Showing papers in "Annals of Applied Biology in 1987"

The decimal code for the growth stages of cereals, with illustrations

Abstract: SUMMARY The decimal code for the growth stages of cereals, devised by Zadoks, Chang & Konzak (1974), is reproduced with stylised drawings of selected stages of wheat, barley and oat plants Expanded definitions of some of the descriptive phrases are designed to assist the application of the code to agrochemical research, development and use in the UK

Epidemiology and control of virus diseases of vegetables

Abstract: SUMMARY The diverse ecological and epidemiological factors which determine virus infection of vegetable crops are discussed. These include the sources and spread of viruses, together with some agricultural and horticultural practices which have influenced their prevalence. Control measures are described, demonstrating ways of avoiding or minimising infection. Developments are reported with insecticides, insect repellents, anti-feedants, and fungicides for the control of virus vectors. Some of the successes and future requirements in breeding vegetable cultivars with virus resistance are listed. An Appendix lists the economically most important vegetable virus diseases present in 28 countries or regions with temperate, Mediterranean-like or subtropical climates. The five most important viruses in field-grown vegetables are transmitted non-persistently by aphids (cucumber mosaic, turnip mosaic, potato virus Y, lettuce mosaic and watermelon mosaic 1 (= papaya ringspot virus)). In contrast, with protectively-grown vegetables, the most important are the mechanically-transmitted tobamoviruses (tomato and tobacco mosaic, Capsicum mosaic and cucumber green mottle mosaic).

Predation of Rhopalosiphum padi (Homoptera: Aphididae) by polyphagous predatory arthropods during the aphids' pre‐peak period in spring barley

Abstract: SUMMARY Polyphagous predators (e.g. Araneae, Carabidae and Staphylinidae), collected from spring barley fields during 1981-85, were examined by either gut dissection or a R. padi-specific antiserum in enzyme linked immunosorbent assay (ELISA) in order to detect predation of Rhopalosiphum padi during the aphids' establishment and exponential growth phases. Overall 18% of c. 3000 carabids dissected were shown to feed on R. padi during the aphids' pre-peak period. No overall relationship was found between percentage carabids with R. padi in the diet and peak R. padi densities. Relatively high proportions of Bembidion spp. (particularly B. lampros) and Pterostichus cupreus fed on R. padi during the aphids' establishment phase, and proportions of those predator taxa containing R. padi increased with increasing R. padi densities in both high and low aphid density years. P. melanarius and Harpalus rufipes mainly fed on R. padi during the aphids' exponential growth phase. Overall 11% of c. 1350 predators examined in ELISA gave positive reactions to the R. padi antiserum. Relatively high proportions of linyphiid and lycosid spiders were positive throughout the aphid pre-peak period. Several Acari, Opiliones, Trechus spp. (Carabidae), Philonthus spp. (Staphylinidae), Cantharidae and Chilopoda were positive mainly during the aphids' exponential growth phase. Sample sizes were small, however. Very few of the Bembidion spp. tested in ELISA were positive compared with those examined by gut dissection. The maximum period of R. padi protein (antigen) detection in B. lampros was related to temperature, i.e. 8.5 h at 30°C, 20.5 h at 20°C and 34.5 h at 10°C, respectively. It is suggested that the rate of R. padi protein digestion in B. lampros is faster at higher temperatures than the rate of elimination of prey solids from the guts. Several key predators (in this case B. lampros, P. cupreus and linyphiid spiders) which are abundant in spring cereal fields at a time when R. padi emigrants arrive in the crop and which feed on R. padi during the aphids' establishment phase, are identified. The results are compared with those from similar investigations elsewhere with predators of Sitobion avenae and Metopolophium dirhodum.

A key for stages of development of the pea (Pisum sativum)

Abstract: SUMMARY A key is presented to described stages of development of the pea (Pisum sativum). The aim was to produce a simple system to aid accuracy in communicating instructions for timing of field operations. The coded description is divided into four principal stages: germination and emergence, vegetative, reproductive and senescence. These are sub-divided into secondary stages. The practical use of the key is discussed with particular reference to the timing of application of agrochemicals.

Incidence of endophytes in seeds from collections of Lolium and Festuca species

Abstract: SUMMARY Seeds from 53 of 64 collections of Lolium perenne from its centre of origin or from old pastures in Europe were found to be infected with endophyte whereas only four of 16 commercial cultivars had infected seed. Almost two thirds of seed samples of L. multiflorum, Festuca arundinacea and F. pratensis collected from plants growing in the wild in Italy contained endophyte but none of the eight commercial cultivars of L. multiflorum and only two of five cultivars of Festuca spp. produced by the Welsh Plant Breeding Station were infected. At least one seed sample from each of six species and varieties of annual ryegrasses contained endophyte mycelium. Endophytes in annual ryegrasses could not be cultured axenically and are probably a different species to the Acremonium lolii present in L. perenne. A correction to the spelling of the specific epithet of A. lolii is explained.

Seasonal changes in the free amino acids of oat and barley phloem sap in relation to plant growth stage and growth of Rhopalosiphum padi

Abstract: SUMMARY The concentrations and composition of free amino acids in phloem sap from two cultivars of oats and barley, both susceptible to the aphid Rhopalosiphum padi, were determined by means of high performance liquid chromatography Sap was collected from excised aphid stylets at three developmental stages (seedlings, tillering plants and plants undergoing stem elongation) from plants given or not given fertiliser and grown outdoors In connection, the growth of individual R padi nymphs was estimated at the same phenological stages on plants grown in the greenhouse The content of free amino acids was consistently higher in seedlings than in plants at the early tillering stage Only in seedlings did the addition of fertiliser increase amino acid levels Barley phloem sap contained more free amino acids than that of oats when fertiliser was added and at later developmental stages Phloem sap of oats and barley showed similar patterns in their composition of free amino acids at the seedling stage, but as the plants grew older the patterns became increasingly different Plants given fertiliser had higher amounts of dicarboxylic amino acids (glutamic and aspartic acid) than unfertilised plants The concentrations of γ-amino butyric acid, glycine, histidine, and methionine were very low in all treatments The relative growth rates of R padi nymphs were low when amino acid content was low and vice versa The results are discussed in relation to host plant suitability and plant resistance mechanisms

Effects of osmotic priming and ageing on the germination and emergence of carrot and leek seed

Abstract: SUMMARY Carrot and leek seed was osmotically primed in polyethylene glycol solution (273 g/kg water and 342 g/kg water respectively) for 10, 14 or 17 days before accelerated ageing for 0, 24, 48, 72 or 96 h. Priming reduced the germination time compared with non-primed seed. Accelerated ageing increased germination and emergence times and decreased percentage germination and emergence to a greater extent for the primed seeds than for non-primed seeds in both species. Primed and dried but non-aged seed from both species was stored at 10°C for 12 months. There was no loss of viability and improvements in germination time due to priming were maintained throughout the storage period for all the priming treatments in leek, and for the 10 and 14 day priming treatments in carrot. Carrot seed primed for 17 days lost some viability after 12 months storage compared with non-stored seed.

The efficiency of visual selection in early generations of a potato breeding programme.

Abstract: SUMMARY The efficiency of visual selection in the early generations of a potato breeding programme is examined. Tubers from 571 potato genotypes were scored by four breeders after being grown, from true seed, in a glasshouse and in the field for three consecutive years. The four breeders were in good agreement as to which clones would be selected in any environment. The association between breeders was greatest when the clones were grown in plots in the field. All correlations of breeders' preferences between different environments were significantly greater than zero, but only accounted for a small percentage of the total variation. Selection in both the glasshouse and first clonal year produced a desirable response. However, such selection carried a high cost in terms of losing clones with commercial potential. Comparison of a random sample of clones with ones from the same crosses which had been selected, indicated that selection in the glasshouse and first clonal year was at best random with some suggestion, however, of a negative effect.

Germination and effect of reduced humidity on expression of pathogenicity in Verticillium lecanii against the glasshouse whitefly Trialeurodes vaporariorum

Abstract: SUMMARY Fifteen isolates of the entomopathogenic fungus Verticillium lecanii, from various hosts and locations, were bioassayed in the laboratory at 19 ± 1°C and > 95% r.h. against fourth instar scales of Trialeurodes vaporariorum. Highly pathogenic isolates generally originated from whitefly; however, there was no correlation between conidiospore size or germination rate on agar, and pathogenicity. LT50 values ranged from 5.7 to > 9 days and LC50 (7 days) from 1.3 × 105 to 4.2 × 107 spores/ml. The effect of periods in low humidity (70% r.h.) following 16 or 96 h at > 95% r.h. after immersion of whitefly scales on tomato leaf discs in a suspension of 1 × 106 spores/ml, was compared for five isolates. Progressively longer periods at 70% r.h. following 16 h at > 95% r.h., reduced significantly (P < 0.001) the pathogenicity of all isolates. In these conditions isolate A was least affected by low-humidity transfer. The high pathogenicity of isolate A was associated with its more rapid development on the host cuticle during the first 16 h in high humidity. When inoculated whitefly scales were transferred to 70% r.h. after a preliminary 96 h incubation in high humidity, all five isolates achieved a higher level of pathogenicity compared with their transfer to low humidity after 16 h high humidity. Thus the screening of V. lecanii isolates in limiting humidity conditions provided a more critical assessment of their pathogenicity and of their potential success in whitefly control relevant to the glasshouse environment.

Virus diseases of subterranean clover

Abstract: SUMMARY Subterranean clover (Trifolium subterraneum) is grown as a pasture legume in several temperate regions of the world where the soils are acidic and infertile, and the rainfall is winter dominant and less than 600 mm annually. It is particularly important in southern Australia where more than 16 million ha have been sown with this species as the pasture legume component. Nine viruses have been recorded infecting subterranean clover in the field. These are alfalfa mosaic, bean yellow mosaic (pea mosaic), beet western yellows, clover yellow vein, cucumber mosaic, pea enation mosaic, soybean dwarf (subterranean clover red leaf), subterranean clover mottle and white clover mosaic. In addition there is an important problem referred to as subterranean clover stunt that was assumed to be caused by a virus but whose aetiology is still unknown. The importance of these diseases is reviewed and details on their epidemiologies are outlined together with details on progress towards their control and some comments on matters worthy of attention in the future. Reference is also made to several exotic viruses known to infect subterranean clover experimentally that could possible cause problems if introduced into Australia.

Multiple components of the resistance of potatoes to potato leafroll virus

Abstract: SUMMARY In glasshouse experiments the ranking of potato genotypes for resistance to infection with potato leafroll virus (PLRV) using three concentrations of aphid-borne inoculum was the same as their field resistance ratings. In field-grown plants this resistance to infection increased in all genotypes as the plants aged but its rate of increase differed between genotypes. In tests on field-grown plants infected by aphid- or graft-inoculation, the proportion of virus-free progeny tubers increased the later the date of inoculation but was greater in resistant than in susceptible genotypes. This trend was most pronounced in the resistant clone G7445(1), in which the virus failed to move from the foliage to the tubers of some plants infected in glasshouse tests. The spread of PLRV will thus be minimised in crops of resistant compared with susceptible genotypes for three reasons: plants have greater resistance to infection, systemic spread of virus from their foliage to tubers is less likely and, as shown previously, the low concentration of virus particles in leaf tissue makes infected plants less potent sources of inoculum for aphids.

Desiccation and storage studies on Dipterocarpm seeds

Abstract: SUMMARY The relationship of seed moisture content (fresh weight basis) to germination, and the effect on viability of various storage conditions were examined for five species of the tropical forest tree genus Dipterocarpus. It was shown that seeds fall into two groups with regard to desiccation tolerance. Firstly, D. obtusifolius and D. turbinatus cannot be dried below about 45% moisture content without damage; a sigmoid curve was found to fit the relationship between germination and moisture content for the latter species. Secondly, D. intricatus, D. tuberculatus and D. alatus can be safely dried to 10%, 12% and 17% moisture contents respectively, but desiccation to near 7% moisture content reduced viability by at least a half. Storage studies showed that seed of D. intricatus and D. tuberculatus possessed increased longevity as moisture contents were reduced within the range 6–20%. It was concluded that seeds in the first group are ‘recalcitrant’ and that those in the second group are ‘orthodox’ in their storage physiology, according to the categories described by Roberts (1973). Wide differences between species in seed desiccation rates were observed. In 15% relative humidity D. intricatus dried to 7% moisture content within a week, whilst D. obtusifolius retained 30% moisture content even after 5 wk; other species had intermediate desiccation rates. Seed size and structure may partly account for the differences observed. Correlations were observed between seed storage physiology and other factors which were investigated. ‘Orthodox’ seeds had quicker desiccation rates, were derived from drier habitats, and had smaller embryos than those of ‘recalcitrant’ seeds. ‘Orthodox’ seeds, with the possible exception of D. alatus, should be kept at 0–3°C with about 12% moisture content in the short term and, provided less than 10% germination is lost on freezing, at-18°C with about 8% moisture content in the long term. ‘Recalcitrant’ seeds should be stored in ventilated containers at 21°C and with moisture contents above 45–50%.

Inhibition of degreening in the peel of bananas ripened at tropical temperatures. II. Role of ethylene, oxygen and carbon dioxide

Abstract: Comparaison de la production d'ethylene et de la cinetique de deverdissage de bananes et bananes-plantains muries a 19-39 degres C en fonction de la composition de l'atmosphere d'entreposage. Hypotheses quant aux mecanismes d'inhibition du deverdissage aux temperatures elevees

Effects of ethylene and acetylene on mango fruit ripening

Abstract: SUMMARY Mangoes (var. Tommy Atkins) were exposed to ethylene and acetylene over a range of concentrations at high humidity for 24 h at 25°C, then ripened in air alone. Ripeness was assessed after 4 and 8 days by analysis of texture, colour development, soluble solids and acid contents. Ethylene in air at concentrations of 0.01 ml litre-1 and above or acetylene at 1.0 ml litre-1 were found to initiate ripening. Treatment with 0.01 ml litre-1 acetylene resulted in limited softening but had no effect on the other ripening changes analysed. Individual ripening processes responded differently to treatment: texture changes were most rapidly affected, while the rate of acidity losses was often reduced in ethylene treated fruits. Acetylene-treated fruits at concentrations of 0.01 and 0.1 ml litre-1 showed delayed ripening when compared to those treated with either 1.0 ml litre-1 acetylene or ethylene. Increased acetylene concentrations of 2.0 ml litre-1 gave a similar response to 1.0 ml litre-1, although in some instances there were indications of inhibitory effects.

Distribution of Rhopalosiphum padi (Hornoptera: Aphididae) on spring barley plants

Abstract: SUMMARY The distribution of Rhopalosiphum padi on spring barley plants in the field and the laboratory is described. Aphids fed mainly on the lower parts of the plants in both the field and the laboratory. A relatively large proportion of the field population was found beneath the soil surface early in the season. In the laboratory, aphids preferred the stem base and auricles of young and old plants respectively. The highest soluble nitrogen concentration was found in the stem base of young plants. The aphids avoided temperatures above 25°C in a temperature gradient (20°C-40°C). The soil surface temperature in a barley stand can reach lethal levels for aphids during clear days early in the season. It is concluded that the preference of R. padi for the lower part of young spring barley plants is mainly a consequence of the stem base being the most nutritious part of the plant and that a harsh microclimate possibly forces the aphids beneath the soil surface. This tendency to feed near or below soil level must be taken into account when assessing field densities of R. padi.

The effects of the foliar fungicide pyrazophos on beneficial arthropods in barley fields

Abstract: SUMMARY The insecticidal properties of the foliar fungicide pyrazophos were investigated in autumn- and spring-sown barley crops using several methods to estimate the density of non-target arthropods and by using manipulative experiments. In autumn-sown crops, pyrazophos significantly reduced densities of cereal aphid natural enemies relative to pre-treatment levels compared to areas of crop that were left unsprayed. These significant differences persisted in most groups for over 45 days after treatment. Groups most affected were aphid-specific predators, polyphagous predators, (Carabidae, Staphylinidae but not Araneae) and parasitoids. Insects known to be preferred food items of wild gamebird chicks and other non-target groups such as the Collembola were also significantly reduced in density on plots sprayed with pyrazophos, the effects again persisting for over 45 days. Densities of beneficial and non-target insects were also reduced in plots of spring barley sprayed with pyrazophos. However, the experimental design meant that levels of reductions were not significant for most arthropod groups. Removal of prey items (Drosophila pupae) placed in sprayed and unsprayed spring barley plots showed that the proportion predated was significantly lower on pyrazophos-treated plots compared to those remaining unsprayed, the difference persisting for at least 7 wk after treatment. Removal of cereal aphids from colonies introduced to sprayed and unsprayed plots was also significantly lower on plots treated with pyrazophos. Difficulties of data interpretation associated with experimental design are discussed together with the consequences of the use of broad-spectrum pesticides in I.P.M. programmes in cereals.

Virus content of leaves of cassava infected by African cassava mosaic virus

Abstract: SUMMARY African cassava mosaic virus (ACMV) was detected in cassava leaves by ELISA. Some normal constituents of cassava leaves interfered with virus detection but leaf extracts of Nicotiana benthamiana did not. The symptom pattern was determined early in the growth of a leaf and subsequently changed little. ACMV was found only in the yellow or yellow green areas of the mosaic pattern. Virus content of the leaves increased with increasing symptom intensity, but decreased with leaf age and ACMV was not detected in mature leaves. Most whiteflies were found on young growing cassava leaves and the number decreased progressively with leaf age. This distribution will aid both the acquisition and inoculation of the virus.

Effects of net blotch on growth and yield of spring barley

Abstract: SUMMARY The effect of net blotch on the growth and yield of cv. Beatrice spring barley was examined in a greenhouse experiment. Separate inoculations at growth stages 21 and 34 reduced green leaf area, root weight, leaf sheath and stem weight and tiller number. The early inoculated plants, which responded and recovered more rapidly than later treated ones, suffered a loss in grain yield and this was related to the amount of disease, the loss in green leaf area and the reduction in unit leaf rate.

Observations on the number of cereal aphids on the soil in relation to aphid density in winter wheat

Abstract: SUMMARY The numbers of cereal aphids on the soil surface was assessed by soil samples and by counting the numbers captured in pitfall traps. A relationship was found by both methods between the density of aphids on the plants and the numbers of aphids on the soil. This relationship indicated that a higher proportion of the aphid population was on the soil surface at the lower densities on the plant. Reasons for this relationship are suggested and discussed.

Satellite RNA for the control of plant diseases caused by cucumber mosaic virus

Abstract: SUMMARY Two virus-protecting strains, S51 and S52, were obtained for the control of cucumber mosaic virus (CMV) by local lesion selection after adding satellite RNA to the RNA genome of CMV. Both were found to protect pepper plants against a virulent strain of CMV under greenhouse and field conditions. Results from 14 localities in China indicated that the use of protective strains decreased the disease index by 21.6% to 82.8% and increased fruit yields by 10.8% to 55.6%. The host reactions and safety of S51 and S52 were tested, and the effects of the strains on plant growth were also investigated. Possible mechanisms of control of CMV-caused plant diseases by mild strains are discussed.

Effects of fungicide spray regimes on incidence of dicarboximide resistance in grey mould (Botrytis cinerea) on strawberry plants.

Abstract: SUMMARY In tunnel experiments, the efficacy of dicarboximide sprays in controlling grey mould of strawberries was greatly decreased by the presence of dicarboximide-resistant forms of Botrytis cinerea. The use of dichlofluanid, as a tank-mix or in an alternating programme, with a dicarboximide fungicide, procymidone, helped to maintain the efficacy of disease control but failed to prevent an increase in the proportion of dicarboximide-resistant forms of the pathogen. Alternative ‘partner’ fungicides (thiram, chlorothalonil) delayed build-up of resistance to dicarboximides. Build-up of resistance was absent or relatively small in unsprayed plots. Application of dichlofluanid alone was always associated with a substantial increase in dicarboximide resistance, although less than in procymidone-treated plots. Monitoring dicarboximide resistance in the tunnels during the winter, when no further sprays were applied, revealed a gradual decline in the proportion of dicarboximide-resistant forms in all previously treated plots. In laboratory studies on inoculated leaf debris, dichlofluanid treatment induced the build-up of dicarboximide-resistant forms of B. cinerea. Leaf-disc tests revealed cross-resistance of dicarboximide-resistant isolates towards dichlofluanid but not towards thiram or chlorothalonil. Dichlofluanid is widely used for control of B. cinerea and the implications of these results for the practical management of dicarboximide resistance in this pathogen are discussed.

The interactions of potato cyst nematodes and Verticillium dahliae on early and maincrop potato cultivars.

Abstract: SUMMARY The effects of potato cyst nematodes (Globodera rostochiensis and G. pallida) on the growth of early and later maturing potato cultivars, with or without the H, resistance gene, were compared in pot experiments and the effects of introducing Verticillium dahliae into the system were studied. The influence of the nematodes on root function and structural integrity was inferred from their effects on calcium and water uptake. Early maturing cultivars were less tolerant of nematode attack than later maturing ones, and those with the H1 resistance gene were more tolerant of G. rostochiensis than G. pallida. When V. dahliae was introduced, Verticillium wilt symptoms appeared much earlier on the early than the maincrop cultivars. Also, Maris Anchor (first early) died before Maris Peer (second early) and death of both when infected by nematodes and fungus was much earlier than uninfected control plants or plants infected with G. rostochiensis only. Maris Peer infected by both organisms snowed symptoms much more severe than when infected by either organism alone, whereas Maris Anchor was almost as severely affected by V. dahliae alone as both organisms together. Pentland Javelin (first early) developed Verticillium wilt symptoms several weeks later than other cultivars and the addition of nematodes failed to increase the severity of the symptoms. These differences in cultivar susceptibility to the combination of nematodes and fungus may be due to the nematodes causing different degrees of trauma in the roots of the three cultivars: measuring calcium uptake per unit water uptake showed that nematodes dramatically increase calcium uptake but that the proportional change is least in Pentland Javelin. If this is a reflection of less damage by nematodes to the endodermis of this cultivar, it may explain the greater resistance of its roots to penetration by V. dahliae.

Inhibition of degreening in the peel of bananas ripened at tropical temperatures. I. Effect of high temperature on changes in the pulp and peel during ripening

Abstract: Etude de la cinetique et des phenomenes de maturation dans le domaine des temperatures de 15 a 35 degres C. On observe, au-dessus de 24 degres C, un ramollissement de la pulpe qui devient sucree alors que la peau reste verte (reduction de la vitesse de degradation de la chlorophylle). De plus, la teneur en carotenoide de la peau est plus elevee a 35 degres C qu'a 20 degres C

The effect of irrigation on powdery scab and other tuber diseases of potatoes

Abstract: SUMMARY In field experiments seed tubers affected with powdery scab cankers were planted and the effect on disease incidence of timing of irrigation and some seed-tuber fungicides was investigated over 3 yr. For 2 yr, irrigation to maintain soil wetter than—20 centibars (—20 kPa) during the first half of the growing season increased disease compared to unirrigated plots. Disease incidence was not affected by irrigation at 2 wk intervals or when applied during the second half of the season. Little disease developed in 1983 even in irrigated plots, probably because of high soil temperatures. None of the fungicides tested gave consistent disease control. Common scab and silver scurf were both decreased by irrigation but in two years, black dot was increased. The relative importance of black dot could increase in irrigated crops where fungicides are used to control silver scurf.

The effect of previously infested spruce needles on the growth of the green spruce aphid, Elatobium abietinum, and the effect of the aphid on the amino acid balance of the host plant

Abstract: SUMMARY The effect of chlorosis induced in needles of Sitka and Norway spruce by the green spruce aphid on growth of the aphid is investigated, and the effect of infestation of the aphid on amino acid levels in Sitka spruce foliage is reported. On both Sitka and Norway spruce green spruce aphids were heavier when reared on chlorotic (previously infested) needles than when reared on green (previously uninfested) needles. The effect was more pronounced on Sitka than on Norway spruce. Infestation of the aphid altered the amino acid balance of Sitka spruce foliage but not the concentration of total amino acids. Possible causes of chlorosis, the influence of individual amino acids on aphid growth, the potential effect of chlorosis on outbreaks of the aphid and the differences in susceptibility of Sitka and Norway spruce to damage by the aphid are discussed.

The effect of cultivar used as host for Polymyxa graminis on the multiplication and transmission of barley yellow mosaic virus (BaYMV).

Abstract: SUMMARY A viruliferous isolate of the fungal vector Polymyxa graminis was grown on roots of barley cultivars immune or susceptible to barley yellow mosaic virus (BaYMV). Zoospores or resting spores of the vector produced on different cultivars were then inoculated to a virus-susceptible test cultivar. Although the vector established in all treatments, transmission of BaYMV was rare and usually nil from immune cultivars; amounts of virus detected serologically in their roots were very low, thus showing that resistance was to virus multiplication. If immune cultivars decrease the virus content of vector populations in the field, this would have important implications for disease control.

Use of monoclonal antibody to potato leafroll virus for detecting groundnut rosette assistor virus by ELISA.

Abstract: SUMMARY Three of 10 monoclonal antibodies (MAbs) produced to potato leafroll luteovirus (PLRV) were found to react in triple antibody sandwich ELISA (TAS-ELISA) with groundnut rosette assistor luteovirus (GRAV), though none reacted with four other luteoviruses (barley yellow dwarf, bean leaf roll, beet western yellows or carrot red leaf)- The most effective PLRV MAb, SCR 6, was used in TAS-ELISA to detect isolates of GRAV from groundnut plants with chlorotic, green and mosaic forms of rosette from Nigeria and Malawi. The test also detected GRAV in extracts of single Aphis craccivora.

The acquisition of a caulimovirus by different aphid species: comparison with a potyvirus

Abstract: SUMMARY The acquisition and transmission of cauliflower mosaic virus (CaMV) by six aphid species and three clones of aphids was studied and compared with that of turnip mosaic virus (TuMV) with Myzus persicae. Two clones of Aphis fabae were unable to transmit CaMV, but the other species, Acyrthosiphon pisum, Brevicoryne brassicae, Megoura viciae, M. persicae and Rhopalosiphum padi transmitted in a bior multi-phasic manner. There was no statistical evidence of a bimodal transmission pattern. R. padi is recorded as a vector of CaMV for the first time. The transmission efficiency of CaMV varied with time of acquisition and suggested that accumulation of the virus occurred with two peaks of efficiency within the anterior region of the insect gut. The time at which these two peaks occurred varied between the species, but the basic pattern was common to all transmitting aphid species in this study. This pattern contrasted with that of TuMV. The transmission data are discussed in terms of bimodal transmission, the influence of feeding behaviour, the role of a helper protein associated with both TuMV and CaMV and the evidence for site specific attachment of CaMV.

The effect of inoculating flowers and developing fruits with Botrytis cinerea on post-harvest grey mould of red raspberry

Abstract: SUMMARY Raspberry flowers were inoculated in the glasshouse and field with dry conidia of Botrytis cinerea and the fruits derived from them subjected to post-harvest rot tests at c. 20°C and high humidity. Apparently healthy fully-ripe picked fruits derived from inoculated flowers developed grey mould faster than those from non-inoculated flowers in all tests. In the glasshouse experiments, fruits from inoculated tightly closed flower buds rotted more slowly than those from inoculated open flowers or those at later developmental stages. Fruits from inoculated whole flowers rotted more rapidly than those from emasculated flowers; the addition of pollen to emasculated flowers had little effect on post-harvest grey mould. In the dry summer of 1984 no fruits in the field from inoculated whole flowers rotted before ripening, but in the wet season of 1985 pre-harvest grey mould was common and the surviving healthy fruits rotted in c. 1 day after picking. Only minor differences were detected in host susceptibility to post-harvest grey mould in both glasshouse and field tests, the ranking of genotypes varied depending on whether or not flowers had been inoculated. The susceptibility of pistils of 40 Rubus genotypes to infection was examined 7 and 28 days after inoculation of stigmas with dry conidia. Conidia germinated on the stigmas and produced hyphae which grew through transmitting tissues of the styles to infect carpels symptomlessly in 17 red raspberries, one blackberry, two Rubus spp. and one hybrid. No germination occurred on stigmas of cv. Carnival and New York Selection 817.