Showing papers in "Annals of Applied Biology in 1964"

Strawberry latent ringspot: a new nematode‐borne virus

Abstract: SUMMARY The properties and mode of transmission of strawberry latent ringspot virus (SLRV) are described Natural infections have been found, in several widely separated localities, on cultivated and wild rosaceous species—strawberry, raspberry, cherry, plum, black currant—and on elder (Caprifoliaceae), but so far no diseases in these plants have definitely been associated with SLRV Similarly, SLRV was transmitted mechanically to a wide range of hosts, many of which it infected symptom-lessly SLRV is transmitted by Xiphinema diversicaudatum (Micoletsky), has polyhedral-shaped particles of about 26 mμ diameter, and has other features that suggest it should be classified along with a group of other similar soil-borne viruses

The effect of planting date and spacing on the incidence of groundnut rosette disease and of the vector, Aphis craccivora Koch, at Mokwa, Northern Nigeria

Abstract: SUMMARY At Mokwa in Northern Nigeria early planting and close spacing increased the yield of groundnuts and decreased rosette incidence. With late planting, increasing the plant population reduced both the rosette incidence and the number of aphid-infested plants. It is suggested that winged Aphis craccivora Koch bring the virus into the crop, and that spacing and planting date affect rosette incidence because of the influence of groundcover on the optomotor landing response of the winged aphids.

Carrot motley dwarf and Parsnip mottle viruses.

Abstract: SUMMARY Carrots that show symptoms of carrot motley dwarf contain two viruses, carrot mottle virus (CMV) and red-leaf virus (RLV). CMV cannot be manually inoculated to carrot, but can be to some other members of the Umbelliferae, as well as to some species of the Solanaceae, Leguminoseae and Chenopodiaceae. The host range of RLV is limited to the Umbelliferae, and it is not manually transmissible but was transmitted by grafting. Cavariella aegopodiae Scop, transmits RLV alone but will transmit CMV only from plants infected with both viruses. Thus aphids were unable to transmit from coriander plants manually inoculated with CMV, but after these plants were infected with RLV by aphids, virus-free aphids acquired and transmitted both viruses from them. Aphids remain infective with both viruses for 1–2 weeks, and retain infectivity through the moult. A minimum total of about 9 hr. is needed for acquisition and transmission; vector-efficiency increases with increasing feeding times up to severaj days. The viruses causing motley dwarf become attenuated in the glasshouse after continued aphid-transmission; avirulent isolates protect their hosts against infection by virulent ones. Infectivity of saps from CMV infected plants was increased by extraction at high pH in the presence of a trace of Zn, and was associated in carrot with particles 30 mμ in diameter. Water-phenol extracts are almost as infective as extracts in buffer, but are inactivated by 0·02 μg./l. pancreatic ribonuclease. Parsnip mottle virus (PMV) resembles CMV in many ways, but also differs in some important respects. Unlike CMV it infects celery and parsnip, and it is transmitted by C. pastinacae as well as C. aegopodiae, the only vector of CMV (in combination with RLV). PMV is transmitted by aphids from plants infected with it alone, whether these plants were infected by aphids or by manual inoculation. Carrot plants infected first with PMV and then with the motley dwarf virus complex developed symptoms of motley dwarf, but in coriander the reverse happened. CMV and PMV appear to interfere with each other's multiplication in the hosts, but CMV is dominant in carrot and PMV in coriander. They have some properties of distantly related strains.

The toxicity to fish of mixtures of poisons

Abstract: SUMMARY Experiments have been made with rainbow trout in solutions of ammonium chloride and zinc sulphate to examine the empirical rule that a mixture of two poisons, P and Q, should be at the threshold concentration for acute toxicity when PS/PT + QS/QT= I, where the suffix S stands for the concentration in solution and T for the threshold concentration of a poison when tested by itself. The most detailed experiment, with a hard dilution water in which the dissolved-oxygen concentration was at the air-saturation value, gave results within 4% of those expected from the hypothesis. Agreement was not so close in a soft dilution water, nor in a hard dilution water containing a reduced concentration of dissolved oxygen, but in these two cases the threshold concentrations for the mixtures were within 26 and 17% of the expected value of unity. In every case the rule under examination provided a better description of the data than models based on the hypothesis of independent joint action.

The feeding, growth and reproduction of Aphis fabae Scop. on Viciu fuba under experimental conditions

Abstract: SUMMARY The total amount of sap ingested by individual larvae and adult (apterous virgino-parae) of Aphis fabae on field beans was estimated by adding the weights of honeydew excreted and of water lost by evaporation to increases in body weight during growth and to the weight of larvae born throughout the lives of the adult insects. The quantity of respiratory gases was ignored. Temperature and lighting were kept constant; air humidity was kept high to lessen evaporation, and air movements were eliminated. A machine was made to collect simultaneously the excreta of ten individual aphids to record their total daily excreta continuously from birth to death. Honeydew was also collected daily in mineral oil from other aphids of the same age on similar plants, to estimate the size of the droplets. The mean excretion rate was estimated from the product of the mean frequency of excretion and the mean size of the droplets. The reproductive rate, fecundity and length of reproductive and post-reproductive life of the adult aphids were also recorded. The larva ingested about 3–5-45 mg. of sap in a life of 7 days and the adult about 30 mg. during a reproductive life of 21 days; only about 10% was used for growth and reproduction. The excretion of the adult rose to a maximum of 30–40 drops per day on the third day of adult life and then declined, apparently because of changes within the aphid itself, for when the insects were transferred to fresh plants the excretion continued to decrease. The rate of feeding, which is about equal to the rate of excretion, therefore also decreased as the insect aged but its rate of reproduction remained fairly steady for about 16 days. The swelling of the abdomen and the slight increase in weight during the post-reproductive life of about 2 weeks suggested that, although excretion had stopped, small amounts of sap continued to be ingested. The aphids ingested about the same amount of sap on two varieties of field bean but were significantly more fecund on one than on the other, a difference probably attributable to differences in the quality of the sap of the two varieties.

Estimation of slug populations

Abstract: SUMMARY It is impracticable to count slugs per unit area in the field, but both slugs and their eggs are recovered efficiently by soil washing in the laboratory. A less laborious method is described in which slugs (only) are expelled from turves progressively immersed in cold water. This method, used with samples of twelve 12×12×4 in. units of substratum, gives satisfactory estimates for Agriolimax reticulatus and Arion intermedim at population densities above I per sq.ft.

Natural mortality of eggs of the black bean aphid, Aphis fabae Scop., on the spindle tree, Euonymus europaeus L

Abstract: SUMMARY Egg mortality of Aphis fabae Scop, ranged from 18 to 73% on individual bushes of Euonymus europaeus L. at different sites in Hertfordshire during the winters of 1958—59 and 1959-60. Field and laboratory experiments indicated that the average mortality is unlikely to exceed about 40% and is probably relatively unimportant in limiting subsequent increase to pest density. Winter temperatures in. Southern England do not harm eggs except perhaps at hatching time. Some eggs are destroyed by Anthocoridae and by birds. Others either fail to develop, or develop fully but fail to hatch, even when the weather is apparently favourable and natural enemies are absent.

The life‐history of the Indian meal‐moth, Plodia interpunctella (Hübner) (Lep. Phycitidae) in a warehouse in Britain and on different foods

Abstract: SUMMARY In a population of Plodia interpunctella living on 4 tons of bagged American maize stored in a Nissen hut, fewer adults than expected emerged in the spring, as many pupae were killed by high temperatures close to the roof. In spite of this, a population of approximately eighteen adults gave rise 3 months later to 643 larvae. There were indications that the life cycle might be completed in 9 weeks, as a second generation of adults started to emerge within this period. Larvae preferred bags stacked flat to those stacked upright. They tended to occur in the upper parts of stacks, to spin their cocoons in the necks of bags and to remain in their existing sites without showing any indication of migrating. Of four food materials tested in laboratory studies, no. 3 N. Manitoba Tough wheat induced quickest development, followed by sultanas, American yellow corn and almonds. Of four types of wheat, Australian was more suitable than no. I N. Manitoba or U.S. Northern Spring; English wheat was the least suitable. Milo (N. American sorghum) was as good as no. I N. Manitoba and U.S. Northern Spring wheats, and Plate maize was comparable to English wheat. Groundnuts were less satisfactory and maize meal gave poorer results than any other food. The main period of emergence of adults was short on those foods which induced the most rapid development but prolonged on those on which the development period was longer. The life cycle was unusually long in a proportion of individuals which were reared on American yellow corn, no. I N. Manitoba wheat and almonds. In these examples the fully grown larvae underwent a long period of rest within the cocoon, suggesting a facultative diapause. Mortality of pre-adult stages appeared to be higher when the period of development was longer.

The toxicity to fish of mixtures of poisons: II. Copper-ammonia and zinc-phenol mixtures

Abstract: SUMMARY Tests with rainbow trout in mixtures of ammonium chloride with copper sulphate and of phenol with zinc sulphate have shown that the threshold of toxic concentration for a 50% mortality occurs in solutions for which a value of I is obtained by summing the concentrations of the individual poisons expressed as fractions of their individual threshold concentrations. With ammonia-copper mixtures this method of predicting the threshold concentration becomes progressively less adequate as lower percentage mortalities are considered.

A form of pea early‐browning virus found in Britain

Abstract: SUMMARY A form of pea early-browning virus (PEBV), found in many crops of peas and a few of lucerne on sandy soils in Norfolk and Suffolk, was transmitted by inoculation of sap to many herbaceous species. Chenopodium amaranticolor and Phaseolus vulgaris were useful as indicator plants, and Nicotiana clevelandii for propagating the virus. Its thermal inactivation point was 74–78°C., dilution end-point about 10-5, and sap was still infective after 1 year at 20°C. Partially purified preparations contained tubular particles about 20 mμ wide, most of which were about 100 or about 200 mμ long. Isolates from different fields in Britain were closely related serologically, but were only distantly related to a Dutch isolate of PEBV; they seemed serologically unrelated to four other viruses with particles of similar shape and size. Some isolates of PEBV were not readily transmitted using sap as inoculum, but readily with extracts made from leaves using water-saturated phenol or bentonite. By contrast with other isolates, they caused recurrent necrotic symptoms in N. clevelandii, sap from which did not contain tubular particles. Pea, lucerne, cucumber, tobacco and sugar-beet seedlings became infected when grown in soil from fields with affected crops. All infested soils contained either Trichodorus viruliferus Hooper or T. primitivus (de Man), sometimes together with other Trichodorus spp.; T. viruliferus transmitted the virus in experiments. This contrasts with PEBV in the Netherlands, which is transmitted by T. teres and T. pachydermus.

Studies on sharp eyespot disease of cereals

Abstract: SUMMARY Several isolates of Rhizoctonia solani Kuhn were obtained from wheat stems bearing lesions of sharp eyespot in the summers of 1960 and 1962. Differences in virulence of these isolates, assessed by severity of attack on seedlings, were demonstrated. Isolates taken from different plants in the same crop were shown to differ in virulence. All isolates obtained from wheat-stem lesions attacked both winter and spring varieties of wheat, barley, oats and rye. Several varieties of spring and winter wheats showed no differences in susceptibility to disease. Infection of the wheat host took place at any time during the growing period, but was most severe in the earlier stages of growth. Sharp eyespot occurs over a wide range of soil types, but the most severe attacks all occurred on lighter soils with neutral to slightly acid pH. Sand-culture experiments showed no effect of pH on disease development over the range 5·9-8·1. Disease development in seedling wheat plants was favoured by cool (9·3°C.) dry (ca. 20% of the water-holding capacity) conditions in the greenhouse. Disease incidence in the field over the period 1959-63 could be correlated with the weather conditions prevailing over this time.

The influence of date of origin of the shoot and level of nitrogen on ear size in three perennial grasses

Abstract: SUMMARY In plants of S.24 ryegrass, S.215 meadow fescue and S.37 cocksfoot grown in the field, or with controlled nutrition in the glasshouse, ear size decreased the later the date of origin of the shoot between October and March, before flowering in late spring. The smaller ear size in shoots arising at successively later dates resulted from decreased numbers of primary branches in the ear, and also from the development of fewer florets on each branch. The decrease in number of primary branches was correlated with a decrease in number of unexpanded leaf primordia accumulated at the shoot apex before reproduction. No effect of nitrogen on ear size was detected when nitrogen was added as ‘Nitro-chalk’ to plants growing one yard apart in the field. In contrast, plants receiving the smaller rates of nitrogen in the glasshouse generally developed ears with fewer florets on each lateral branch. Lack of nitrogen also decreased the number of primary branches in ears of ryegrass and prevented many shoots of all three varieties from flowering.

Studies on the lettuce big-vein virus and its vector Olpidium brassicae (Wor.) Dang

Abstract: SUMMARY It was demonstrated by serial graft transmission experiments that the big-vein disease of lettuce was caused by lettuce big-vein virus (LBVV). An Olpidium sp., always found in the roots of naturally affected plants, induced the disease when its zoospores were transferred to healthy plants. The fungus was identified as O. brassicae (Wor.) Dang. The same fungus was found in the roots of healthy lettuce, but zoospores from this source would not induce big-vein when transferred to healthy plants. When a non-viruliferous isolate of O. brassicae was grown in the roots of lettuce affected by big-vein the fungus acquired LBVV and was able to transmit the disease. Conversely, the viruliferous Olpidium was converted to a non-viruliferous form by culture in the roots of Plantago major or Veronica persica. These results were not caused by the selection of non-vector strains of the fungus during its culture in these species, as the fungus reacquired and transmitted LBVV when again cultured in big-vein affected lettuce roots. The results suggested that LBVV did not multiply in P. major or V. persica, or in the fungus during its growth in them. Attempts to transmit LBVV with Cuscuta campestris, C. gronovii, C. reflexa and C. subinclusa and by sap inoculation were unsuccessful. No causal relationship between tobacco necrosis virus (TNV) and big-vein was found: the reasons for the frequent association of TNV with the disease are discussed.

The weather and mass flights of Thysanoptera

Abstract: SUMMARY Mass flights of Thysanoptera occur when temperatures rise above the take-off threshold after migrants have accumulated on plants at temperatures too low for flight. Most species fly in sunny, settled weather with slight convection and a maximum temperature of at least 20°C.

Glasshouse experiments on apple scab I. Foliage infection in relation to wet and dry periods

Abstract: SUMMARY A technique of investigating apple scab infection periods using MM 109 rootstocks in the glasshouse is fully described. Inoculation by ascospores in aqueous suspension was less reliable than that by sedimenting the spores direct from source leaves on to the host plants, but fresh conidia in aqueous suspension consistently gave high levels of infection under optimum conditions. Ascospores required a shorter period of continuous wetness (6 hr.) than conidia (7–9 hr.) for infection at near-optimum temperatures. Maximum infection from both sources was reached after about 18 hr. continuous wetness; much longer periods were sometimes inimical. With discontinuous wetness, most ascospores tolerated a dry interval of 24 hr. on the host leaves, although infection was somewhat reduced if the dry period began when the spores were starting to germinate. Conidia were more inhibited than ascospores by 24 hr. drying during minimal infection periods, but many survived and produced lesions. Some ascospores survived dry periods of at least 96 hr., but mature leaves had acquired resistance during the interval and thus infection was reduced. The reduction was partly offset by greater infection of the youngest leaves, which meantime had expanded and were thus easier to wet. No infection resulted, however, when the dry interval was extended to 10 days. The implications of the results are discussed in relation to the interpretation of infection periods in the field.

The uncoupling of oxidative phosphorylation in pea shoot mitochondria by 3,5-diiodo-4-hydroxybenzonitrile (ioxynil) and related compounds

Abstract: SUMMARY The effect of the new herbicide, ioxynil, and several related compounds, on the oxidative phosphorylation of respiring, isolated pea shoot particles has been studied. Ioxynil and its analogues were found to depress the uptake of inorganic phosphate and, to a lesser extent, of oxygen by the particles; the calculated P/O ratio was eventually reduced to zero. The effect of ioxynil was far greater than that of the well-known uncoupling agent 2,4-dinitrophenol and was similar in magnitude to that of the contact herbicide dinitro-ortho-cresol.

Studies on a strain of raspberry ringspot virus occurring in England

Abstract: SUMMARY A strain of raspberry ringspot virus (RRV-E) infecting blackberry in Essex was transmitted by inoculation of sap to twenty-six herbaceous species, and caused symptoms in Nicandra physaloides, Datura metel and Gomphrena globosa that differentiated it from the Scottish strain of the virus (RRV-S). In sap, with an infection end-point of 10-5, it was inactivated in 10 min. at 74° C, and in 5 weeks at 23° C. It was precipitated without inactivation by a 30% acetone or 30%-saturated ammonium sulphate solution, but was inactivated when acidified to less than pH 4. Partially purified preparations of RRV-E contained approximately equal amounts of three components with sedimentation rates of 50, 90 and 127S; electron micrographs of preparations mounted in neutral sodium phosphotungstate showed three kinds of particles with diameters about 30 mμ but with different internal structure. A preparation of RRV-S contained a main component with a sedimentation rate of 129s, and a minor one with 50S. Petunia hybrida, cucumber and French bean seemed equally susceptible to infection with RRV-E when grown in soil containing the nematode vector Longidorus macrosoma, but inoculation of sap infected the roots of P. hybrida much more readily than roots of the other two species. Cucumber seedlings became infected when exposed for 1 day to infective L. macrosoma, and virus-free L. macrosoma acquired the virus from plants in 4 days. Infective L. macrosoma transmitted readily at 20° C, occasionally at 25° C, and not at 30° C; feeding seems inhibited at 30° C. RRV-E was transmitted to seedlings grown in soil containing L. macrosoma that had been kept free from plants for 34 days. Of sixty-eight extracts of infective L. macrosoma inoculated to Chenopodium quinoa plants, only one caused infection.

Some effects of other viruses and of temperature on the multiplication of potato virus X

Abstract: SUMMARY The severity of symptoms shown by tobacco plants infected with potato virus X (PVX) was correlated with virus concentration. The virus multiplied optimally between 20 and 24deg;C. and increasing temperature above 25°C. decreased symptoms and virus concentration. PVX did not multiply detectably in plants at 34°C. Tobacco leaves systemically infected with both PVX and potato virus Y (PVY) contained more PVX than leaves infected with PVX alone. The greatest relative increase was at 31°C. because at this temperature PVX alone barely multiplied and failed to move out of the inoculated leaf. The concentration of PW was not altered by the presence of PVX and the optimum temperature for its multiplication appeared to be 28°C. Three other viruses (namely tobacco mosaic virus, cucumber mosaic virus (yellow strain), and henbane mosaic virus) that multiply at 31°C. also assisted the systemic spread of PVX at this temperature, possibly by aiding its movement between mesophyll cells and into the phloem. PVY may also aid PVX at lower temperatures mainly by increasing the number of cells it infects.

Studies on sharp eyespot disease of cereals II. Viability of sclerotia: persistence of the causal fungus, Rhizoctonia solani Kühn

Abstract: SUMMARY Sclerotia of Rhizoctonia solani survived for long periods in the laboratory. When left undisturbed in the soil, 79% of buried sclerotia survived for a period of 6 months. Sclerotia retained their infectivity towards seedling wheat plants throughout all viability tests. Sclerotia germinated readily in response to various stimuli and were able to regerminate at least ten times: it is considered that this property enhances their survival value. Although wheat stem isolates decomposed cellulose in pure culture and competitively colonized certain types of cellulose in soil, they were ineffective in colonizing cereal straws in the soil. The pathogen quickly died out in artificially infested soil and showed only limited survival in naturally infected cereal straw buried in soil. In pot experiments the pathogen persisted parasitically under a number of crops.

Slug activity in relation to weather

Abstract: SUMMARY Multiple regression analysis was carried out on the effect of certain meteorological factors on the numbers of slugs attracted by metaldehyde and bran biscuits at Cardiff in the autumn months. By far the greatest reduction in the variance in numbers of slugs attracted each morning was achieved by taking out the effects of two factors: (1) the length of time the biscuits had been exposed, and (2) the average night air temperature. The percentage relative humidity considered alone had little effect on the variance. Regression coefficients, at each site, for factors (I) and (2) on slug numbers appeared to be in close agreement and it is suggested that these figures would serve as a measure of slug activity. Arion hortensis behaved differently from the other species studied, its day-to-day variation in numbers not being tied so closely to the meteorological factors examined. Methods of assessing slug numbers in the field usually rely on the animals' activity. Barnes & Weil (1944) made direct counts on the slugs observable in half-hourly periods, and Thomas (1944) based estimates of the number attracted to metaldehyde and bran biscuits overnight; Duthoit (1961) used baits of wheat seed in making weekly estimates. Measures of activity, however, may be less directly related to the actual population present than to day-to-day climatological variations. The aim of the work described below was to find if it was possible to arrive at more reproducible population estimates by using standard slug biscuits, and allowing for the effect of some of the meteorological variables.

Purification and properties of lettuce mosaic virus

Abstract: SUMMARY Lettuce mosaic virus (LMV) was partially purified from homogenates of infected lettuce leaves in 0·5 M sodium borate buffer (pH 7·5) containing 0·1% thioglycollic acid. The filtered homogenate was clarified by adding butanol and the virus was concentrated and partially purified by differential centrifugation. Such preparations were infective at dilution up to 10-3. Comparable preparations made in potassium phosphate buffer were not infective. Electron-micrographs showed the virus preparations to contain long, flexuoiis particles with a mean length of 746 and width of 13 mμ. Antisera made by injecting such preparations intravenously into rabbits precipitated specifically with the preparations and with extracts from infected leaves.

Necrotic ring spot and prune dwarf viruses in Prunus and in herbaceous indicators

Abstract: SUMMARY When scions from sweet cherry trees with tatter-leaf disease were used to infect a range of Prunus species they induced necrotic leaf spot and stunt in peach, prune dwarf in Italian Prune and necrotic leaf spot and yellows in sour cherry. Inoculum prepared from such infected sweet cherry leaves caused two types of lesions on inoculated cucumber cotyledons from which single-lesion cultures yielded two viruses differing in physical properties and herbaceous host ranges. One of these viruses reacted with antiserum prepared against a North American isolate of necrotic ring spot virus and, when returned from cucumber to Prunus, it caused tatter-leaf in sweet cherry, necrotic leaf spot in peach and sour cherry, and no symptoms in Italian Prune. The other virus, which reacted with antiserum prepared against a North American isolate of prune dwarf virus, caused prune dwarf in Italian Prune, stunt in peach and only slight leaf necrosis in sweet cherry. Sour cherry trees developed yellows only when infected with both viruses, but in sweet and sour cherry infection with one virus reduced the severity of the necrotic shock symptoms induced by the other.

The effect of motley dwarf virus on yield of carrots and its transmission in the field by Cavariella aegopodiae Scop

Abstract: SUMMARY In 1959 and 1961, when the willow-carrot aphid, Cavariella aegopodiae, infested carrots at Rothamsted and Woburn early and severely, crops were infected with motley dwarf virus in late May or early June and yielded about 6 tons of roots per acre. In 1962, when invasion was late and sparse, the crops remained almost uninfected and yielded 24–25 tons/acre. In 1960, when aphids invaded early but multiplied slowly, about 85% of carrots on unsprayed plots became infected in July and August, and the yield was 9.2 tons/acre. Spraying three times with Metasystox starting at an early stage of growth affected yield little in 1961, or in 1962, but increased yield by about 3 tonslacre in 1960. Field-plots experimentally infected in 1962 by aphids fed on infected plants in the glasshouse, lost II tons/acre from infection in early June, 8 tons/acre from infection in late June and 6 tons/acre from infection in July. Plots cultured with virus-free aphids in early June yielded as much as control plots. Experimental infection did not affect yield in 1959 and 1961, when the crop became naturally infected before treatment. The yields in different years were linearly related to the log. mean weekly numbers of C. aegopodiae caught on sticky traps near the sites, and the regression accounted for much of the variance in yield. The residuals of the log. mean weekly trap-counts were negatively related to residual weekly rainfall in inches; I in. of rain above average approximately halved the increase in aphids. This may explain the failure of early invading aphids to become numerous at Woburn in 1960, when an inch of rain fell in three consecutive weeks in June. Treating seed or seedlings with systemic insecticide did not prevent young plants from becoming infected when infective aphids were cultured on them 10–14 days after treatment. Aphids taken from willow in the spring did not transmit motley dwarf to healthy carrots, but did so after they had fed on infected carrots. Aphids from wild umbellifers often transmitted motley dwarf to healthy carrots.