bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of wheat and barley isolates of Septoria nodorum to passage through barley and wheat cultivars
Authors: FITZGERALD W. , COOKE B. M.
Published: April 2007

A single‐spore wheat isolate of S. nodorum was passaged once through barley and a barley isolate passaged once through wheat. Reisolations from barley leaves were designated as either ‘original‐type wheat’ (OTW) and resembled the wheat isolate used for inoculations in morphology, or ‘sector‐type barley’ (STB) resembling the known morphology of barley isolates. Reisolations from wheat were similarly designated either OTB or STW. Sub‐cultures of STB were significantly more pathogenic to barley in a glasshouse experiment than OTW, and vice versa. Similarly STW was significantly more pathogenic to wheat than OTB, and vice versa.

A single‐spore wheat isolate was also passaged 0, 1, 2, 3 or 4 times through barley and a barley isolate passaged similarly through wheat. Disease assessment and yield data from a field experiment showed that the pathogenicity of the passaged wheat isolate remained largely unaltered from that of the original isolate. However, the barley isolate responded after the third wheat passage by causing significantly less disease and significantly higher yields in barley than the unpassaged isolate; conversely, on wheat, disease levels significantly increased and yield slgnficantly decreased after the second wheat passage.

Data obtained are discussed in the context of cultural observations made on colony morphology during host passage sequences and possible genetic mechanisms responsible.
Breakdown of potato virus X resistance gene NX: selection of a group four strain from strain group three
Authors: JONES R. A. C.
Published: April 2007

Isolate DX of potato virus X (PVX) caused the typical reactions of a group three strain, systemic top necrosis in presence of potato hypersensitivity gene Nx and mosaic with gene Nb. When tubers harvested from DX‐infected plants of the Nx: Nb cultivars Maris Piper and Pentland Dell were, grown on, most progeny plants were healthy, but some had systemic top necrosis caused by DX while others had mosaic symptoms in upper leaves and severe necrosis in lower ones. Infective sap from the plants with mosaic and necrosis always caused similar symptoms when inoculated to Pentland Dell. Only group four PVX strains can cause systemic infection without top necrosis in Nx:Nb cultivars, so the affected plants all contained a group four strain. That the severe necrosis of their lower leaves resulted from a shock reaction rather than from isolate DX also being present was indicated because the plants partially recovered, inoculations from near to the dilution end‐point failed to demonstrate any separation of strains and behaviour on back‐testing to Pentland Dell was unchanged after passage twice through tubers of this cultivar. Also, although DX caused severe necrotic symptoms in tubers of both Nx: Nb cultivars, these symptoms did not develop in tubers of plants with mosaic and necrosis. When cultured serially in Nicotiana glutinosa, the group four strain eventually reverted to group three.
Ultrastructure of the host‐pathogen interface of Peronospora viciae in cultivars of pea which show different susceptibilities
Authors: BEAKES G. W. , SINGH H. , DICKINSON C. H.
Published: April 2007

The ultrastructure of interactions of pea downy mildew (Peronospora viciae) on the leaves and petioles of two cultivars of pea, Superb and Maro, was examined. Tissue fixed at the time of sporulation (10 days after inoculation) revealed that many of the intercellular hyphae in Maro were showing evidence of partial or complete autolysis. The penetration matrices were enclosed in a thicker layer of callose‐like material than in Superb, and many of the haustoria had collapsed, distorted profiles. Analysis of organelles lying close to the extra haustorial membrane revealed fewer associations with endoplasmic reticulum in Superb.
Species of Armillaria in southern England
Authors: RISHBETH J.
Published: April 2007

Isolates of Armillaria obtained from a wide variety of material were identified by means of the mating test devised by korhonen and by their growth on various media. Pathogenicity was tested by inoculating small pines. Five species were found, of which Armillaria mellea (Vahl ex Fr.) Kummer and A, ostoyae (Romagn.) Herink were highly pathogenic: the former killed a wide variety of broadleaved trees and conifers whilst the latter killed fewer species, mainly conifers. A. bulbosa [Armillariella bulbosa (Barla) Romagn.] was much less pathogenic and was found in trees weakened by suppression or in other ways;it also caused extensive butt‐rot in some broad‐leaved trees. A. tabescens (Scop, ex Fr.) Emel, was less common and occurred in stumps of broadleaved trees: it was virtually non‐pathogenic. A species provisionally designated B by Korhonen was discovered only once. Brief accounts are given of these species with respect to rhizomorph behaviour and factors affecting their occurrence in woodland and gardens.
Populations of plant pathogens: some constraints on analysis of variation in pathogenicity
Authors: WOLFE M. S. , KNOTT D. R.
Published: April 2007

Population surveys of plant pathogens can be used to determine the frequencies of particular pathogenicity genes and of changes in frequency with time. Such data can also be used to search for linkage disequilibrium (the non‐random association of alleles) which is of particular interest if it is due to selection. However, a linkage disequilibrium may arise for several other reasons which may be confounded with the effects of selection. Two principal reasons, often overlooked, are the lack of recombination between pathogen genotypes in the population, and the failure to define the boundaries of the sampled population. Examples from the literature illustrate some of these limitations. Recommendations are made for the conduct of surveys for particular objectives.
Distribution of polygalacturonase, total phenolic substances, polyphenol oxidase and peroxidase in rot zones in sweet potato
Authors: ARINZE A. E. , SMITH I. M.
Published: April 2007

Botryodiplodia theobromae causes a spreading rot of sweet potato, while Botrytis cinerea, Phoma exigua var. foveata and Fusarium solani var. coeruleum cause rots of limited extent. Cladosporium cucumerinum does not rot sweet potato tuber tissue. Whichever of these fungi is inoculated into tubers, a zone at the margin of the lesion can be clearly distinguished, from slightly affected but uninfected tissue on one side and infected rotted tissue on the other, by its high content of phenolic substances and polyphenol oxidase and peroxidase activities. Polygalacturonase is present in this zone for spreading B. theobromae lesions but not for the limited lesions caused by the other fungi. Total content of phenolic substances is generally greater in and around limited lesions.
Residual effects of triadimefon in soil on powdery mildew and yield of spring barley
Authors: RAWLINSON C. J. , MUTHYALU G. , CAYLEY G. R.
Published: April 2007

Residual triadimefon (or a breakdown product), from a spray application (2 kg/ha) to field soil in 1978, significantly decreased powdery mildew on spring barley throughout two subsequent growing seasons, with consequent yield increases of 42% in 1980 and 18% in 1981.

In other field experiments triadimefon applied to soil at rates >0.06 kg/ha decreased mildew in barley growing in the soil 11 months later. In these experiments triadimefon, but not benomyl, imazalil or prochloraz (all at 0.5 kg/ha) significantly decreased mildew up to harvest and increased yield by 22%.

Triadimefon incorporated into a loam soil and a peat‐based compost at rates >0.1 ng/g significantly decreased mildew on barley grown in pots under glasshouse conditions. Plants grown in the treated compost at the same time but in isolated pots supplied with filtered moistened air and capillary watering required more triadimefon (>100 ng/g) in soil for significant mildew control.

Despite strong adsorption of triadimefon to soil (Kd 19.4), an active substance appears to remain available for uptake and translocation by barley plants over long periods. The sensitivity of barley mildew to extremely small residues of triadimefon is discussed in relation to the siting of field experiments on mildew control. The implications for widespread commercial use of formulations containing triadimefon are discussed in relation to disease control practice in cereal growing systems.
Computer mapping of records of beet cyst nematode (Heterodera schachtii), 1928–77
Authors: WHITEWAY JENNIE A. , ALPHEY T. J.W. , MATHIAS P. L. , SOUTHEY J.F.
Published: April 2007

Early records of beet cyst nematode (Heterodera schachtii Schmidt) in Britain and the history of regulatory measures to control it are summarized. Data collected between 1928 and 1976 were computer mapped on a 10 km grid scale to illustrate the cumulative distribution of beet cyst nematode in Britain. The distribution of the nematode was compared with that of its principal host, sugar beet. Data collected between 1962 and 1977 in East Anglia were computer mapped on a 1 km grid scale to show the detailed distribution of beet cyst nematode in that area. The advantages of computer‐generated distribution maps over manually produced maps are discussed.
Variation in resistance to Verticillium wilt within seedling populations of some varieties of lucerne (Medicago sativa)
Authors: LATUNDE‐DADA A. O. , LUCAS J. A.
Published: April 2007

Verticillium wilt was assessed in seedling populations of five lucerne varieties: Euver, Maris Kabul, Sabilt, Verneuil and Vertus. Visual assessments of disease severity in Vertus were compared with estimates of fungal biomass obtained by a maceration‐dilution plate method and glucosamine assays. Symptom severity correlated with the amounts of fungus present only at the lower disease ratings. In contrast, direct correlations were obtained between visually assessed disease severities and the chlorophyll contents of plant shoots. Wide variation in disease reaction type were found within populations of all five varieties and disease development was found to differ in two environments with differing temperatures. The significance of these variations is discussed in relation to the genetic background of the host and studies on the biochemical basis of resistance to Verticillium wilt.
Latent infection of winter oilseed rape by Leptosphaeria maculans
Authors: NATHANIELS N. Q. R. , TAYLOR G. S.
Published: April 2007

Plants of oilseed rape, cultivars Primer and Jet Neuf, were grown in a glasshouse and inoculated at G.S. 2.4–2.7 with pycnidiospores or ascospores of Leptosphaeria maculans. The plants were kept for a further 2–4 weeks at 14°C and then transferred, together with uninoculated plants, to a polythene tunnel in winter. The majority of stems of inoculated plants did not have macroscopic symptoms of L. maculans infection 6 weeks after inoculation. Examination of whole mounts of peripheral tissue and transverse sections of fixed and embedded portions of these stems revealed intercellular septate fungal hyphae, often deep in non‐necrotic cortical tissue, in symptomless inoculated plants but not in uninoculated plants. L. maculans was recovered following surface sterilization of adjacent portions of the same stems. When symptomless inoculated plants were transferred to a glasshouse at 18–20°C, cankers soon developed. The significance of these latent mycelial infections to canker development in the field is discussed.
Subterranean clover mottle virus: another virus from Australia with encapsidated viroid‐like RNA
Authors: FRANCKI R. I. B. , RANDLES J. W. , HATTA T. , DAVIES C. , CHU P. W. G. , McLEAN G. D.
Published: April 2007

A new virus, subterranean clover mottle virus (SCMoV) was found at several locations in Western Australia in Trifolium subterraneum L. (subterranean clover) with severe disease symptoms. Paiticles of the virus were shown to share many physical properties with members of the sobemo‐virus group. However, in addition to the single‐stranded RNA of MJ about 1.5 × 106 which is characteristic of sobemoviruses, SCMoV particles also contained circular and linear viroid‐like RNAs of two size classes, one about 400 and the other about 300 nucleotides long. At present it is not clear if the two types of viroid‐like RNAs are components of the same SCMoV strain or of closely related strains of the virus which are able to confect subterranean clover.

SCMoV was shown to be serologically related to lucerne transient streak virus (LTSV). However, the relationship was remote and whereas most high‐titred antisera to LTSV reacted with SCMoV particles, antisera to SCMoV failed to recogaize those of LTSV. Neither SCMoV nor LTSV are serologically related to velvet tobacco mottle virus (VTMoV) or Solanum nodiflorum mottle virus (SNMV). However, particles of all four viruses have many physical and chemical properties in common, including RNA complements consisting of both virus‐like and viroid‐like RNAs. Because of their affinities and unique RNA complements, we suggest that SCMoV, LTSV, VTMoV and SNMV may warrant inclusion in a new taxonomic group.
Fungicides for control of Phragmidium mucronatum on Rosa laxa hort.
Authors: SHATTOCK R. C. , BHATTI M. H. RAHBAR
Published: April 2007

The control of the rust fungus, Phragmidium mucronatum by seven fungicides (benodanil, fenpropimorph, oxycarboxin, thiram, triadimefon, triazbutyl and triforine), was examined both in vivo and in vitro. Oxycarboxin applied at monthly intervals to field‐grown Rosa laxa gave excellent control. Similar results were obtained on detached leaflets using the fungicide as a protectant or eradicant. A benodanil‐resistant isolate was identified in axenic culture.
Measurement of healthy and diseased haulm area for assessing late blight epidemics in potatoes
Authors: ROTEM J. , KRANZ J. , BASHI ESTHER
Published: April 2007

The advantages of assessing disease severity by visual grading and by measuring healthy and diseased plant area were compared in four mild to moderate late blight epidemics during spring and in two severe epidemics during autumn in Israel. Disease progress curves obtained through visual grading showed a continuous increase, but the area of lesions tended to fluctuate during the cropping season and often reached a maximum in plots in which the total amount of foliage was also largest. The healthy haulm area differed with disease intensity and undefined seasonal and cultural influences. The decrease in healthy haulm area was not related to expansion of the blighted area only, but also to the breaking of plants at stem lesions. This phenomenon was especially evident in the warm spring season and was not determined by visual grading of disease severity. Each kind of assessment revealed different features of the epidemics and suited different applications. Visual grading enabled the easiest comparison of epidemic patterns. Lesion areas reflected patterns of inoculum potential, while healthy haulm areas reflected the integrated influences of factors affecting the crop and disease and thus provided useful data for simulating epidemics and for estimating yield losses.
Studies of crop loss in potato blight caused by Phytophthora infestans
Authors: ROTEM J. , BASHI ESTHER , KRANZ J.
Published: April 2007

Relationships between healthy haulm area (HHA) and yield, and between losses of HHA and yield in the potato late blight system, were evaluated in several seasons and fields variously affected by the disease in Israel. The results showed that because of the different yield potential of potatoes cultivated in different conditions, evaluation of crop losses cannot be separated from evaluation of yield potentials of the crop as influenced by environmental and cultural factors.

In one calculation the yield and the HHA in the healthiest plot in each field were equated to 100% and losses in other plots were derived from comparisons with this plot. In such a calculation the relationships of yield loss to HHA loss in all fields and seasons fitted one regression equation, and a high correlation was obtained between both parameters. However, the actual haulm areas and yield weights differed widely from one field to another, even in the healthiest plots. Also, a similar percentage of destroyed haulms sometimes corresponded to different areas of the remaining haulms and to different yields. So no correlation was found between HHA and yields over all fields and seasons. Such a correlation was found only for several plots, variously affected by late blight, in the same field and season and in different fields and seasons yields responded in a different way to increases in HHA.
Identification of barley yellow dwarf virus and cereal aphid Infestations In winter wheat by aerial photography
Authors: GREAVES D. A. , HOOPER A. J. , WALPOLE B. J.
Published: April 2007

In 1976 distinctive patterns were identified on aerial photographs of winter wheat crops in East Anglia. The patterns consisted of numerous dark foci which were found to be associated with sooty moulds (mostly Cladosporium spp.) in the crops. Both green and mature crops were photographed in 1977 and the patterns were matched with crop inspection data. These suggested that barley yellow dwarf virus (BYDV) was the cause of the patterns and that sooty moulds secondarily invaded the infected plants. A different type of focal pattern appeared to be associated with damage caused by aphid feeding. All crops showing the pattern associated with BYDV were sown before 13 October but there was no relationship with sowing date for the crops damaged directly by aphids. Yield losses within foci were estimated by sampling and the total crop areas affected were calculated using an image analysis computer: yield losses were estimated to range from 10% (BYDV) to 2% (aphid feeding). The epidemiology of BYDV is discussed and reasons are suggested for the development and appearance of the foci.
Seasonal variation in the components of partial resistance of seedlings of winter wheat cultivars Maris Huntsman and Maris Ranger to Septoria nodorum
Authors: JEGER M. J. , GRIFFITHS ELLIS , JONES D. GARETH
Published: April 2007

Components of partial resistance of two winter wheat cultivars, Maris Huntsman and Maris Ranger, to Septoria nodorum were measured on potted seedlings exposed in the open during the spring and early summer of 1978. The number of lesions 10 days after inoculation was always greater for Maris Ranger than for Maris Huntsman but the relative differences changed during the season: about 10:1 in March, April and May, but only 3:1 in June. The time from infection to first sporulation (latent period) on Maris Ranger was always shorter, especially in March. The percentage leaf area covered by lesions at the end of the latent period was usually greater on Maris Ranger, but variation in the percentage leaf area necrotic at this time did not follow a distinct seasonal trend, nor did cultivars differ in this respect. Twice as many spores per unit area diseased were produced on Maris Ranger as on Maris Huntsman. Seasonal variation in these components could partially be interpreted in terms of the changing weather conditions to which the plants were exposed.
Purification, serology and physico‐chemical properties of a peanut mottle virus isolate from India*
Authors: RAJESHWARI R. , IIZUKA N. , NOLT B. L. , REDDY D. V. R.
Published: April 2007

A procedure developed for the purification of peanut mottle virus (PMV) isolated from peanuts in India yielded 30–40 mg of virus/kg of plant tissue. Purified virus sedimented as a single component of 151 S. The virus coat protein migrated as a single component in each of two polyacrylamide gel concentrations and had an estimated molecular weight of 34 000 daltons. The molecular weight of the nucleic acid was 3.10 × 106 daltons. In the precipitin ring interface test (PRIT) PMV showed a serological relationship with soybean mosaic virus (SMV). Using the double antibody sandwich form of ELISA, PMV was shown to be distantly related to adzuki bean mosaic (ABMV), amaranthus leaf mottle (ALMV), clover yellow vein (CYVV) viruses and SMV. Immunosorbent electron microscopy (ISEM) showed PMV to be closely related to ABMV, ALMV, CYVV and SMV. In PRIT, ELISA and ISEM tests no specific serological reaction was noted between PMV and antisera to groundnut eye spot, peanut green mosaic, pepper veinal mottle, potato virus Y, sugarcane mosaic and turnip mosaic viruses.
Conidial concentration as an important factor determining the type of prepenetration structures formed by Botrytis cinerea on leaves of French bean (Phaseolus vulgaris)
Authors: VAN DEN HEUVEL J. , WATERREUS LYDIA P.
Published: April 2007

inoculations of primary leaves of French bean (Phaseolus vulgaris) with conidia of Botrytis cinerea, suspended in 0.11 or 0.28 M glucose supplemented with 0.067 M KH2PO4 or 1 mM Na‐ATP as infection stimulants, yielded mostly spreading lesions. Light microscopy revealed that the fungus could develop three types of prepenetration structures from which penetration started: germ tube apices (GA) either non‐swollen or appearing as an appressorium‐like swelling; appressoria (HA) of different forms produced on branched germ tubes or superficial liyphae; and infection cushions (IC). These structures were also formed on leaves of cucumber and tomato.

Penetration from the prepenetration structures was not markedly influenced by the glucose concentration in the inoculum or by host plant species, and varied only slightly with the isolate of B. cinerea. Penetration occurring from GA was greatly enhanced at high conidial concentrations. Low conidial concentrations, however, enhanced penetration starting from HA or IC, penetration from these structures also being dependent on the nature of the stimulant added to the glucose in the inoculum. The high proportion of GA in inocula with a high conidial concentration was associated with a rapid penetration and a rapid formation of spreading lesions.
Sarocladium attenuatum as one of the causes of rice grain spotting in Nigeria
Authors: NGALA G. N.
Published: April 2007

The cause of rice grain spotting (dirty panicles) in Nigeria was studied. The fungus isolated most frequently from discoloured grains was Sarocladium attenuatum. Pathogenicity studies showed that it was capable of causing dirty panicle disease in the absence of insects. Disease severity increased with increasing inoculum. This is the first evidence that S. attenuatum is one of the major causes of dirty panicle disease of rice in Nigeria. Four isolates of S. attenuatum from different locations did not differ significantly in their virulence to three rice cultivars under upland conditions. Inoculations of cultivar BG 6850 at panicle initiation and booting resulted in severe disease and indicated the potential of the fungus to reduce yields. Trials under upland conditions of 69 cultivars of Oryza sativa and 89 of O. glaberrima indicated considerable variation in reactions, dwarf cultivars being generally more susceptible than taller ones.
Metabolic alteration induced by Botrytis allii in two onion cuitivars with different resistances to neck rot
Authors: MAGRO P. , MARCIANO P. , DI LENNA P.
Published: April 2007

Disease index, dry weight loss and leakage of K+ ions in the tissues of two onion cultivars demonstrated that the red cultivar Tropeana had a greater susceptibility to neck rot caused by Botrytis allii than the white cultivar Rovato. The comparison between the cultivars showed that the less susceptible one was characterized by lower polygalacturonase activity (with fewer isoenzyine forms), more rapid accumulation of phenolic compounds in the early stages and faster activation of peroxidase. Polyphenoloxidase was not found in either the healthy or the diseased tissues of the two cultivars. The significance of these findings is discussed in relation to possible host defence mechanisms.
Infection of potato and wheat by isolates of Rhizoctonia solani and R. cerealis
Authors: HOLLINS T. W. , JELLIS G. J. , SCOTT P. R.
Published: April 2007

Isolates of Rhizoctonia were obtained from potato crops with stem canker or black scurf and from cereal crops with sharp eyespot. Those with many nuclei per cell, wide cells, darkening colonies and fast growth were assigned to R. solani; those with two nuclei per cell, narrow cells, pale colonies and slow growth were assigned to R. cerealis. Only R. solani was obtained from potatoes and only R. cerealis from cereals. On young plants in the glasshouse, the isolates of R. solani infected potato substantially but not wheat; R. cerealis infected wheat substantially and potato slightly. This host preference was shown at temperatures between 10 and 25°C in growth rooms. R. solani on potato caused more disease with increasing temperature; no trend with temperature was observed for R. cerealis on wheat.
Effects of fungicide movement between plots in field experiments
Authors: JENKYN J. F. , DYKE G. V. , TODD A. D.
Published: April 2007

Interactions between plots of spring barley which were either unsprayed, or sprayed with triadi mefon or tridemorph to control powdery mildew (Erysiphe graminis f.sp. hordei) were measured in experiments of balanced design in 1978 and 1979. The average amounts of mildew in untreated plots with triadimefon‐reated neighbours on the predominaotly up‐wind side were usually less than half those in untreated plots with tridemorph‐treated neighbours on the up‐wind side. Triadiniefon‐treated plots had most effect on the adjacent sides of their untreated neighbours but there was evidence that their influence extended across the whole widths of these neighbouring plots. Amounts of mildew in tridemorph‐treated plots were increased by untreated neighbours.

Differences in amounts of disease between these plots of spring barley with differently treated neighbours had no significant effects on grain yield. However, in a rando'mized block experiment with spring wheat in 1975 there was evidence that similar inter‐plot interactions caused consider able bias in the yield data. Possible causes of the observed effects are discussed.
The effect of temperature before or after inoculation with Phoma exigua var. foveata on the development of gangrene in potato tubers
Authors: ADAMS M. J. , GRIFFITH R. L.
Published: April 2007

Potato tubers of five cultivais were incubated at five temperatures between 2 and 20°C for 1 month and then inoculated with Phoma exigua var. foveata and stored at 5°C. Larger rots usually developed on tubers previously incubated at the higher temperatures but cultivar differences were greatest where tubers had been incubated at 2°C. In another experiment, rot size was related to the duration of incubation at 20°C before inoculation.

In a series of experiments, tubers were stored at different temperatures after inoculation; other factors (e.g. wound type or r.h.) were also investigated in some of these. Combining the results of all experiments a linear decrease of % wounds infected (logit transformation) with storage temperature was demonstrated. The size of rots was not simply related to temperature, but tended to increase over the range 2–10°C and then stabilized or declined at higher temperatures. Relative humidity treatments of 75% v. 95% did not consistently affect either the incidence of rotting or rot size. The other factors investigated did not usually interact significantly with temperature.

The relevance of the results for resistance testing is discussed and a simple equation relating disease incidence to inoculum levels, type of damage and temperature is proposed.
A whole leaf clearing and staining technique for host specificity studies of rust fungi
Authors: BRUZZESE E. , HASAN S.
Published: April 2007

A whole leaf clearing and staining technique used in specificity studies of rust fungi is described. The method is effective on a large number of plant/rust fungus associations.
Infection of cultivars of onion, leek, garlic and A llium fistulosum by Sclerotium cepivorum
Authors: COLEY‐SMITH J. R. , ESLFR G.
Published: April 2007

In two field experiments on land severely infested with Sclerotium cepivorum largo differences in the incidence of white rot in four Allium species were recorded. There was inuch less disease ° Cultivars of leek than in those of onion, garlic or A. fistulosum. Differences between cultivars within species were either small or absent.
Heat treatment of seed tubers for control of potato blackleg (Erwinia carotovora subsp. atroseptica) and other diseases
Authors: MACKAY J. M. , SHIPTON P. J.
Published: April 2007

The thermal death points of Erwinia carotovora subsp. atroseptica and subsp. carotovora were determined in relation to duration of heat treatment, age of culture and culture medium. No isolates cultured in liquid media survived heating at 53°C for 5 min while those on solid media were killed by heating at 54°C for 10 min. After immersing naturally contaminated potato tubers for 10 min in water at 55°C, Erwinia could not be detected. The same treatment of naturally or artificially contaminated seed tubers gave complete absence of blackleg infection in the field and decreased the amounts of powdery scah(Spongospora subterranea) and black scurf (Rhizoctonia solani) on progeny tubers.
Effect of sharp eyespot (Rhizoctonia cereatis) on yield loss in winter wheat
Authors: CLARKSON J. D. S. , COOK R. J.
Published: April 2007

A single‐shoot assessment method was used at 18 locations in England and Wales from 1976 to 1981 to compare the average yield of large numbers of shoots naturally infected with sharp eysspot (Rhizoctonia cerealis) with the yield of healthy shoots. Slight sharp eyespot infection had. on average, little effect on yield. Moderate infection significantly reduced yield per ear and 1000‐grain weight by 5 and 4% respectively. Severe infection significantly reduced yield per ear and its components, grain number per ear and 1000‐grain weight, by 26, 20 and 11% respectively. Application of the formula y = 0‐05 x1+ 0.26 x2 (where y = percentage yield loss, X1= percentage of moderately Infected shoots and x2= percentage of severely infected shoots) to the results of ADAS winter wheat disease surveys from 1975 to 1982 gave estimated national yieid losses due lo sharp eyespot ranging from less than 0.1 to 0.9%. Survey results indicated that increased disease incidence and associated yield losses are associated with trends towards earlier drilling and, possibly, with increased use of carbendazimgenerating fungicides, combined with more favourable infection weather.
Biological control of Pythium ultimum–induced damping‐off by treating cress seed with the mycoparasite Pythium oligandrum
Authors: AL‐HAMDANI A. M. , LUTCHMEAH R. S. , COOKE R. C.
Published: April 2007

Incorporation of the aggressive mycoparasite Pythium oligandrum into a carboxymethyl cellulose‐based seed coating decreased damping‐off of cress seedlings by Pythium ultimum in both naturally infested soil and artificially infested sand. This effect is attributed to the germination of P. oligandrum oospores on the seed surface with subsequent generation of a protectant mycelium around the seedling.

P. oligandrum oospores survived storage periods of 10—20 weeks at zero relative humidity both on glass slides and within seed coatings. The mycoparasite also survived an 18–month burial in natural soil, probably in the form of oospores.

The implications of these observations for biocontrol of seedling diseases by P. oligandrum are discussed.
Interaction of three lucerne cultivars and eleven English isolates of stem nematode (Ditylenchus dipsaci), ‘lucerne race’
Authors: WHITEHEAD A. G.
Published: April 2007

In pots, 11 English isolates of lucerne race of stem nematode induced hypertrophy in the shoot apices of young lucerne seedlings of the cultivars Europe, Sverre and Vertus. All but one isolate multiplied freely in the shoots of susceptible Europe plants and all isolates multiplied freely in the shoots of supposedly resistant Sverre plants. Some plants of both cultivars appeared resistant cut in the resistant cultivar Vertus, some plants were susceptible to several isolates. There were at least two pathotypes among the 11 nematode isolates used. In selecting for resistance to lucerne s;em nematode, several nematode isolates should be used and the inoculated plants should be grown to maturity.
The effect of continuous rearing of a population of Globodera pallida (Pa 2) on susceptible or partially resistant potatoes
Authors: FORREST J. M. S. , PHILLIPS M. S.
Published: April 2007

A population of the white potato cyst nematode, Globodera pallida, (pathotype Pa 2) was reared for 5 years, in outdoor plots in eastern Scotland, on one susceptible and two partially resistant hybrids bred from Solanum vernei. No selection for increased multiplication rate was apparent. Results of a glasshouse pot test after 5 years showed that selection for a small but significant increase in nematode fecundity had occurred in a population produced for five generations on a clone which was 90% resistant.
A laboratory assay to determine the sensitivity of Rhynchosporium secalis to the fungicide triadimenol
Authors: HOLLOMON D. W.
Published: April 2007

Thirty single‐spore isolates of Rhynchosporium secalis were assayed in vitro to assess relative sensitivities to the fungicide triadimenol. Minimum inhibitory concentrations ranged from 0.2 to 3.2 μg/ml. Isolates collected in 1981 from winter barley crops treated with triadimenol + tuberidazole, triadimefon, or prochloraz were as sensitive as those from untreated crops, and four isolates collected prior to the widespread use of these fungicides were not especially sensitive. All isolates tested in the greenhouse on winter and spring barley were controlled by Baytan (triadimenol and fuberidazole).
Nutritional factors affecting the behaviour of Uromyces viciae‐fabae uredospores on broad bean leaves
Authors: PARKER ANN , BLAKEMAN J. P.
Published: April 2007

Both germination of Uromyces viciae‐fabae uredospores and growth of germ tubes were increased when spores were leached for 12 h at 0.4 ml/min water flow whereas leaching at aflow rate of 2.8 ml/min completely inhibited germination. Washing uredospores once in water caused a reduction in growth of germ tubes and in the numbers of lesions produced on detached leaves of the host, broad bean (Vicia faba).

During germination uredospores from recently formed pustules leaked considerably moreendogenous nutrients on hydration than older uredospores. However, the majority of the leaked compounds were reabsorbed by young uredospores within a few hours. Concentrations ofglucose and leucine equivalents leaked from uredospores and from leaves were compared.

Leaf leachates stimulated growth of uredospore germ tubes to an extent similar to that caused by low concentrations of glucose and amino acids but the addition of pollen inhibited growth of germ tubes. A variety of nutrients caused stimulation of uredospore germination and growth of germ tubes at low concentrations whereas higher concentrations of exogenous nutrients inhibited these processes. The response of uredospores was affected by their age.

Utilization of exogenous 14C‐labelled nutrients by germinating uredospores was very low compared with that of cells of a leaf surface yeast, Cryptococcus sp. Cryptococcus; cells could consume over 90% of the glucose in a solution of glucose and amino acids of concentrations similar to those in leaf leachates before germinating U. viciae‐fabae uredospores had taken up 10%.
The spread oi Erysiphe graminis f. sp. hordei in mixtures of barley varieties
Authors: CHIN K.M. , WOLFE M. S.
Published: April 2007

A model is proposed of mechanisms which might affect the progress of Erysiphe graminis f. sp. hordei in mixtures of barley varieties. Results obtained from two field trials indicate that the efffect of mixtures may be panitioned into three categoriesof the influence of the reduced density of the susceptible plants, the barrier effect of the resistant plants, and the induced resistance due to the non‐virulent pathogen biotypes. In the early stages of plant growth the lower density of susceptible plants accounted for most of the reduction in pathogen development in mixtures. As the epidemic progressed, the barrier and induced resistance effects increased in importance and the total mixture effect was at a maximum mid‐way through epidemic development. Towards the end of the trials the overall mixture effect declined though the influence of induced resistance was at its maximum. The reasons for these changes and their implications for the use of host varietal mixtures in disease control are discussed.

Mixtures also protected the crop against a pathogen other than the target organism.
The incidence of bacterial wilt caused by Xanthomonas campestris pv graminis in pasture grasses in the West of Scotland
Authors: CHANNON A. G. , HISSETT R.
Published: April 2007

Temporary hay and silage fields with a high proportion of perennial or Italian ryegrass (Loliumperenne and L. multiflorum) in Ayrshire, Dumfriesshire, Lanarkshire, West Perthshire and Stirlingshire were surveyed in mid‐summer in 1979 and 1980 for the presence of bacterial wilt. The preliminary survey in 1979 showed that the disease was present in approximately half of the fields in the area. A quantitative survey of 24 fields in 1980 revealed the disease in 71% of these fields at densities between 100 and 380,000 symptom‐bearing tillers per hectare. Most disease was found in ryegrass, but occasionally diseased plants of cocksfoot (Dactylis glomerata) and timothy (Phleum pratense) were found. Tall and meadow fescue (Festuca arundinacea and F. pratensis) were also susceptible to infection in the laboratory (cut leaf and root dip inoculations). Ryegrass cultivars varied in their susceptibility to laboratory inoculation. Cultures of Xanthomanas campestris pv graminis showed no loss of virulence following freeze‐drying and revival.
The inheritance of virulence in Bremia lactucae to match resistance factors 3, 4, 5, 6, 8, 9, 10 and 11 in lettuce (Lactuca sativa)
Authors: MICHELMORE R. W. , NORWOOD J. M. , INGRAM D. S. , CRUTE I. R. , NICHOLSON P.
Published: April 2007

The inheritance of virulence in Bremia lactucae to match specific resistance factors in lettuce was studied by crossing heterothallic isolates of B. lactucae. Avirulence seemed to be dominant to virulence. Although virulence to some R‐factors was inherited at a single locus, thus supporting the hypothesis of a gene‐for‐gene interaction between B. lactucae and L. sativa, inheritance of virulence to other R‐factors was more complex. Two loci seemed to determine virulence to R11; the determinants of virulence to R5, R8 and R10 were either closely linked or allelic; virulence to these loci appeared to be epistatic to virulence to match R9. Virulence to R4 probably involved the interaction of two loci, one of which inhibited avirulence. Determinants of fitness of B. lactucae and possibly genes of minor effect modifying specific virulence factors also segregated. These studies emphasized the potential variability in B. lactucae and implied that isolates should not be assigned to distinct races.
Pathology and taxonomy ofCladosporiumleaf blotch of onion (Allium cepa) and leek (A. porrum)
Authors: KIRK P. M. , CROMPTON J. G.
Published: April 2007

Cross‐inoculations to leek and onion plants using isolates ofCladosporiumfrom leaf blotches on leeks or onions showed that no cross‐infection occurred between isolates and their respective hosts. The species causing leaf blotch on leeks was morphologically distinct from that causing a similar disease on onions and the differences, augmented by the results obtained from the cross‐pathogenicity tests, indicate that two taxa should be recognized at the rank of species. Following an examination of type or authentic material it was concluded that the nameC. allii(Ell. & G. W. Martin) P. M. Kirk & Crompton comb. nov. should apply to the species causing leaf blotch on leeks andC. allii–cepae(Ranojevi) M. B. Ellis to that on onions.
Inhibition of browning, phenoxyacetic acids and phenolic metabolism in potato tuber discs: a model system to study chemicals that control common scab
Authors: BURRELL M. M.
Published: April 2007

The browning of tuber discs was used as a model system to study the effect of substituted phenoxyacetic acids on tuber metabolism. Those substituted phenoxyacetic acids that reduce scab reduced browning but several compounds that do not affect scab also reduced browning. Evidence presented indicates that 3,5‐dichlorophenoxyacetic acid preferentially inhibited phenolic metabolism rather than generally inhibiting the changes that occur after cutting (wounding). It is suggested that the decrease in potato common scab by foliar sprays of 3,5‐D is due to a modified host metabolism which involves inhibition of phenolic biosynthesis but which has no effect on terpenoid biosynthesis.
Studies on metalaxyl‐resistant Phytophthora infestans in potato crops in south‐west Scotland
Authors: HOLMES S. J. I. , CHANNON A. G.
Published: April 2007

In 1981 metalaxyl‐resistant Phytophthora infestans was found in 44% of the 63 crops examined in south‐west Scotland. In 1982, when fungicides containing acylalanines (metalaxyl or ofurace) were not used in the area, it was detected in 15%. Metalaxyl‐resistant strains were found in several crops which had been sprayed only with non‐acylalanine fungicides or had received no fungicidal treatment. In neither year was resistance associated with a significant breakdown of disease control.

Metalaxyl‐resistant isolates of the blight fungus were obtained from tubers from crops in which resistance was detected on the foliage.

In detached leaf experiments, resistant isolates retained their ability to grow on leaves treated with 100 μg/ml of metalaxyl after 52 weekly transfers on untreated leaves, and produced sporangia on leaves treated with up to 2000 μg/ml of metalaxyl or ofurace. In mixtures with sensitive sporangia the proportions remained stable after nine weekly transfers on untreated leaves. However, at concentrations as low as 50 μg/ml, metalaxyl and ofurace reduced the extent of colonization and the numbers of sporangia produced by resistant isolates by an average of 50%.
The use of undisturbed soil cores to study methods of controlling rhizoctonia patch of cereals
Authors: MacNISH G. C.
Published: April 2007

Methods of controlling rhizoctonia patch including cultivation, compaction and fertilizer were investigated using undisturbed soil cores removed from patches. Root rot on wheat seedlings was reduced by deep mixing (5 and 10.5 cm) but not shallow mixing (2.5 cm); deep mixing increased root dry weight from 6 mg per plant in undisturbed soil to 15 and 21 mg respectively. Mixing dry and mixing moist gave similar results. Compaction of undisturbed soil from bulk density 1.45 to 1.74 had no measurable effect, but the same level of compaction on soil mixed to 10.5 cm did cause a significant reduction in root weight. Top dressings of sodium nitrate, ammonium sulphate or urea had no effect on root rot. None of the treatments affected the root growth of seedlings grown in cores from adjacent non‐patch sites.
Assessment of the reaction of some spring barley cultivars to Pyrenophora teres using whole plants, detached leaves and toxin bioassay
Authors: SHARMA H. S. S.
Published: April 2007

Twenty‐one spring barley cultivars were tested for their reaction to Pyrenophora teres using three methods of assessment: inoculation of plants grown outdoors, a detached‐leaf inoculation assay, and bioassay with P. teres toxins produced in vitro. Dram was the most resistant of the cultivars tested; a number of other cultivars including Goldmarker, Egmont and Georgie were also moderately resistant. Akka and Havila were highly susceptible. Good correlation was obtained between results from the three test methods.
Effect of the herbicides EPTC and linuron on cotton diseases caused by Rhizoctonia solani and Fusarium oxysporum f. sp. vasinfectum
Authors: El‐KHADEM M. , PAPAVIZAS G. C.
Published: April 2007

The herbicides EPTC and linuron applied to soil in the field at three different concentrations X2X, 1X, and 2X of recommended dose) decreased post‐emergence, but not pre‐emergence daraping‐off in cotton incited by Rhizoctonia solani. Both herbicides at the two high concentrations significantly reduced wilt incited by Fusarium oxysporum f. sp. vasinfectum. Both herbicides reduced germination of chlamydospores of Fusarium in natural soil, but not in steamed soil. The 2X concentration of EPTC and linuron reduced the saprophytic activity of R. solani in soil. The effects of EPTC and linuron on post‐emergence damping‐off and wilt were attributed Ic their ability to suppress the saprophytic ability of R. solani and chlamydospore germinability ofFusarium in soil, respectively.
Biological control of two‐spotted spider mite (Tetranychus urticae) by Phytoseiulus persimilis on strawberries grown in walk‐in’ plastic tunnels, and a simplified method of spider mite population assessment
Authors: CROSS J.V.
Published: April 2007

During 1980 and 1981, a large‐scale trial of the biological control of two‐spotted spider mite (Tetranychus urticae Koch) on protected strawbenies, using the predatory'mite Phytoseiulus persimilis Athias‐Henriot, was done in 52 ‘walk‐in’ plastic tunnels on a commercial nursery in southern England. Introductions of predatory mites in March or early April at a rate of one per plant were consistently successful. In 1980, when predators had not been introduced the previous year (so enabling large numbers of spider mites to overwinter) peak mite populations were large, causing slight foliar damage in some tunnels before control was achieved. In 1981, only a small residual population of spider mites had survived from the previous year and peak numbers were small; the crop appeared healthy and there was no visible damage by mites. For jdequate control, reintroduction of predators was found to be necessary when CTops were replanted in the summer following soil cultivation and sterilization with methyl bromide.

A population assessment method for two‐spotted spider mite based on counting aggregations of the mites was devised. The mean number of spider mites (all stages) per leaf was found to be approximately the same as the number of leaves with five or more mites present in a 25‐leaf sample.
Laboratory studies on the growth and reproduction ofCladosporium allii‐cepae, the cause of leaf blotch of onion
Authors: HALL K. , KAVANAGH J. A.
Published: April 2007

Cladosporium allii‐cepaeis a slow‐growing pathogen of onion which, on malt extract agar, had a mean colony diameter of 2.7 cm after 28 days at 16°C. Growth and reproduction were greatest on malt onion leaf agar and were poor on synthetic media. The optimum and maximum temperatures for growth were 20 and 28°C, respectively. Sporulation was most abundant at 10–15°C. The fungus grew poorly in buffered Czapek Dox medium at pH 2.2–7.8 and most growth was recorded at pH 6.5. Sporulation was enhanced by exposure of colonies to near ultraviolet light.

A large proportion of spores germinated in distilled water and at 100% r.h. In distilled water germination was greatest at 15–20° and in air at 100% r.h. at 20°C. Of 10 fungicides tested, fentin hydroxide, fentin acetate/maneb and iprodione were the most effective in inhibiting spore germination, growth and reproduction of the fungus.
Rose mosaic disease: symptoms induced in roses by graft inoculation with both prunus necrotic ringspot and apple mosaic viruses
Authors: THOMAS B. J.
Published: April 2007

Symptoms induced in rose by single isolates of the cherry serotype of prunus necrotic ringspot virus (PNRSV) and an apple serotype (apple mosaic virus; ApMV) were characteristically different, and appeared at different times throughout the growing season according to the ambient temperature. These features remained discrete, even in roses infected by both viruses and were shown by immunospecific electron microscopy to be a reliable indication of infection by either virus.

However, cross‐protection between the two isolates was not reciprocal; mixed infections were established only when roses were simultaneously graft‐inoculated with ApMV and PNRSV, or when PNRSV‐infected roses were supei‐infected with ApMV. The significance of these results in relation to the possible natural occurrence of mixed infections in rose or of isolates of intermediate serotype is discussed.