Presence of Phytophthora fragariae var. fragariae in Norway

The strawberry red core disease caused by Phytophthora fragariae var. fragariae has until recently not been reported from Norway. During 1995 and 1996, samples from 323 Norwegian strawberry fields were tested in a root-tip bait test for possible detection of red core. Symptoms of the disease developed in test plants cultivated in growth medium containing root tips from 21 fields at eight locations in four different counties. Disease symptoms included wilting of plants, root rot, red steles in the roots, and oogonia and oospores identical in size and appearance to those of P.f. fragariae developing along the root steles. In V8 juice agar, the mycelium was slow-growing, thick, fluffy and aerial. Sporangia were large, mainly inversely pyriform, and without papillae. Optimum temperature for mycelial growth was 21°C, and the fungus ceased to grow at 25°C. In infested fields, the most severe attacks were found in low, often poorly drained areas. The means by which red core may have been introduced and spread in the country are discussed, together with preventive action to avoid further dissemination.     

Histological observation of cucumber infected with <Emphasis Type="Italic">Corynespora cassiicola</Emphasis>

Erwinia amylovora is the causative agent of fire blight, which is a destructive bacterial disease of rosaceous plants. In Hungary Erwinia amylovora (Burrill) Winslow et al. was first detected in 1996. Since the appearance of fire blight, E. amylovora samples have been collected from different host plats from various geographic locations. A motif of eight nucleotides (ATTACAGA) is repeated 3–15 times in the PstI fragment of the pEa29 plasmid in Erwinia amylovora strains, and represents a valuable tool for strain classification. The number of short-sequence DNA repeats in plasmid pEa29 of 30 Hungarian isolates were determined by PCR assays and they ranged from five to ten. The SSR test is suitable for distinguishing the individual strains between the E. amylovora isolates. The examined isolates showed high pathogenicity on immature pear fruits. Several biochemical techniques, such as miniaturized API 20E, were applied on the samples. Differences were also revealed in microbiological assays like levan formation and colony morphology on semi-selective media. Examining the Hungarian Erwinia amylovora population by molecular analysis we can draw the conclusion that the population consists of different strains, which shows great diversity. E. amylovora is a widespread pathogen in Hungary, which is supported by the 30 strains isolated from various host plants from many parts of the country. The phenotypic diversity-evaluation of the E. amylovora strains showed, that they differ metabolically, like other plant pathogenic bacteria as reported by several authors. This is the first report on the diversity of E. amylovora strains isolated from Hungary.     

Incidence of grapevine trunk diseases is influenced by soil,topology and vineyard age,but not by <Emphasis Type="Italic">Diplodia seriata</Emphasis> infection rate in the Tokaj Wine Region,Hungary

Grapevine Trunk Diseases (GTD) are of great importance worldwide, including Hungary, a Center European country with long wine producing history. Several GTD pathogens have been described till now in Europe, but only a few from Hungary. The presence of a GTD pathogen in the vine does not necessarily result in the immediate appearance of disease symptoms, and information on the importance of environmental factors related to disease incidence are still limited. The aim of this research was to assess the occurrence of GTD in the Tokaj Wine Region, and to determine the biotic and abiotic factors influencing disease incidence. Five vineyards within 15 km radius – each with different topology, soil types, varieties and age – were studied for three consecutive years (2013 – 2015). The incidence of GTD-infection was determined every year for each vineyard. Diplodia seriata was isolated with incidence ranging from 50 to 100%, while Diaporthe spp. were the only other – minor – GTD pathogen found. Topology and soil type appeared to be major abiotic factors affecting incidence of GTD symptom. Disease incidence was also positively correlating with the age of the vineyards, and it was in fact found to be the definitive biotic factor regarding incidence. In contrast, D. seriata infection rate appeared unrelated to disease incidence or to any of the biotic or abiotic factors investigated.     

Environmental conditions influencing Sclerotinia sclerotiorum infection and disease development in lettuce

The environmental factors that influence infection of lettuce by ascospores of Sclerotinia sclerotiorum , and subsequent disease development, were investigated in controlled environment and field conditions. When lettuce plants were inoculated with a suspension of ascospores in water or with dry ascospores and exposed to a range of wetness durations or relative humidities at different temperatures, all plants developed disease but there was no relationship between leaf wetness duration or humidity and percentage of diseased plants. Ascospores started to germinate on lettuce leaves after 2–4 h of continuous leaf wetness at optimum temperatures of 15–25°C. The rate of development of sclerotinia disease and the final percentage of plants affected after 50 days were greatest at 16–27°C, with disease symptoms first observed 7–9 days after inoculation, and maximum final disease levels of 96%. At lower temperatures, 8–11°C, disease was first observed 20–26 days after inoculation, with maximum final disease levels of 10%. Disease symptoms were always observed first at the stem base. In field-grown lettuce in Norfolk, 2000 and 2001, inoculated with ascospore suspensions, disease occurred only in lettuce planted in May and June, with a range of 20–49% of plants with disease by 8 weeks after inoculation. In naturally infected field-grown lettuce in Cheshire, 2000, disease occurred mainly in lettuce planted throughout May, with a maximum of 31% lettuce diseased within one planting, but subsequent plantings had little (≤ 4%) or no disease. Lack of disease in the later plantings in both Norfolk and Cheshire could not be attributed to differences in weather factors.     

Crown rot caused by Phytophthora cactorum in Norwegian strawberry production

Crown rot of strawberry, caused by Phytophthora cactorum , was detected for the first time in Norway in 1992. This paper reports on surveys for P. cactorum in Norwegian certified strawberry plant production and on the distribution of the pathogen in regular strawberry production. In 1996 and 1997, samples of plant material from all certified strawberry plant growers in the country were investigated by isolation on artificial growth medium and using an enzyme-linked immunosorbent assay (ELISA). P. cactorum was not detected in any of the samples. A total of 171 isolations from plants with symptoms resembling crown rot were made from plants in a survey of the distribution of Phytophthora fragariae var. fragariae and from other samples. P. cactorum was detected at 35 different strawberry-producing farms in 11 of the 19 counties of Norway. The fungus was most frequently isolated from cv. Korona (at 18 locations), followed by cv. Inga (at 10 locations).     

Identification and incidence of virus diseases of Capsicum annuum in the Lusaka Province of Zambia

Commercial capsicum fields in Lusaka Province were surveyed for the presence of viruses during 1996-01/06. The survey demonstrated the occurrence of five viruses in 13 fields. Virus identification was based on field disease syndrome, host range studies, DAS-ELISA and electron microscopy. The identified viruses were alfalfa mosaic alfamovirus (AMV), potato Y potyvirus (PVY), tobacco mosaic tobamovirus (TMV), cucumber mosaic cucumovirus (CMV) and pepper mild mottle tobamovirus (PMMV). The most prevalent and widespread virus, recovered from 70% of the surveyed fields, was AMV, and this was followed by PVY and TMV, which were detected in 50% and 40% of the fields respectively. CMV and PMMV were less common and occurred in 30% of fields. The study also showed that PVY could infect capsicum plants alone or in combination with CMV or TMV. The average plant infections caused by AMV was 80–100% and by TMV and PVY 50% and 60% respectively. The disease incidence in the case of CMV was 15–60% and for PMMV 30–40%. This is a first report on the identification of viruses that infect capsicum in Zambia.     

Biology and Control of the Fall Webworm (Hyphantria cunea Drury) in the Middle- and East European Countries

The fall webworm was first discovered in Hungary in 1940 and severe outbreaks occurred in 1945. This insect which goes through 7 larval instars usually has two annual generations under the conditions prevailing in the infested areas of this country. The optimal conditions are met most often in Central and South Hungary (1,950 - 2,050 sunshine-hours yearly, 17°C average temperature during the vegetation period, a humidity of 65–70% and 300–350 mm. of precipitation). Three categories of host-plants are distinguished: first-grade host-plants for which the pest has a clear preference and on which it develops best; second-grade host-plants on which the larvae feed mostly during the outbreak years and third-grade host-plants on which the larvae only feed when their original host-plants are almost completely defoliated. Special attention is paid to the natural enemies of Hyphantria cunea Drury comprising predators and parasites. From larvae and pupae 8 Tachinids, 5 Ichneumonids, 13 Chalcidids and 3 Braconids were reared. The importance of natural enemies in controlling the pest seems to be greater in North America than in Europe.
Despite drastic control measures, there has been a marked increase in the dissemination of the fall webworm in Hungary in 1969 and 1970 but is was possible to reduce the crop losses. A network of survey and forecasting posts facilitates the carrying out of mechanical and chemical methods. Strict quarantine regulations are in force to keep the pest under control.     

Effects of Ascochyta blight (Mycosphaerella pinodes) on the photosynthesizing leaf area and the photosynthetic efficiency of the green leaf area of dried-pea (Pisum sativum)

The effects of Ascochyta blight (caused by Mycosphaerella pinodes ) on the net photosynthetic rate of glasshouse-grown dried pea were studied on foliar discs and whole plants in pots showing different disease intensities, assessed visually using a disease scale (scores 0 to 5) or by an estimation of the fraction of leaf area with necrosis using an image analyser. The photosynthetic rate of foliar discs was measured using a leaf disc electrode; for plants it was assessed by CO₂ exchange rate measurements in a closed chamber. A reduction in the net photosynthetic rate of diseased plants was correlated with an increase in disease score. A 53–56% reduction was found in foliar discs with a mean disease score of 3. On whole plants, mean scores of 3.5 and 4.0 were associated with reductions of 36% and 98% respectively. The disease also induced a decrease in the photosynthetic efficiency of the non-necrotic leaf area. The photosynthetic rate was zero when 30–40% of foliar area was necrotic on foliar discs and on whole plants. A function was derived from the foliar disc data that described the dependence of photosynthetic rate on the fraction of leaf area without necrosis. The model is discussed with reference to data obtained from entire plants and other pathosystems.     

Mapping of atrazine resistance for Amaranthus retroflexus L. in Hungary

The study extending over all sixteen counties of Hungary has shown atrazine resistant biotypes of Amaranthus retroflexus L. to grow not only in and around maize monocultures but also in rotationally grown maize and even along highways and ruderal areas. In the present study made in 1983 resistant A. retroflexus was found in five counties (Bács-Kiskun, Csongrád, Hajdu-Bihar, Nógrád and Szabolcs-Szatmár) where Hartmann recorded it as absent in 1976. In addition, resistant populations were also found in the counties of Szolnok and Veszprém. The area in which populations of A. retroflexus have developed resistance to atrazine therefore appears to be extending.     

Fusarium ear blight of wheat: the use of quantitative PCR and visual disease assessment in studies of disease control

Quantitative PCR analysis and visual disease assessment (VDA) were used to study Fusarium culmorum and F. poae ear blight of wheat and its fungicidal control in three glasshouse trials (1994–5 and 1996–7). VDA indicated high levels of both diseases in the trials, while PCR analysis showed that the amounts of F. poae detected in infected plants were low relative to the amounts detected for F. culmorum . PCR and VDA analysis both indicated that the demethylase-inhibiting (DMI) fungicides prochloraz and tebuconazole significantly decreased F. culmorum and F. poae ear blight. The PCR results, however, revealed levels of disease control by fungicide treatments that were consistently higher than those suggested by VDA. Overall, both fungicides appeared equally effective in controlling the two pathogens. PCR and VDA analysis indicated that the anilino-pyrimidine fungicide pyrimethanil had no significant effect on F. culmorum ear blight. Correlations between VDA at cereal growth stage 80 and PCR analysis were similar for F. culmorum and F. poae . Yield analysis, as measured by 1000 grain weight, indicated that DNA content more accurately predicted yield loss than did VDA scores. Inoculation with F. culmorum significantly reduced yield and significant relationships were observed between F. culmorum disease (as assessed visually or by PCR) and yield, with yield decreasing as disease increased. In contrast, inoculation with F. poae had no significant effect on yield and no significant relationships were observed between F. poae disease and yield. These results have important implications for field studies of Fusarium ear blight of wheat because they highlight the importance of identification of the causal organisms to the species level.     

Effects of bean rust (Uromyces appendiculatus) epidemics on host dynamics of common bean (Phaseolus vulgaris)

Epidemics of bean rust ( Uromyces appendiculatus ) and their effects on host dynamics of common bean ( Phaseolus vulgaris ) were studied in three controlled greenhouse experiments, with and without fungicide sprays, on two susceptible bean cultivars, Dufrix and Duplika. Bean plants were artificially inoculated with a suspension of 10⁵ U. appendiculatus urediniospores mL⁻¹ water and temporal disease progress, as well as host growth dynamics (leaf size and defoliation), were monitored on a leaflet basis in comparison with non-inoculated plants, which were sprayed with deionized water. Progress curves of bean rust, expressed as the proportion of leaf area occupied by pustules (uredinia), or as the proportion occupied by total lesion area (= halo areas + pustule area), were well described by logistic functions with maximum disease levels clearly lower than 1. Bean rust epidemics substantially affected host growth by reducing the total leaf area formed by 17·4–35·6% and 35·3–46·2% compared with healthy plants for cvs Dufrix and Duplika, respectively. Fungicide sprays mitigated the negative effect of bean rust, leading to a gain in leaf area of 17–21% compared with unsprayed plants in both cultivars in two experiments, while in another experiment, disease control had no effect in Dufrix, but a clear effect in Duplika. In addition to the growth depression, bean rust also led to pronounced losses of leaf area as a result of reduced leaf size (leaf shrivelling) and accelerated defoliation.     

Development of a Downy Mildew Advisory Model Based on Downcast

A downy mildew advisory model for use in practical onion growing was constructed according to DOWNCAST, an existing downy mildew forecasting model. The model was empirically improved after comparison between observed and calculated disease development. Onion plants grown in pots were placed as trap plants in artificially inoculated onion fields (one in 1995, three in 1996 and one in 1997) for 1–7 days, then removed and incubated outdoors in a sheltered place at 1km distance from the onion field. Symptom development was observed. Hourly measurements of leaf wetness, temperature and relative humidity were taken in the crop and hourly data on rainfall were obtained from a nearby automatic weather station. Sporulation of the fungus was visually observed in the onion crop in the morning on several days in all three years. Sporulation-infection periods and sporulation as predicted by the model were compared with symptom development on the trap plants and observations on sporulation in the field. The initial model corresponded to the trap plant observations in only 18 out of 42 and to visual sporulation in 25 out of 40 occasions. Criteria in both the sporulation and infection submodels of the advisory model were subsequently calibrated to obtain a best fit between the model and observations. In 30 out of 42 occasions the improved model corresponded with trap plant observations while 30 out of 40 sporulation observations were now calculated correctly. The improved model needs to be evaluated with additional and independent data.     

Fireblight in Békés County (Hungary) in 1996/20021

Fireblight (Erwinia amylovora) appeared in Hungary in 1996. Most damage occurred on apple, pear, quince and medlar, and also on the ornamentals Pyracantha, Sorbus, Cotoneaster and Crataegus. In 1996–2006, an official programme for elimination of infected parts of plants started in Békés county. This mainly concerned trees in towns and villages, since there are few pome‐fruit orchards in the county. Work teams under official direction pruned back or cut down trees. In total, some 13 000 trees were pruned back and nearly 11 000 were cut down. In addition, 21 villages were subjected to special phytosanitary measures. Infection decreased considerably between 1996 and 2002, but over 90% of the inhabited areas in the county remained subject to special measures, because of the very dispersed occurrence of fireblight.     

Evaluation of oilseed rape seed yield losses caused by <Emphasis Type="Italic">Leptosphaeria biglobosa</Emphasis> in central China

Phoma stem canker of oilseed rape (Brassica napus), caused by Leptosphaeria maculans/L. biglobosa is a globally important disease. Severe phoma stem canker symptoms have been observed on winter oilseed rape in China but the seed yield loss caused by this disease remains unknown. In May 2012 and May 2013, 17 and 13 crops were surveyed, respectively, in seven counties of Hubei Province, central China. Stems with phoma stem canker disease symptoms were sampled for pathogen isolation and identification. Only L. biglobosa was identified by culture morphology and species-specific PCR; no L. maculans was found. To evaluate the yield losses, yield components (number of branches per plant, number of pods per plant, 1000-seed weight, number of seeds per pod) were assessed on healthy and diseased plants sampled from crops in four counties and on plants from inoculated pot experiments (plants of three cultivars were inoculated at the green bud stage by injecting L. biglobosa conidia into the stem between the first and second leaf scars). Results of the field surveys showed that diseased plants had 14–61% less branches and 32–83% less pods than healthy plants, respectively. The estimated seed yield loss varied from 10% to 21% and from 13% to 37% in 2012 and 2013, respectively. In the pot experiments, there were no differences in numbers of branches or pods but there were differences in number of seeds per pod between inoculated and control plants. For the three cultivars tested, the inoculated plants had yield losses of 29–56% compared with the control. This study indicates that L. biglobosa could cause substantial seed yield loss in China.     

Sclerotinia rot losses in processing tomatoes grown under centre pivot irrigation in central Brazil

Sclerotinia rot caused by Sclerotinia sclerotiorum is one of the most important diseases of processing tomatoes in Central Brazil. Yield losses in tomato cultivars (cv.) IPA-5 were assessed in mature plants from 1995 to 1997, and related to different disease intensities, in a naturally infested area irrigated by centre pivot. Over the 3 years, there were no differences (Tukey at 5%) in fruit numbers between plants without symptoms (NS) and with intermediate symptoms (IS), which yielded higher numbers than plants with severe symptoms (SS). The greatest reduction in fruit number was 56.8% in 1997. Significant differences were observed in fruit weight and size among NS, IS and SS plants in 1995 and 1997. In 1996, NS and IS plants were similar, but different from SS, which yielded significantly less. Weight and size reductions in SS plants reached 84.3% and 62.0%, respectively, in 1997. In 1996 and 1997, yield losses related to time of symptom appearance and physiological age were also assessed. Significant correlations were found ( P  < 0.01), with nearly total losses observed when plants were infected from early to mid bloom, as opposed to plants infected near harvest, which had lower disease incidence and produced economically acceptable yields. Quadratic and exponential models best fitted the relationship between yield and time of symptom appearance, and yield vs physiological age could be explained by logistic and Gompertz functions.     

Variation in virus populations and growth characteristics of two sugarcane cultivars naturally infected by Sugarcane yellow leaf virus in different geographical locations

Two sugarcane cultivars (R570 and SP71-6163) naturally infected by Sugarcane yellow leaf virus (SCYLV) were each imported from several geographical locations into a sugarcane yellow leaf-free environment (Montpellier, France). Plants were grown as plant cane for 5–6 months and the experiment was repeated for three consecutive years (2003–2005) in a greenhouse. Several sugarcane-growth and disease characteristics were monitored to identify variation in pathogenicity of SCYLV. Depending on their geographical origin, sugarcane cvs R570 and SP71-6163 were infected by SCYLV genotypes BRA-PER or REU, or a mixture of the two. Severity of symptoms did not vary between plants of cv. R570, but variation in disease severity between plants of cv. SP71-6163 from different geographical locations suggested the occurrence of pathogenic variants of SCYLV. For each sugarcane cultivar, differences in stalk length, number of stalk internodes, virus titre in the top visible dewlap leaf, and percentage of infection of leaf and stalk phloem vessels were also found between plants from different geographical origins. However, these differences were not always reproducible from one year to another, suggesting occurrence of different plant responses to SCYLV isolates under varying environmental conditions.     

Biological control of Botrytis stem infection of greenhouse tomatoes

Botrytis cinerea infects stem wounds of greenhouse tomatoes and can cause serious economic losses. A bioassay using stem sections was developed to study wound infection and to screen potential fungal antagonists for activity against Botrytis Cladosporium cladosporioides reduced infection from 80–100% to 0–10%. A much smaller proportion of Trichoderma harzianum gave this reduction. Similar results were obtained on whole plants. Penicillium isolates varied widely in activity. The concentration of Cladosporium and Trichoderma which gave the highest level of protection was c . 10⁸ cfu/mL. When only half the wound was treated, simulating poor spray coverage, Cladosporium isolates still prevented infection. By contrast, Trichoderma isolates and four fungicides failed to give the same level of protection. The ability of certain fungal isolates to colonize the wound surface was thought to be partly responsible for this activity. The successful application of antagonists to whole plants using both aqueous suspensions and gel secateurs is described.     

Sorghum ergot can develop without local Claviceps africana inoculum from nearby infected plants

Batches of glasshouse-grown flowering sorghum plants were placed in circular plots for 24 h at two field sites in southeast Queensland, Australia on 38 occasions in 2003 and 2004, to trap aerial inoculum of Claviceps africana. Plants were located 20–200 m from the centre of the plots. Batches of sorghum plants with secondary conidia of C. africana on inoculated spikelets were placed at the centre of each plot on some dates as a local point source of inoculum. Plants exposed to field inoculum were returned to a glasshouse, incubated at near-100% relative humidity for 48 h and then at ambient relative humidity for another week before counting infected spikelets to estimate pathogen dispersal. Three times as many spikelets became infected when inoculum was present within 200 m of trap plants, but infected spikelets did not decline with increasing distance from local source within the 200 m. Spikelets also became infected on all 10 dates when plants were exposed without a local source of infected plants, indicating that infection can occur from conidia surviving in the atmosphere. In 2005, when trap plants were placed at 14 locations along a 280 km route, infected spikelets diminished with increasing distance from sorghum paddocks and infection was sporadic for distances over 1 km. Multiple regression analysis showed significant influence of moisture related weather variables on inoculum dispersal. Results suggest that sanitation measures can help reduce ergot severity at the local level, but sustainable management will require better understanding of long-distance dispersal of C. africana inoculum.     

The recent history of Puccinia striiformis f.sp. tritici in Denmark as revealed by disease incidence and AFLP markers

Disease observations and amplified fragment length polymorphism (AFLP) markers were used to study recent developments in the Puccinia striiformis f.sp. tritici population in Denmark. The fungus appeared spontaneously at 10 locations in Denmark in 1997 after it was not observed under natural conditions in 1996. The pattern of disease development and prevailing winds suggested that the fungus reappeared by airborne spores from the south or west. In 1998, disease incidence was more evenly distributed throughout the country. Forty-eight single lesion isolates were collected from most crops where the disease was observed in these years; all except one from 1997 belonged to two pathotypes that were not previously detected in the country, and both possessed the newly discovered Yr17 virulence. The isolates were characterized with AFLP markers together with 28 isolates representing eight of 13 pathotypes observed prior to 1996. Initial screening of 240 Pst I/ Mse I AFLP primer combinations on four isolates showed that a primer combination, on average, revealed 0·4 polymorphisms between any isolate pair. A selection of 21 primer combinations resulted in 28 AFLP markers, which revealed 16 AFLP phenotypes among all 76 isolates. The two Yr17- virulent pathotypes consisted of three AFLP phenotypes, which were observed in both 1997 and 1998; the two most frequent AFLP phenotypes occurred at most sampling locations and often within the same crop. AFLP diversity was larger among samples collected prior to 1996, and also in this period most AFLP phenotypes were observed at different sampling locations. These results are consistent with the features of an entirely asexually reproducing pathogen dispersed by aerial spores across large areas.     

OAK DECLINE AND THE STATUS OF OPHIOSTOMA SPP. ON OAK IN EUROPE

This paper brings together the individual reports of 11 countries on oak decline presented at an EPPO ad hoc Panel meeting at Lillafüred (HU) on 1989–06–20/22. Most countries (Austria, Czechoslovakia, FRG, Hungary, Italy, Netherlands, Poland, Yugoslavia) reported significant oak decline in the 1980s. However, none was reported in Denmark. In France, periods of decline mainly occurred earlier in the century, and only local decline was seen in the 1980s. In the United Kingdom, decline has never been considered a major problem and only local dieback occurs. In nearly all the countries with significant oak decline, water stress, due to severe drought in one or several years in the 1980s, is cited as the major cause. This predisposes trees to attack by various pests, of which the most frequently cited are Armillaria spp. (attacking the roots) and leaf-feeding insects. Because Ophiostoma spp. have been cited in the literature as primary pathogens in eastern Europe, a search has been made in several countries for Ophiostoma spp. in declining oaks. The general conclusion is that they are found, but too rarely and irregularly to be of any primary significance. Several authors report Ophiostoma piceae , with which O. roboris is considered synonymous. Only in Czechoslovakia is it supposed that Ophiostoma spp. are pathogens, and then only with drought as the predisposing factor. Several other fungi are cited as pathogens of drought-stressed oaks: in Italy, Quercus cerris and Q. pubescens are attacked especially by Hypoxylon mediterraneum; in the Netherlands, Pezicula cinnamomea is frequently found on Q. robur. In no country was it suggested that oak decline might involve an introduced or spreading pest, of possible quarantine significance.