bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the taro leaf blight fungus Phytophthora colocasiae in Solomon Islands: control by fungicides and spacing
Authors: JACKSON G. V. H. , GOLLIFER D. E. , NEWHOOK F. J.
Published: February 2008

With mist blower application, copper oxychloride at 2.25 kg/ha was effective in controlling PHYTOPHTHORA colocasiae but mancozeb at 3.6 kg/ha was not. Phytotoxicity from captafol at 1.8 and 3.6 kg/ha nullified any potential gain in yield from control of blight. Leaf removal from healthy plants to maintain four leaves per plant for 90 days, to simulate roguing of leaves for disease control, was shown to cause no loss in yield. However, regular roguing of diseased leaves over the same period in plots affected by a severe epiphytotic did not eradicate the pathogen. When roguing ceased at 90 days disease increased rapidly to epidemic proportions that seriously affected final corm yield.

An attempt to reduce the effect of blight by wider than traditional spacing was unsuccessful. Under continuous epiphytotic conditions disease had the maximum possible impact regardless of spacing. Whereas plants free from competition normally bear six to seven leaves, this number was reduced by severe disease to three or four, the same number as was borne by plants under the competitive conditions of closer‐than‐traditional spacing. Instead of the traditional 20–30 000 plantdha, it was shown that density can be doubled under conditions of high leaf blight hazard and increased yields still be obtained.
Scab disease of cowpea (Vigna unguiculata) caused by Sphaceloma a species of the fungus
Authors: EMECHEBE A. M.
Published: February 2008

Scab disease of cowpea (Vigna unguiculuta) was shown to be caused by Sphaceloma sp. It affects all above ground parts of the plant. The first symptom of the disease, appearing within 3 to 6 days of inoculation, is puckering of the lamina. Spots on mature leaves are white with or without brown margins. Typical scab lesions on petiole, stem, peduncle and pod are white turning dark brown when chlamydospores are formed and are oblong‐elongate except for pod lesions that are ovoid. The most destructive phase is scab of the flowering axis which causes flower and, or, pod abortion or completely prevents flower formation.

Inoculation of asparagus pea (V. sesquipedalis) with a cowpea isolate of Sphaceloma sp. produced symptoms similar to those on cowpea. Inoculated hyacinth bean (Lablab niger) produced atypical mild lesions. The following legumes were not affected when artificially inoculated with the fungus: black gram (Phaseolus mungo), green gram (P, aureus), French bean (P. vulgaris), Lima bean (P. lunatus), groundnut (Arachis hypogaea), and soyabean (Glycine max). The characteristics of the fungus on potato dextrose agar are described.
The role of seed‐tuber and stem inoculum in the development of gangrene in potatoes
Authors: ADAMS M. J.
Published: February 2008

To determine the relative importance of seed tubers and stems as sources of inoculum for potato gangrene in progeny tubers, different levels of inoculum of Phoma exigua var. foveata were established in field experiments by planting rotting or contaminated seed tubers and by inoculating stems shortly before haulm desiccation.

The pathogen was only occasionally detected by isolation from inside green stems in June and July on plants growing from contaminated but unrotted seed. The incidence of pycnidia on desiccated stems increased with increasing concentration of inoculum contaminating seed tubers and with increasing time interval between desiccation and harvest. Stem infection was probably derived from inoculum on seed tubers spreading via the soil to the stem bases. Stem inoculation of plants growing from uninoculated or uncontaminated seed greatly increased both the gangrene potential of progeny tubers (defined as % wounds with gangrene after uniformly damaging tubers and storing them at 5°C for 12 wk), and tuber contamination (defined as % wounds with gangrene after spreading tuber‐borne soil onto test tuber slices and storing them at 5°C for 8 wk). However, when stems of plants growing from rotting or contaminated seed were cut at ground level and removed before desiccation, gangrene potential of progeny tubers was only slightly less than that of tubers from untreated plots. There was no evidence that soil inoculum or aerial spread played a significant role in disease development.

Gangrene potential and contamination of progeny tubers were related to Contamination levels on seed tubers. Some transmission also occurred from rotted seed tubers to progeny. Inoculum levels around progeny tubers increased rapidly after desiccation even in plots where stems had previously been cut at soil level and removed to eliminate pycnidial development above ground as a source of inoculum. Both gangrene potential and contamination of progeny tubers were greater on cv. Ulster Sceptre than on cv. Pentland Crown. The results showed that the inoculum on seed tubers, whether from rots or surface contamination, contributed more to the contamination of progeny tubers at harvest than did the inoculum from pycnidia on stems following desiccation of the haulm.
Effect of inoculum density, stage of plant growth and dew period on the incidence of black point caused by Alternaria alternata in durum wheat
Authors: SOUTHWELL R. J. , BROWN J. F. , WONG P. T. W.
Published: February 2008

Glasshouse studies showed that the incidence of black point caused by Alternaria alternata in durum wheat was positively correlated with both the density of the inoculum and the growth stage of the wheat plants at the time of inoculation. A curvilinear relationship of the form Y=a + log X was found between inoculum density and disease incidence. The incidence of black point was linearly related to the stage of plant growth, between anthesis and the late milk stages of development, at the time of inoculation. A better relationship between growth stage and disease incidence was found when plant growth was expressed as days after anthesis than when the Romig scale was used (R2= 0.30 and 0.24 respectively). A threshold dew period of 3–6 h was required for black point symptoms to develop. The incidence of black point increased with increasing duration of the dew period until maximum disease incidence occurred after exposure to a dew period of 48 h.
Crimson clover latent virus ‐ a newly recognised seed‐borne virus infecting crimson clover (Trigolium incarnatum)
Authors: KENTEN R. H. , COCKBAIN A. J. , WOODS R. D.
Published: February 2008

Crimson clover latent virus (CCLV) was detected in five seed lots of crimson clover (Trifolium incarnatum) from Europe and in one from the United States of America. Ninety‐seven per cent of all crimson clover plants examined were found to be infected but were without symptoms. Keeping crimson clover plants at 32–38°C for 34 days failed to free them from CCLV. The virus was not transmitted by Myzus persicae, but was transmitted by inoculation of sap to Chenopodium album, C. amaranticolor and C. quinoa. Twenty‐four other plant species from seven families were not infected. CCLV was best propagated in C. quinoa in which it caused stunting and systemic chlorosis. Sap from infected C. quinoa was infective after dilution to 10‐2 but not 10‐3, after 10 min at 60°C but not 65°C, and after 20 days at 20°C.

In neutral phosphotungstate, CCLV had isometric particles c. 26 nm in diameter with a hexagonal profile. About 20 to 80 A1cm,260 units of purified virus were obtained from 1 kg of infected C. quinoa or C. amaranticolor leaves by extraction in 0.5 M phosphate buffer, pH 7.5, containing 0.01 M ethylene diamine tetra‐acetate and 0.4% 2–mercaptoethanol and clarification with chloroform‐butanol followed by two precipitations with polyethylene glycol (mol. wt 6000) and several cycles of differential centrifugation. Purified virus sedimented as three components with sedimentation coefficients (s°20, w) of 52S, 101S and 122S. The 101S and 122S components had buoyant densities in CsCl of 1.438 and 1.495 g/cm3 respectively. From these values the nucleic acid content of the 101S and 122S components was estimated to be 32–35% and 40–41% respectively. The virus contained a single protein with an estimated mol. wt of 52 000 and two single‐stranded RNA species of estimated mol. wt 1.6 × 106 and 2.2 × 106. CCLV was serologically unrelated to 31 other morphologically similar viruses. Although its vector is unknown, CCLV seems to have affinities with nepoviruses.

The cryptogram of CCLV is R/1:2.2/40–41 + 1.6132–35:S/S:S/*.
Treatment of seed and ware potato tubers with thiabendazole for control of storage diseases
Authors: HIDE G. A. , CAYLEY G. R. , READ P. J. , FRASER J. H.
Published: February 2008

In March 1977 and 1978 King Edward seed potatoes from three commercial stocks and one stock derived from stem cuttings (healthier seed) were treated with thiabendazole at 320 g a.i./t and 46% of the material applied was deposited on tubers. Seed was stored on trays to sprout and in April samples were planted in replicated plots on two farms in Lincolnshire. Treatment did not consistently affect numbers of stemslplant or total yields but decreased infection of underground stems by Polyscytalum pustulans and Rhizoctonia solani and of tubers at harvest by P. pustulans, R. solani and Helminthosporium solani. In samples stored for 20 wk at Sutton Bridge Experimental Station seed treatment decreased the incidence of skin spot from 25 to 4%, of black scurf from 36 to 20% but had less effect on silver scurf (untreated 52% tubers, treated 47%) and did not affect the incidence of black dot (Colletotrichum coccodes) on stored tubers.

In another series of experiments 1 t samples of seed from six King Edward stocks (1977) and four King Edward and one Maris Piper stocks (1978), collected from different farms in Lincolnshire in March, were treated with thiabendazole at 40 g a.i./t. Tubers retained 48% of the material applied. The treated seed was planted on the respective farms in a single large plot adjacent to untreated seed similarly stored and sprouted. Seed treatment significantly decreased the incidence of skin spot, black scurf, silver scurf and gangrene in tubers stored at Sutton Bridge in 1977–78. After lifting the experiment in 1978 samples from treated and untreated seed were treated with thiabendazole (40 g a.i./t) before storage (ware treatment). Skin spot was decreased more by seed treatment than ware treatment whereas silver scurf was controlled best by ware treatment. Incidence of black dot was not consistently affected by seed or ware treatment.
Beet curly top virus from phloem exudate of Amsinckia douglasiana
Authors: MAGYAROSY A. C.
Published: February 2008

Amsinckia douglasiana when infected with beet curly top virus (BCTV) produces more exudate, which is highly infective, than any other known host. Attempts were made to purify BCTV from the phloem exudate of infected Amsinckia douglasiana by differential centrifugation and sucrose density gradient fractionation. A260/280 ratio of virus preparations was 1.58; S values were 74 and 147. Infectivity was distributed among several fractions during density gradient purification. Electron microscopy revealed the presence of pentagonal and hexagonal particles of 14–23 nm, some of which were paired. The virus was insensitive to DNAse, RNAse, and trypsin when these enzymes were tested individually but infectivity was substantially decreased when the virus was subjected to trypsin treatment followed by DNAse, suggesting that DNA is associated with the beet curly top virus.
Beet curly top virus transmission by artificially fed and injected beet leafhoppers (Circulfer tenellus)
Authors: MAGYAROSY A. C.
Published: February 2008

The transmission of beet curly top virus (BCTV) by leafhoppers, Circulifer tenellus, fed virus through Parafilm® membranes was compared with their transmission when injected with virus from phloem exudates of Amsinckia douglasiana. Virus uptake from 32P‐labelled test solutions and the resulting virus transmission, as measured by an infectivity index, varied widely. By contrast, insects injected with virus transmitted with similar efficiencies. If insects were fasted for 3, 5, or 7 h before a 6 h acquisition access period on test solutions, their 32P, and presumably virus uptake, was greater than that of nonfasted insects and their variability in virus transmission decreased. The proportion of insects transmitting curly top virus, after fasting and given a 6 h acquisition access period, was similar to that of insects injected with virus. Maximum liquid uptake by the beet leafhopper occurred with a 12% sucrose solution.
Effects of infection with the cabbage black ringspot strain of turnip mosaic virus on turnip as a host to Myzus persicae and Brevicoryne brassicae
Authors: HODGSON C. J.
Published: February 2008

When turnip plants with 3–7 leaves were inoculated with cabbage black ringspot virus (CBRSV) on the 3rd rough‐leaf, symptoms only appeared on leaves that had been less than 15 mm long at the time of inoculation, although infection decreased the area and both fresh and dry weight of all leaves. Leaves were ‘aged’ by their appearance and placed in Leaf Age Categories (LACs). Leaves with symptoms senesced (‘aged’) prematurely.

CBRSV‐infection of cv. Green Top White did not change the distribution of populations of Myzus persicae between LACs, but increased the proportion of the plant suitable for colonisation. All suitable LACs were quickly colonised by adult apterae and nymphs. On CBRSV‐infected plants the nymphal period was shorter, F1 adults deposited larvae more frequently and the live body weight and tibial length of the F2 generation was greater, than on healthy plants.

The distribution of Brevicoryne brassicae populations on cv. Green Top White differed from that of M. persicae but was also unchanged by CBRSV‐infection. On healthy plants the largest colonies were on mature leaves, so that on virus‐infected plants premature senescence shortened the life of the colony. On CBRSV‐infected plants the nymphal period was prolonged and the live weight of F1 and F2 adult apterae was less than on healthy plants. The differences between the biology of M. persicae and B. brassicae on CBRSV‐infected cv. Green Top White were associated with the accelerated senescence of CBRSV‐infected leaves.

The possibility that CBRSV‐infection might reduce the resistance of turnips to aphid infestation was tested. M. persicae and B. brassicae were cultured on two favourable and two less favourable cultivars. No improvement in population growth rate was found when the less favourable host cultivars were infected with CBRSV, but both aphid species weighed less and/or had smaller nymphal populations on cultivars showing the severest symptoms. These results are discussed in relation to the evolution of non‐persistent virus transmission by aphids.
Effect of soybean canopy closure on landing rates of aphids with implications for restricting spread of soybean mosaic virus
Authors: HALBERT SUSAN E. , IRWIN M. E.
Published: February 2008

Alate Aphis citricola and Myzocallis punctatus were caught more abundantly on horizontal ermine‐lime canopy‐level sticky traps in a closed soybean canopy than on similar traps in an open canopy. This is the first reported case in which more alate aphids were collected on traps in fields with relatively more ground cover. Capitophorus elaeagni were caught more abundantly on traps in relatively more open canopy, and Lipaphis erysimi, Rhopalosiphum maidis and Schizaphis graminum were collected in statistically similar numbers in open and closed canopies. Our trapping technique was designed in an attempt to collect only those aphids which would otherwise have landed on the soybean canopy. Landing rates differed among species; therefore, the efficacy of using ground cover manipulation to reduce spread of soybean mosaic virus would depend upon seasonal occurrence of the important local vector species.
The use of egg counts and suction trap samples to forecast the infestation of spring‐sown field beans, Vicia faba, by the black bean aphid, Aphis fabae
Authors: WAY M. J. , CAMMELL M. E. , TAYLOR L. R. , WOIWOD I. P.
Published: February 2008

Daily suction trap samples at a height of 12·2 m collected throughout the year, winter egg and ‘spring’ population counts on the spindle tree, Euonymus europaeus, and initial infestations of the black bean aphid, Aphis fabae, on field bean, Vicia faba, crops are available from Southern England since 1970. In different areas, estimates of the sizes of the autumn migrations, the over‐wintering egg populations, the spring fundatrigeniae and the spring migrations, have been used to forecast field bean crop infestation levels which, in turn, project subsequent trap catches of alatae.

The forecasts of crop infestation become progressively more accurate from the autumn migration to the following spring migration, accounting for 28%, 54%, 54% and 64% of the variance respectively. In areas where traps are sited, the spring migration trap samples give the most accurate estimate of the size and timing of crop infestation.

Autumn trap catches are particularly useful as very early forecasts of likely very large or very small populations on field beans about 8 months later, but otherwise they lack precision. Egg sampling in winter provides a considerably more accurate forecast approximately 5 months before crop infestations. In spring (May), fundatrigeniae sampled on spindle are most useful for predicting time of migration, and provide approximately 2 weeks' warning for insecticide application, if needed. Finally, trap sampling of the spring migration provides the latest estimate of both the sizes of crop infestations and the timing of insecticide treatment.

The E. europaeus and aerial sampling systems are complementary, the traps providing systematic, continuous information and the E. europaeus samples greater detail. Combined, they can provide excellent long‐term fore‐warning of the need for chemical control and short‐term warning of control timing. Forecasts have been 90% correct in eight years out of nine. The error in the ninth year may be due to immigration from the European mainland.
The effect of benomyl on some invertebrate inhabitants of a red raspberry, Rubus idaeus, plantation in relation to fruit yield
Authors: MASON D. T. , WOODFORD J. A. T. , TRUDGILL D. L.
Published: February 2008

The growth and yield increases in red raspberry which followed the repeated application of benomyl were not due to the suppression of pests. Benomyl had little effect on numbers of aphids and nematodes which, anyway, were insufficiently abundant to cause damage. Benomyl did, however, decrease the earthworm population.

In the following years, when benomyl was no longer applied, significantly more canes died from midge blight in the plots treated most frequently with benomyl than in the untreated. This was probably a consequence of increased infestation by larvae of the raspberry cane midge (Resseliella theobaldi) in the benomyl‐treated plots because benomyl increased the extent of cane splitting and hence the number of egg‐laying sites for cane midge.
Some epidemiological aspects of post‐bloom fruit drop disease (Colletotrichum gloeosporioides) in citrus
Authors: DENHAM T. G. , WALLER J. M.
Published: February 2008

Fluctuations in the incidence and amount of post‐bloom fruit drop disease of citrus caused by Colletotrichum gloeosporioides in Belize prevent economic disease control. During the cooler drier months of the year when blossom infection is common there are variations in the incidence of rainfall and associated climatic parameters, and in the pattern of flowering. Large amounts of disease develop when periods of rain followed by prolonged wetness occur during peak blossoming periods. Blossoms are most susceptible during the open flower stage and infection of terminal flowers invariably results in infection of all other flowers on the spike. Disease incidence is greater in the lower parts of the trees, but flowering is greater in the upper regions. Large numbers of Colletotrichum spores are produced during wet conditions from apparently healthy leaves and from diseased flowers, but these rapidly lose viability when dried. Few spores are produced from old persistent calices (buttons). Although spores from leaves were a less potent inoculum source than those from flowers, they could provide the initial inoculum to commence flower infection when blossoming starts.
Effects of some fungicides used against cereal pathogens on the growth of Rhizobium trifolii and its capacity to fix nitrogen in white clover
Authors: FISHER D. J. , HAYES ANN L.
Published: February 2008

Fungicide residues in soils may affect nitrogen fixation by legumes. Effects of nine systemic fungicides, used against cereal pathogens, on Rhizobium trifolii and white clover were measured. Fenarimol and oxycarboxin inhibited growth of R. trifolii in vitro. The weight of clover plants after 10 weeks' growth in soil containing carboxin, oxycarboxin, benodanil, tridemorph and pyracarbolid was reduced. Symbiotic nitrogen fixation was decreased by carboxin, oxycarboxin and tridemorph present in soil at concentrations somewhat greater than that likely to result from several applications of the fungicide. Only tridemorph reduced nodulation. None of the compounds seems likely to affect nitrogen fixation in the field if applied at the recommended rate.
Cellulose xanthate as a soil conditioner: implications for weed control with some soil‐applied herbicides
Authors: ROBERTS H. A. , BOND W. , WALKER A. , PAGE E. R.
Published: February 2008

Applications of cellulose xanthate equivalent to 50 kg cellulose/ha to fresh seedbeds preserved surface microtopography and prevented capping after rainfall. Numbers of weed seedlings were up to 50% greater than on untreated soil where capping occurred. The efficiency of nine soil‐acting herbicides was not impaired when applied at normal rates either before or after cellulose xanthate. There was no evidence of interaction and the numbers of surviving weeds were proportional to the numbers where no herbicide had been applied. With propachlor, however, weed control was consistently less when applied shortly before or after cellulose xanthate, and analyses showed that in the presence of the soil conditioner the rate of herbicide loss was enhanced. This effect decreased the longer propachlor application was delayed, but was still evident with an interval of 96 h.
Genetic aspects of resistance to cocoa swollen‐shoot virus in Ghana
Authors: LOCKWOOD G.
Published: February 2008

The inheritance of resistance in cocoa to infection with cocoa swollen‐shoot virus was studied in seed inoculation experiments with progenies of Upper Amazon, Trinitario and West African Amelonado parents. In an eight parent diallel cross grown in two seasons and in six male × female factorial experiments, general combining abilities were much more important than specific combining abilities. The diallel cross revealed significant maternal effects but there was little evidence of specific reciprocal differences. Estimates of general combining abilities corresponded with expectation and were positively correlated with maternal effects, the latter indicating that tester parents should be used as males.

The results from scaling tests with hybrids between selections from the River Nanay (a Peruvian tributary of the River Amazon) and Amelonado fitted a model with additive resistance; there was no evidence of dominance.

Attempts to obtain stronger sources of resistance by hybridisation and selection were unsuccessful. In three crosses the resistance of individual seedlings was compared with that of the parents using test crosses but no evidence of transgressive segregation was obtained. In further experiments seedings of two hybrids between contrasting parents were heavily inoculated with virus so that few healthy survivors remained. Test crosses showed that these survivors and randomly selected seedlings of the same parentage did not differ as resistance sources.
The effect of different water regimes on plant growth and nodule structure of greenhouse‐grown winged bean (Psophocarpus tetragonolobus)
Authors: RATHFELDER ERICA L.
Published: February 2008

Plants of Psophocarpus tetragonolobus cv. Chimbu Illinois were germinated under uniform conditions, after which they were transferred to three water treatments, ‘wet’, control and ‘stress’. Those plants given most water (i. e. ‘wet’) grew best and produced most root nodules.

Water stress delayed nodule formation and quantitative microscopic examination showed that nodules from stress plants had more bacteroid‐containing cells per unit area up to 4 wk than nodules from either of the other treatments. Bacteroid‐containing cells were found to be vacuolated in P. tetragonolobus.
Benefits of ethylene removal during apple storage
Authors: KNEE M. , HATFIELD S. G. S.
Published: February 2008

The potential use of an ethylene absorbent in controlled atmosphere storage of two varieties of apple has been investigated. With Golden Delicious, the rise in ethylene concentration during controlled atmosphere storage can be delayed for about 40 days but not prevented by inclusion of potassium permanganate in the storage container. But with Bramley's Seedling, potassium permanganate can delay ethylene accumulation for over 200 days. Ethylene treatment of Bramley's Seedling in a flowing stream of 5% CO2:3% O2:92% N2 caused accelerated softening, accumulation of α‐farnesene and earlier onset of superficial scald. Use of potassium permanganate to remove ethylene during storage in static controlled atmosphere conditions retarded all three processes in Bramley's Seedling kept in 5% CO2:3% O2 and in 9% CO2:12% O2. However, in one experiment, ethylene removal in 5% CO2:3% O2, led to external and internal symptoms of CO2 damage. A subsequent investigation of the combined effects of harvest date, store temperature and ethylene removal in 5% CO2:3% O2 did not show any damage or accumulation of succinic acid which is known to be involved in CO2 injury. This experiment revealed that ethylene removal could be successfully accomplished on Bramley fruit harvested up to a month after the usual date and little α‐farnesene accumulated in this fruit. Nevertheless scald did develop on late picked fruit and this raises doubts about the causal role of farnesene in scald.
Quantitative studies on the uptake and retention of potato leafroll virus by aphids in laboratory and field conditions
Authors: TAMADA T. , HARRISON B. D.
Published: February 2008

Enzyme‐linked immunosorbent assay (ELISA) was adapted for the efficient detection and assay of potato leafroll virus (PLRV) in aphids. Best results were obtained when aphids were extracted in 0.05 M phosphate buffer, pH 7.0, and the extracts incubated at 37 °C for 1 h before starting the assay. Using batches of 20 green peach aphids (Myzus persicae), about 0.01 ng PLRV/aphid could be detected. The virus could also be detected in single aphids allowed a 1‐day acquisition access period on infected potato leaves. The PLRV content of aphids depended on the age of potato source‐plants and the position of source leaves on them. It increased with increase in acquisition access period up to 7 days but differed considerably between individual aphids. A maximum of 7 ng PLRV/aphid was recorded but aphids more usually accumulated about 0.2 ng PLRV per day. When aphids were allowed acquisition access periods of 1–3 days, and then caged singly on Physalis floridana seedlings for 3 days, the PLRV content of each aphid, measured subsequently, was not strongly correlated with the infection of P. floridana. The concentration of PLRV in leaf extracts differed only slightly when potato plants were kept at 15, 20, 25 or 30 °C for 1 or 2 wk, but the virus content of aphids kept on leaves at the different temperatures decreased with increase of temperature. PLRV was transmitted readily to P. floridana at all temperatures, but by a slightly smaller proportion of aphids, and after a longer latent period, at 15 °C than at 30 °C.

The PLRV content of M. persicae fed on infected potato leaves decreased with increasing time after transfer to turnip (immune to PLRV). The decrease occurred in two phases, the first rapid and the second very slow. In the first phase the decrease was faster, briefer and greater at 25 and 30 °C than at 15 and 20 °C. No evidence was obtained that PLRV multiplies in M. persicae. These results are compatible with a model in which much of the PLRV in aphids during the second phase is in the haemocoele, and transmission is mainly limited by the rate of passage of virus particles from haemolymph to saliva.

The potato aphid, Macrosiphum euphorbiae, transmitted PLRV much less efficiently than M. persicae. Its inefficiency as a vector could not be ascribed to failure to acquire or retain PLRV, or to the degradation of virus particles in the aphid. Probably only few PLRV particles pass from the haemolymph to saliva in this species.

The virus content of M. euphorbiae collected from PLRV‐infected potato plants in the field increased from early June to early July, and then decreased. PLRV was detected both in spring migrants collected from the plants and in summer migrants caught in yellow water‐traps. PLRV was also detected in M. persicae collected from infected plants in July and August, and in trapped summer migrants, but their PLRV content was less than that of M. euphorbiae, and in some instances was too small for unequivocal detection.
Effects on straw decay of the herbicides paraquat and glyphosate in combination with nitrogen amendments
Authors: GROSSBARD E. , HARRIS D.
Published: February 2008

The effects of paraquat were studied at 4.7 kg a. i./ha and of glyphosate at 9.4 kg a. i./ha on the weight loss and rate of oxygen uptake by stems of barley straw, incubated on the soil surface for various periods of time, and stems and leaves of wheat straw on the soil surface or covered with a shallow layer of soil. In general, paraquat reduced weight loss and frequently oxygen uptake. Glyphosate normally had no effect but occasionally it was stimulatory. However, in isolated instances, paraquat was inactive and glyphosate slightly inhibitory. Leaves decayed faster than stems. Burial, as well as the addition to straw of leaf protein, Nitrochalk, urea and clover plants increased decomposition in all treatments, but nitrogen amendments were less effective in those with paraquat. For example, urea enhanced weight loss after 21 wk from 19 to 34% of the initial weight in unsprayed wheat straw, from 12 to 24% in paraquat‐treated and from 20 to 37% in glyphosate‐treated straw, indicating that conditions stimulating decomposition may attenuate but not entirely eliminate the inhibitory effects of paraquat. A repeated addition of nitrogen to straw in various stages of decay increased oxygen uptake in all treatments but least in the paraquat‐treated straw, implying that a complete recovery from the initial curtailment of microbial activity, brought about by this herbicide, did not occur. Although the concentration of paraquat used was nine times greater than the minimum recommended for field application, the degree of inhibition observed in these laboratory experiments was probably not sufficiently great to be of marked economic importance.
Resistance of rin and nor tomato mutants to postharvest Rhizopus infection
Authors: BARKAI‐GOLAN RIVKA , KOPELIOVITCH E.
Published: February 2008

Fruits of the two non‐ripening mutants of tomato, rin and especially nor, were markedly more resistant to Rhizopus stolonifer infection than the normal Rutgers fruit. Following artificial inoculations by contact with a diseased normal tomato covered with mycelium and sporangia, no infection of unwounded nor fruit occurred at its mature‐green stage. At the mature stage the resistance of nor mutant fruit was manifested by a prolongation of the incubation period of the disease as well as by a markedly reduced incidence of rotted fruits. Chilling injury of fruit, prior to spore inoculation, was found to be a good means for indicating the relative resistance of the mutants as compared with the normal tomato.

The relationship between the resistance of the mutant tomatoes to Rhizopus infection and their response to induced peel damage as a result of the contact or the chilling procedure, led to the assumption that fruit resistance is associated with the inability of the fungus to penetrate the periderm, rather than with fungal development within the fruit.
Growth compensation for destroyed and replaced plants in Central African field tobacco*
Authors: SHAW M. J. P. , WIXLEY R. A. J.
Published: February 2008

Plants surrounding a gap in stand compensated to some extent for leaf yield lost to missing plants. The contribution of plants in an adjacent row was much less than that of plants next to the gap within the row. Losses were reduced and quality was improved by replacing destroyed plants within two weeks of the original planting.
Effect of 2, 4‐D analogues on the induction and maintenance of callus in maize tissue culture1
Authors: JIMÉNEZ ESTELA SÁNCHEZ DE , ALBORES MARTHA , LOYOLA‐VARGAS VICTOR M.
Published: February 2008

Six analogues of 2, 4‐D: 2(2‐methyl‐4‐chlorophenoxy) propionic, 2(2,4‐dichloro‐phenoxy) propionic, 2(2‐methyl‐4‐chlorophenoxy) butyric, 2(2,4‐dichlorophenoxy) butyric, 2(2,4‐dichlorophenoxy) butyric acids and the separated enantiomers of 2(2, 4, 5‐trichlorophenoxy) propionic acid were examined for their ability to induce callus development and maintain its growth in maize (Zea mays) tissue cultures. The results indicate that the analogues were more effective than 2, 4‐D in both respects and that alkyl substitution on the carbon side chain of the acids increased the auxin effect. It was also shown that only the (+) isomer of the two enantiomers studied, had auxin activity.
Effects on dry weight and nitrogen content of grains of semi‐dwarf and tall varieties of winter wheat caused by decreasing the number of grains per ear
Authors: THORNE GILLIAN N.
Published: February 2008

The number of grains in ears of six varieties of winter wheat growing in the field was decreased by removing the top half of the ear 6 days after anthesis (halving). In the semi‐dwarf varieties Hustler, Sentry and Hobbit, and in the taller varieties Armada and Flanders, the mean dry weight per grain in the lower six spikelets of halved ears was about 23% greater than the dry weight of grains in the comparable part of intact ears. In Maris Huntsman the increase in grain size amounted to only 13%. Halving increased the number of grains in the semi‐dwarf varieties but not in the others. Consequently, the increases caused by halving in the total weight of grain in the lower six spikelets ranged from 41% in Hustler and Hobbit to 7% in Maris Huntsman.

Halving increased the amount of nitrogen in the grain of the lower half of the ear similarly in all varieties, and relatively more than it increased dry weight. So nitrogen per cent dry weight of grain was increased, especially in Armada, Flanders and Maris Huntsman which responded least in dry weight. The uptake of nitrogen into the stem plus ear after anthesis was unaffected by halving. Most of the nitrogen that normally moved to the upper grains accumulated in the lower grains of halved ears.

More nitrogen moved into the grain of intact ears of tall than of semi‐dwarf varieties after anthesis, because there was greater uptake of nitrogen into the shoot from the roots.
Fungus diseases on potato seed tubers planted in England and Wales, 1963‐76
Authors: HIDE G. A.
Published: February 2008

During 1963‐76 samples of potato tubers from commercial seed stocks of cvs King Edward (14 yr), Pentland Crown (9 yr), Majestic (7 yr), Pentland Dell (3 yr), Record and Arran Pilot (2 yr) were received from farms in England and Wales. Fifty tubers from each sample were examined macroscopically for fungus diseases and eyes were excised from a 20‐tuber sub‐sample, incubated and examined for pathogenic fungi; 50 tubers were stored on trays to sprout and examined for diseases and sprouting in May and in most years samples of 50 tubers were wounded by dropping onto expanded metal, stored at 5° C and examined for gangrene and dry rot after 12 wk.

Amounts of disease varied between years and during 14 yr black scurf and powdery scab on King Edward tended to increase and skin spot and late blight decrease. On average 44% of King Edward tubers were affected with skin spot, 25% with black scurf and 16% with powdery scab. Gangrene affected 5% of tubers and 97% of the isolates from rots were identified as Phoma exigua var. foveata. Wounding tubers increased the incidence of gangrene three‐fold.

During 1963‐69 late blight affected 2% of King Edward tubers but fewer in later years and in other cultivars. Majestic had most common scab (44% tubers) and Arran Pilot most dry rot (9% tubers) and this disease was increased by wounding tubers. Conidiophores of Helminthosporium solani (silver scurf) were more common on excised eyes of Pentland Crown, Record and Arran Pilot than of other cultivars, and isolations from verticillate conidiophores that developed on the side of incubated eye plugs of King Edward and Majestic stocks gave pure cultures of Verticillium tricorpus (78%), V. nigrescens (9%) and V. nubilum (3%).

Proportions of tubers with different diseases were affected by their country of origin; Scottish seed had most skin spot and gangrene, Irish seed most powdery scab and English seed most common scab, late blight and H. solani. There was also evidence of differing disease incidence in seed from different geographical areas in Scotland and England.

Up to half the King Edward and Pentland Crown stocks examined in 1975 and 1976 were derived from stem cuttings and average amounts of diseased tubers were similar to those in stocks not derived from stem cuttings.

Annual and cultivar differences in disease incidence and effects of date of receipt of seed on farms are discussed.
Studies on the survival and infective ability of dicarboximide‐resistant strains of Botrytis cinerea
Authors: DAVIS R. P. , DENNIS C.
Published: February 2008

Few dicarboximide‐resistant strains of Botrytis cinerea produce macroconidia either on culture media or on natural substrates, although, the viability of such conidia was similar to those of sensitive strains. The ability of dicarboximide‐resistant strains to infect strawberries was similar to that of sensitive strains and most of the resistant strains competed successfully with sensitive strains when inoculated in equal numbers onto detached strawberries and onto flowers of field‐grown plants, especially after treatment with dicarboximide fungicides. All resistant strains tested survived for at least 9 months on inoculated strawberry leaf litter although their incidence was ‘diluted’ by wild type sensitive strains. Sporulation and dispersal of resistant strains from the litter was very limited resulting in a low incidence of fruit infection even after treatment with dicarboximides. Consequently, there was no significant increase of resistant strains in the plantation and control of infection was maintained with iprodione and dichlofluanid. Poor sporulation of dicarboximide‐resistant strains of B. cinerea is considered to be the single most important factor in limiting their development in the field.
Seed and soil: sources of inoculum for the colonisation of the foliage of solanaceous hosts by Pseudomonas solanacearum
Authors: MOFFETT MELDA L. , WOOD BARBARA A. , HAYWARD A. C.
Published: February 2008

Pseudomonas solanacearum was transmitted from contaminated seed to the cotyledons of capsicum (Capsicum frutescens) at 92, 73 and 60% r. h. and to the cotyledons of tomato (Lycopersicon esculentum) seedlings at 92% r. h. Subsequent epiphytic colonisation of the true leaves of capsicum occurred at 92 and 73% r. h. An increase in the population on capsicum cotyledons was detected at 92 and 73% r. h. but only at the higher r. h. was an increased population of P. solanacearum associated with the colonisation of the true leaves. Lesions developed on the true leaves of capsicum at 92% r. h. Transmission of P. solanacearum from capsicum seeds was affected by inoculum concentration, occurring at an infestation level of ∽ 103 propagules seed‐1 but not at 50 propagules seed‐1. Pseudomonas solanacearum was detected on the cotyledons of capsicum held at 98% r. h. after germination of seed in soil infested with 2 × 108 propagules g‐1 soil; lesions were detected on cotyledons 11 days after planting and invasion occurred in 10 stems and one root of the 20 seedlings sampled. The movement of the pathogen from the soil to the seedlings was affected by the level of soil infestation. Pseudomonas solanacearum was detected in four pairs of cotyledons, two stems and one root of the 36 seedlings sampled from soil infested with 107 propagules g‐1 soil but it was not isolated from seedlings sampled from soil infested with 105 or 4 × 103 propagules g‐1 soil. Leaf and stem prints demonstrated the epiphytic nature of this organism on the cotyledons and stems of seedlings.
A possible virus cryptic in carnation
Authors: LISA VITTORIA , LUISONI E. , MILNE R. G.
Published: February 2008

Small isometric virus‐like particles were found in low concentration in apparently healthy carnations of the Mediterranean, miniature and Chinese type but not in eleven Sim cultivars tested. Most carnations containing these particles were from Italy but some were from France and the USA. The particles were not transmitted by grafting or by mechanical inoculation but were seed‐transmitted to a large proportion of seedlings. Antisera to partially purified particles were obtained. The particles did not react with antisera to twenty‐eight isometric plant viruses or virus‐like particles but were serologically related to similar particles found in carnations in England, Holland and Israel. When negatively stained, the particles were isometric with a diameter of about 29 nm and a rounded rather than angular profile, but without clear substructure; some particles were penetrated by the stain. The particles remained intact in neutral sodium phosphotungstate. After isopycnic centrifugation in CsCl solution, preparations of particles formed a main band of mean density 1.377 g/ml and other fainter bands that varied in intensity and position in different preparations. In thin sections of carnations, no virus‐like particles or cytological abnormalities were observed.
Observations on the population dynamics and vertical distribution of trichodorid nematodes in a Scottish forest nursery
Authors: BOAG B.
Published: February 2008

The population dynamics of Trichodorus primitivus, T. velatus and Paratrichodorus pachydermus was followed between April 1974 and March 1977 in a forest nursery growing young Sitka spruce (Picea sitchensis) trees. Soil samples taken at 10 cm intervals between 0–50 cm indicated that nematode and root distribution were not correlated and numbers of T. velatus were greatest between 0–29 cm and T. primitivus between 30–49 cm. After 3 yr trichodorid numbers between 0–19 cm had increased and those between 40–49 cm had decreased.

The sex ratio of T. primitivus and T. velatus males to females was 1:1.6 and 1:1.5 respectively while for P. pachydermus it was 1:1.0. The ratios of adults to larvae varied with depth, the proportion of T. primitivus and T. velatus larvae increasing with depth but for P. pachydermus the greatest larval to adult ratio was in the top 10 cm.

No consistent seasonal fluctuations were observed in the populations of all three species although larval numbers were proportionally greater than adult numbers in the summer and autumn of 1975 and 1976.
An analysis of the epicuticular wax of Chenopodium album leaves in relation to environmental change, leaf wettability and the penetration of the herbicide bentazone
Authors: TAYLOR F. E. , DAVIES L. G. , COBB A. H.
Published: February 2008

The fine‐structure, epicuticular wax and contact angle characteristics of Chenopodium album leaf surfaces have been examined with respect to the control of this weed by the herbicide bentazone. Epicuticular wax analysis and contact angle measurements suggest a relative impermeability to bentazone (BAS 35107H), that may be enhanced by the inclusion of the oil adjuvant Actipron (BP Oil Ltd) to the formulation. Under different regimes of light, temperature and relative humidity the chemical composition of the epicuticular wax layer remained relatively constant, whereas herbicide efficacy was greatly altered. These findings are discussed in relation to the mode of action and penetration of bentazone in this species.
Uptake of 32P labelled phosphate by clover and ryegrass growing in mixed swards with different nitrogen treatments
Authors: GOODMAN P. J. , COLLISON M.
Published: February 2008

Lolium perenne cv. S.23 and Trifolium repens cv. Olwen were sown together in 1975, fertilised then and in 1976, and finally given nitrogen doses of either 50, 100, 200 or 400 kg/ha (as N) combined with 0.64 times as much potassium (as K2O) in 1977. As nitrogen increased, grass yield increased, but clover decreased. Grass roots absorbed more 32P than clover roots, and nitrogen increased this difference. Grass roots bore more mycorrhiza than clover roots. The difference in 32P uptake between grass and clover was less in June and July than in August. Clover roots took up most phosphate from the upper layers of soil, while grass absorbed 32P rather uniformly down to 25 cm. It was concluded that optimum fertiliser placement for clover growth was a surface dressing in the early season.
Biochemical changes in tomatoes stored in modified gas atmospheres. I. Sugars and acids
Authors: GOODENOUGH P. W. , THOMAS T. H.
Published: February 2008

During long‐term storage in modified gas atmospheres (MGA), some of the biochemical changes occurring in tomato fruit, cv. Sleaford Abundance, were compared with those in fruit of some Israeli cultivars which had been selected for firmness and slow ripening. The MGA used in the experiments did not succeed in completely restricting changes in sugars and acids during storage, although colour change was prevented. This separation of processes is discussed in relation to the practice of long‐term storage and its implications for fruit flavour.
Biochemical changes in tomatoes stored in modified gas atmospheres. II. Isoenzymes involved in glycolysis and the citric acid cycle
Authors: GOODENOUGH P. W. , THOMAS T. H.
Published: February 2008

A comparative study of the isoenzymes involved in sugar and organic acid metabolism was made during long‐term storage of Sleaford Abundance, a poor storing tomato cultivar, and several breeding lines selected for fruit firmness or retarded ripening. Of the enzymes investigated, major changes occurred in hexokinase, enzymes of the hexose monophosphate shunt, NADH and NADPH dehydrogenase during storage but no major differences in the patterns of enzyme change were detected between cultivars.