bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term control of Phytophthora diseases of cocoa using trunk‐injected phosphonate
Authors: GUEST D. I. , ANDERSON R. D. , FOARD H. J. , PHILLIPS D. , WORBOYS S. , MIDDLETON R. M.
Published: April 2007

Pod rot and stem canker, caused by Phytophthora palmivora, are serious diseases of cocoa causing pod losses of up to 63% and the death of up to 10% of trees annually on Kar Kar Island. Papua New Guinea. Trials were conducted on commercial cocoa plantations to compare the effectiveness of potassium phosphonate when applied as trunk injections, trunk paints and foliar sprays, and trunk injections of Aliette CA and of Ridomil 250EC, with conventional Ridomil‐based spray programmes. The results show that, in trials conducted over 5 years, injections of potassium phosphonate give the highest healthy pod yield and lowest incidence of Phytophthora pod rot and stem canker when compared with Ridomil‐based spray programmes or trunk injections of Ridomil 250EC or Aliette CA. The increase in ripe healthy pod yields was due to both pod rot and stem canker control. The level of control is independent of the seasonal timing of injection. Optimum control was achieved with annual injections of 15 g a. i. per tree, and varied with tree size and disease severity. Injections of phosphonate will, under the range of conditions found in our trials. provide the most cost‐effective control of Phytophthora diseases.
Potential biocontrol of Sclerotinia homoeocarpa and Bipolaris sorokiniana on the phylloplane of Poa pratensis with strains of Pseudomonas spp.
Authors: HODGES C. F. , CAMPBELL D. A. , CHRISTIANS N.
Published: April 2007

Four Pseudomonas strains were evaluated for their ability to control Sclerotinia homoeocarpa and Bipolaris sorokiniana on the phylloplane of Poa pratensis (Kentucky bluegrass). The strains evaluated were Pseudomonas fluorescens (PSD‐4, PSD‐5, PSD‐6) and Pseudomonas lindbergii (PSD‐42). All evaluations were conducted on the upper epidermis of intact attached leaves of Poa pratensis and antagonism was measured as the ability of strains of Pseudomonas to prevent chlorophyll loss from leaves inoculated with either S. homoeocarpa or B. sorokiniana. All strains prevented infection and loss of chlorophyll following inoculation with S. homoeocarpa. Only P. lindbergii (PSD‐42) was antagonistic to B. sorokiniana. None of the P. fluorescens strains controlled disease induced by B. sorokiniana.
Pathogenicity of Ganoderma boninense tested by inoculation of oil palm seedlings
Authors: SARIAH M. , HUSSIN M. Z. , MILLER R. N. G. , HOLDERNESS M.
Published: April 2007

The pathogenicity of Ganoderma boninense isolated from oil palm was tested using wood blocks from a rubber tree as the substrate for the inoculum. Seedlings with roots placed in close contact with the inoculum blocks gave 100% infection. There was a progressive desiccation of leaves from the oldest to the youngest. Sporophores emerged as a white mass of mycelial tissue which rapidly became button‐like. This was followed by the development of the stipe. Bracket‐shaped sporophores formed within 12–16 weeks after inoculation. Longitudinal sections of affected seedlings revealed bole and stem decay. Hyphae were detected in the cortex, endodermis, pericycle and vascular tissues of infected roots. Gummosis and the production of tyloses in xylem vessels were common.
Records of foliage pathogens of Pinus species in tropical countries
Authors: IVORY M. H.
Published: April 2007

Mycosphaerella gibsonii is reported from 19 countries on 24 Pinus spp., especially from seedlings and young plants, including first records for eight countries and five hosts. Mycosphaerella pini is also reported from 12 countries on 10 Pinus spp., especially from derelict research plots and abandoned plantations, including new records for Nepal, Philippines, Sri Lanka and Zambia. Records of M. gibsonii and M. pini from remote native blue pine forests and M. gibsonii from native Chir pine forests in Nepal suggest that both fungi are endemic to the Himalayan region as well as to Central America. Variation between ecotypes of these fungi from Asia and Africa suggests that both fungi are present in these regions as different ecotypes.

Records of Sphaeropis sapinea confirm its widespread occurrence as a shoot blight pathogen and as a facultative pathogen in tropical countries; whereas the paucity of records for M. dearnessii and needle rusts (Coleosporium spp.) suggests that spread of these fungi is less readily achieved.
Studies on the biology of black mould (Aspergillus niger) on temperate and tropical onions. 1. A comparison of sources of the disease in temperate and tropical field crops
Authors: HAYDEN N. J. , MAUDE R. B. , PROCTOR F. J.
Published: April 2007

Aspergillus niger colonies were present on 60–90% of the leaves sampled from onion crops grown under hot, tropical conditions (Shambat, Sudan), but only on 21% of leaves in crops grown under temperate conditions (Wellesbourne, UK). The seed stocks used in the Sudan were naturally contaminated with A. niger, whereas the fungus was absent from seed used in the UK. Inoculation of seed with A. niger resulted in an increase in the incidence of the fungus on onion plants (mean 83% of plants with affected leaves) in the field and on bulbs in store in crops grown in the UK. In the UK, A. niger is infrequent in the soil and air, but it is a major component of the soil and air mycoflora in the Sudan. Most of the bulbs grown in Sudan were contaminated with A. niger at harvest because of the high incidence of the fungus in the field.
Detection of Xanthomonas campestris pv. undulosa infested wheat seeds by combined liquid medium enrichment and ELISA
Authors: FROMMEL M. I. , PAZOS G.
Published: April 2007

An enzyme‐linked immunosorbent assay (ELISA) was standardized for detecting Xanthomonas campestris pv. undulosa (Xcu) in plant tissues. Antiserum prepared against somatic antigens of Xcu reacted with cells of pathovars undulosa, cerealis, translucens and phleipratensis, but not with other bacterial species belonging to the genera Xanthomonas, Pseudomonas, Agrobacterium, Clavibacter, and Erwinia. The lower limit of detection of pure cultures was 5 × 103 cfu/ml. A semi‐selective enrichment broth (SSEB) improved the recovery of Xcu in cultures mixed with contaminating bacteria commonly found on wheat seeds. In ELISA tests the enriched samples gave two‐ to three‐fold increases in A405nm readings when viable cells of Xcu were present. By enrichment, X. campestris pathovars undulosa, cerealis, translucens and phleipratensis were detected in samples that originally had less than 5 × 102 cfu/ml. Semi‐selective enrichment combined with ELISA (SSEB‐ELISA) allowed for determination of the percentages of infestation of wheat seed lots. Potential seedling infection (PSI) of naturally infested wheat seed lots was obtained by growing seed samples in the greenhouse under conditions optimal for disease development. Three methods were evaluated for their capacity to estimate the PSI: ELISA, combined SSEB and ELISA, and direct plating onto semi‐selective XTS agar. Percentages of seed infestation determined by combined SSEB and ELISA resulted in a highly significant correlation with the PSI (r = 0·87, P× 005), whereas determinations made by ELISA or direct plating onto XTS did not significantly correlate with the PSI determined in the greenhouse. This test may constitute a convenient tool for fast initial screening of wheat seed lots in wheat certification programmes.
Transmission of barley yellow dwarf virus by cereal aphids collected from different habitats on cereal farms
Authors: MASTERMAN A. J. , HOLMES S. J. , FOSTER G. N.
Published: April 2007

Cereal aphids were collected from cereal crops, from Poa annua within cereal fields, from Lolium perenne pastures and from wild grasses in hedge bottoms and around farm buildings. The frequency of barley yellow dwarf virus (BYDV) transmission was assessed by aphid transmission tests. There were differences in transmission rates between aphid species, between host species and between years. The transmission rates of Rhopalosiphum padi from the different host species were broadly similar whereas for Sitobion avenae, P. annua within cereal fields was significantly better than the other host species. Wild grasses other than P. annua were relatively poor sources of virus. A large percentage of aphids frequently transmitted more than one strain, suggesting that host plants are often infected with more than one BYDV strain.
The effect of heat on the growth and recovery of Aspergillus spp. from the mycoflora of onion seeds
Authors: HAYDEN N. J. , MAUDE R. B.
Published: April 2007

Temperature optima for growth of Aspergillus niger and A. flavus on agar lay between 30°C and 35°C; the optimum for A. fumigatus was 40°C. A. flavus grew less rapidly in culture than the other two species. These fungi were recovered when a single sample of onion seeds, produced in Sudan, was plated out onto agar and incubated over a range of temperatures from 15°C to 45°C. In line with the growth optima of the fungus, the recovery of A. niger was greatest between 25°C and 35°C; recovery of A. flavus was greatest between 30°C and 35°C and recovery of A. fumigatus greatest between 40°C and 45°C. Hot‐water treatment for durations of up to 60 min at 50°C failed to reduce the incidence of recovery of seedborne A. niger and A. flavus from seeds incubated at 30°C on agar; A. fumigatus was not recovered from seeds treated in this way. However, when seeds were hot‐water treated at 60°C and incubated on agar at 30°C, A. niger was virtually eliminated by a treatment duration of 15 min or more; the incidence of recovery of A. fumigatus was significantly increased compared with the 50°C treatment and there was no change in the incidence of A. flavus. Hot‐water treatment at 60°C for more than 30 min significantly reduced seed germination.
Modelling the spread of fungal diseases using a nearest neighbour approach: effect of geometrical arrangement
Authors: GOLENIEWSKI G. , NEWTON A. C.
Published: April 2007

A discrete model of the nearest neighbour type is used to model the growth and spread of fungal disease in a two‐cultivar mixture assuming an unspecialized pathogen. Disease dynamics and dispersal are represented by a spatial, single pathotype version of Gumpert's (1992) model that simulated the temporal evolution of a number of pathotypes on a cultivar mixture. Spore dispersal occurs by discrete rules between a cell and its four orthogonal neighbours in a rectangular grid. Parameters termed transmission efficiency rates control the extent of successful inoculum exchange between two neighbouring cells depending on the cultivars present. Spatially averaged disease progress curves are computed for regular block and strip patterns in addition to the mean curve for twenty 1:1 random mixture patterns. These sets of curves are exhibited relative to the appropriate pure stand comparison for a range of auto‐ and cross‐deposition parameters. We conducted simulations for uniform initial infection and also averaged over 20 random initial infection patterns at a comparable mean level. In the former case, provided the ratio of cross‐deposition to auto‐deposition is high enough and the disease progress curves take sufficiently long to reach their saturation value, the ranking of the geometrical patterns can eventually be interpreted once initial oscillations have subsided. The geometry with the largest proportion of links between neighbouring cells of different cultivar type generally corresponds to the lowest average disease level, but not for averaged simulations based on random initial infection patterns.
Reaction of somaclonal variants of wheat to the take‐all fungus (Gaeumannomyces graminis var. tritici)
Authors: EASTWOOD R. F. , KOLLMORGEN J. F. , HANNAH M. , WILLIAMS W. M.
Published: April 2007

More than 20000 wheat plants, derived from callus culture of immature wheat embryos were assessed for reaction to the take‐all fungus (Gaeumannomyces graminis var. tritici) using a test‐tube assay. Lines with less root and shoot blackening and more remaining green tissue than parental lines were identified in the SC3 generation. However these lines had more root and shoot blackening and less remaining green tissue in subsequent generations. The changes in reaction to the fungus may therefore have been epigenetic. The potential of this tissue culture derived material for breeding take‐all resistant wheats is discussed.
Host mixture efficacy in disease control: effects of lesion growth analyzed through computer‐simulated epidemics
Authors: LANNOU C. , DE VALLAVIEILLE‐POPE C. , GOYEAU H.
Published: April 2007

Lesion growth varies among foliar parasites and in order to study the effect of lesion growth on the efficacy of host mixtures to control epidemics, we altered the epidemic simulator Epimul by integrating a lesion growth function into the model. A theoretical study was performed by simulating epidemics caused by parasites with different lesion growth rates, spore dispersal gradients and multiplication rates. We found that increases in lesion growth rates resulted in large decreases in the effectiveness of mixtures for disease control and interacted strongly with parasite multiplication rate and spore dispersal gradient. The decline in mixture efficacy for epidemics with high lesion growth rates was reduced when parasite multiplication rate was higher and spore dispersal gradient steeper. Our results suggested that the lower number of infections on susceptible plants in the mixture as a result of inoculum loss on resistant hosts was partially compensated by lesion growth.
Rapid diagnosis of apple proliferation mycoplasma‐like organism using a polymerase chain reaction procedure
Authors: FIRRAO G. , GOBBI E. , LOCCI R.
Published: April 2007

The rapid diagnosis of apple proliferation mycoplasma‐like organism, using polymerase chain reaction amplification of part of the 16S rRNA gene is reported. Apple proliferation MLO can be detected in as little as 0·3 g of diseased tissue. Results compare favourably with those obtained by other PCR‐based methods. Operational speed, sensitivity, specificity and ease of performance of the method, with particular reference to indexing purposes, are discussed.
Smoke pollution and the effects of root‐knot nematodes on the growth of eggplants
Authors: KHAN M. R. , KHAN M. W.
Published: April 2007

Single and combined effects of smoke pollution and the root‐knot nematode, Meloidogyne incognita race 1, were studied on eggplant in 1988 and 1989 at two sites (K1 and K2) 1 and 2 km respectively away from a coal‐fired thermal power plant, and a control site at the Department of Botany, Aligarh Muslim University (AMU). Mean concentrations of SO2, NO2 and suspended particulate matter (SPM) were respectively 172, 95 and 626 μg/m3 in 1988 and 144, 97 and 556 μg/m3 in 1989 at K1; and 258, 150 and 344 μg/m3 in 1988 and 226, 113 and 293 μg/m3 in 1989 at K2. Peak levels of the gases and SPM were recorded in the early (12.00–15.00) and late (15.00–18.00) afternoon respectively. Concentrations of the pollutants at a control site were very low. Marginal browning appeared on the leaves of eggplants grown at site K2 whether or not they were infected by the nematodes. The galling caused by nematodes was severe at both polluted sites but egg mass production was inhibited at K2. Egg laying was significantly reduced at both polluted sites. M. incognita significantly reduced plant growth, yield and leaf pigment production of eggplant at the control and polluted sites. Most non‐infected plants also showed significant reductions in these plant varieties i.e. from the effects of pollution at K2. Foliar concentrations of sulphur were significantly increased at both polluted sites, being greater in infected plants. The interaction of smoke pollution and M. incognita infection led to greater suppressions at the polluted sites, which were mostly significant at K1. At the polluted sites, leaves had more and longer trichomes; also the number and size of stomata were decreased but their openings were wider especially in infected plants at the two polluted sites.
The identification of a pathotype‐specific DNA probe for the R‐type of Pseudocercosporella herpotrichoides
Authors: NICHOLSON P. , REZANOOR H. N. , HOLLINS T. W.
Published: April 2007

A 6·7‐kb DNA fragment has been isolated from an R‐type isolate of Pseudocercosporella herpotrichoides that exhibits specific hybridization to R‐type isolates and not to W, C or S pathotypes or to P. anguioides. R‐type isolates are polymorphic with respect to this fragment and three sizes were present (11·6, 6·7 and 4·5 kb) in EcoRI‐digested DNA from isolates of a world‐wide collection. Infection of rye seedlings was demonstrated by hybridization of this probe to DNA extracted from infected plants.
The use of species‐specific DNA probes for the identification of Mycosphaerella fijiensis and M. musicola, the causal agents of Sigatoka disease of banana
Authors: JOHANSON A. , CROWHURST R. N. , RIKKERINK E. H. A. , FULLERTON R. A. , TEMPLETON M. D.
Published: April 2007

The polymerase chain reaction (PCR)‐based technique of random amplification of polymorphic DNA (RAPD) was used to differentiate DNA from species of the genus Mycosphaerella. DNA from two pathogens which cause Sigatoka leafspot diseases of banana, M. fijiensis and M. musicola, and two other Mycosphaerella species which are commonly found on banana, M. musae and M. minima, gave distinct RAPD banding patterns with all PCR primers tested. PCR, using primer RC07, amplified a 1250bp RAPD fragment from all isolates of M. fijiensis obtained from 11 geographical origins. This fragment was absent from the other species of Mycosphaerella. In Southern blots of genomic DNA, this band hybridized exclusively to DNA from M. fijiensis, and the pattern of hybridization suggested that it was binding to repeated DNA. A RAPD band amplified with primer PM06 obtained from M. musicola was also found to be species‐specific. Southern analysis suggested that the fragment hybridized to a single‐copy sequence in the M. musicola genome. Total genomic DNA from M. musicola was found to be a species‐specific hybridization probe. Dot‐blots confirmed the specificity of these probes, and could be used to identify isolates of Mycosphaerella which cause Sigatoka disease of banana in south‐east Asia.
A South African isolate of ryegrasss mosaic virus
Authors: SALM S. N. , REY M. E. C. , WOLFSON M. M.
Published: April 2007

An isolate of ryegrass mosaic virus (RMV‐SA) was found in Italian ryegrass plants in two areas in South Africa. Preliminary characterization indicated that the virus exhibited the same symptoms and host range as RMV strains previously found in Canada and the UK. The virus was transmitted by the eriophyid mite Abacarus hystrix. Particle structure and size were comparable to the USA and UK strains. The coat protein and RNA were found to be slightly larger than previously reported, being 32kDa and 2·8 × 106, respectively. The virus exhibited serological cross‐reactivity with antisera to RMV‐Wales and RMV‐Canada but was not serologically related to other Rymovirus members.
Laboratory production of oospores of Peronospora parasitica (crucifer downy mildew) and the recovery and characterization of sexual progeny from crosses between isolates with different host specificity
Authors: MOSS N. A. , CRUTE I. R. , LUCAS J. A.
Published: April 2007

The production of viable oospores of Peronospora parasitica under laboratory conditions and the recovery of isolates (referred to as sexual progeny) from these oospore populations are described. Oospores were produced when isolates of opposite sexual compatibility type, specialized to the same or different Brassica species, were grown together in seedling cotyledons of a host line capable of supporting growth of both isolates. Recovery of sexual progeny from oospore populations produced from two out of four pairings between isolates specialized to the same host species (homologous pairings) proved relatively easy. On the basis of their characterization with respect to virulence, response to phenylamide fungicides, sexual compatibility type and isoenzyme polymorphisms, there was evidence that the sexual progeny from these homologous pairings could be of hybrid origin. For the first time in a member of the Peronosporaceae, it proved possible to recover and successfully characterize a few sexual progeny from pairings between isolates specialized to different host species (heterologous pairings). However, the majority of such isolates sporulated weakly and as a consequence proved difficult to maintain and were lost. Nevertheless, some evidence for the hybrid nature of progeny from heterologous pairings was obtained.
Effects of temperature and light on non‐race‐specific resistance of potato leaflets to late blight
Authors: HARRISON J. G. , LOWE R. , WILLIAMS N. A.
Published: April 2007

Effects of temperature and illumination on colonization by Phytophthora infestans of detached leaflets of five potato cultivars differing in field resistance to blight were investigated using an ELISA system to quantify the pathogen. Leaflets of cvs Teena and Shelagh, and in one experiment cv. Brodick, were more resistant to colonization when infected leaflets were incubated at 10°C than at 20°C, but temperature conditions before inoculation had little effect. Both photoperiod and light intensity during illumination of intact plants before inoculation interacted with genotype to determine subsequent colonization of infected leaflets incubated in darkness. Leaflets from plants of cv. Teena were more resistant to colonization after exposure to low, rather than to high, light intensities but photoperiod had no apparent effect. Leaflets of cv. Shelagh grown in a 20 h day were more resistant than those grown in a 10 h day but light intensity had no effect. Leaflets of cv. Brodick were more resistant after a 20 h day than a 10 h day and after exposure to low, rather than to high, light intensities. Leaflets of cv. Bintje were extensively colonized and those of cv. Torridon remained relatively resistant to colonization, irrespective of temperature and lighting conditions. There was a high level of unexplained variation in all the experiments.
Screening winter rye cultivars for snow mould (Microdochium nivale) resistance
Authors: HÖMMÖ L. M.
Published: April 2007

The snow mould (Microdochium nivale) resistance of 13 winter rye cultivars was studied in field trials and in three different laboratory tests: snow mould chamber tests, enzymatic assay tests and leaf segment tests. On the basis of the results, it is suggested that both the field trials and the snow mould chamber tests describe more the general winterhardiness of plants involved in the survival of the crown tissue of plants during prolonged incubation under the snow cover, than the snow mould resistance. The results from the enzymatic assay and the leaf segment tests indicate that there are other, more specialized snow mould resistance mechanisms in the plant that act also at the single leaf level. At least some of these resistance reactions seem to be induced by the lytic enzymes secreted by M. nivale.
First record of ascomata of Leptosphaeria maculans on winter‐grown oilseed rape in Denmark
Authors: JENSEN L. B.
Published: April 2007

The ascomata of Leptosphaeria maculans were observed for the first time in Denmark in 1991. Morphological data and cultural characteristics were consistent with previously published data.
First record of Colletotrichum dematium as a pathogen of Asystasia nemorum and A. gangetica in Singapore
Authors: TAN T. K. , TOW S. A.
Published: April 2007

The ability of Colletotrichum dematium to infect Asystasia nemorum and A. gangetica was investigated. Both host species were susceptible to the fungus, showing chlorosis, necrosis, premature defoliation and stunted growth. Wounding did not affect the degree of infection. This is the first description of the pathogenicity of C. dematium on Asystasia.
Seasonally induced chaotic dynamics and their implications in models of plant disease
Authors: SHAW M. W.
Published: April 2007

Two models of plant disease in crops regulated by a virus disease or by a hyperparasite are introduced. If the host crop is annually harvested or dies back, the pathogen population at the end of each year may fluctuate indefinitely and irregularly in a way which depends very precisely and for ever on the initial populations. This means that even in an environment which is identical every year, the pathogen populations in each year vary enormously and erratically. However, the combinations of pathogen and virus incidence or hyperparasite infection that can occur exhibit very well defined patterns, even if parameters in the model exhibit substantial random annual variation. It is important that pathologists should be aware that population fluctuations may not be caused by environmental fluctuations and may be, in principle, unpredictable by a deterministic model.
Epidemiology and population ecology of kiwifruit blossom blight
Authors: EVERETT K. R. , HENSHALL W. R.
Published: April 2007

A study of the ecology and epidemiology of kiwifruit blossom blight, believed to be caused by the bacterium Pseudomonas viridiflava, was made at the Horticulture and Food Research Institute's Kumeu Research Orchard during spring 1991. Populations of Pseudomonas species, progression of disease symptoms, and micrometeorological conditions were monitored during flowering. No correlations were found between disease progress and the climate variables measured. The rate of increase in disease incidence changed with the transition of buds to flowers. Changes in the rate of increase, logit transformed, were compared with climate variables using cross‐correlation. Populations of P. viridiflava were related to the number of diseased blossoms remaining on the vine. The population of a saprophytic bacterium, P. fluorescens, increased as flowering progressed and as dead flower parts became available for colonization. Other Pseudomonas species were only present in low numbers. The population of P. viridiflava and the rate of disease progress decreased at fruit set. A comparison of simulated disease progress curves (calculated using disease model formulae) with disease progress curves from real data suggested that the epidemic was polycyclic, and observations suggested that disease was spreading to unopened buds.
Evaluation of fungicides for control of eyespot disease and yield loss nationships in winter wheat
Authors: JONES D. R.
Published: April 2007

Following the discovery of resistance to benzimidazole fungicides in the cereal eyespot pathogen Pseudocercosporella herpotrichoides in the UK in 1981, and an initial in vitro screen to select the fungicides with greatest activity against the pathogen, 40 field experiments were carried out between 1983 and 1986 to evaluate alternative fungicides for control of eyespot. At the majority of experimental sites, benomyl‐resistant strains of the pathogen were present, and carbendazim did not control eyespot. Prochloraz was the most effective fungicide, reducing the eyespot index by 30–60%. There was no extra benefit from adding carbendazim to prochloraz. Flusilazole was almost as effective as prochloraz, but other fungicides had little or no effect. At sites with a high incidence of eyespot, prochloraz, with or without the addition of carbendazim, generally gave the largest yield increase. The mean yield increases each year were in the range 0·36–0·85 t/ha, and the greatest yield increase at any site was 2·27 t/ha. Most other fungicides increased yield, but carbendazim did not from 1984 to 1986. There were also yield increases at many sites with a low incidence of eyespot. Yield increases were associated with increases in thousand‐grain weight at the majority of sites, but in only a few instances were there associated increases in specific weight. Prochloraz application at GS30‐31 was cost effective at 71% of sites. At most sites, in regression of yield on eyespot, eyespot accounted for less than 25% of the variance in yield. The mean relationship between severe eyespot lesions and yield loss was such that each 1% increase in the percentage of tillers affected by severe eyespot was associated with a yield loss of 0·21 %. There was a significant positive correlation between eyespot at GS75 and GS30‐31, and between yield increase from prochloraz treatment (at GS30‐31) and eyespot at GS75, but not between yield increase and eyespot at GS30‐31. The ADAS threshold for fungicide application of 20% tillers affected at GS30‐31 was a reliable indicator of the cost‐effectiveness of treatment at 60% of sites.
Characterization of Polymyxa species by restriction analysis of PCR‐amplified ribosomal DNA
Authors: WARD E. , ADAMS M. J. , MUTASA E. S. , COLLIER C. R. , ASHER M. J. C.
Published: April 2007

A molecular method is described to aid identification of the obligate parasite Polymyxa and discriminate between species (P. betae and P. graminis) and isolates. DNA was extracted from zoospores, resting spores and roots infected with P. betae and P. graminis and compared with that from negative control plants that were not inoculated with Polymyxa but were grown at the same time under the same conditions. The ribosomal internal transcribed spacers and 5.8S rDNAs were amplified by the polymerase chain reaction and digested with restriction enzymes to detect molecular differences between the species and isolates. There were differences between P. betae and P. graminis and two subgroups within P. graminis but so far this has not been correlated with any other biological property.
Association of Rhizoctonia strains with bare patch disease of wheat in Western Australia
Authors: YANG H. A. , SIVASITHAMPARAM K. , ALEMOHAMMAD J. , BARTON J. E. , O'BRIEN P. A.
Published: April 2007

Rhizoctonia‐like fungi were isolated from the roots of diseased wheat plants sampled from the centre and periphery of three bare patches, and from apparently healthy plants from outside the patches. Of the isolates recovered, 81% were multinucleate and belonged to R. solani anastomosis group 8, and pectic zymogram group 1‐1; the remaining isolates were binucleate Rhizoctonia spp. The multinucleate isolates could be grouped into highly virulent, intermediately virulent, and weakly virulent types. The binucleate isolates were all non‐pathogenic. The multinucleate isolates were obtained at a significantly higher frequency from plants within the patches compared with outside the patches, and with the exception of a single isolate, the highly virulent isolates were not found outside the patches. The weakly virulent isolates were present at much lower frequencies than the highly virulent and intermediately virulent forms within the patches. The frequency of occurrence of binucleate isolates did not vary significantly among the locations sampled. None of the multinucleate isolates contained plasmids. Some of the isolates contained a prominent single dsRNA species and one or more minor dsRNA species. The distribution of these dsRNAs was not correlated with pathogenicity.
A potyvirus isolated from solanaceous hosts
Authors: WALKEY D. G. A. , SPENCE N. J. , CLAY C. M. , MILLER A.
Published: April 2007

A potyvirus was isolated from Datura stramonium, Lycopersicon esculentum (tomato) and Solanum nigrum in the Yemen. It was transmitted mechanically and by Myzus persicae in a non‐persistent manner. Its flexuous rod‐shaped particles had a mean length of 719 nm and some of its pinwheel inclusion bodies in infected Nicotiana clevelandii leaves were unusual in that they were dichotomously branched. The virus infected various solanaceous species, but the symptoms it induced were distinct from those of pepper veinal mottle (PVMV) and potato Y viruses. Its particles were purified from N. glutinosa and their coat protein had an atypically high molecular mass a potyvirus of 41·5 kDa. They showed a distant serological relationship to those of PVMV and potato virus V in ISEM decoration tests, but did not react with antisera to particles of any other potyvirus tested. The virus has been tentatively named tomato mild mottle virus.
Foot canker and sudden wilt of Hevea brasiliensis associated with Nattrassia mangiferae
Authors: JAYASINGHE C. K. , SILVA W. P. K.
Published: April 2007

An unreported foot canker of Hevea seedlings has been proved to be caused by the fungus Nattrassia mangiferae. Sun‐scorch predisposes the seedlings to infection.
Leaf spot and blight of Dieffenbachia amoena caused by Pseudomonas marginalis pv. marginalis
Authors: SCORTICHINI M.
Published: April 2007

Leaf spot and blight of Dieffenbachia amoena caused by Pseudomonas marginalis pv. marginalis are described for the first time. Symptoms were noticed during winter on plants in the greenhouse, the first signs were small, elongated, light brown lesions on the surface of the leaves. As the infection spreads, leaves become completely brown and collapse. The identity of the causal agent was determined by biochemical, nutritional and pathogenecity tests as well as by comparison of whole‐cell protein profiles of the isolates under study with those of type strains.
Molecular variation within some Japanese isolates of Verticillium dahliae
Authors: CARDER J. H. , BARBARA D. J.
Published: April 2007

Eight isolates of Verticillium dahliae from Japan, classified into four groups based on pathogenicity to differential hosts, were compared with isolates in previously defined RFLP groups. Within each of two of the pathogenicity groups (JB and JC) the pairs of haploid isolates were closely related but those in a third group (JA; isolates not pathogenic to sweet pepper or tomato) were not. Only one of the six haploid isolates (one of the two in the JA group) could be placed in an existing RFLP group. The two diploid isolates (the JD pathogenicity group) were similar to RFLP group D and only distantly related to the six haploid isolates. Of the Japanese pathogenicity groups, only JD corresponded to an existing RFLP group.
The influence of Thrips obscuratus on infection and contamination of kiwifruit by Botrytis cinerea
Authors: FERMAUD M. , GAUNT R. E. , ELMER P. A. G.
Published: April 2007

Infestation of kiwifruit flowers by Thrips obscuratus, and inoculation with Botrytis cinerea, increased the amount of flower infection, external contamination and internal infection of fruit at harvest. Combination of these treatments was synergistic. The mechanisms of this role of T. obscuratus in the epidemiology of B. cinerea and development of stem‐end rot after cool storage are discussed in relation to commercial production, harvesting and handling procedures. Significant reductions in inoculum available for fruit infection may be achievable by control of populations of T. obscuratus in orchards during flowering.
Biochemical and histological studies on susceptible and resistant maize leaves infected by Helminthosporium maydis
Authors: ANGRA‐SHARMA R. , SHARMA D. K.
Published: April 2007

Biochemical, histological and fluorescent microscopy studies were conducted on susceptible and resistant maize leaves infected with Helminthosporium maydis. Histochemical observations revealed the presence of proteins, lipids, lignins and phenolics; tannins, however, were absent. Biochemical examination showed high levels of protein and phenolic compounds in the resistant variety compared with the susceptible host. The levels of lipids were, however, lower in the resistant host, and decreased with time of incubation of the host–pathogen complex. Aniline blue gave a high fluorescence intensity for the host at the germ tube and infection site for the resistant variety compared with the susceptible variety, indicating a greater quantity of callose in the infected tissue. The rate of increase in carbohydrates in the infected susceptible host was less than in the infected resistant host. This suggests that the infection is restricted from progressing further in the resistant variety. Higher levels of proteins, lignins, phenolics and callose synthesized in the resistant variety may play a role in inhibiting the infection.
Antifungal activity of sugar beet chitinase against Cercospora beticola: an autoradiographic study on cell wall degradation
Authors: NIELSEN K. K. , JØRGENSEN P. , MIKKELSEN J. D.
Published: April 2007

Two independent bioassays demonstrated an antifungal effect of a basic sugar beet chitinase on Cercospora beticola, the causal agent of leaf spot disease in sugar beet (Beta vulgaris). In one assay, the growth of submerged spore cultures of C. beticola in microtitre wells was followed by measuring the increase in absorbance at 620 nm. Addition of chitinase to the culture resulted in a delay in germination and a slower initial growth rate. A more detailed picture of the action of the chitinase on the fungal cell wall was provided by an autoradiographic study. An intense labelling was observed at the apex of fungal hyphae grown in medium containing [3H]N‐acetylglucosamine, through incorporation of the radioactive chitin monomer into newly synthesized chitin in the cell wall. After fixation of the fungal specimen, the radioactive labelling could be removed by treatment with purified chitinase, i.e. nascent chitin chains were hydrolysed by the enzyme. When the fungal culture was subjected to a chase phase prior to fixation, the radioactive depositions were less accessible to hydrolysis by the chitinase. HPLC analysis of the radioactive hydrolysis products released from the apex of the fungal hyphae showed that the main products were small chito‐oligosaccharides, mainly dimers, trimers and tetramers of chitin.
Detection of the mycoplasma‐like organism associated with lethal yellowing disease of palms in Florida by polymerase chain reaction
Authors: HARRISON N. A. , RICHARDSON P. A. , KRAMER J. B. , TSAI J. H.
Published: April 2007

DNA amplification by polymerase chain reaction (PCR) was used specifically to detect the mycoplasma‐like organism (MLO) associated with lethal yellowing disease of palms in Florida. For PCR, a pair of oligonucleotide primers was synthesized according to partial sequences of a cloned 1·3 kbp fragment of lethal yellowing MLO‐specific genomic DNA isolated from a diseased windmill palm (Trachycarpus fortunei). A DNA product of about 1 kbp was specifically amplified by PCR in reaction mixtures containing template DNA derived from either heart, inflorescence or leaf tissues of lethal yellowing‐affected palms. PCR performed for 35 cycles with as little as 5 pg of DNA template, in some instances, was sufficient consistently to amplify the same lethal yellowing MLO DNA product from hearts of 11 species comprising 30 symptomatic palms. Similar reliable and reproducible detection of the lethal yellowing MLO in palm inflorescence spikelets was also achieved after 35 cycles of PCR. When template DNA for PCR was derived from tissues of the the most immature emerging leaf, a 40‐cycle reaction was sufficient for consistent foliar detection of the pathogen in all coconut palms including palms with earliest visible symptoms of disease.
Random amplified polymorphic DNA (RAPD) analysis of Crinipellis perniciosa isolates from different hosts
Authors: ANDEBRHAN T. , FURTEK D. B.
Published: April 2007

DNA sequence polymorphisms among isolates of Crinipellis perniciosa, causing witches’ broom disease in several genera and species in the Sterculiaceae, Solanaceae and Bixaceae, were revealed by random amplified polymorphic DNA (RAPD) banding patterns. Comparisons were made among isolates from Theobroma cacao (cultivars SCA6 and SVB), T. grandiflorum, T. obovatum, T. subincanum, Herrania sp. (all collected near Belém, Brazil, at three plots within two kilometres of each other), and Bixa orellana and Solanum rugosum (150 and 1440 km from Belém, respectively). Genetic similarities, as determined by Sorensen's coefficient (Scij; fraction of shared bands), ranged from 1·00 (T. cacao SCA6 and T. grandiflorum) to 0·56 (S. rugosum and T. subincanum). Results indicate that proximity is more important than host species for determining the genetic relationships among isolates, that there were two independent sources of inoculum at the site near Belém, and that the isolate from B. orellana is most closely related to the isolate from T. cacao SVB. Comparisons were also made among multispore cultures from different basidiocarps on the same T. cacao SVB broom, as well as monospore cultures from the same S. rugosum basidiocarp. Banding patterns were similar among basidiocarps on the same broom, but differences were detected among monospore cultures from the same basidiocarp.
Crown gall of hop caused by Agrobacterium tumefaciens biovar 1 in South Africa
Authors: SERFONTEIN S. , STAPHORST J. L.
Published: April 2007

Crown gall of hop caused by Agrobacterium tumefaciens biovar 1 is reported for the first time from South Africa. The causal organism was inhibited in vitro by the agrocin of A. radiobacter strain D286 but not by that of the control strain K84. Nevertheless, control was achieved on hop stems in glasshouse inoculations by both biological control strains.
Canker and die‐back of Eucalyptus in South Africa caused by Botryosphaeria dothidea
Authors: SMITH H. , KEMP G. H. J. , WINGFIELD M. J.
Published: April 2007

Die‐back and canker of several Eucalyptus species and clones were observed during a survey of the most important forestry areas of South Africa. Disease was often associated with extreme environmental conditions such as drought, hot winds and frost. Botryosphaeria dothidea, which is well known as a cause of canker and die‐back of Eucalyptus in other countries, was consistently isolated from symptomatic trees. Artificial inoculations of Eucalyptus nitens resulted in lesion development, confirming the pathogenicity of 5. dothidea to Eucalyptus in South Africa. This is the first report of this disease in South Africa.
Occurrence of Pseudomonas syringae pv. actinidiae on kiwifruit in Italy
Authors: SCORTICHINI M.
Published: April 2007

Pseudomonas syringae pv. actinidiae has been isolated from kiwifruit plants for the first time in Italy. Biochemical tests were consistent with those characterizing the type‐strain; pathogenicity tests yielded severe blights in the inoculated kiwifruit plants and no symptoms on lilac, pear and peach. Nutritional tests as well as whole‐cell protein profiles revealed slight differences between the strains isolated in Japan and those of the present study. The main symptoms observed in the field are a red‐rusty exudation covering the bark of twigs and trunks, blight of young canes and plants, angular leaf spots surrounded by chlorotic haloes and tiny cankers along the twigs.
Isolation of R‐type progeny of Tapesia yallundae from apothecia on wheat stubble in England
Authors: DYER P. S. , PAPAIKONOMOU M. , LUCAS J. A. , PEBERDY J. F.
Published: April 2007

Apothecia of Tapesia yallundae were collected from a set‐aside straw stubble site in Lincolnshire in March 1993. Single ascospore isolates were obtained which produced colonies with morphologies and growth rates characteristic of the R‐pathotype of Pseudocercosporella herpotrichoides. Isolates were confirmed to be R‐type by the use of randomly amplified polymorphic DNA (RAPD) markers. These observations confirm that T. yallundae is the teleomorph of the R‐type of P. herpotrichoides and represent the first detection of the sexual stage of the R‐type in the UK.
The incidence of three virus diseases of winter oilseed rape in England and Wales in the 1991/92 and 1992/93 growing seasons
Authors: HARDWICK N. V. , DAVIES J. M. L. , WRIGHT D. M.
Published: April 2007

The incidence and severity of three diseases of oilseed rape, caused by beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV) and turnip mosaic potyvirus (TuMV), were assessed in England and Wales in the springs of 1992 and 1993. In 1992, 62% of oilseed rape crops examined were found to contain BWYV, with an average of 28% plants infected; 14% of crops contained CaMV, with an average of 5% plants infected; and TuMV with 3% crops and < 1% plants infected. In 1993, BWYV was found in 42% of crops and 12% of plants infected; CaMV in 25% of crops and 7% of plants infected; and TuMV in 14% of crops and 5% plants infected. The yields of plants showing severe virus symptoms were reduced by an estimated 70 to 79%. The high incidence of CaMV and TuMV in oilseed rape crops could have important consequences for rapeseed production in the UK and also serve as a source of virus for vegetable brassicae.
The occurrence in Portugal of the bacterial disease of maize crops caused by Erwinia chrysanthemi
Authors: FERREIRA‐PINTO M. M. , CRUZ M. L. , OLIVEIRA H.
Published: April 2007

A bacterial disease causing stalk rot of maize was observed in Portugal, during the summer of 1991, in overhead sprinkler‐irrigated fields. Affected plants showed symptoms of a soft rot disease and isolations made from infected tissues consistently yielded a bacterium. On the basis of morphological, cultural, biochemical, physiological and pathological properties, the pathogen was identified as Erwinia chrysanthemi. According to biovar discrimination tests, the maize isolates were allocated to biovars 2 and 3 of E. chrysanthemi.
Collar rot and wilt: a new disease of Java citronella (Cymbopogon winterianus) caused by Fusarium moniliforme Sheldon
Authors: ALAM M. , CHOURASIA H. K. , SATTAR A. , JANARDHANAN K. K.
Published: April 2007

Commercial plantations of Java citronella (Cymbopogon winterianus) in Lucknow, Pantnagar and their adjoining areas were affected by a collar rot and wilt disease. The causal organism was identified as Fusarium moniliforme, anamorph of Gibberella fujikuroi. Isolates of the pathogen originating from Lucknow and Pantnagar differed in their pathogenicity on the host plant under glasshouse conditions. There were also differences in growth rates, pigment production and sporulation between isolates.
‘Dead skin’ on yams (Dioscorea alata) caused by Colletotrichum gloeosporioides
Authors: GREEN K. R. , SIMONS S. A.
Published: April 2007

A storage rot of yams (Dioscorea alata), commonly referred to as ‘dead skin′, has recently become a major constraint to yam production in the Caribbean. The fungal pathogen Colletotrichum gloeosporioides was consistently isolated from affected tubers and re‐inoculation of healthy yam tubers resulted in the development of typical symptoms of dead skin.
Codiaeum rust
Authors: BOEREMA G. H. , COOK R. T. A. , DICKENS J. S. W. , PISI A. , BELLARDI M. G. , MORDUE J. E. M.
Published: April 2007

A rust affecting Codiaeum variegatum (‘Croton’, Euphorbiaceae) imported into the UK from Ivory Coast in 1978 was originally identified as Aecidium codiaei H. Sydow. However, studies on germination of spores, pathogenicity tests and examinations of sori under light microscope and scanning electron microscopy (SEM) revealed that the rust belonged to the tribe Pucciniosireae (a diverse group of mostly tropical microcyclic rust genera characterised by their stages being telescoped into aecidioid telia). Attention was drawn to the transfer of this Aecidium species to Dietelia (a member of the Pucciniosireae) following imports of the disease into the Netherlands from Ghana in 1978. Dietelia codiaei (H. Sydow) Boerema was subsequently confirmed as the causal agent of Codiaeum rust on recent imports into the UK and Italy. It is believed to be distinct from D. emasculata recorded on Breynia, another euphorbiaceous host.