Pathogenicity to Wheat of Isolates of Pseudocercosporella herpotrichoides (Fron) Deighton from Five Graminaceous Hosts

Eleven isolates of Pseudocercosporella herpotrichoides were obtained from field material of the Gramineae Agropyron repens, Alopecurus myosuroides, Apera spica-venti, Hordeum vulgare and Triticum aestivum. Four of these isolates belonged to the variety acuformis and 7 isolates to the variety herpotrichoides of the fungus. In a greenhouse experiment, winter wheat was inoculated with these isolates. All isolates were pathogenic on wheat. They differed in virulence, but these differences could not be related to the nature of their original hosts nor to their classification as variety acuformis or herpotrichoides.     

Sensibilité des plantules de Triticinées àľagent Pathogène du Piétin-Verse [Pseudocercosporella herpotrichoïdes (Fron) Deighton]

Sensitiveness of seedlings of Triticinae against the pathogenic agens of Pseudocercosporella herpotrichoides (Fron) Deighton The study of the sensitiveness of 16 varieties or lines of Triticinae against two races of Pseudocercosporella herpotrichoides shows that, whatever the strain used, the importance of the attacks is much less serious on seedlings of Ae. ventricosa no. 11, Ae. squarrosa no. 15, Ae. squarrosa no. 33 and Roazon, Roazon was the least sensitive among the Triticum. It is obvious that Ae. ventricosa is the most resistant one in all varieties or lines used.     

Der Einfluβ von Sauerstoff und UV-Licht auf die Konidienproduktion von Pseudocercospordh herpotrichoides (Fron) Deighton, Merkmale zur Morphologie des Erregers und dessen Nachweis an Dikotyledonen

The influence of oxygen and U.V.-light for the conidia production of Pseudocercosporella herpotrichoides (Fron) Deighton, morphological characters of the pathogen and its evidence on dicotyledons The particular importance of oxygen was detected for sporulation of Pseudocercosporella herpotrichoides. Four methods have been elaborated for different sporulation requirements of P. herpotrichoides. Only for a few populations three methods were necessary for rapid conidia production. The best method for maximum conidia production consisted of the following conditions: a constant temperature of 10 °C, permanent moistening with liquid water for inoculated materials, oxygen and U. V.-light. Infected stalks and leaves from cereals were sporulating after 3 days and inoculated materials after 3 to 6 days. Maximum conidia production was reached after 7 to 21 days. Good sporulation was obtained also under cool temperatures, permanent moisture and air and light conditions in the open. But the conidia production was stronger under controlled conditions. Different isolates of P. herpotrichoides were compared with respect to morphological characteristics of hyphae, mycelia and conidia. Thus far observed only on cereals and grasses. P. herpotrichoides was found also on dicotyledons by the sporulation method described. This evidence has been obtained on an isolate of 00-winter rape (Brassica napus, ssp. Oleifera). Moreover P. herpotrichoides has been found on chlorotic and necrotic leaves of rape, flesh-coloured trefoil (Trifolium incarnatum), madia-oil plant (Linum usitatissimum L.) and lady's-thistle (Silyhum marianum [L.] Gaertn.) in high frequency. P. capsellae was found on necrotic leaves of chickweed (Stellaria media).     

Untersuchungen zur Bildung extrazellulärer Hemicellulasen durch Pseudocercosporella herpotrichoides in vitro

Investigations on the production of extracellular hemicellulases by Pseudocercosporella herpotrichoides in vitro For all 15 isolates of Pseudocercosporella herpotrichoides investigated, xylanase as well as arabanase activity could be demonstrated. After cultivation of 3 weeks, the activity of the enzymes reached a peak. The activity of xylanase was considerably increased by addition of xylan in comparison to Maltzin as the sole source of carbohydrate. Also the arabanase activity could be increased significantly by addition of araban or xylan as compared to the Maltzin variant. The optimum temperature with regard to activity and stability of xylanase ranged at 50°C. The pH-optimum for xylanase activity was found to be at pH 5.0, and the enzyme was stable in ° range between pH4.0 and 8.0 (9.0). In case of arabanase, the temperature optimum varied between 40 and 50°C; up to this temperature, the enzyme was also stable. At pH 5.0, the arabanase activity reached its optimum; stability was observed in - pH range between 4.0 and 9.0. In extracts prepared from autoclaved wheat coleoptiles which were inoculated with Pseudocercosporella herpotrichoides, the presence of the enzymes xylanase, arabanase, cellulase and polymethylgalacturonase could be demonstrated. The enzyme activities of the inoculated samples were considerably higher than those of non-inoculated controls. The differences, in most cases, were statistically significant. Der Deutschen Forchungsgemeinschaft danken wir für finanzielle Unterstützung.     

Control of Rhizoctonia solani and Cotton Seedling Disease by Laetisaria arvalis and a Mycophagous Insect Proisotoma minuta (Collembola)

Population changes in Pseudocercosporella herpotrichoides with and without fungicide selection A conidium mixture of W (wheat-type) and R (rye-type) strains of Pseudocercosporella herpotrichoides (W:R = 1:1) was incubated on PD-agar without fungicide or amended with the imidazole prochloraz or the triazole cyproconazole. The W:R ratio was assessed over four generations using the different benomyl sensitivity of the strains as marker. In untreated mixtures, the R strain completely dominated the population already after two generations. Similarly, in cyproconazole-treated mixtures, the R strain increased to 100% after the second generation, whereas in prochloraz-treated mixtures the R strain either followed the same pattern as in untreated mixtures or fluctuated around the initial proportion of 50% over four generations. The W and R strains displayed different fitness properties. The average hyphal growth rate was 8.5 mm/10 d and 4.5 mm/10 d for the W and the R strains, respectively; the sporulation capacity was 80 and 400 conidia/colony, respectively, for the two strains. The different fitness resulted in a strong dominance of the R strains both in vitro and in field populations towards the end of the vegetation period. This shift towards R-dominance occurred about equally fast with or without fungicide selection.     

Strategies for control of eyespot (Pseudocercosporella herpotrichoides) in UK winter wheat and winter barley

This review considers strategies for control of eyespot (Pseudocercosporella herpotrichoides) in winter wheat and winter barley in the UK. Varietal resistance to eyespot may take the form of direct resistance to the growth of the pathogen in the stem base or of indirect tolerance to eyespot through resistance to lodging. The French variety Cappelle-Desprez has been a source of resistance for most UK wheat varieties and a new source of resistance in wild goat grass has been discovered recently. Use of fungicides for control of eyespot increased rapidly after the introduction of the highly effective MBC fungicides in the 1970s, but has decreased recently because UK populations of P. herpotrichoides are now predominantly resistant to MBC fungicides and alternative fungicides are more expensive. Historically, cultural methods, especially crop rotation, have been important in the control of eyespot. The importance of cultural control of eyespot is now increasing because more non-cereal break crops are being grown and fungicide use is declining.     

Effects of water potential and temperature on the development of eyespot lesions in wheat

Growth of Pseudocercosporella herpotrichoides on potato dextrose agar at water potentials from -0.5 to -6.9 MPa was optimal at 20°C. At 12 and 20°C, six isolates of P. herpotrichoides grew more rapidly at -0.5 to -2 MPa than at -6.9 MPa. Wheat plants inoculated with P. herpotrichoides and grown in columns of soil at either 15 or 20°C developed more severe eyespot lesions under a heavy watering regime than under medium or light watering regimes. P. herpotrichoides penetrated leaf sheaths of inoculated plants grown in compost more rapidly at 10°C night/15°C day temperatures than at 5/10°C; death of leaf sheaths was also more rapid and consequently there were fewer living infected leaf sheaths at 10/15°C than at 5/10°C. Irrigating for 5 wk before harvest increased the severity of eyespot lesions in a 1983 wheat crop.     

Development of Pseudocercosporella herpotrichoides (Fron) Deighton var. herpotrichoides and var. acuformis on Wheat Plants Measured by ELISA

Using the ELISA method, the development of Pseudocercosporella herpotrtchoides var. herpotrichoides and var. acuformis in a susceptible cultivar of winter wheat was compared under controlled and held conditions. In the greenhouse, var. acufornis grew less vigorously, was slower in penetrating the coleoptile and the successive leaf sheaths and in colonizing the stem tissue than var. herpotrichoides. In the field, these differences were confirmed on the last leaf sheaths and the stem. At ripening stage, however, identical ELISA values were measured for both varieties. Moreover, a significant variation was observed between the individual isolates of each variety. Comparison of the effect of both varieties of P. herpotrichoides on 20 wheat cultivars characterized by different resistance levels showed significant interactions. The cultivars carrying the Pch-1 gene always remained the less diseased genotypes. In general, var. acuformis developed less antigen in the cultivars than var. herpotrichoides. It is concluded, that in tests for resistance to P. herpotrichoides mixtures of many highly pathogenic isolates of both fungus varieties should be used. Less complex mixtures or single isolates may result in wrong estimates of resistance.     

Negative cross-resistance between benomyl and MDPC in British isolates of Botrytis cinerea, Pseudocercosporella herpotrichoides and Verticillium fungicola var. fungicola

Fifteen isolates of Pseudocercosporella herpotrichoides, four isolates of Botrytis cinerea and four isolates of Verticillium fungicola var. fungicola were examined on potato dextrose agar amended with benomyl or methyl N-(3, 5-dichlorophenyl)-carbamate (MDPC). Negatively correlated cross-resistance was clearly demonstrated with the isolates of P. herpotrichoides and B. cinerea. There were indications that the same phenomenon might also operate with the isolates of V. fungicola var. fungicola.     

Epidemiology of eyespot (Pseudocercosporella herpotrichoides) on winter wheat, with particular reference to the period of infection

The period of infection by Pseudocercosporella herpotrichoides was investigated by transplanting winter wheat from uninfested to infested sites at Cambridge. Maximum infection was found on plants moved between November and March; most conidia were trapped during winter but infection was not closely related to the numbers of conidia. Plants exposed at intervals on infested land and incubated in a standard environment became infected throughout the period from October to July; infection was not closely related to the numbers of conidia trapped or plant age, but was positively correlated with the number of wet days/wk. Thus, while enough P. herpotrichoides conidia were dispersed throughout the life of winter wheat crops to cause substantial infection, environmental factors limited the development of new infections from April onwards. Practical implications of these results for the choice of sowing date, the development of resistant varieties, and fungicide use, are discussed.     

Réactions histologiques de blés, résistants ou non àľinfection par Pseudocercosporella herpotrichoïdes

Histological reactions of wheat resistant or sensitive against infection of Pseudocercosporella herpotrichoides The microscopic observations reveal important histological differences between the sensitive or resistant varieties. The disease rapidly affect the whole of the first three leafsheath tissues in the “Étoile de Choisy” variety; in the “Roazon” variety, it only affects the first two sheaths. The inter- or intracellular mycelia can be observed both under the form of filaments more or less dilated or under the form of dense segments in the sensitive variety. However in the resistant variety, only short segments can be observed. The tissues of those two varieties are gradually destroyed when they are in contact with P. herpotrichoides hyphae, whereas the hyphae remain undamaged. In “Etoile de Choisy” the hyphae develop in great quantity whereas in “Roazon”, the development remains limited. In the variety Ae. ventricosa no. 11, which is very resistant, the parasite rarely penetrates into the more external cell layers of the first leaf sheath,‘those invaded host cells are destroyed by the mycelium but, at the same time, the mycelian hyphae degenerate and dilate. Thus, the Ae. ventricosa no. 11 tissues seem to be the seat of a strong fungic toxic reaction.     

Dispersal of Pseudocercosporella herpotrichoides Spores from Infected Wheat Straw

Evidence from spore samples collected amongst infected straw spread on fallow ground supported the conclusion that spores of Pseudocercosporella herpotrichoides are dispersed mostly by rainsplash. Most spores travelled a short distance in the larger ballistic splash droplets, although some may have travelled further in smaller airborne droplets. Weekly spore counts from microscope slides under rainshields, a funnel and an impinger, evaluated as samplers for spores of P. herpotrichoides, showed a similar seasonal pattern. The funnel, as the largest sampler, generally collected most spores, but the impinger collected more spores per unit area of sampling surface. Slides sometimes collected spores when none was recovered from other samplers. Young wheat plants, exposed with the samplers and changed weekly, subsequently developed eyespot symptoms for most of the season.     

Development of Eyespot and Brown Foot Rot in Wheat Plants Inoculated with Mixtures of Pseudocercosporella herpotrichoides Types and Fusarium Species

The effects of Fusarium avenaceum, F. culmorum and Microdochium nivale on eyespot development and of types of the eyespot fungus Pseudocercosporella herpotrichoides on brown foot rot caused by the Fusarium or Microdochium spp. were investigated by sequential inoculation of wheat plants grown in pots in a controlled environment. The W-type of the eyespot fungus induced more severe disease than the R-type, but its symptons were suppressed to a greater extent by Fusarium spp., especially F. avenaceum. Brown foot rot symptoms were sometimes suppressed by P. herpotrichoides but were occasionally more severe when the Fusarium inoculum was applied after the P. herpotrichoides. There, sults are discussed in relation to observations of natural infections.     

Surveys of stem base diseases and fusarium ear diseases in winter wheat in England, Wales and Scotland, 1989–1990

An investigation into the incidence of stem base diseases and the pathogens associated with them was undertaken on winter wheat samples collected at growth stages 31 and 73–75 in 1989 and 1990. Symptoms at growth stage 31 were classified into 10 different types based on visual characteristics. Although Pseudocercosporella herpotrichoides was associated mainly with eyespot lesions and Rhizoctonia spp. with sharp eyespot lesions, a significant number of isolates of each pathogen were taken from lesions classified as fusarium. Different types of fusarium lesion on stem bases at both growth stages were not associated with any one particular Fusarium or Microdochium species. 98% of P. herpotrichoides isolates obtained from eyespot lesions at growth stage 31 in 1989, and 87% of those obtained in 1990 were identified as the sub-species P. herpotrichoides var. acuformis, Microdochium nivale was more common than any of the Fusarium species at both growth stages, and was particularly prevalent in samples from Scotland at the earlier growth stage in 1989. Isolations from the top internodes at growth stage 73–75 indicated that systemic infection by Fusarium species, although present in some stems, was of little importance. Fusarium ear blight affected 0.4% of ears in 1989 and 0.5% in 1990. Glume spot lesions on the ears in 1990 were predominantly associated with Fusarium poae.     

Sensitivity to prochloraz in populations of the eyespot fungus, Pseudocercosporella herpotrichoides, in relation to fungicide treatments and their efficacy in continuous winter wheat

Eyespot was assessed and grain yields determined in the eighth and ninth years (1992 and 1993) of a field experiment in which the fungicides carbendazim and prochloraz were applied, separately or in mixtures, to plots of successive crops of winter wheat. Populations of the eyespot fungus, Pseudocercosporella herpotrichoides, were characterised by the proportions of cultures grown on agar from infected stems that were W-type or R-type, or were carbendazim-resistant or carbendazim-sensitive. Sensitivity to prochloraz in agar was determined for isolates from populations sampled in 1992 using restricted maximum likelihood analysis of EC50s (concentrations needed to decrease colony growth by 50%), to deal with the unbalanced data, and comparisons were made by Wald statistics. Control by prochloraz was maintained but in 1992, as in some previous years, its application with carbendazim was more effective than its application alone. Selection by prochloraz for strains sensitive to carbendazim continued to occur and may have contributed to its sometimes relatively poorer performance in the absence of carbendazim. R-type isolates taken from prochloraz-treated plots, with or without carbendazim, in 1992 were less sensitive to prochloraz than were isolates from plots untreated with prochloraz. There was evidence of a greater range of sensitivities to prochloraz in R-type than in W-type isolates (although some uncertainty results from the small numbers of W-type isolates obtained from some treatments), which would explain the selection of the R-type by prochloraz. The significance of these findings to modern wheat growing practices is considered.     

Surveys of diseases of winter wheat in England and Wales, 1976–1988

Samples from 300 – 400 randomly selected winter wheat crops were taken annually at growth stage 73 – 75 from 1976 to 1988 with the exception of 1983 and 1984. The number of samples from each region was proportional to the area of wheat grown in each region. The percentage of the area of the top two leaves affected by diseases, the severity of ear and stem base diseases and, in 6 years, the severity of take-all were recorded. Septoria tritici and Septoria nodorum were, on average, the most severe of the foliar diseases and eyespot (Pseudocercosporella herpotrichoides) was the most severe of the stem base diseases. Regional differences in levels of S. tritici, brown rust, sharp eyespot and nodal fusarium were significant. Cultivar resistance affected disease severity, and previous cropping patterns particularly affected take-all and eyespot. Eyespot and sharp eyespot were less severe in late- than in early-sown crops. The percentage of crops treated with a fungicidal spray increased from 14% in 1976 to over 90% between 1983 and 1985. Use of benzimidazole fungicides applied at growth stage 31 declined, while use of morpholines from flag leaf emergence onwards increased between 1985 and 1988.     

The Development of Eyespot on Seedling Leaf Sheaths in Winter Wheat and Winter Barley Crops Inoculated with W-type or R-type Isolates of Pseudocercosporella herpotrichoides

In 1986–88 the development of eyespot lesions in winter wheat or winter barley differed plots inoculated with W-type isolates of Pseudocercosporella herpotrichoides and plots inoculated with R-type isolates. In the spring of 1986, after a cold winter, the incidence (%shoots infected) and severity (number of leaf sheaths penetrated) of eyespot lesions in wheat before GS 30/31 were greater in plots inoculated with R-type isolates than in those inoculated with W-type isolates. In 1987, after amild winter, eyespot incidence and severity in both wheat and barley were initially greater in W-type plots than in R-type plots. However, by GS 30/31 or 1987. In 1988, when the crop was October-sown, eyespot incidence and severity were greater in W-type than in R-type plots at GS 30/31. Differences in eyespot incidence and severity between W-type and R-type plots were smaller in barley than in wheat. Both the incidence and severity of eyespot were greater in early-sown than in late-sown plots. Seed rate, had little effect on the rate of lesion development in 1987, but in 1988 the rate of penetration was less at the low seed rate for both wheat and barley.     

Aerial application of mixed virus formulations to control joint infestations of Panolis flammea and Neodiprion sertifer on lodgepole pine

An aerial spray using mixed formulations of two viruses, Panolis flammea nuclear polyhedrosis virus (NPV) and Neodiprion sertifer NPV was conducted against mixed populations of the two pests, P. flammea and N. sertifer on lodgepole pine. These were compared with single virus formulations sprayed against their respective host pests and an unsprayed control. One hectare plots of 14 yr old pine were sprayed by helicopter using ultra low volume techniques. Larvae from each plot were assessed weekly for virus and this showed that the mixed formulations gave the same level of control as separate applications of each NPV. Levels of infection in P. flammea reached 95 – 100% 9 wk post-spray, and in N. sertifer reached 100% 6 wk post-spray. Later P. flammea pupal sampling showed no viral infection in the control but significant levels in sprayed plots, which ranged from 37–9% in the plot sprayed with the high dose of N. sertifer NPV to 75% in the plot sprayed with the low dose of NsNPV.     

Potential long-term storage of the predatory mite <Emphasis Type="Italic">Phytoseiulus</Emphasis><Emphasis Type="Italic">persimilis</Emphasis>

Increasing the ability to store mass-reared natural enemies during periods or seasons of low demand is a critical need of the biocontrol industry. We tested the hypothesis that chemicals can enhance long-term cold storage of a predatory mite Phytoseiulus persimilis Athias-Henriot. The research objective was to determine the effect of cryoprotectant and carbohydrate chemicals on in-storage survival of predators. In-storage survival at 8°C was greater for predators sprayed with glycerol (5%, v/v) or glucose (10% and 20%, v/v) than with water spray controls. After 74 days in the cryoprotectant experiment, predator survival declined to 11.5% in the 5% glycerol treatment and 7.8% in the water spray control. After 88 days in the carbohydrate experiment, predator survival declined to 22% in the 20% glucose treatment and 2% in the water spray control. Although many individuals expired within 50 days in both experiments, a few females survived more than 200 days. This research suggests that select cryoprotectants and carbohydrates have a limited capacity to facilitate long-term storage of P. persimilis.     

Genetic Diversity in W- and R-type Populations of Pseudocercosporella herpotrichoides Based on DNA Restriction Fragment Length Polymorphisms

Thirty-seven isolates of Pseudocercosporella herpotrichoides belonging to W-type and 31 isolates belonging to R-type were analysed for DNA restriction fragment length polymorphisms (RFLPs). They represent diverse geographic origins and different phenotypes related to sensitivity to fungicides. Total DNA digested with EcoRI was hybridized with 22 random DNA probes from a P. herpotrichoides EcoRI-restricted DNA library. Four probes showing polymorphisms among isolates within W-type and R-type and generating a total of 44 RFLPs were retained for cluster analysis. Two main groups were distinguished corresponding to W- and R-types. The genetic diversity among isolates was greater for the W-type than for the R-type isolate, four and three distinct EcoRI-restricted mitochondrial DNA patterns were identified in W- and R-type isolates, respectively. The variability of profiles within each pathotype confirmed a higher degree of polymorphism in the W-type.