bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies in the mechanism of fungicidal action: V. Non‐metallic and sodium dithiocarbamic acid derivatives
Authors: Parker‐Rhodes A. F.
Published: February 2008

This investigation has as its object the elucidation of the mode of action of dithiocarbamic acid derivatives as fungicides, with die help of the theory of variability, heavy metal salts being dealt with separately.

The experiments were carried out usingMacrospcrium sarcinaeformeas the test organism; the chemical materials used are listed.

Deviations from the experimental and mathematical techniques described in previous papers of this series are explained.

From the results it is inferred that: (a) dithiocarbamates are decomposed by the spores to a greater or lesser degree into amine and carbon disulphide, both being toxic; (b) the amines can be absorbed only in a combined form, which may be the dithiccarbamate itself but is more probably a derivative, possibly an ester; (c) the carbon disulphide probably acts through the mediation of a thiocarbonate; (d) thiuramsulphides act through being decomposed to dithiocarbamates (or their derivatives mentioned above). The monosulphides are largely, and the disulphides slightly, decomposed; in the latter case with reduction.

It is suggested that the greater toxicity of the methyl‐derivatives over all others tested is due to the shortness of the hydrocarbon chain.

It is concluded that the role of the carbon disulphide is chiefly that of a chemical carrier of the amino group, but that, owing to the negative index of variation of the spores to the latter, the carbon disulphide must play an essential part in completing the toxicity.

It is suggested that heavy‐metal dimemyldithiocarbamates may show promise against M. sarcinaeforme, but that others may be effective against other fungi.
The biology of Tribolium destructor Uytt. I. Some effects of fertilization and food factors on fecundity and fertility
Authors: Reynolds J. M.
Published: February 2008

A brief review of recent papers on Tribolium destructor Uytt. is given, and its potential danger as a pest noted. It is shown that 85 % extraction flour leads to about double the fecundity found on 60 or 75% extraction flour. The pre‐oviposition period is shown to be affected by both larval and adult food. Unfertilized females lay eggs, but these are relatively few in number, and are all sterile. Oviposition appears to be stimulated when males associate with unfertilized females, and also when they are removed from fertilized females: the presence of five males seems to lead to greater oviposition than when only one male is present, but the use of small numbers makes these conclusions rather insecure. Although copulation occurs at frequent intervals, females will lay viable eggs for as long as 250 days after the removal of the male. Fertility remains virtually constant throughout life when males are present, and is not increased by the presence of more than one male. Fertility varies inversely with the number of eggs laid. The oviposition period is long and the average curve has a characteristic form, despite considerable daily and individual fluctuations. Oviposition may continue until death or may end some weeks before. Poor conditions tend to lengthen both the oviposition period and the length of life, the latter being greater for males than for females.
The Fungistatic Activity of Ethylenic and Acetylenic Compounds
Authors: GROVE J. F.
Published: February 2008

A series of derivatives of acetylene dicarboxylic, halogenofumaric and related acids have been prepared and their fungistatic activities assessed. The lower halogeno‐ and thiocyanofumarates and acetylene dicarboxylates are highly fungistatic. The mode of action of these compounds is discussed.
BIOASSAY SYSTEMS FOR THE PYRETHRINS II
Authors: PAGEa A. B. P. , BLACKITH R. E.
Published: February 2008

The components of ‘synergistic action’ are reviewed in the light of recent work. It has been shown that for sesamin and isobutylundecylenamide at least, synergistic action remains after physical effects are eliminated. The toxicity of the pyrethrins is increased by a factor of three when up to equimolecular proportions of the above synergists are added, further additions having no effect. It is suggested that a surface complex between synergist and insecticide is formed at the peripheral nerve sheath interfaces, resulting in the reorientation of the pyrethrins molecules to give a more efficient discharge of the resting potential at the interface.
THE SPATIAL DISTRIBUTION OF INSECT‐BORNE PLANT‐VIRUS DISEASES
Authors: GREGORY P. H. , READ D. R.
Published: February 2008

Various workers have proposed formulae to express the spatial distribution of insect‐borne diseases. All the published data examined, as well as the Rothamsted data for the spread of rugose mosaic and leaf‐roll from point sources in potato crops, were fitted as well by the simple empirical expression log I=a + bx as by more complex expressions (I= number of infective punctures at a distance x from the source after a given time, and a and b are constants for any one given set of field conditions). It is suggested that distances should always be given in metres, in order to give comparable results from one investigation to another. In the analysis of data on rugose mosaic and leaf‐roll in'different years, it is shown that a and b vary independently.
THE IMPORTANCE OF THE HOST SPECIES IN DETERMINING THE ACTION OF VIRUS INHIBITORS
Authors: GENDRON YVES , KASSANIS B.
Published: February 2008

Some plant species from which viruses are difficult to transmit to other species by sap inoculation contain substances that inhibit infection. The extent to which infection is inhibited by these substances depends on the species of plants to which inoculations are made and not on the identity of the virus. The inhibitors are largely ineffective in preventing infection of the species which contain them.

Infection of cucumber was less affected than any of the other species by all the inhibitors tested.
THE ABSORPTION, TRANSLOCATION AND BREAKDOWN OF SCHRADAN APPLIED TO LEAVES, USING 32P‐LABELLED MATERIAL
Authors: THOMAS W. D. E. , BENNETT S. H.
Published: February 2008

A study of translocation of 3aP‐labelled schradan in apples, chrysanthemums, broad and runner beans and Coleus, has shown light to be an important factor.

The main direction of translocation is upwards but some schradan does travel downwards. In apples translocation takes place mainly in the phloem but some may take place in xylem particularly upwards.

No major difference has been observed in the ratio translocated/absorbed for Coleus, beans and chrysanthemums but in apples this proportion is greater.

The breakdown of schradan into non‐chloroform extractables varies between the plant species and is far greater in beans than in Coleus.

In chrysanthemums and apples the breakdown appears similar throughout the plant whilst in beans and possibly Coleus the breakdown in the untreated sections is higher.

Concentrations necessary for the kill of certain species of aphides are given.
STUDIES ON PLANT CUTICLE: THE COMPOSITION OF THE CUTICLE OF APPLE LEAVES AND FRUITS
Authors: RICHMOND D. V. , MARTIN J. T.
Published: February 2008

The levels of deposition of the waxy and cutin components of the cuticles of the mature leaves and developing fruits of the Merton Worcester and Cox's Orange Pippin varieties of apple over a period of 4 months are reported. The waxy materials on the leaves remain approximately constant at 20 μg./cm.2, and the cutin at about 100 μg./cm.2 of surface. The waxy and cutin deposits on the fruits increase markedly during the period of development, the wax and oil present on the surface and embedded within the cutin rising to 500 μg./cm.2 and the cutin to a little under 1000 μg./cm.2 of surface. Phenolic and acidic substances in the cuticles of the fruits are determined, and the possibility of their occurrence in surface deposits on the leaves is discussed.

An examination is made of the effect of nutrient deficiency upon the formation of waxy and phenolic substances in the leaves. Nitrogen deficiency in Worcester Pearmain leaves leads to a reduced deposition of waxy materials, and nitrogen, phosphorus and potassium deficiency results in higher contents of phenolic compounds. The separation and nature of the waxy covering on leaves, the effect of environmental conditions on its formation, and its importance in relation to the application of crop protection chemicals are discussed.
Investigations on fungitoxic derivatives of salicylaldehyde
Authors: SMITH R. J. , READ W. H.
Published: February 2008

The eradicative and protective activities of the salicyl‐, 3‐chlorosalicyl‐, 5‐chlorosalicyl‐ and 3,5‐dichlorosalicyl‐anilides and ‐para‐chloroanilides, against cucumber powdery mildew (Erysiphe cichoracearum DC.) and tomato leaf‐mould (Cladosporium fulvum Cke.) have been determined by in vivo glasshouse tests on pot plants. No compound was more effective than salicylanilide against either disease at a non‐phytotoxic concentration.

In addition, the in vitro fungitoxic activities of these compounds against spores of tomato leaf‐mould have been determined; several were considerably more active than salicylanilide.
Potato haulm resistance to Phytophthora infestans
Authors: LAPWOOD D. H.
Published: February 2008

The slower increase of blight (Phytophthora infestans) (Mont.) de Bary in field plots of Majestic (MJ) and Arran Viking (AV) than of Up‐to‐Date (UD) and King Edward (KE) potatoes seems more closely related to the production of fewer spores than to greater resistance of leaves to infection.

Sporing was decreased, not by differences in generation time, but because fewer spores were produced per lesion on MJ and AV, especially when lesions were small (young). Infected cells of AV died more rapidly than cells of UD and KE and so left a smaller area of sporing tissue in young lesions. Although the fungus advanced at much the same rate in leaves of the four varieties, sporing annuli were narrower on older (larger) lesions on AV unless high relative humidity persisted continuously. Sporangiophores and sporangia were formed more rapidly on UD than AV when non‐sporing lesions were transferred to high humidity. The ecoclimate of a crop of UD did not increase the sporulation on infected leaves of AV exposed within it, but sporulation was slightly decreased when infected UD leaves were exposed in a crop of AV. Generally KE behaved like UD, with MJ intermediate between these and AV.

The lower leaf‐surface was more susceptible to infection than the upper. Differences in susceptibility of lamina between varieties were inconsistent. MJ and AV were more resistant than UD and KE when inoculated in leaf axils.
The depletion of insecticides on sheep fleece
Authors: HARRISON I. R. , JOHNSON C. A.
Published: February 2008

Sheep have been dipped in various concentrations of aldrin and dieldrin and the rate of loss of insecticide on the wool has been determined using a biological assay method. In one experiment with aldrin, the biological assay method was confirmed by chemical analysis. Depletion is rapid immediately following dipping for a period of 2–4 weeks, after this it is much slower. It has been shown that when dipping is carried out at the normal time, i.e. May to June, the chemical persists for a period of 3–4 months. When sheep are dipped in late July and August, however, the period of protection is much greater. The distribution of insecticide over the fleece has been examined; the area with least pick‐up of insecticide is in the tail region where the wool is coarse. Weather and rate of wool growth could not be correlated with rate of insecticide loss.
Studies on the fungitoxicity of captan
Authors: RICHMOND D.V. , SOMERS E.
Published: February 2008

The solubility, olelyl alcohol‐water partition coefficient, fungistatic activity to Alternaria tenuis and Neurospora crassa, and spore uptake by N. crassa of captan and six analogues have been determined. The analogues were structurally similar, possessing a phthalimide moiety and ‐NSCCl3 group, but differed in their lipid solubility. This variation in lipid solubility was not reflected in either fungitoxicity or spore uptake except for the two compounds with the lowest partition coefficients, N‐(trichloromethylthio)‐3,6‐endoxohexahydrophthalimide and N‐(trichloromethylthio)‐4,5‐epoxyhexahydrophthalimide. The high levels of uptake of the compounds required to inhibit spore germination and the high values of their estimated thermodynamic activities suggest unspecific mechanisms of toxicity and possible detoxication of the fungicides before they reach vital cellular sites.
Yellow‐net virus of sugar beet
Authors: WATSON MARION
Published: February 2008

A virus found in sugar beet in England causes similar symptoms to the Californian virus called yellow‐net (YNV) by Sylvester (1948). It persists in the feeding vectors for at least 7 days. The minimum feeding time needed for aphids to acquire virus from infected leaves was 6 hr. and the minimum needed to acquire and transmit was 12 hr., but ability to transmit was greatly increased by increasing feeding time up to 2 days on infected and 24 hr. on healthy plants. These properties agree with those of the American virus. Experiments using different aphid numbers feeding for constant times suggested that susceptibility of sugar beet to infection varies and this may account for some of the delay in infecting healthy plants.

YNV was accompanied in beet by a second virus, yellow‐net mild yellows (YNMYV). YNMYV did not infect Nicotiana clevelandi Gray or N. bidlovia, which are susceptible to YNV, but from which YNV could not be recovered by aphids. Neither virus is transmissible by inoculation with sap from infected plants. It is suggested that YNMYV is a ‘carrier’ virus, without which YNV cannot be transmitted. Possibly it combines with YNV to form an aphid‐transmissible combination, but it may merely help YNV to invade sugar beet.

YNMYV causes similar symptoms and has similar properties and host range to other viruses that cause mild yellowing diseases of sugar beet, including avirulent strains of beet yellows virus (BYV), Irish mild yellows (IMSV) and ‘41 yellows’ (41 YV). No such virus has been reported associated with YNV in America, and possibly it is peculiar to the British isolate.
Studies on plant cuticle
Authors: BAKER E. A. , BATT R. F. , MARTIN J. T.
Published: February 2008

Work is described on the isolation of wax‐free cuticular membranes by enzymic and chemical treatment, and on the products of hydrolysis of the membranes. Fatty acids in the approximate range C12 to C12 are associated with hydroxylated fatty acids in the apple cutin complex. Methods for the determination of cutin in cuticular membranes are discussed.
Studies on plant cuticle
Authors: SILVA FERNANDES A. M. S.
Published: February 2008

A standardized test of permeability to aqueous solutions is described. No diffusion of copper from solutions of copper acetate or sulphate or of mercury from a solution of phenylmercuric acetate occurs through stomata‐free leaf membranes containing 0.1 mg./cm.2 or more of cutin, but diffusion occurs through membranes containing stomata. Wax is an important barrier to the penetration of mercury through cuticular discs of apple fruits, but the effect of the wax depends upon its composition. Sorption of mercury by the discs is increased by an increase in the percentage content of esters in the wax, by a rise in temperature or in the presence of wetter.
Greenhouse evaluation of chemicals for control of powdery mildews
Authors: KIRBY A. H. M. , FRICK E. L. , GRATWICK M.
Published: February 2008

2,6‐Dinitro‐4‐s‐alkylphenols were found to protect apple foliage against powdery mildew more effectively than isomeric 2,4‐dinitro‐6‐s‐alkylphenols; regression lines for four para‐alkyl compounds were of similar slope but were much steeper than those for two ortho‐alkyl compounds (including dinocap phenol). The ED50 and ED95 values of the most active compound studied, 2,6‐dinitro‐4‐(I‐ethylhexyl)phenol, were in the ratios to those of dinocap phenol of 1:13 and 1:125, respectively, and the protective action of this compound was greater than the curative, especially at the higher ED values. Protection of barley seedlings against powdery mildew was also greater by I‐ethyl‐ or I‐propyl‐alkyl compounds than by I‐methylalkyl or n‐alkyl isomers.

For phytotoxic and acaricidal actions, the ortho‐alkyl isomers are more effective than para‐alkyl. Nevertheless, the acaricidal activity of dinocap phenol is exceeded by that of the isomeric 2,4‐dinitro‐6‐(I‐ethylhexyl) phenol.

The control of these powdery mildew diseases given by commercial products, supposed to be based on dinocap, cannot be accounted for by the activity shown for dinocap phenol. It can, however, be accounted for by the activities of 2,6‐dinitro‐4‐(I‐ethylhexyl)‐ and ‐(I‐propylpentyl)‐phenols, now known to be present in commercial products in larger amounts than dinocap phenol itself. The phytotoxic and acaricidal actions of such products, however, are mainly due to the ortho‐octyldinitrophenols present; in view of the small proportion that is dinocap phenol, the acaricidal activity is likely to be due almost entirely to the other ortho‐octyl isomers.

It is suggested that the common name dinocap be retained for the mixture of dinitrooctylphenols now known to be present in commercial products, and that the two main groups be differentiated as 2,4‐dinocap and 2,6‐dinocap, respectively. The advantages for powdery mildew control of a product based on 2,6‐dinocap are discussed.
The redistribution of fungicides on plants
Authors: HISLOP E. C.
Published: February 2008

In field trials amounts of soluble copper were found in rain water collected form apple trees sprayed with copper fungicides, but the copper was relatively non‐toxic. The solution of copper did not appear to be correlated with the number of micro‐organisms on the leaves. Rain washings phate. Some evidence for beneficial redistribution by solution is presented.

By contrast, in a greenhouse experiment small amounts of copper were washed by very light rain from coffee seedlings sprayed with copper oxychloride and Bordeaux mixture. The soluble fraction of these washings was generally small and did not vary with ageing of the deposit up to 32 days. There was no changes in the toxicity of the washings from deposits aged up to 32 days.

Under static laboratory conditions more copper was usually solubilized form standardized deposits of Bordeaux mixture, copper oxychloride, and cuprous oxide on leaves than on glass. The amount of copper solubilized varied with the leaf used, the nature of the deposit, the presence of adjuvants and the length of time water was left in contact with the deposit. Deposits of Bordeaux mixture and Bordeaux mixture was equally toxic on a leaf surface which caused solution and one which did not. Soluble copper extracts leaves were less toxic than equivalent quantities of copper supplied as copper sulphate.
Studies on plant cuticle
Authors: BAKER E. A. , MARTIN J. T.
Published: February 2008

The cuticles of plants of the Saxifragaceae, Rosaceae and Leguminosae are compared by chemical methods. Wide differences occur in the deposits of surface wax and cuticular membrane even within species of one genus. The relative proportions of four hydroxy‐fatty acids in the cutin acids of plants of the families are assessed and the value of cutin analysis as a taxonomic criterion is discussed.
Phenylazothioformamide, the active principle in the fungitoxic action of 1‐phenylthiosemicarbazide
Authors: SIJPESTEIJN A. KAARS , PLUIJGERS C. W. , VERLOOP A. , TEMPEL A.
Published: February 2008

Laboratory trials using Aspergillus niger indicate that the antifungal effect of 1‐phenylthiosemicarbazide is based upon its conversion into an oxidation product, phenylazothioformamide. This conversion takes place much more slowly at pH 5 than at pH 7 and is completely prevented by the reducing agent sodium thioglycollate. Both acidity of the medium and the presence of reducing agents lower the fungitoxicity of 1‐phenylthiosemicarbazide.
Parsnip mosaic virus, a new member of the potato virus Y group
Authors: MURANT A. F. , MUNTHE T. , GOOLD R. A.
Published: February 2008

Parsnip mosaic virus (PMV) occurs commonly in parsnip in Britain and is transmitted after acquisition access periods of 2–5 min by the aphids Cavariella aegopodii, C. theobaldi and Myzus persicae. It was transmitted by manual inoculation of sap, infecting parsnip, chervil, coriander and carrot plants systemically, and causing local lesions without subsequent systemic infection in eight Chenopodium spp., Spinacia oleracea, Gomphrena globosa, and Toreniafournieri. It lost infectivity in Chenopodium quinoa sap after dilution to 10‐3–10‐4, heating for 10 min at 55–58 °C, or storage at room temperature for 7–10 days. Preparations partially purified by n‐butanol or chloroform clarification, followed by acid precipitation and/or chromatography on columns of 2% agarose beads, contained filamentous particles, many of which were aggregated or fragmented. Preparations made with chloroform and without acid precipitation contained unaggregated particles of 755 nm normal length, with a sedimentation coefficient of 149 S. PMV did not react with antisera to any of fourteen other viruses with filamentous particles. The present cryptogram for PMV is */*: */*:E/E:S/Ap.
Transmission of rayado fino virus of maize (Zea mays) by Dalbulus tnaidis
Authors: GÁMEZ RODRIGO
Published: February 2008

Rayado fino virus (RFV) of maize (Zea mays) was transmitted by the leaf‐hopper Dalbulus maidis in a manner characteristic of viruses that multiply in their insect vectors. Individual insects fed on infected plants transmitted the virus after incubation periods of 8–22 days; males had shorter incubation periods than females but died sooner. Insects retained infectivity for 1–20 days. Transmission by most insects was intermittent. Inoculativity by D. maidis decreased with time, but the virus was recovered from insects that had lost their ability to transmit. Extracts of plants infected with RFV and viruliferous insects were injected into healthy insects, which became viruli‐ferous. Infectivity of the extracts was not affected by tetracycline hydrochloride (Achromycin). D. maidis was able to transmit simultaneously RFV and the corn stunt agent. Other than maize, Teosinte (Euchlaena mexicana) was the only plant susceptible to the virus, among a number of species of Gramineae tested.
Quantitative relationships between infection by the hop downy mildew pathogen, Pseudoperonospora hutnuli, and weather and inoculum factors
Authors: ROYLE D. J.
Published: February 2008

Experiments are described in which successive groups of healthy, susceptible, potted hop‐plants were exposed, each 24 h, to the weather and to sources of Pseudoperonospora kumuli inoculum in an unsprayed hop garden for 48 h periods during May and June in 1969, 1970 and 1971. The infection which arose after standardized incubation in isolation was measured and then related, both by inspection and by multiple regression analysis, to the conditions during exposure.

Severe infection could be associated with certain sequences of events in which rain contributed substantially to plant wetness; relatively light or no infection developed when dew provided the wetness of a period. Infection was markedly correlated with the occurrence of infection periods, as defined from earlier growth‐room studies, especially when dew‐wetness was omitted.

The regression analysis showed that, in all years, infection was highly correlated with variables reflecting wet conditions. It was inconsistently correlated with vapour pressure deficit (VPD) and with sunshine, not at all with temperature, and with airborne spore concentration only in the combined years. The spore catches of a funnel trap, used in 1971, which depended upon rain varied closely with infection. R2 values for multiple regression equations indicated that, in the years separately and together, well over 70% of the variation in infection could be explained by the environmental variables and, in 1971, almost 90%. Variables (temperature, VPD, airborne spores) which singly were poorly correlated with infection often significantly improved regression equations which were based on variables expressing wetness. When prediction of each year's infection levels was attempted using selected regression equations calculated from data of the other 2 years there was, in general, very good agreement between measured and estimated values. The best predictions were given by an equation utilizing rain‐wetness duration, rainfall amount and airborne spore concentration while an equation based solely on relative humidity and rainfall was only slightly inferior.

The results are discussed in relation to the possible value of the regression models for short‐term forecasting of hop downy mildew.
Infection of potato tubers with soft rot bacteria
Authors: WEBB L. E. , WOOD R. K. S.
Published: February 2008

Stolons attached to developing potato tubers were inoculated with the soft rot bacterium Erwinia carotovora var. atroseptica.

Almost all the stolons rotted, but soft rots developed in less than 10% of new tubers; the bacterium was isolated later from these tubers. No rots developed in the other tubers but the bacterium was later isolated from about half of them. It could not be isolated from tubers attached to inoculated stolons where the rot on them did not extend to the tuber or from tubers attached to stolons that were not inoculated though many of these rotted.

The bacterium was reisolated from almost all arrested lesions in tubers inoculated 8 month earlier with E. carotovora var. atroseptica. Blackleg did not develop from plants grown fom these tubers under various soil conditions. It did develop in a large proportion of plants from tubers inoculated shortly before planting and grown in cool, wet soil.

Less than 1% blackleg developed in plants grown from tubers from plants with blackleg or from plants immediately adjacent.

The presence of pectolytic bacteria and E. caratovora var. atroseptica in seed and new tubers was investigated during June, July and August. Although E. caratovora var. atroseptica was obtained from c. 40% tubers, only c. 0·3% of c. 8400 plants developed blackleg. The bacterium was isolated from only three of 160 new tubers sampled during the summer.
Effect of fungicides on the mycelial growth of soft fruit spoilage fungi
Authors: COHEN E. , DENNIS C.
Published: February 2008

The in vitro activity of a range of fungicides was tested on strains of Botrytis cinerea, Mucor mucedo, Rhizopus stolonifer, and R. sexualis. Di‐chlofluanid and dichloran were more active than the other fungicides against all of the strains of B. cinerea, while dichloran, dichlorophen and the dithiocarbamate fungicides were the most active against the Rhizopus species. Only dichlorophen and thiram markedly inhibited the growth of M. mucedo.
Studies on the possibility of increasing resistance to cocoa swollen‐shoot virus by breeding
Authors: KENTEN R. H. , LOCKWOOD G.
Published: February 2008

In tests using seed, the resistance of cocoa progenies to primary infection with cocoa swollen‐shoot virus by mealybugs was stable to inoculum pressure and effective against several virus strains. The results suggested that the resistance would be effective throughout the cocoa growing areas of Ghana. There were indications that resistance factors from different cocoa populations could be accumulated to give progenies of higher resistance than presently available.
Preliminary glasshouse and field tests of soil partial sterilants for clubroot control
Authors: BUCZACKI S. T. , WHITE J. G.
Published: February 2008

Experiments were made on field plots and in individually dosed pots to investigate the effects of ten soil partial sterilants on percentage infection of cabbage with clubroot. Additionally, cores of naturally‐infested soil or samples of artificially infested and buried soil removed from some treated plots were also sown with cabbage in a glasshouse and the seedlings then assayed for the presence of clubroot. There was evidence that the partial sterilants were optimally effective at different depths. Dowfume M.C.2 and Basamid having the unique properties of effectiveness at deep and shallow horizons of the soil respectively. Chloropicrin at 60 ml/m2 and Dowfume M.C.2 at 98 g/m2 were the most effective partial sterilants in controlling clubroot while Basamid and Telone were also considered to merit further testing. All other partial sterilants reduced percentage infection in pot experiments and field crops to varying extents although formaldehyde was least effective.
Mutational tolerance to carbendazim in Botrytis cinerea
Authors: GEESON J. D.
Published: February 2008

No spontaneous mutation for tolerance to the fungicide carbendazim was detected in C. 108 conidia from each of eight carbendazim‐sensitive field isolates of Botrytis cinerea. Conidia of B. cinerea were highly insensitive to u.v.‐irradiation, although after severe irradiation treatments mutant strains showing the same levels of tolerance as two groups of carbendazim‐tolerant field isolates were selected at frequencies of between 10‐9 and 10‐6 of survivors. Mutants with low levels of tolerance (ED50 > 10 μg ml‐1 carbendazim; ‘partially‐tolerant’) were selected from irradiated conidia obtained from sensitive field isolates and a further series of mutants capable of growth on 10 000 μg ml‐1 carbendazim (‘fully‐tolerant’) were selected from irradiated conidia from either partially‐tolerant mutants or from partially‐tolerant field isolates. Both mutation steps were confirmed in similar experiments in which tolerance to an unrelated fungicide, 2, 6‐dichloro‐4‐nitroaniline (DCNA), was incorporated as a genetic marker in the parent strains.
Incomplete specific resistance to Bremia lactucae in lettuce
Authors: Crute I. R. , Norwood Judith M.
Published: February 2008

The complementary pair of dominant genes. Dm 7/1 and Dm 7/2 and the single dominant gene Dm 6 for specific resistance in Bremia lactucae in lettuce, condition incomplete resistance to non‐virulent (incompatible) isolates of B. lactucae in both seedling and mature tissue. This incomplete resistance is characterised by a marked reduction in spotophore production compared with fully susceptible (compatible) race/cultivar combinations and by macroscopically visible hypersenstive cell necrosis. The incomplete resistance. In seedling the resistance conditioned by genes giving more complete resistance. In seedlings the resistance conditioned by genes Dm 7/1 and 7/2 was incomplete in outdoor ‘crisp’ lettuce genotypes and the resistance conditioned by gene Dm 6 was only completely expressed at 20°C.
Distribution of nematicides in soil and its influence on control of cyst‐nematodes (Globodera and Heterodera spp.)
Authors: BROMILOW R. H. , LORD K. A.
Published: February 2008

Incorporation of nematicide granules by L‐bladed rotavator gave more reliable yield increases and better control of cyst‐nematode increase than incorporation by Roterra (rotary harrow), and measurements of granule distribution suggested that this could be attributed to the deeper distributions of granules achieved by rotavation. Pot tests showed that the variability of the granule distribution in the field is unlikely to limit the efficacy of oxamyl, but may limit the efficacy of fenamiphos, and these differences can be attributed to the greater mobility of oxamyl in soil.
Epidemiology and strategy for the control of halo‐blight of beans
Authors: TAYLOR J. D. , PHELPS KATHLEEN , DUDLEY C. L.
Published: February 2008

A halo‐blight epidemic model based on the equation of Van der Plank (1963) is described. The model has been used to determine tolerance levels for seed infection and to compare the effectiveness of chemical control measures based on foliar sprays and seed treatments.

Reduction of primary inoculum, derived from infected seed, by disease exclusion through seed testing, or by chemical seed treatment will give effective disease control under British conditions (i.e. with an expected apparent infection rate (r) of 0.15 per infected plant per day). Under climatic conditions more favourable for the disease where higher r values would occur, control treatments directed against primary inoculum only would be less effective. Under such conditions, it is predicted that chemical sprays, which have no effect on primary inoculum but cause a reduction in the rate of disease increase, would be more effective. The most effective disease control, however, would be a combination of treatments.
The distribution of poplar mosaic virus in hybrid poplars and virus detection by ELISA
Authors: COOPER J. I. , EDWARDS MARY LOU
Published: February 2008

Purified poplar mosaic virus (PMV) at a concentration of 8 ng/ml was readily detected by enzyme‐linked immunosorbent assay (ELISA). Bioassay in Nicotiana megalosiphon was more sensitive (detecting 1–4 ng/ml) and latex flocculation less sensitive (c. 25 ng/ml) than ELISA assays. While the foliar sap of fresh, naturally‐infected poplars (e.g. Populus. euramericana cv. Robusta) was not infective at dilutions greater than 2 . 10–2, ELISA easily detected PMV antigen when sap was diluted 4 . 10–3 in buffer or when one part of infected tissue was triturated with 99 parts healthy leaf. Furthermore, although sap from poplar leaves stored at ‐20 °C for 6 months was not infective, PMV was still detectable in ELISA tests. PMV antigen in poplar leaves was not all pelleted after centrifugation for 2.5 h at 130 000 g yet parallel tests using unbuffered sap from systemically infected Nicotiana megalosiphon foliage showed that infectivity was restricted to the pellet. In poplar foliage, the concentration of PMV antigen was generally greatest where symptoms were most obvious; least antigen was detected in the overwintering leaves located at the bases of long shoots. In winter, when root and inner bark tissue in the trunk was an erratic source of PMV, the virus was readily detected in buds, the concentration being greatest in the bases, including the meristem, of terminal buds.

Propagation from single node cuttings of P. euramericana cv. Regenerata allowed the selection of clones that consistently showed either ‘severe’ or ‘mild’ foliar symptoms. The associated virus isolates also infected another poplar clone causing symptoms characteristic of their source. ELISA consistently detected less PMV antigen in field‐grown cv. Regenerata than in cv. Robusta foliage, but this was reversed when the associated virus isolates were propagated in Nicotiana glutinosa at 24 °C.

During 6 yr, 21 out of 127 poplars at a site in Western England, became infected with PMV. By contrast, in Eastern England, none of 46 were infected. The aphids Pterocomma populea and Myzus persicae did not transmit PMV.
Variation in monoculture and in mixture for grain yield and other characters in spring barley
Authors: VALENTINE J.
Published: February 2008

Fourteen north‐west European spring barley cultivars were grown alone or in binary mixtures sampled according to a partial diallel scheme. On the basis of the association between cultivars in mixture and monoculture, three groups of characters were distinguished. Group A characters, plant height, ear weight/tiller, grain yield/tiller, number of grains/tiller and 1000‐grain weight, showed strong positive associations between performance in monoculture and mixture. Group B characters, number of tillers/plant and harvest index showed incomplete positive associations, while for group C characters, dry matter/plant, ear weight/plant, grain yield/plant and number of grains/plant, associations were weak or non‐existent. Compound characters in group C showed less genetic variation in monoculture and lower general competitive effects in mixture than component characters in groups A or B.

These results clearly indicate that while selection for grain yield and other characters on a per plant basis (group C characters) is confounded by intergenotypic competition, characters such as the yield components number of grains/tiller and 1000‐grain weight (group A characters) are hardly affected in this range of cultivars. Selection for opposing group A characters may start in the F2 generation, while any selection for group B and C characters should be delayed until later generations.

The merits of indirect selection for yield using visual assessment of yield components are discussed.

Separate analyses obtained by the inclusion of spring wheat cv. Timmo in monoculture and in the set of mixtures indicated that the use of spring wheat plants to minimise intergenotypic competition ranges from superfluous (group A characters) to useless (group C characters).

A large degree of mixture advantage and the lack of complementary dominance and suppression between competitor and associate was attributed to the relatively low density of plants in the experiment which, though suitable for single plant selection, is not typical of normal seed rates for cropping.
The effects of mixing barley cultivars on incidence of powdery mildew (Erysighe graminis) and on yield in Northern Ireland
Authors: WHITE ETHEL M.
Published: February 2008

Sowing mixtures of cereal cultivars has been advocated as a strategy to reduce yield loss resulting from disease in the short term and to delay adaptive changes amongst the races in the pathogen population in the long term. Six spring barley cultivars, Midas, Athos, Sundance, Mazurka, Goldmarker and Golden Promise, and seven selected paired mixtures of these, combined according to the compatibility of their resistance genes, were grown in field experiments during 3 yr. Where natural infection by powdery mildew (Erysiphe graminis) was severe, as in 1980, levels of infection in the mixtures were less than the mean of the components in monoculture. Yields were generally increased by combining cultivars; mixtures of Athos with Midas and with Mazurka gave yields over 8% higher than the mean yields of their components but these apparent synergistic effects could not be associated with reductions in levels of mildew infection.
Associations between weather factors and the spring migration of the damson‐hop aphid, Phorodon humuli
Authors: THOMAS G. G. , GOLDWIN G. K. , TATCHELL G. M.
Published: February 2008

The dates of the beginning and end of the spring migration of P. humuli, as monitored by the Rothamsted Insect Survey suction traps at Wye College and Rosemaund Experimental Husbandry Farm, were linearly regressed on temperature, rainfall and sunshine for varying periods. The beginning of migration at both sites was associated with temperature in late March and early April, and periods of rainfall in mid‐January and mid‐April, while the end of migration was associated with temperature and sunshine in mid‐ and late June, and with mid‐January rainfall. These regression equations were used to predict the timing of the migration in 1980 and 1981, those for mean maximum temperature predicting most accurately both the beginning and end of migration. The use of multiple regression equations did not increase the accuracy of predictions. The critical periods of weather are discussed in the context of the life‐cycle of the aphid.
Bioassay of metalaxyl in plant tissue
Authors: WYNN E. C. , CRUTE I. R.
Published: February 2008

A method for determining the concentration of metalaxyl in methanolic extracts of plant tissue is described. Extracts were applied to filter papers in Petri dishes and covered with small volumes of lima bean agar. The growth of an isolate of Pythium ultimum sensitive to metalaxyl was related to the quantity of fungicide applied. The bioassay could detect quantities as low as 0·025 μg in the filter paper, a sensitivity which was confirmed by using 14C‐metalaxyl. Whilst untreated extracts of lettuce and brassicas were not fungitoxic to the isolate of P. ultimum employed, this was not the case with tobacco and grape‐vine. Hence alternative test organisms may be required before the method can be generally applied to all species.
Effects of environment and host on vector biology and incidence of two whitefly‐spread diseases of legumes in Nigeria
Authors: VETTEN H. J. , ALLEN D. J.
Published: February 2008

Seasonal periodicity in the incidence of cowpea golden mosaic (CGM) and lima bean golden mosaic (LBGM), two whitefly‐spread virus‐like diseases, corresponded closely with fluctuations in population density of their vector, Bemisia tabaci, at two contrasting sites in southern Nigeria. Peak catches of the vector followed the onset of rains after very high temperatures during the dry season; populations declined abruptly with continuous, heavy rainfall. At Onne, B. tabaci infested legumes at emergence and remained and reproduced on them but at Ibadan infestation was delayed and there was no evidence of reproduction on legumes.

B. tabaci preferred LBGM‐susceptible lima beans (Phaseolus lunatus) to resistant ones and more pupae of B. tabaci occurred on CGM‐susceptible cowpea (Vigna unguiculata) cultivars than on resistant ones but these observations did not relate to the yellow‐sensitivity of whiteflies. Resistance to CGM in cowpea, and to LBGM in lima bean, was identified amongst germplasm exposed to natural infection. Resistance was, in each case, associated with lower disease incidence, slower spread and milder expression of symptoms relative to susceptible cultivars. Vector non‐preference for resistant cultivars may have contributed to reduced secondary spread.
Pyrazophos: a fungicide with insecticidal properties including activity against chrysanthemum leaf miner (Phytomyza syngenesiae) (Agromyzidae)
Authors: LEDIEU M. S. , HELYER N. L.
Published: February 2008

Pyrazophos was more effective than dioxanthion against chrysanthemum leaf miner (Phytomyza syngenesiae Hardy) when applied as a mist onto bed‐grown plants irrespective of the stage of development of the pest. When pyrazophos was applied at the feeding mark stage no eggs developed but when it was applied at the young mine, mature mine or pupal stages 3–5%, 3‐1% or 45‐5% reached adulthood. Pyrazophos applied every 17‐5 days kept damage levels acceptably low.

The potential of pyrazophos within an integrated control programme for chrysanthemum is discussed.
A bacterial leaf spot of Protea cynaroides (king protea)
Authors: WIMALAJEEWA D. L. S. , HAYWARD A. C. , GREENHALGH F. C.
Published: February 2008

The etiology of a new leaf spot disease on king protea was investigated. The causal organism was a Gram negative rod‐shaped bacterium with between two and seven flagella. On the basis of cultural, biochemical and physiological characters it was identified as a pathovar of Pseudomonas syringae.
Assessment of the losses caused to potatoes by the potato cyst nematodes, Globodera rostochiensis and G. pallida
Authors: BROWN E. B. , SYKES G. B.
Published: February 2008

Nine field trials were carried out from 1967 to 1973 on sandy loam soils in Staffordshire and Worcestershire to study the relationship between potato yield and numbers of potato cyst nematodes (Globodera spp.).

Three (probably five) of these trial sites appeared to be infested with G. rostochiensis only, whereas both species occurred on the remaining four sites which grew the resistant variety, Maris Piper. Although mixtures of the two species occurred on some plots they tended to have different distributions within each trial site.

The results from this work have been analysed, together with those from earlier work in the Eastern Counties on peat and silt soils, over two population density ranges, 0–40 eggs/g (5 sites) and 0–160 eggs/g (16 sites). There is no evidence of any difference in the regression of yield on eggs/g amongst the five sites in the lower range (b =–0.90 + 0.11) nor amongst 15 of the 16 sites in the higher range (b = ‐0–40 ± 0–02). Analysis of 10 sites with sufficient data in the 40–160 eggs/g range gave b = ‐0.24 ± 0.06. Thus the regression lines are essentially parallel for each of the two ranges, covering several potato varieties, soil textures and different potential yields and suggest that the varieties used are equally tolerant. The losses are 6.25 t/ha/20 eggs/g for the 0.40 eggs/g range, 1.67 t/ha/20 eggs/g for the 40–160 eggs/g range, and 2.75 t/ha/20 eggs/g as a mean for the whole range. A maximum loss of 22 t/ha is indicated.

Peat soils are less dense than mineral soils but there was no need for adjustment in nematode counts. Losses caused by potato cyst nematodes are better expressed as actual yield losses rather than as percentage decreases.
Effect of soil cultivation and anaerobiosis on cavity spot of carrots
Authors: PERRY D. A.
Published: February 2008

Cultivating between rows and narrow beds of carrots reduced the severity of cavity spot in one year and reduced the incidence and severity in single rows in a second year on land where the disorder was endemic. Growing carrots on ridges initially reduced symptoms more than inter‐row cultivation.

Soluble carbohydrates leached from carrot rootsin vitroand the quantities increased when anaerobic conditions were imposed. Untreated and cell‐free extracts of soil suspensions amended with 1% glucose and incubated anaerobically applied to carrots in the laboratory caused the outer layers of the secondary phloem to collapse resembling a cavity spot lesion. Unamended and fresh soil solutions had no effect.
Emergence of cabbage seedlots in field soils with different cropping histories
Authors: WHITE J. G.
Published: February 2008

In three non‐sterilised soils with different long‐term cropping histories of continuous mixed vegetables, continuous brassicas and continuous grassland, emergence of cabbage seedlots was lower than values obtained in laboratory germination tests. The greatest reductions occurred in soil (mixed vegetables) infested with Pythium ultimum. The presence of Pythium irregulare in the continuous brassicas soil had less effect on emergence, but the ranking for emergence of four of the seedlots was identical in the two soils. When the soils were sterilised and re‐inoculated with their respective Pythium isolate emergence was less than that in non‐sterilised soil but the rankings were similar. The pre‐emergence, and post‐emergence losses which occurred in these two soils, were controlled by seed treatment with 1 g metalaxyl/kg seed. In the continuous grassland soil although Pythium irregulare was present, emergence from most of the seedlots was high.
A method for sampling the populations of large termite nests
Authors: DARLINGTON JOHANNA P. E. C.
Published: February 2008

A method for sampling the population of large Macrotermes nests is described. Fumigation with methyl bromide was followed by complete extraction of the nest contents. Termites and fungus comb fragments were separated from soil by flotation in water.

Results for fumigated and live‐dug nests were compared. Sampling without prior fumigation caused the population and biomass to be underestimated by up to an order of magnitude. Caste and instar ratios were also distorted in ways that were not consistent but were affected by the size of the nest.

It is therefore concluded that methyl bromide fumigation is a valuable technique for sampling the populations of Macrotermes nests.
The use of vesicular‐arbuscular mycorrhizal roots grown by the nutrient film technique as inoculum for field sites
Authors: ELMES R. P. , HEPPER CHRISTINE M. , HAYMAN D. S. , O'SHEA J.
Published: February 2008

Bean roots grown by the nutrient film technique and infected with vesicular‐arbuscular mycorrhizal fungi were successfully used as inoculum for red clover growing in an unsterile field site. The endophyte introduced with the roots became well established in the presence of indigenous mycorrhizal fungi.
The effect of Solanum tuberosum×S. vernei hybrids on hatching of the potato cyst nematode Globodera pallida
Authors: FORREST J. M. S. , PHILLIPS M. S.
Published: February 2008

The hatching activity of partially resistant Solanum tuberosum×S. vernei clones and susceptible cultivars was investigated in a series of tests with G. pallida conducted in pots in the glasshouse. Differences in hatching were apparent, with the partially resistant clones generally stimulating a lower total hatch than the S. tuberosum cultivars. It is concluded that reduced hatching activity can make a small contribution to overall resistance and perhaps also to the tolerance of a clone to G. pallida.