bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission of raspberry ringspot virus by Longidorus caespiticola, L. leptocephalus and Xiphinema diversicaudatum and of arabis mosaic virus by L. Caespiticola and X. diversicaudatum*
Authors: Valdez R. B.
Published: February 2008

Using a micro‐container inoculation technique, an English strain of raspberry ringspot virus (RRV) was transmitted by Longidorus caespiticola Hooper, L. leptocephalus Hooper and Xiphinema diversicaudatum (Micol.) to petunia test plants. RRV persisted in starved X. diversicaudatum for at least 10 days. From a mixed infection of RRV and a typical strain of arabis mosaic virus (AMV), batches of fifty X. diversicaudatum transmitted both viruses, but AMV the more readily, whereas batches of twenty‐five L. caespiticola transmitted both viruses with equal facility.
Effects of Pyrenochaeta lycopersici infection on nutrient uptake by tomato plants
Authors: GOODENOUGH P. W. , MAW G. A.
Published: February 2008

The growth of young tomato plants in nutrient solution or in soil and infected with Pyrenochaeta lycopersici Schneider & Gerlach, the cause of tomato brown root rot, was decreased relative to that of uninfected plants. The roots of plants grown in nutrient solution and infected with a mycelial mat of the pathogen contained lower concentrations of potassium and higher concentrations of calcium than roots of uninfected plants. These changes occurred largely in the visibly affected tissue, as opposed to the root system as a whole. The concentrations of magnesium, total nitrogen and phosphorus in the roots of infected plants were not significantly different from those of control plants.

Magnesium, nitrogen and phosphorus concentrations in the tops of infected plants were also not significantly different from those of healthy plants, but no consistent changes were found in the concentrations of calcium and potassium.

Young tomato plants grown in soil infested with P. lycopersici contained lower concentrations of phosphorus and potassium in the tops than plants grown in sterilized soil. It was not possible to separate intact damaged root systems of infected plants from soil.

The changes in composition found in infected plants are discussed in relation to possible methods of manipulating the nutrition of the plant to offset the effects of the disease on crop yield.
Storage losses of taro corms in the British Solomon Islands Protectorate
Authors: GOLLIFER D. E. , BOOTH R. H.
Published: February 2008

In two storage trials, corms of taro (Colocasia esculenta) decayed and became unfit for human consumption after 1 to 2 weeks. There were three fairly distinct types of rot: A dry rot caused by Fusarium solani, a spongy black rot caused by Botryodiplodia theobromae, and a Sclerotium rot caused by S. rolfsii. Although it was found that, under humid conditions, all three fungi could penetrate and rot undamaged corms most natural infection is thought to occur through wounds. None of the pathogens rotted corms at low humidity.
Histology of Hevea roots infected by Forties lignosus
Authors: PERIES O. S. , IRUGALBANDARA Z. E.
Published: February 2008

Inspection of naturally or artificially infected Hevea roots showed that Forms lignosus can penetrate undamaged roots directly, but does so more readily through wounds or natural openings like lenticels, or through the bases of lateral roots and bark scales. Therefore, Pomes‐infected trees should be identified by leaf symptoms rather than by uncovering and inspecting roots, as this generally leads to root injury, which facilitates fungal penetration.

Initial fungal entry into host tissue appears to be by mechanical pressure alone, but deeper penetration is through the action of extracellular enzymes. The fungus remains intercellular in the cortex but is intracellular in the woody tissue. Ray cell walls are penetrated mechanically, but the xylem through pits. The time taken for various stages of infection to occur is assessed.

The amount of damage done by the fungus to roots and the blocking of xylem vessels by tyloses suggest that yellowing, curling and buckling of leaves on infected trees are drought symptoms and not a reaction to fungal toxins. The host reacts to the invasion of the cortex by forming a cork cambium and to the invasion of the woody tissue by blocking individual cells with phenols and resins, which could be important when breeding disease resistant Hevea root stocks.
The elimination of viruses from Narcissus tazetta cv. Grand Soleil d'Or, and rapid multiplication of virus‐free clones
Authors: STONE OLWEN M.
Published: February 2008

Arabis mosaic virus and narcissus degeneration virus were eliminated from Narcissus tazetta L. cv. Grand Soleil d'Or by meristem‐tip culture. Cultures grew equally well in two liquid nutrient media, but tubes 25times75 mm size and temperature c. 12 oC were optimal for growth and survival. Virus‐free bulbs grew more vigorously than infected bulbs, and gave more and larger flowers with a better colour. To increase the normal multiplication rate, either sector cuts were made in the basal plate, or bulbs were divided into chips (c. 1 g), before planting. Multiplication was greater by chip‐cutting. Five virus‐free bulbs were propagated to over 2000 in 8 years; theoretically, 20000000 bulbs should be produced in a further 5–6 years, sufficient to replant the Isles of Scilly with virus‐free stock.
Effects of growing resistant potatoes with gene H1 from Solarium tuberosum ssp. andigena on populations of Heterodera rostochiensis British pathotype A
Authors: TRUDGILL D. L. , PARROTT DIANA M.
Published: February 2008

Pure pathotype A populations of Heterodera rostochiensis produce a few females on ex andigena hybrids with the H1 gene for resistance. As the proportion of larvae able to become female on ex andigena hybrids was not increased by reproducing the nematodes on such hybrids for 3 years, these females seem not to be genetically different from the rest of the population. The proportion increased rapidly when the initial population contained a few pathotype (species) E nematodes but again no increase in the proportion of pathotype (species) A larvae able to become female on ex andigena was detected and pathotype E replaced pathotype A.
Causes and development of hollow heart in pea seed
Authors: PERRY D. A. , HARRISON J. G.
Published: February 2008

Predisposition to hollow heart in pea seeds (Pisum sativum L.) is caused by high ambient temperatures during their maturation on the plant, and by drying them when immature. Symptoms develop during germination, and the proportion of seeds affected in any sample depends on the rate of water imbibition. It is suggested that predisposed cells die during rehydration.
Effects of hollow heart on growth of peas
Authors: HARRISON J. G. , PERRY D. A.
Published: February 2008

Hollow heart of pea seed (Pisum sativum L.) delayed germination and reduced seedling growth. Plants from seeds with the disorder were smaller and yielded less than those from normal seeds. Affected cells were dead, but immobilization of starch reserves within them could not wholly account for the reduced growth and evidence suggested the presence of a germination and growth inhibitor.
Yield compensation in gappy potato crops and methods to measure effects of fungi pathogenic on seed tubers
Authors: HIRST J. M. , HIDE G. A. , STEDMAN O. J. , GRIFFITH R. L.
Published: February 2008

Pathogens damage potatoes in so many ways and at so many stages of cropping, transport and storage that it is difficult to estimate their total effect. This paper describes methods used to measure how fungal pathogens affected crop health and yield, and experiments that measured how much the yield lost through gaps was compensated by extra growth of neighbouring plants.

Some tubers in stocks were diseased, so healthy controls were not available and contrasts could be made only by selecting grades differing in symptom severity. The differences measured represented only part of the damage because many infections are symptomless, and vigorous plants compensate for the small yields of weak or absent neighbours.

Plots gapped randomly to varying degrees at emergence or flowering showed that yields were decreased by 0–332 (± 0–129) %and“833 (± 0–094) % respectively, for every 1 % of plants removed. When up to 24 % of plants were removed the regression of percentage gaps on yield did not become significantly non‐linear.
Effects of skin spot (Oospora pustulans) on potatoes
Authors: HIDE G. A. , HIRST J. M. , STEDMAN O. J.
Published: February 2008

King Edward and Majestic seed potatoes selected as ‘clean’ (macroscopically symptomless), moderate and severe according to the extent of skin spot were planted in field experiments at Rothamsted between 1964 and 1968. Usually crops from ‘clean’ and moderately infected seed did not differ detectably in growth or yield. Plants from severely infected seed tubers emerged more slowly, had fewer stems and yielded less (King Edward 20 %, Majestic 13 %). Seed infection also affected tuber size distribution; severely infected seed of King Edward yielded almost 4 tons/acre less of 1 1/4‐2 1/4 in tubers and Majestic, 1 ton/acre less of these and 2 tons/acre less 2 1/4‐3 1/4 in tubers. However, the total yield from diseased seed stocks was only slightly less (King Edward, o‐6 ton/acre and Majestic o‐8 ton/acre) than the yields from the ‘clean’ tubers selected from them. Seed severely infected by Oospora pustulans often increased infection of the progeny tubers, and usually decreased their infection by Rhizoctonia solani and sometimes by Helmintho‐sporium solani.

Another series of experiments compared King Edward seed tubers classified according to the number of live eyes showing in March. Seed with one, two, three and more live eyes yielded equally. About half the tubers without live eyes in March eventually produced plants, but late, with few stems and giving only half the yield of seed with three or more live eyes. Surprisingly, the progeny tubers from seed without live eyes were least infected by O. pustulans, R. solani and H. solani.

Progenies of King Edward and Majestic seed from a common source grown on seven widely separated farms were infected more in 1963 than in 1964, but in each year infection differed widely between farms. Often where O. pustulans was common, R. solani was scarce and vice versa. By contrast, when King Edward stocks very differently infected by O. pustulans were grown at Rothamsted their progenies were almost uniformly infected by O. pustulans and R. solani.
The effect of time of harvest on the viability and pre‐emergence mortality in soil of pea (Pisutn sativum L.) seeds
Authors: MATTHEWS S.
Published: February 2008

A series of harvests from field plots of peas showed that the younger seeds were at the time of harvest the lower was their percentage viability and the greater their percentage mortality in soil. Young seed also showed a high degree of solute leaching into steep water and had a high moisture content at harvest compared with older seeds. Heavy rainfall just prior to harvesting reduced the percentage viability of the dried seed and increased the moisture content of the seed at harvest as well as the leaching of solutes from the dried seed into steep water. Comparisons of moisture content at harvest and seed condition after drying suggested that cotyledons and embryo axes were only able to withstand enhanced drying after removal from the plant if the seed moisture content had already begun to decline whilst the seed was still on the plant.
The photosynthesis of ryegrass leaves grown in a simulated sward
Authors: WOLEDGE JANE
Published: February 2008

Plants were taken from simulated swards of perennial ryegrass (Lolium perenne) grown in a controlled environment and the rates of photosynthesis of the youngest fully expanded leaves, and the second and third youngest leaves on the same tillers were measured. The youngest leaves had the highest rates and the third the lowest, with the second leaves intermediate.

The rate of photosynthesis in bright light of successive youngest expanded leaves decreased as the swards increased in leaf area, but did not when plants were grown so that the main stem was not shaded. When plants were grown at different densities and the photosynthetic rates of leaves of a particular ontogenetic rank were measured, it was found that leaves on plants from higher densities had lower rates of photosynthesis. Also leaves on plants grown in bright light had higher photosynthetic rates than those on plants grown in dim light.

It is concluded that the decline in the photosynthetic capacity of successive leaves in a rapidly growing simulated sward is due to the intense shading to which they are subjected during their expansion.
Distribution of cabbage root flies in brassica crops
Authors: FINCH By S. , SKINNER G.
Published: February 2008

Changes in the distribution of adult cabbage root flies were determined in 0–05‐0‐4 ha brassica plots during 1970 and 1971 using yellow water‐traps.

The three generations of flies occurred at similar times in both years and the numbers caught generally decreased from the first to the third generation. In resident populations, the numbers of males and females declined by 70 and 40% respectively, between the second and third generations. When there was no decline, immigration presumably compensated for flies trapped or otherwise lost. The results confirmed that male cabbage root fly movement is trivial, that wind has little effect on distribution at a brassica plot and that females move into the crop independently of males. They failed to confirm that females aggregate markedly at hedgerows or fences, that they spend little time in the crop or that they regularly return to hedgerows.

Differences in the dispersal behaviour of the male and female flies were reflected in the numbers caught. Some males dispersed actively during the first 2 weeks after emergence but many were displaced slowly downwind. Once at a plot, wind appeared to have little effect on distribution of young males, but older males tended to shelter just downwind of the hedge. Relatively few males were caught near hedges but they tended to aggregate along the crop‐interfaces, particularly during the first generation. Plot size did not appear to influence the pattern of fly distribution greatly. Females dispersed more actively than males and were generally more uniformly distributed through the crops even during periods of immigration. Gravid females entered an isolated plot without accompanying males, inferring that they are migratory and mate near the site of emergence. Female distribution was not related to the stage of ovarial development except during maximum oviposition when those that had laid some eggs visited the hedgerow. Aged females became progressively easier to capture and usually died in the crop.
Effects of sublethal doses of pesticides on the oviposition behaviour of Encarsia formosa
Authors: IRVING By S. N. , WYATT I. J.
Published: February 2008

Female Encarsia formosa were enclosed in artificial arenas containing twenty‐five Trialeurodes vaporariorum scales on a Cellophane substrate. Either the substrate or the scales were previously treated with chemicals. The number of oviposition wound marks on the scales was used as a measure of effect on parasite behaviour. The insecticides, tetradifon and γ‐BHC, had their greatest effect when applied to scales. The fungicides, benomyl and dichlofluanid, were more active on the Cellophane. Pirimicarb applied to the scales decreased oviposition, but greatly increased it when applied to the substrate. It is concluded that even sublethal amounts of pesticides may seriously impair the effectiveness of this parasite in commercial biological control.
The toxicity to foraging honeybees, Apis mellifera, of endosulfan, malathion and azinphos‐methyl applied to flowering oil seed rape, Brassica napus
Authors: NEEDHAM P. H. , STEVENSON J. H.
Published: February 2008

Wettable powder and emulsifiable concentrate formulations of endosulfan and azinphos‐methyl and an emulsifiable concentrate of malathion were sprayed on oil seed rape in full flower to assess their relative toxicities to foraging honeybees. Endosulfan was very much safer to honeybees than the two organophosphate insecticides, but there was little difference between the two types of formulation.
The effect of fungicides on incidence of Sporobolomyces spp. and Cladosporium spp. on flag leaves of winter wheat
Authors: JENKYN J. F. , PREW R. D.
Published: February 2008

Sprays of benomyl, thiophanate methyl, NF 48 and captafol considerably decreased incidence of Sporobolomyces spp. and Cladosporium spp. on flag leaves of winter wheat. BAS 3170 F affected both genera but much less. Tridemorph and triforine had relatively little effect on Sporobolomyces spp. but tridemorph did decrease Cladosporium spp. Sandoz 52.133 affected only Cladosporium spp. and ethirimol affected neither genus.
Growth and wilting of radish seedlings, Raphanus sativus, infested with the aphid, Myzus persicae
Authors: FORREST J. M. S. , HUSSAIN A. , DIXON A. F. G.
Published: February 2008

After 10 days of infestation by the aphid Myzus persicae growth of radish seedlings was reduced by 38 %, and the volume of sap bleeding from the stumps of cut stems of infested seedlings was 4% of that exuding from the stumps of uninfested seedlings of the same age. Diminished bleeding could not be accounted for by the 52 % reduction in the weight of the roots of infested seedlings. After 14 days of infestation, necrotic patches developed along the veins of the cotyledons which yellowed noticeably. If freed of aphids the seedlings subsequently resumed growth and their was an increase in the volume of bleeding sap produced by their cut stems. Symptoms associated with aphid infestation cannot be attributed either to virus disease or initially to exhaustion of the seedling's carbohydrate and nitrogen reserves. Possible causes of the symptoms described are discussed.
Review
Authors: BYRDE R. J. W.
Published: February 2008

Phytotoxins in Plant Diseases. Edited by R. K. S. Wood, A. Ballio and A. Graniti.
East African strains of cowpea aphid‐borne mosaic virus
Authors: BOCK K. R.
Published: February 2008

Cowpea aphid‐borne mosaic virus (CAMV) was isolated for the first time in East Africa where three distinct strains, type, veinbanding and mild, were differentiated by host range and serology. The three strains infected 17/38, 18/37 and 10/35 legume species, and 11/21, 7/21 and 3/19 non‐legume species, respectively.

The viruses were propagated in cowpea and assayed in Chenopodium amaranticolor. Isolates of all three strains had similar in vitro properties: dilution end point between 10‐3 and 10‐4; thermal inactivation point between 56 and 58 °C; longevity in vitro between 2 and 3 days. Infectivity of sap from frozen leaves was high after 4 wk but much less after 7 wk; infectivity was largely precipitated by 50% acetone but inactivated by 50% ethanol. High yields of virus were consistently obtained from cowpea by extracting systemically infected leaves in 0.5 m sodium citrate containing 1% mercaptoethanol (pH 8.1), and clarifying with 8.5 ml n‐butanol/100 ml sap. Virus preparations contained numerous unaggregated and aggregated virus particles c. 750 nm long and contained components with sedimentation coefficients (s°20, w) of 150S and 175S (presumably unaggregated and aggregated particles, respectively). CAMV is serologically distantly related to bean common mosaic virus, but not to bean yellow mosaic or eight other morphologically similar viruses. It is a typical but distinct member of the potato virus Y group.
Soil fumigation with methyl bromide: the uptake and distribution of inorganic bromide in tomato plants
Authors: KEMPTON R. J. , MAW G. A.
Published: February 2008

Tomato plants grown in soil previously fumigated with methyl bromide accumulated inorganic bromide in the foliage. The concentration present depended on the rate of application of methyl bromide to the soil and on the interval between, soil fumigation and planting, two factors determining the concentration in the soil of inorganic bromide arising from the breakdown of the fumigant.

The concentration of bromide in the leaves decreased from the base to the tip of the plant, and increased with the age of the tissue.

Bromide was accumulated in the fruit, but to a lesser extent than in the leaves. Mature fruit from plants grown in soil fumigated at the commercially applied rate of 1.5 lb/100 ft2 (73 g/m2) contained at the most 45 μg/g of fresh tissue, and generally not more than half this value. The concentration of bromide in fruit was related to the concentration of inorganic bromide present in the soil, but not to the state of ripeness or the position of the fruit on the plant.

Similar results were obtained for leaves and fruit from plants grown in soil supplemented with inorganic bromide.
The early relative growth rates of six lettuce cultivars as affected by temperature
Authors: SCAIFE M. A.
Published: February 2008

Six lettuce cultivars were grown to a dry weight of about 0.2 g per plant at four constant temperatures with high light intensity and ample nutrients. Relative growth rates (RGR) were sigmoidally related to temperature, averaging 0.11 g/g/day at 10 °C and 0.35 g/g/day at 22 °C. The cultivars Cobham Green and Avoncrisp had higher RGRs than the others, but the cultivar‐temperature interaction was not statistically significant. Temperature affected both components of RGR, i.e. net assimilation rate and leaf area ratio, about equally: the faster‐growing cultivars had higher net assimilation rates than the others. Growth rate predictions from the cabinet work agreed fairly well with observations made in the field.
Infection of cereal aphids by the fungus Entomophthora
Authors: DEAN G. J. W. , WILDING N.
Published: February 2008

Three species of Entomophthora killed many Metopolophium dirhodum, M. festucae and Sitobion avenae on wheat at Harpenden, Hertfordshire, in 1971. Rainfall was low and aphid numbers were small in May and there was no Entomophthora infection. E. planchoniana first infected M. dirhodum early in June and the percentage of each aphid species infected increased during and after heavier rain in the first 2 weeks of June. M. dirhodum and S. avenae were most often infected by E. planchoniana, and the less common M. festucae mostly by E. aphidis and E. thaxteriana. Relative frequencies of E. aphidis and E. thaxteriana were largest before, and of E. planchoniana after, mid‐July. The largest percentages infected were 53% of M. dirhodum and 30% of S. avenae during the second half of July and 60% of M. festucae in late June. The percentages of old nymphs and apterous adults that were infected were similar and only about half those of infected alatae.
Effects of black scurf (Rhizoctonia solani) on potatoes
Authors: HIDE G. A. , HIRST J. M. , STEDMAN O. J.
Published: February 2008

King Edward and Majestic seed tubers, selected as ‘clean’ (macroscopically symptomless), moderate and severe according to the extent of black scurf, were planted in field experiments at Rothamsted between 1964 and 1968. Seed infection sometimes delayed plants emerging but did not affect final plant populations. Crops from severely diseased seed yielded, on average, 7% less than ‘clean’ tubers (King Edward 6–8% less and Majestic 0–20% less). Seed infection affected tuber size distribution; compared with ‘clean’ seed, severely infected King Edward seed yielded slightly more chats (< 1 ½ in, 3.8 cm) and 1.5 ton/acre (3.8 t/ha) less large tubers (2 ¼–3 ¼ in, 5.7–8.3 cm). The effects were similar with Majestic although differences were smaller. However, total yields from diseased stocks (unselected) seldom differed significantly from the ‘clean’ tubers selected from them. Crops from moderately and severely diseased seed had more Corticium on stems and black scurf on tubers and usually less Oospora pustulans than from ‘clean’ seed.
A comparison of some properties of four strains of cherry leaf roll virus
Authors: JONES A. T.
Published: February 2008

The elm mosaic and golden elderberry strains of cherry leaf roll virus (CLRV) and a strain from cherry and from rhubarb were very similar in their host range, symptomatology and properties in vitro. However, only the rhubarb isolate infected rhubarb systemically and only the golden elderberry isolate infected Sambucus nigra systemically. Purified preparations of all strains contained isometric particles which sedimented as two nucleoprotein components with sedimentation coefficients of about 115 S and 128 S. The elm mosaic strain was the least stable in vitro and was the most difficult to purify. In plant‐protection tests, one‐way protection occurred between tomato ringspot virus and each of the four CLRV strains. However, whereas the elm mosaic, golden elderberry and the cherry strains protected against one another, they did not protect against infection with the rhubarb strain.
Hollow heart of pea (Pisum sativum)
Authors: GANE A. J. , BIDDLE A. J.
Published: February 2008

Samples of pea seed which had failed in the field were frequently found to be affected by hollow heart and it was noted that most of those affected by the disorder were triangular in cross‐section, rather than square. Seedlings from triangular seed were less vigorous and more readily killed in adverse conditions of soil and weather. Peas selected as of high vigour by the electro‐conductivity test showed differences in percentage hollow heart which were associated with differences in field losses. Laboratory tests showed that the proportion of seeds displaying symptoms varied according to the substrate used and that both the proportion showing symptoms and the germination capacity fluctuated during storage.
Some factors influencing spore germination and penetration of Alternaria longipes
Authors: NORSE D.
Published: February 2008

The ranges over which the germination of conidia of Alternaria longipes was > 50% were 10–35 °C on agar and 15–30 °C on tobacco leaf disks. Germination was optimal at 22.5 °C; so was germ‐tube growth, reaching c. 300 and 102 μm on agar and leaf disks respectively after 12 h. On average, 27% more conidia germinated and germ‐tubes were 62% longer on disks from leaves washed for 5 min under running water than on disks from unwashed leaves.

At controlled saturation deficits germination after 8 h at 1.1 and 2.3 mb was 42.3 and 9.3% respectively and the rate of germ‐tube growth was < 0.8 μm/h, compared with 94.4% and 8.3 μm/h in standing water. These results, together with some field data, suggests that germination in the field is largely restricted to periods when free moisture is present on leaves. In Malawi, leaf temperatures and the duration of dew at night were adequate to allow germination and penetration in the absence of rain.

Pollen, when applied with the inoculum, had little effect on the number of germinated conidia, but caused a c. tenfold increase in the number of successful penetrations.
Colonization of adult lettuce plants by Bremia lactucae
Authors: DIXON G. R. , TONKIN M. H. , DOODSON J. K.
Published: February 2008

Studies were made of the infection by Bremia lactucae of a range of lettuce cultivars at the adult plant stage, under conditions of artificial and natural epidemic. The pathogen invaded at least the ten oldest leaves of many cultivars, the leaf area affected declining from the oldest to the youngest leaves. Two assessment methods were compared: (1) the percentage area infection on individual leaves and (2) the percentage area infection on the inverted basal area as a whole. Results from the two methods agreed closely under conditions of artificial inoculation and in a natural epidemic. It is concluded that both methods should be used for detailed studies, but method 1 restricted to the oldest five leaves. At least two assessment dates are required since on individual cultivars there were differences in the leaf area infected at various assessment dates. This is probably influenced by the cycle of growth and sporulation of B. lactucae and by the effects of invasion by secondary pathogens such as Botrytis cinerea.
The influence of the testa, damage and seed dressing on the emergence of groundnut (Arachis hypogea)
Authors: CARTER J. B. H.
Published: February 2008

The effects of damaging the testa and the application of seed dressings were examined in field trials on several short‐and long‐season cultivars of groundnut (Arachis hypogea) with differently‐pigmented testas at Samaru, Nigeria, in 1967. There was a high correlation between the number of seedlings which emerged in these trials and the resistance or susceptibility of the seed to invasion by the fungus Aspergillus flavus, as assessed by laboratory tests. When the testa was undamaged the emergence of white (susceptible) seed was only 50% while that of coloured (resistant) seed was between 95 and 98%. Damage to the testa by scratching greatly decreased emergence. The application of seed dressing increased the emergence of susceptible seed and also restored the emergence of scratched seeds to the level of undamaged seeds. The effect of the complete removal of the testa was not counteracted by seed dressing; naked seeds, with and without dressing, gave c. 10% emergence. The importance of pigment in the testa, the condition of the seed and the effects of seed dressing are discussed.
Effects of heat shock treatment on symptom development in tobacco leaves inoculated with potato mop‐top virus
Authors: JONES R. A. C.
Published: February 2008

PMTV normally causes necrotic ringspot local lesions in Xanthi‐nc tobacco leaves at 15 °C but not at 22°. Dipping the leaves once in hot water at different intervals after inoculation induced necrotic reactions even at 22°. Successive concentric rings, one for each day of the interval between inoculation and treatment, were sometimes induced at 22°; these even formed in continuous lighting, suggesting an intrinsic diurnal rhythm. No lesions were induced at 22° by dipping inoculated leaves in ice‐cold water.

Samsun tobacco inoculated with PMTV developed very few lesions at 15°. Many more were induced however, by dipping the leaves in hot water after inoculation.

The results suggest some similarities between PMTV and TMV, and the two viruses have been reported as serologically related; but PMTV did not protect plants against TMV, for TMV challenge‐inoculations induced lesions within existing PMTV lesions.
Influence of rooting‐medium temperature on growth of Lycopersicon esculentum
Authors: COOPER A. J.
Published: February 2008

The influence of rooting‐medium temperatures (maintained constant for 54 days from sowing) on tomato seedling growth was exerted primarily on development during the first 2 weeks after sowing, when an optimum emerged at 25 °C. This influence was attributable to an effect of temperature on the partitioning of dry matter between root and shoot during a few days before and after the start of photosynthesis. The adverse effect of suboptimal (but not supra‐optimal) temperature was also associated with a reduction in the phosphorus content of the tissue, there being little effect on either nitrogen or potassium content.
Verticillium wilt of pea (Pisum sativum)
Authors: ISAAC IVOR , ROGERS W. G.
Published: February 2008

A wilt disease of garden pea (Pisum sativum) caused by Verticillium dahliae is described and the range of pathogenicity of the isolate investigated. It is pathogenic to potato, sweet pea, antirrhinum and broad bean and isolates of V. dahliae from potato, lucerne and sweet pea and V. albo‐atrum from lucerne are pathogenic to pea.

Since the most common disease symptoms, acropetal progression of chlorosis and necrosis of the leaves followed by premature defoliation are indistinguishable from natural senescence, it is probable that disease and senescence symptoms are confused in the field.

The premature defoliation results in marked reduction in green leaf area, leaf dry weight and pod yield.
The influence of normal tillage and of non‐cultivation on Verticillium wilt of the hop
Authors: SEWELL G. W. F. , WILSON J. F.
Published: February 2008

The influence of a non‐cultivation (herbicide) regime on wilt incidence was compared with that of normal tillage in three observation trials on commercial hop farms. Non‐cultivation resulted, on average, in 28% wilt control when wilt incidence was high. When wilt incidence was low there was a tendency for more wilt to occur with non‐cultivation.

The reduction in wilt under non‐cultivation was probably mainly due to the virtually complete eradication throughout the year of alternative weed host plants, but other possible influential factors were: (i) the absence of root severance which could result in increased inoculum potential, (ii) changes in the pattern of hop root distribution, and (iii) the inhibiting action of simazine on root growth in surface soil resulting in reduced contact between roots and surface‐borne inoculum.

The lack of disease control with non‐cultivation when wilt incidence was low was attributed to differential effects of the treatments on nitrogen metabolism or availability.

The factors contributing to disease control under non‐cultivation were considered to represent aspects of the process of sanitation, and the data were interpreted in terms of the sanitation ratio (sensu van der Plank). When wilt incidence was high the sanitation ratios at the three sites were similar.

Modified cultural practices provide an important supplement to genetic resistance in the control of hop wilt. These practices (restricted use of nitrogen fertilizers and efficient sanitation with respect to the crop plant as well as to weeds) have proved economical and beneficial for hop culture in presence of wilt, under the threat of wilt, and in the absence of wilt.
Effects of cultural conditions on the mycelial growth of healthy and virus‐infected cultivated mushroom, Agaricus bisporus
Authors: LAST F. T. , HOLLINGS M. , STONE OLWEN M.
Published: February 2008

There was a significant inverse correlation (P= 0=001) between concentrations of mushroom viruses 1 and 2 in sporophores and amounts of mycelial growth on malt agar of isolates taken from them. Increasing virus concentrations decreased linear growth of one mushroom strain from 76 mm (healthy) to 35 mm (mildly infected) and 7 mm (severely infected) when incubated at 25°C for 3 wk.

Mycelial growth rates of isolates from healthy and from virus‐infected mushrooms were compared on eleven agar media. All media clearly differentiated between healthy and severely infected isolates, but fewer separated healthy from mildly infected isolates. Those that did contained maltose, sucrose or starch as carbon source. Media containing peptone usually gave better differentiation than those with other sources of nitrogen, but the best differentiation was obtained with malt agar.

Growing healthy and infected isolates on a range of media affected their subsequent growth on malt agar, the growth of some isolates apparently being changed permanently after 2 months on some of the different media. Whereas none of the infected isolates grew less rapidly after this treatment, the growth of some of the mildly infected isolates improved to such an extent that they could no longer be distinguished from healthy isolates.

After heat‐treatment (1–6 wk at 33°C), mycelial growth rates of infected isolates were increased, but viruses 1 and 2 were not always eliminated unless the heat‐treatment was begun immediately after subculture.

Mycelial growth rate and colony characters are not infallible criteria of the presence or absence of virus, a feature of particular significance when checking the health of mushroom spawn.
The photosynthetic activity of the developing hop cone
Authors: PEAT W. E. , THOMAS G. G.
Published: February 2008

Carbon dioxide exchange of the developing hop cone was measured in field and laboratory experiments. Older cones showed a clear response of CO2 exchange to light intensity, indicating photosynthetic activity, but this rarely exceeded respiratory loss. Cones therefore made little photosynthetic contribution to their growth. Young cones showed no response of CO2 exchange to light intensity and therefore possessed negligible photosynthetic activity. The initiation of photosynthesis was sudden and coincided with the onset of rapid cone growth and with the response of water loss to light intensity. It is suggested that the maturation of stomata is linked with the initiation of gas exchange.
Incidence and control of Colletotrichum musae on bananas in the Windward Islands
Authors: GRIFFEE P. J. , BURDEN O. J.
Published: February 2008

Colletotrichum musae was isolated from banana hands I wk after bunch emergence and in subsequent weeks both from fingers and from crown tissue. Other fungi including Fusarium semitectum and Nigrospora sphaerica were also isolated. Four pre‐harvest sprays of benomyl, each at 1000μg/ml, controlled these fungi on unripe fruit, but unsprayed bunches covered with polyethylene showed rather increased infection rates.

Latent infections of C. musae giving lesions on ripe fruit were also largely controlled by the above sprays, but crown rot appearing at this stage was not reduced. One post‐harvest benomyl dip at 250 μg/ml however effectively controlled crown, wound and latent infections. For this reason and also because of the demonstrated risk of benomyl‐resistant isolates of C. musae resulting from pre‐harvest treatment, it is suggested that pre‐harvest spraying is unnecessary.
A virus causing ringspot of Passiflora edulis in the Ivory Coast
Authors: WIJS J. J. De
Published: February 2008

A mechanically transmissible virus causing leaf mottling and ringspotting of Passiflora edulis var. flavicarpa in the Ivory Coast is described. Its particles are flexuous rods 810–830 nm long and 15 nm wide. It infects mainly species of Passifloraceae and Leguminosae; Passiflora foetida is a good diagnostic host. Aphis gossypii and Aphis spiraecola transmit the virus after brief acquisition feeds. Seed transmission was not detected. In crude sap of P. edulis, infectivity was lost after 10 min at 65–70 °C, 12–14 days at 24 °C or dilution to 10‐7. A purification method is described, using Triton‐X‐100 as clarifying agent. The virus is serologically related but not identical to passionfruit woodiness virus from Queensland. The virus seems to belong to the potato virus Y group and has the cryptogram */*:*/(6):E/E:S/Ap. It is designated passionfruit ringspot virus.
Nematodes associated with forest and woodland trees in Scotland
Authors: BOAG B.
Published: February 2008

A survey of the nematode genera associated with trees in Scotland showed that Tylenchus sensu lato, Aphelenchoides, Tylencholaimus, Trichodorus, Helicotylenchus, Rotylenchus, Criconemoides s.l., Hemicriconemoides, Tylencho‐rhynchus, Pratylenchus and Paratylenchus s.l. were commonly found in soil samples collected from around the roots of coniferous and deciduous trees. Only Criconemoides s.l. appeared to have a significant preference for deciduous woods.

The presence of undergrowth in woods and forests was associated with significantly greater numbers of plant‐parasitic nematodes.

Measurements of abiotic factors indicated that, in mineral soils, pH affected the incidence of most genera, but soil type, moisture content and altitude had little effect.
Heritability of bulb shape in some north European onion varieties
Authors: DOWKER B. D. , FENNELL J. F. M.
Published: February 2008

Heritabilities for shape index (the ratio of bulb height to diameter), based on parent—offspring regressions, were calculated for north European onion cultivars and inbred lines derived from them. Heritability estimates of 0·46 and 0·47 respectively were obtained for the two groups, S0 parent bulbs giving S1 progenies, and S1 parent bulbs giving S2 progenies.

Within each offspring progeny, the regression of bulb shape index on loge bulb weight was significant. The regressions were used to estimate the mean shape indices of the progenies at the same mean bulb weight as their parents, and a series of ‘corrected’ progeny shape means thus obtained. Recalculation of the heritabilities using these ‘corrected’ progeny means gave increased estimates (0·78 and 0·84).

By using this regression approach, the breeder can achieve high heritabilities when selecting for a specific mean shape index.
Some factors affecting the efficiency of water‐traps for capturing cabbage root flies
Authors: FINCH S. , SKINNER G.
Published: February 2008

Several factors influencing the efficiency of water‐traps in capturing cabbage root flies were studied at Wellesbourne in 1971 and 1972. In both the laboratory and field, approximately twice as many flies were caught in fluorescent as in non‐fluorescent yellow traps. Depending upon trap density, addition of a source of the attractant allylisothiocyanate (ANCS) increased the numbers of females captured by approximately twofold in fluorescent traps and from two‐ to sevenfold in non‐fluorescent traps. Traps were equally efficient irrespective of whether the ANCS was renewed every 2, 3, 4 or 5 days. On the first day of trapping, the number of flies caught per unit area was linearly related to the square root of the number of traps in that area. On the following days the rate was probably in equilibrium with the combined effect of immigration and the rate of development of responsive flies in the trapping zone. Most males were caught 30 cm above the soil surface and most females at soil level. Traps 120 cm above the soil surface caught few flies.

Populations of marked flies were released into large field cages containing both a section of hedgerow and a plot of cauliflowers. Even after a week, only 81 % of the males and 55 % of the females had been recaptured from the most responsive of these captive populations. Furthermore, only 30 % of females were recaptured when they were more than 8 days old, the age at which most probably enter the new host‐crop.
Observations on the occurrence, pathogenicity and control of Pratylenchus vulnus, P. thornei and Xiphinema diversicaudatum associated with glasshouse roses
Authors: WINFIELD A. L.
Published: February 2008

About half the nurseries and glasshouses in the Lea Valley of Hertfordshire were found to be infested with either or both Pratylenchus vulnus and Xiphinema diversicaudatum. The latter nematode probably occurred naturally in the soil on which the glasshouses were built but P. vulnus is thought to have been imported with rose rootstocks and is not known to occur outdoors in Britain. Both nematode species can cause decline of roses and even small numbers seem harmful. Numbers of P. vulnus can increase greatly, especially on rootstocks of Rosa canina, although numbers were often smaller when roses were severely damaged than on healthier crops. Numbers of X. diversicaudatum increased more slowly and R. canina was a better host for it than R. chinensis. X. diversicaudatum seemed to respond less quickly than P. vulnus to reduced host‐plant vigour. The two rootstocks exhibited different host‐status for the two species of nematode and cuttings of various rose cultivars showed different host‐status to P. thornei, another species of lesion nematode which is not known to be pathogenic to roses. Two applications of dibromochloropropane liquid at the rate of 70 l/ha in a large volume of water maintained nematode densities at an acceptably low level, and growers who adopted this treatment as a supplement to pre‐planting steam sterilisation and/or DD (dichloro‐propane: dichloropropene) prolonged the productive life of their crops for several years.
Intraspecific variation of Myzus persicae on sugar beet (Beta vulgaris)
Authors: LOWE H. J. B.
Published: February 2008

Differences in inherited resistance among seven sugar‐beet stocks had similar effects on Myzus persicae clones representing the range of variation in aphid response to resistant and susceptible sugar beet observed in fifty‐eight clones collected between 1969 and 1971. Three sugar‐beet stocks were consistently resistant. Statistically significant interactions between beet stocks and aphid clones did not indicate the existence of biotypes with specific abilities to overcome resistance. M. persicae clones differed in their vigour of colonizing sugar beet, irrespective of the differences between beet stocks. The readiness of adult aphids to settle determined the size of aphid population produced and included a component related to the response of the aphid clone to sugar beet as a host, and a component related to the resistance ranking of the beet stock. Breeding sugar beet with resistance to aphids will be simplified, as the results indicate that, at present, differences between aphid biotypes need not be considered a problem.
Investigations on fungicides.
Authors: BURDEN R. S. , ROGERS PAMELA M. , WAIN R. L.
Published: February 2008

Uninoculated roots of pea (Pisum sativum) and French bean (Phaseolus vulgaris) have been shown to exude a number of antifungal compounds when grown in a non‐sterile aqueous aerated medium. These have been identified and their possible importance in relation to disease resistance is discussed.
A model for the mechanism of stimulation of latex flow in Hevea brasiliensis by ethylene
Authors: OSBORNE DAPHNE J. , SARGENT J. A.
Published: February 2008

A model is proposed for ethylene stimulation of latex flow from tapping cuts of Hevea brasiliensis, based on the predicted effects of ethylene on the plasticity and structure of cell walls of the latex vessels. Evidence for the model comes from the effects of ethylene on etiolated shoots of Pisum sativum.
Tolerance to ryegrass mosaic virus and its inheritance
Authors: WILKINS P. W.
Published: February 2008

Plant yield within and between four cultivars of perennial ryegrass infected with ryegrass mosaic virus (RMV) was closely related to symptom severity.

Distribution of symptom severity was continuous in four perennial ryegrass and four Italian ryegrass cultivars infected with a severe RMV isolate, and also in another perennial ryegrass cultivar infected with a severe isolate of the virus, a mild one and one of intermediate severity. Symptom expression was polygenically inherited in both Italian (cv. RvP) and perennial (cv. S.24) ryegrass. Both additive and non‐additive genetic variation was present in RvP, but the variation in S.24 was additive only. No significant maternal inheritance was present in either species.
Some effects of freezing temperatures on overwintering larvae of the large elm bark beetle (Scolytus scolytus)
Authors: BARSON G.
Published: February 2008

Overwintering final instar larvae of Scolytus scolytus were tested for coldhardiness by exposure to a range of sub‐zero temperatures (–7°Cto –31 °C) in a frost‐gradient apparatus for 7 days. The Lt50 for larvae removed from the bark (– 20.5 °C) was significantly different (P < 0.01) from the Lt50 (–18.3 °C) for larvae insulated by the bark (thickness of 7 mm ± 2 mm). Larvae with food in their digestive tract were more susceptible to freezing than the overwintering final instars which had voided their stomach contents. Duration and intensity of cold did not cause any adverse long‐term effects. Most of the larvae which survived the sub‐zero treatments were able to pupate or reach the adult stage. The mean supercooling point of the overwintering larvae (–30.85 °C) confirmed their cold‐hardiness.
The effect on gangrene incidence of dusting seed potatoes with benomyl at time of planting
Authors: LOGAN C.
Published: February 2008

In 1 out of 2 years' field trials benomyl applied as a dust treatment at time of planting seed potatoes resulted in an increase in potato gangrene in the progeny of both gangrene‐free tubers planted in land contaminated with Phoma exigua var. foveata and gangrene‐diseased tubers planted in clean land. Gangrene‐infected seed tubers treated with benomyl also produced more stems infected with var. foveata than untreated tubers. Two hypotheses are presented to account for this increase in gangrene which does not occur in seed potatoes treated shortly after lifting.

In all cultivars tested an organo‐mercury dip‐treatment increased total numbers of tubers in the seed and chat‐size grades without increasing total weight whereas benomyl dust increased the numbers in these grades in Majestic only. The treatment of gangrene‐diseased seed with benomyl dust affected neither total weight nor total number of tubers.