild upward curling in the leaves, were found to be infected with ToCV in a greenhouse heavily infested with the whitefly Bemisia tabaci in the province of Almería, southeastern Spain. This study investigated the prevalence of ToCV in tomato and pepper crops in the major growing areas of southeastern Spain (Murcia, Almería and Málaga provinces) over a 3‐year period. In addition, an experimental system was developed for ToCV inoculation using B. tabaci as a vector, which allowed analysis of susceptibility of different pepper cultivars to the virus. The disease syndrome and yield losses induced by ToCV in pepper were also studied under experimental conditions, confirming severe yield reduction in infected plants.  相似文献   

12.
Plasmopara viticola, the causal agent of grapevine downy mildew, requires fungicide treatments to avoid severe yield losses, so epidemiological models have been elaborated to better manage fungicide scheduling. Primary oosporic inoculum plays a key role in epidemic development, and some of these models have been elaborated following an empirical approach to define quantitative relationships between occurrences of primary infections and weather factors influencing them. Recently, a mechanistic dynamic model was elaborated which accounts for the biological effects of weather on the different stages of the primary infection chain, from the progressive breaking of dormancy in the overwintering oospore population to infection establishment. In this work, three widely used models (3–10 rule, EPI and DMCast) were compared with this model (named UCSC model) on the basis of their theoretical approaches and their accuracy was tested against real data collected over a 9‐year period in Sardinia (Italy). The two empirical models, 3–10 and EPI, seem to be too over‐simplified to simulate correctly a complex biological phenomenon such as the sexual stage of P. viticola they lack consideration of some key stages of the infection chain and simultaneously simulate various biological events, each of which are influenced by specific weather conditions. EPI, in particular, needs specific calibrations and ongoing processes of adaptation that make its use in disease warning difficult. DMCast overcomes these problems because of its mechanistic approach; nevertheless, the empirical method used to model oospore maturation requires validations and, as in the present case, modifications before practical use. The UCSC model, due to its fully mechanistic approach, does not present this problem and provides accurate dynamic simulations of the sexual stage of P. viticola, with a high degree of detail and requiring neither calibrations nor corrections.  相似文献   

13.
Interactions between Plasmopara helianthi, Glomus mosseae and two plant activators DL--amino-n-butyric acid (BABA) and CGA 245704 (acibenzolar-S-methyl (BTH)) in sunflower plants susceptible to downy mildew were studied in four experiments using different methods of treatment and pathogen inoculation. Both chemicals were applied as soil drenches and foliar sprays, whereas P. helianthi infection was obtained by root and cotyledon inoculations of the seedlings. Soil drenches at the rates of 50 and 100mgkg–1 soil of BABA and BTH given 1 and 3 days before P. helianthi inoculation, respectively to mycorrhizal plants, provided moderate protection against the pathogen (about 50–55%). Morphological changes and decrease in mycorrhizal colonization in roots of BTH-treated plants and in BTH-treated mycorrhizal plants were also observed. Delay in the emergence and reduction of the root systems were more evident at the highest concentration but decreased with time. These effects were absent with the BABA treatment.Foliar spray treatment of BABA and BTH, applied at 4000 and 200µgml–1, respectively (1 day post-inoculation) to mycorrhizal plants provided good protection (about 80%) against P. helianthi foliar infections. No effects on mycorrhizal colonization or on root systems were observed. In vitro tests on the effect of the compounds on the mycorrhizal fungus showed that the germination of G. mosseae sporocarps increased with BABA treatment whereas it was greatly inhibited by BTH treatment.  相似文献   

14.
Clubroot, caused by Plasmodiophora brassicae, is a worldwide disease affecting Brassica. Until now, the detection of genetic factors (QTLs) implicated in clubroot resistance has been based on estimates of disease index. However, as the amount of resting spores released in soil after club disintegration influences clubroot epidemics and resistance‐breaking dynamics, its genetic control may deserve specific attention. In a previous report, it was shown that nitrogen fertilization modulated quantitative partial resistance toward clubroot symptom development in rapeseed. The present work aimed to identify genetic factors involved in the control of resting spore production and to assess their regulation by nitrogen supply. A flow cytometer method was adapted for rapidly estimating resting spore content in a large series of samples. Linkage analysis was conducted to detect QTLs implicated in resting spore production in a Brassica napus doubled haploid progeny from the cross Darmor‐bzh × Yudal. DH lines inoculated with the P. brassicae isolate eH were grown under low‐ and high‐nitrogen supply. Under low‐nitrogen conditions, resting spore production was reduced compared to high‐nitrogen conditions, regardless of genotypes. Genetic architecture controlling resting spore production and clubroot symptom development was similar. Under high‐nitrogen conditions, resting spore production was controlled by one major QTL (C09a) and a few small‐effect QTLs. By contrast, two major QTLs (C02 and C09a) controlled resting spore production under low‐nitrogen conditions. This work highlighted a large see‐saw effect between the relative contribution of the C09a QTL (high effect under high‐nitrogen conditions) and the C02 QTL (high effect under low‐nitrogen conditions), with possible implications in resistance breeding.  相似文献   

15.
Zymoseptoria tritici ascospores and pycnidiospores are considered the main forms of primary and secondary inoculum, respectively, in septoria tritici blotch epidemics. The pathogenicity of the two types of spores of the same genotypic origin were compared through a two‐stage inoculation procedure in controlled conditions. Adult wheat leaves were inoculated with ascospores collected from field sources, yielding 119 lesions; pycnidiospores collected from 12 lesions resulting from these ascospore infections were then used for inoculation. Lesion development was assessed for 5 weeks; latent period, lesion size, and pycnidium density were estimated for different isolates. The latent period was calculated as the maximum likely time elapsed between inoculation and either the appearance of the majority of the sporulating lesions (leaf scale) or the appearance of the first pycnidia (lesion scale). The latent period was significantly longer (c. 60 degree‐days, i.e. 3–4 days) after infection with ascospores than with pycnidiospores. No difference was established for lesion size and density of pycnidia. A comparison with other ascomycete fungi suggested that the difference in latent period might be related to the volume of spores and their ability to cause infection. Fungal growth before the appearance of lesions may be slower after inoculation with an ascospore than with a pycnidiospore. The mean latent period during the very beginning of epidemics, when first lesions are mainly caused by ascospores, may be longer than during spring, when secondary infections are caused by pycnidiospores. Disease models would be improved if these differences were considered.  相似文献   

16.
X. Cheng  Y. Lu  D. Chen  C. Luo  M. Li  C. Huang 《Plant pathology》2019,68(4):689-699
Annual epidemics of black spot, a serious disease of marigold (Tagetes erecta), developed in Beijing and surrounding areas from 2011 to 2015. Alternaria tagetica was isolated from marigold showing symptoms from Beijing and Hebei province, and pathogen characteristics and meteorological factors influencing disease development were investigated. The optimum growth temperature of the fungus was 20–25 °C. Field experiments conducted from 2011 to 2014 to evaluate diseased residual branches indicated that marigold residues from the previous year are a likely source of primary inoculum. Regression analysis showed that temperature and precipitation were explanatory factors for disease development from 2013 to 2015. Structural equation modelling indicated that the contributions of temperature degree-day and rainfall to disease intensity were 27% and 30%, respectively. Augmented Dickey–Fuller test results indicated stability in the residual sequence and co-integration between the variables daily average temperature, daily average precipitation, daily average humidity and daily disease intensity. Error-correction modelling showed that temperature, lagged order of temperature, precipitation, lagged order of precipitation, lagged order of disease intensity and the error term were significant. Research indicated that A. tagetica was the primary pathogen of marigold black spot, and that crop rotation could play a useful role in management of the disease, whilst increased rainfall and reduced temperature provide superior conditions for disease spread and infection. There is potential for the results of this study to be used by municipal agriculture authorities in the prediction of marigold black spot in Beijing.  相似文献   

17.
Orobanche cumana is a weed that grows as a root parasite on sunflower. In general, the O. cumana–sunflower parasitic system is regarded to follow the gene‐for‐gene model, although this has never been demonstrated at the genetic level in O. cumana. The Or5 dominant gene in sunflower confers resistance to O. cumana race E, but not to race F. The objective of this research was to study the inheritance of avirulence/virulence in crosses between plants of O. cumana lines classified as races E and F. Four race E and three race F lines were developed, from which four race E × race F cross‐combinations were made, in three cases including reciprocals. In all cases, F1 seeds did not have the ability to parasitise sunflower line P‐1380 carrying the Or5 gene, indicating dominance of race E avirulence allele(s). Five F2 populations comprising a total of 387 F2:3 families were evaluated on sunflower line P‐1380. In all cases, one‐fourth of the F2:3 families did not possess the ability to parasitise P‐1380 plants, suggesting that race E avirulence and race F virulence on P‐1380 are allelic and controlled by a single locus. This study demonstrated the gene‐for‐gene interaction in the O. cumana–sunflower parasite system and provided useful information to identify genes involved in O. cumana virulence. The approach followed in this research can contribute to define precisely races of the parasite on the basis of the presence of avirulence genes.  相似文献   

18.
T. Rder  P. Racca  E. Jrg  B. Hau 《EPPO Bulletin》2007,37(2):378-382
During a three‐year project from 2003 to 2006, two models have been developed to predict leaf rust (Puccinia recondita and P. triticina) occurrence and to simulate disease incidence progress curves on the upper leaf layers of winter rye (PUCREC) and winter wheat (PUCTRI). As input parameters the models use air temperature, relative humidity and precipitation. PUCREC and PUCTRI firstly calculate daily infection favourability and a cumulative infection pressure index and, in a second step, disease incidence is estimated. An ontogenetic model (SIMONTO) is used to link disease predictions to crop development. PUCREC and PUCTRI have been validated with data from 2001 to 2005. Both models give satisfactory results in simulating leaf rust epidemics and forecasting dates when action thresholds for leaf rust control are exceeded.  相似文献   

19.
A sequence of 47 potato late-blight ( Phytophthora infestans ) epidemics in the Netherlands, from 1950 to 1996, was analysed using agronomic and meteorological variables. The intensity of annual epidemics was characterized by an index of disease intensity (DI, 0 = absence of late blight; 4 = severe epidemic). Three periods were identified, with average DIs of 2·9, 0 and 2, respectively. Period I (1950–68) had relatively regular epidemics; period II (1969–78) was virtually blight free; and period III (1979–96) showed large variations in disease intensity. Disease-enhancing factors were number of days with precipitation, and number of hours with temperatures between 10 and 27°C and relative humidity >90% during the growing season. Limiting factors were number of hours with temperatures >27°C, and amount of global radiation. Linear discriminant analysis of DI using the blight status of the previous year and meteorological variables correctly classified up to 40 years out of 47 (87·0%), with five out of the six incorrectly classified years falling in period III. Blight status of the previous year and number of days with precipitation were important discriminating variables.  相似文献   

20.
The effects of four planting patterns of bean (Phaseolus vulgaris) (bean only, maize–bean (MB), sorghum–bean (SB), and maize–bean–sorghum (MBS)) and four cropping systems (sole cropping, row, mixed, and broadcast intercropping) on the temporal epidemics of bean common bacterial blight (CBB) caused by Xanthomonas campestris pv. phaseoli were studied. The experiments were conducted during two consecutive spring and summer seasons in 1999 and 2000 in replicated field experiments. The Gompertz model described disease progress curves better than the logistic model. Intercropping delayed epidemic onset, lowered disease incidence and severity, and reduced the disease progress rate. The type of cropping system and planting pattern affected CBB incidence and severity at initial, final and overall assessments and also affected the rate of disease development. Statistical significance of treatment interactions based on disease assessments was found for incidence in all four experiments and for severity in three experiments. A slower disease progress rate and lower incidence and severity occurred on beans planted with maize or sorghum in row, mixed and broadcast intercropping than on bean planted alone. Incidence was reduced 36% and severity 20% in intercropping compared to sole cropping. The built-in disease delay and the slowing of the disease progress rate could provide protection for beans from severe CBB epidemics in intercropped systems. Variation between years appeared to be related to relative humidity (RH).  相似文献   

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