摘要:

SUMMARYCylindrical and horizontal sticky traps painted in a range of spectral colours were used to determine the flight and landing behaviour of aphids. Data are also presented on aphid catches in suction traps at two heights and in light traps. Apart from colour sensitivity (yellow versus white) there was apparently a separate response to colour which in some species varied with season. Within yellow‐sensitive species there was also a differential response to colour. With the experimental methods used, it was not possible to define mathematically the active and passive landing components on cylindrical traps. Though the active landing component was large it varied between aphid species. Most species caught on horizontal traps at ground level had been flying above 1 m. In some species the response of males to colour and their landing behaviour differed from that of viviparae and oviparae.Four years data from suction traps suggest that aphid species can be divided into three categories on the basis of the height at which they normally fly. One group, mostly tree‐feeders, always show the greatest density at a high level (12.2 m) throughout the season. The second group always have the highest density at a low level (1 m) whilst a third group of species change at a specific date each autumn from a maximum density at 1–12.2 m. Attraction to light (moth trap) appeared to be linked with the grouping of species by height of flight. The interpretation of catch data is discussed in the light of these observa

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07747.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe response to plant spacing by flying and landing aphids has been studied using cylindrical and horizontal sticky traps over cocksfoot and kale crops. Some aphid species showed a significant response to spacing, being caught more frequently over wide‐than close‐spaced crops; the regressions of catches over widely‐spaced on those over close‐spaced plants suggested that most of the species caught followed this trend irrespective of the host plant. The landing response to spacing on horizontal traps at 0.3 m was normally greater than that on cylindrical traps at 1 m. At 1 m, some species (e.g.Aphis fabaegp.) gave a different response to spacing in the two crops, whilst others (e.g.Rhopalosiphum oxyacanthaé) responded similarly to both crop spacings. In contrast to previous results with other aphid species and spaced groundnuts, the landing response ofRhopalosiphumspp. was elicited both when there was a cover crop (clover) between widely‐spaced drills of cocksfoot and by widely‐spaced cocksfoot alone. It is suggested that one stimulus eliciting the landing response with widely‐spaced plants is the electromagnetic emission from bare earth between the plants. Aphid landing behaviour was influenced by the spacing of both cocksfoot a

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07748.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYIn field sowings at Cambridge 2–15% of field bean seeds carryingAscochyta fabaeproduced seedlings with leaf lesions. The fungus spread for distances up to 10 m in an average season and usually infected the new crop of seed. The amount of such infection arising from a single lot varied widely when samples were grown at different centres, presumably because of differences in local weather conditions.Seed lots with approximately 1% infected seeds seem suitable for ware crop production but little or noA. fabaecan be tolerated in seed intended for multiplication. Infection in British‐grown commercial seed has been greatly reduced by the selection of clean seed. Health standards adopted in the Field Bean Seed Scheme may have eliminatedA. fabaefrom one culti

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07749.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe ranges over which the germination of conidia ofAlternaria longipeswas>50% were 10–35 °C on agar and 15–30 °C on tobacco leaf disks. Germination was optimal at 22.5 °C; so was germ‐tube growth, reachingc.300 and 102 μm on agar and leaf disks respectively after 12 h. On average, 27% more conidia germinated and germ‐tubes were 62% longer on disks from leaves washed for 5 min under running water than on disks from unwashed leaves.At controlled saturation deficits germination after 8 h at 1.1 and 2.3 mb was 42.3 and 9.3% respectively and the rate of germ‐tube growth was<0.8 μm/h, compared with 94.4% and 8.3 μm/h in standing water. These results, together with some field data, suggests that germination in the field is largely restricted to periods when free moisture is present on leaves. In Malawi, leaf temperatures and the duration of dew at night were adequate to allow germination and penetration in the absence of rain.Pollen, when applied with the inoculum, had little effect on the number of germinated conidia, but caused ac.tenfold increase in the number of successf

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07750.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYStudies were made of the infection byBremia lactucaeof a range of lettuce cultivars at the adult plant stage, under conditions of artificial and natural epidemic. The pathogen invaded at least the ten oldest leaves of many cultivars, the leaf area affected declining from the oldest to the youngest leaves. Two assessment methods were compared: (1) the percentage area infection on individual leaves and (2) the percentage area infection on the inverted basal area as a whole. Results from the two methods agreed closely under conditions of artificial inoculation and in a natural epidemic. It is concluded that both methods should be used for detailed studies, but method 1 restricted to the oldest five leaves. At least two assessment dates are required since on individual cultivars there were differences in the leaf area infected at various assessment dates. This is probably influenced by the cycle of growth and sporulation ofB. lactucaeand by the effects of invasion by secondary pathogens such asBotrytis cinerea.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07751.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe effects of damaging the testa and the application of seed dressings were examined in field trials on several short‐and long‐season cultivars of groundnut (Arachis hypogea) with differently‐pigmented testas at Samaru, Nigeria, in 1967. There was a high correlation between the number of seedlings which emerged in these trials and the resistance or susceptibility of the seed to invasion by the fungusAspergillus flavus, as assessed by laboratory tests. When the testa was undamaged the emergence of white (susceptible) seed was only 50% while that of coloured (resistant) seed was between 95 and 98%. Damage to the testa by scratching greatly decreased emergence. The application of seed dressing increased the emergence of susceptible seed and also restored the emergence of scratched seeds to the level of undamaged seeds. The effect of the complete removal of the testa was not counteracted by seed dressing; naked seeds, with and without dressing, gavec.10% emergence. The importance of pigment in the testa, the condition of the seed and the effects of seed dressing are disc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07752.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYDuring investigations on the parasites ofChondrillajunceain the Mediterranean region, the rust,Puccinia chondrillina, was found to be one of the most damaging. This macrocyclic and autoecious rust which is specific to the genusChondrilla, remains active throughout the year and attacks all stages and all parts of the plant. In the Mediterranean region the rust appears to multiply solely by the uredo‐stages and the teleutospores produced at the end of the summer have no obvious role in the life‐cycle of the fungus. The uredospores germinated at temperatures of 0–36 °C and were used for inoculation ofChondrillaseedlings in the greenhouse.The rust occurs from the cold continental climates of southern Siberia to the hot, Mediterranean ones of Portugal and North Africa. In many situations the rust has been found to play an important role in the reduction ofC. junceapopulations. Young seedlings were highly susceptible to attack and were often destroyed. Older rusted plants gave many fewer viable seeds than healthy plants and were also often unable to produce new rosettes from their

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07753.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYGrafting to virus‐free Mistletoe chrysanthemums was the most reliable method of detecting the chrysanthemum stunt agent, but specific light and temperature conditions were required for the diagnostic ‘measles’ symptoms to develop. Although stunt agent was highly infectious, leaf‐rubbing inoculations with chrysanthemum sap gave erratic results. Colorimetric and electrophoretic tests were unreliable for indexing chrysanthemums.Stunt agent infected eight of twenty‐nine species in the family Compositae, but none of 116 species in forty‐seven other families. Stunt spread rapidly by foliage contact and by handling plants, but dipping the hands in 2% trisodium orthophosphate when handling plants increased the amount of spread. Stunt agent was not transmitted by four species of aphids, the glasshouse redspider mite, dodder (Cuscuta campestris) or through chrysanthemum seed.Stunt agent withstood 10 min atc.98 °C and dilution to 10‐4, was not pelleted by ultracentrifugation, and was inactivated by RNase in weak, but not strong, buffer, suggestive of an uncoated RNA ‘viroid’. Partially purified preparations were made by homogenizing frozen chrysanthemum leaves in 0.5mphosphate buffer with antioxidant atc.2 °C, and clarification by n‐but‐anol and chloroform, followed by centrifugation. Highly infective RNA was precipitated from the supernant fluid by 2.5 vol. cold ethanol, and resuspended in a small volume of buffer.The u.v. absorption spectra of infective preparations and the u.v. absorbance profiles of density‐gradients, were very similar to those of preparations from healthy chrysanthemum. Infective partially purified preparations of stunt agent withstood exposure to 2% formaldehyde or tri‐sodium orthophosphate, u.v. irradiation, and sonication. Stunt preparations contained no virus particles recognizable by electron microscopy, gave no distinct peak on analytical ultracentrifugation, and did not consistently contain any specific antigen. Although similar to the ‘viroids’ potato spindle tuber and citrus exocortis, stunt agent did not infectCitrus li

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07754.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYPMTV normally causes necrotic ringspot local lesions in Xanthi‐nc tobacco leaves at 15 °C but not at 22°. Dipping the leaves once in hot water at different intervals after inoculation induced necrotic reactions even at 22°. Successive concentric rings, one for each day of the interval between inoculation and treatment, were sometimes induced at 22°; these even formed in continuous lighting, suggesting an intrinsic diurnal rhythm. No lesions were induced at 22° by dipping inoculated leaves in ice‐cold water.Samsun tobacco inoculated with PMTV developed very few lesions at 15°. Many more were induced however, by dipping the leaves in hot water after inoculation.The results suggest some similarities between PMTV and TMV, and the two viruses have been reported as serologically related; but PMTV did not protect plants against TMV, for TMV challenge‐inoculations induced lesions within existing P

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07755.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYIn the Ivory Coast, an apparently undescribed virus was isolated from okra (Hibiscus esculentus) in which it caused mosaic and leaf vein banding. The virus was sap transmissible to a wide range of plants and had a thermal inactivation point of 80 °C. It was named okra mosaic virus (OMV). A purification procedure was developed. Electron microscopy and analytical and density gradient centrifugation showed that OMV was an isometric virus accompanied by empty shells (top component). Serological tests showed OMV to be a member of the tymovirus group

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1973.tb07756.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY