摘要:

SummaryGreenbugs, Schizaphis graminum (Rondani), were reared on intact and excised leaves of varieties of sorghum which differed in their suitability as hosts for this aphid. Aphids grew poorly on intact leaves of three resistant varieties, but grew well on excised leaves of the same varieties. Leaf excision did not affect aphid growth on three susceptible varieties. By electronically monitoring the feeding behaviour of aphids on two resistant and one susceptible variety, significant differences were found in many parameters between aphids assayed on excised vs. intact leaves of only the resistant varieties. Aphids on excised leaves of the resistant varieties, and on excised or intact leaves of the susceptible variety, made fewer probes to the phloem, spending more time ingesting from phloem during each probe, compared to aphids on intact resistant plants. There was a higher level of free amino acids in excised leaves of all varieties, but aphid growth and feeding behaviour improved as a result of excision only on resistant varieties. This observation, coupled with the fact that intact plants of all varieties have similar amino acid levels, indicates that these nutrients are not of primary importance in sorghum suitability to the greenbug. Other explanations for the aphids' responses to excised leaves are discussed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06598.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryTwenty‐six direct or derived criteria were assessed, eight wk after infestation, of the effect of an initial inoculum of 0, 5, 25 or 50 Brevicoryne brassicae on the growth and dry matter distribution of Brussels sprout plants. Twenty‐four of these criteria showed significant (P>0.05) effects of aphid infestation, though increasing aphid infestation above 5/plant had little further effect. Total fresh and dry weight (as well as of the components — leaves, stems and roots) was reduced by 25–730 with infestation, particularly so the root. The number of leaves as well as individual leaf area was reduced, and leaves on infested plants were less efficient assimilators. This could be explained by the drain on assimilates caused by the aphids, the leaf curling and the reduced density of stomata. The latter was also considered to account partly for the increased moisture content of infested plants. There was a general reduction in the concentration of leaf amin

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06599.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryMycelium, oospores and zoospore cysts of Pythium spp. were fed to larvae of the fungus gnat Bradysia impatiens. The fungal structures were all ingested and provided a complete nutritional source for the insect's development from egg to adult. Mycelium seemed the major source of food as only empty fragments were found either in the digestive tract or in larval faeces. Oospores appeared intact and were viable both during passage through the tract and when expelled. Germination of oospores was normal. Most encysted zoospores also survived passage through the gut, although some appeared damaged. After transferring recently‐fed larvae to a new food source, oospores were still detected in the digestive tract 48 h later. These results show that the larval stage of B. impatiens may serve as an important vector for Pythium sp

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06600.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryAcetaldehyde (AA) vapour reduced the in vitro growth of the fruit‐infecting fungi Botrytis cinerea and Rhizopus stolonifer, and decreased the respiration of R. stolonifer. Spore germination, germ tube elongation and sporulation were inhibited in both fungi. AA induced the leakage of electrolytes from B. cinerea and R. stolonifer membranes. The conductivity found in the fungal extracts was positively correlated with the AA concentration applied. The leakage of reducing sugars and amino acids suggest that cell membranes are irreversibly disrupted by AA as a first step in inhibition of the fungi in vitr

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06601.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe effects of moisture deficit stress, plant population density and pathogen inoculation technique on charcoal stalk rot in the sorghum hybrid CSH 6 were studied in the 1980–81 and 1981–82 post‐rainy seasons at three locations in India. Incidence and severity of charcoal rot caused by Macrophomina phaseolina were compared in three plant population densities, subjected to different moisture stress regimes created by withholding irrigation at various plant growth stages. Natural infections were compared to artificial inoculation with M. phaseolina. Combinations of moisture stress, plant population and inoculation treatments were compared to identify the combination most likely to develop maximum disease. Lodging, the first external symptom of charcoal rot, was significantly correlated with other disease symptoms used to measure charcoal rot, such as soft stalk, number of nodes crossed by M. phaseolina infection, root damage and plant senescence. In both seasons the highest incidence of lodging occurred when moisture stress was induced at the ‘flag leaf visible in the whorl’ growth stage. The greatest incidence of the disease was recorded in the highest plant population (266 700 plant ha‐) at all three locations. No significant differences were found between artificially and naturally inoculated treatments. The maximum number of lodged plants was found at a density of 266 700 plants ha‐1when moisture stress was induced at the ‘flag leaf visible in the whor

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06602.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryHealthy seed tubers and seed tubers with gangrene or inoculated with Rhizoctonia solani to induce stem canker were planted 38 or 76 cm apart or alternately at 38 cm spacing in 2‐row (1985) or 4‐row (1986) plots at Rothamsted.At 38 cm spacing, stem canker decreased yield by 5% and 8% respectively in 1985 and 1986 and gangrene by 5% and 14%, but usually by twice these amounts when seed was spaced at 76 cm. In all experiments, yields from plots with alternate healthy and inoculated seed (50% disease) were similar to yields from healthy seed, although within these mixed populations individual plant yields from healthy seed were larger and those from diseased seed were smaller than from plots of healthy or inoculated seed respectively. Samples in August showed a similar effect on fresh weight of foliage.Disease usually decreased the number of stemdplant but in 1985 gangrene increased stem numbers and probably accounted for small amounts of compensatory growth from neighbouring healthy pla

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06603.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe effects of gamma irradiation and disease control treatments on disease severity and post harvest quality of several mango cultivars were investigated.In mangoes cv. Kensington Pride, irradiation doses ranging from 300–1200 Gy reduced disease, but the level of control was not commercially acceptable. Hot benomyl immediately followed by irradiation provided effective control of anthracnose (Colletotrichum gloeosporioides) and stem end rot (Dothiorella dominicana) during short‐term storage (15 days at 20°C). The effects of the two treatments were additive.Satisfactory disease control was achieved during long term controlled atmosphere storage when mangoes were treated with hot benomyl followed by prochloraz and then irradiated. Effects of fungicide treatment and irradiation were additive. Fungicide, or irradiation treatments alone, were unsatisfactory.Irradiation of cv. Kensington Pride at doses in excess of 600 Gy caused unacceptable surface damage (i.e. lenticel spotting, surface discolouration and retardation of degreening) which was particularly severe after long‐term controlled atmosphere storage.In a separate short‐term storage trial, several other mango cultivars were assessed. Hot benomyl followed by prochloraz controlled anthracnose on all cultivars and stem end rot on some. Irradiation at 600 Gy contributed only minor improvements to disease control. The severity of surface damage that developed following irradiation and fungicide treatment varied with c

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06604.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryEight rhabdoviruses from grass and cereal hosts and their antisera were used to examine virus relationships by gel‐diffusion serology. Nucleocapsid (Nc) preparations from digitaria striate virus (DSV) and maize sterile stunt virus (MSSV) both contained a major protein of c. 52 OOO daltons, and antisera prepared to these readily discriminated related planthopper‐transmitted rhabdoviruses. MSSV showed a moderately close relationship to barley yellow striate mosaic virus (BYSMV) when an antiserum prepared to whole virus was used, but the Nc antiserum showed clearer discrimination. Worthern cereal mosaic virus and DSV showed a distant relationship to BYSMV and MSSV. There was no serological relationship between any of these viruses and cereal chlorotic mottle virus, cynodon chlorotic streak virus, festuca leaf streak virus or maize mosaic vi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06605.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe occurrences and distributions of hop stunt (HSVd) and hop latent (HLVd) viroids were assessed by a nucleic acid hybridisation assay, using samples from 476 commercial hop plantings in the UK. These samples represented about half of the UK production.HLVd was detected in c. 17% of the samples, with infection in different cultivars ranging from 0% to 89%. This viroid was found in all cultivars sensitive to Verticillium wilt except cv. Sunshine, an old cultivar grown on only one farm in the UK. Two minor wilt‐tolerant cultivars were also found to be infected at low frequencies, but the main commercially‐important wilt‐tolerant cultivars were all uninfected. A high proportion of the nuclear stock mother plants in the “A +” house at the Institute of Horticultural Research Dept of Hops Research, Wye College were infected. Circumstantial evidence, based on the planting dates of infected gardens, suggests that infection became established in the hop propagation system during the late 1970s and that there was a major increase in the prevalence of HLVd as a result. Whether this contamination of propagating material arose because of spread from long‐standing infections or because the viroid was newly introduced into the UK, is not known.All samples were also tested for HSVd but this viroid was not detected in any UK h

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06606.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryA number of iron and aluminium compounds were compared as contact‐acting poisons against the slug Deroceras reticulatum, by confining slugs on treated surfaces of glass and wet soil in laboratory tests. Simple metal salts were effective poisons when applied to a glass surface, but were rapidly inactivated when applied to wet soil. Chelation of both metals with organic ligands retarded the rate of attenuation on wet soil. In a field trial D. reticulatum and Arion spp. slugs were killed by a broadcast application of the chelate iron (III) 2,4‐pentanedionate applied at 40 kg a.i. h

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06607.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY