摘要:

SUMMARYSpring wheat, var. ‘Phoebus’, drilled at 11/2times the usual rate and grown with three rates of nitrogen was treated with 2.5 or 5 lb. CCC per acre at the sixth‐leaf stage. At maturity, the height of treated plants was only 60% of that of untreated plants, but the percentage shortening was less as nitrogen increased. Although untreated plants did not lodge, CCC increased mean grain yield by 5% by increasing the number of ears and number of grains per ear. Grain weight per ear and thousand‐grain weight were decreased by CCC. The explanation of the increase in shoot number by CCC is not known, but possibly less light was intercepted by the shorter plants, so that later‐formed shoots survived to produce ears.CCC decreased assimilatory area by shortening stems and hence leaf sheath area; lamina area was little affected. It delayed ear emergence by up to 8 days, Leaf‐area index was decreased by CCC and as it increased, net assimilation rate decreased. CCC did not affect nitrogen uptake per unit area of land but it increased nitrogen as percentage of dry matter because it decreased dry‐

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01254.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYInfectivity of soil was measured by incubating samples on potato tuber slices during and after outbreaks of potato blight in three years. Surface soil was always more infective than deeper soil, the most infective surface soil containing the equivalent of 2100 sporangia ofP. infestansper ml. Infectivity usually diminished rapidly with increasing depth, and only occasionally did infectivity below 2 in. exceed the equivalent of 100 sporangia per ml. Exceptionally large infectivity was once found at all depths sampled after heavy rain, but rain did not consistently affect infectivity. The surface soil remained infective for at least 32 days after the haulm was killed with acid, but the concentration of viable spores declined to a small value during the first week after treatment. In the laboratory infectivity persisted for 11 weeks after sporangia were mixed with unsterilized soil originally with a moisture content of 20%.P. infestansmycelium grew only in sterilized soils, perhaps because some soil micro‐organisms inhibit its growth, and others (e.g.Trichoderma viride) parasitize it or lyse it (e.g. byRhizoctonia solani). The three soils tested all contained substances that inhibit the germination of sporangi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01255.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYInfection of hop rootstocks byPseudoperonospora humulihas been shown to occur as a result of inoculation of the tips of shoots 15 cm. or less in length. No rootstock infection developed when shoots were more than 17.5 cm. long at the time of inoculation. Infection via the base of shoots can occur at any time during the growing season and is thought to be the main source of rootstock disease under natural conditions. The importance of direct infection of hop rootstocks by zoospores ofP. humuli, which occurs readily under laboratory conditions, is not known.Application of Bordeaux (6.5% Cu) and captan (15% a.i.) dusts to the crowns and shoot bases of field plants retarded development of rootstock disease and shoot infection (basal spikes) in originally disease‐free plantings of Golding hop

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01256.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYTwo races ofBremia lactucaeare described; race W.1, which can attack various lettuce varieties now being grown commercially but cannot attack the resistant lettuces bred at Wellesbourne, and race W.2, which can infect not only the market varieties but also some of the W.1‐resistant lines. Race W.2 was shown to arise directly from race W.1, possibly by mutation.The length of incubation time from inoculation to sporulation of the mildew in lettuce leaves decreased as the number of spores applied in the inoculum increased. This fact was used to assess the concentration of race W.2 spores in naturally occurring spore populations, by comparing the effects on W.1‐resistant plants of graded dilutions of spores from the field with those of known concentrations of race W.2. These tests showed that race W.2 was most prevalent where W.1‐resistant lettuces had been grown for some years. Race W.2 spores were found, however, where no W.1‐resistant lettuces had been grown, and it appears that race W.2 may be a normal constituent of mostBremiapopulations. The importance of these findings in relation to future breeding for downy mildew resistance is di

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01257.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYThe fungicidal properties of thirty‐three N‐substituted S‐esters derived from dithiocarbamic acid were examined. Several compounds inhibited the germination of spores ofBotrytis fabae in vitroat concentrations below 100 p.p.m., but activity againstErysiphe graminiswas considerably lower. In greenhouse tests the compounds were not effective againstB. fabaewhen sprayed on broad bean seedlings but several gave more than 80% reduction of mildew infection when sprayed on wheat seedlings. Some compounds also showed a marked eradicant action against wheat mildew.The effect of pH, plant sap and amino acids upon their fungitoxicity was also studied and the degree of activity shown by the compounds is discussed in relation to these and other fa

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01258.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYWhen applied in the soil at the time potato tubers were planted, phorate and disulfoton were more effective than dimethoate and menazon in controlling aphids on the foliage of the crop in dry years, but all four were equally effective in wet years. The reason was sought by comparing the ability of the roots of wheat seedlings to absorb these systemic insecticides from air and from water. When absorbed from solution in water, all four insecticides were almost equally effective in killingRhopalosiphum padifed on the leaves, but when the roots were in contact only with the vapours of the insecticides, phorate and disulfoton were much more effective than dimethoate or menazon. This is thought to be the first demonstration that sufficient of the vapours of systemic insecticides can be absorbed by the roots of a plant to render the leaves toxic to insects feeding on them.These results and the physical properties of the insecticides suggest that only insecticides as volatile as phorate and disulfoton can move through dry soil to the roots of plants, and that even in moist soil phorate and disulfoton probably move mainly through the air rather than through the soil water. The more soluble and less volatile dimethoate and menazon are probably absorbed in amounts able to make the foliage toxic to aphids only when they can move to the roots through water.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01259.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYThe movement and persistence of the systemic insecticide dimethoate and its metabolites in the cacao tree have been studied by the use of radio‐phosphorus in Rogor 40.In trunk‐injection experiments only 11% of the insecticide entered effectively into the tree and of this 83% remained within 1 ft. of the point of injection. The remainder was quickly translocated upwards but was unevenly distributed in the canopy.Uptake of dimethoate from soil into the stem and branches proceeded continuously but slowly and was much less than from injections.In mature pods, over 86% of the dimethoate was found to be degraded into non‐toxic metabolites: thus there is little hazard from dimethoate residues in cacao

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01260.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYThe important aphid pest of carrots,Cavariella aegopodiiScop., overwintered in the egg stage on all the common willows (Salixspp.) found in the English Midlands, and showed no host preference between willows on the same site. The eggs were found more frequently onSalix albaandS. fragilis, however, probably because these trees, being larger and generally growing in less sheltered conditions than other species of willow, provide obvious targets for the migrating aphid. Neither eggs nor fundatrices were found onSalix babylonica.The spring migration from willow to carrot started in May, reached its peak about the beginning of June and was over before July. April‐sown carrots were the most severely attacked and high, damaging aphid populations sometimes developed on these within 6–7 weeks from the onset of immigration.The number of aphids on carrots declined in July when winged forms developed among the second and third alienicolae generations and dispersed. Some of these winged alienicolae flew to later‐sown carrots, where they did little colonizing but might have furthered the spread of motley dwarf virus.Natural enemies did not check aphid multiplication: years of highest aphid numbers were those with low rainfall over the first half of the spring migration period.Seasons when motley dwarf virus disease was most troublesome were those in whichC. aegopodiiapterae survived on overwintered carrot

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01261.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYFour cultivars of chrysanthemum (B.G.A. Tuneful, Giant No. 4 White Indianapolis, Bluechip and Yellow Princess Anne) were infested withMyzus persicae(Sulz.) in an insect‐proof glasshouse. Four weeks of rapid reproduction led to temporary overpopulation, but the mean density was soon regulated to a constant level by the production of alatae. When the density was highest, the same proportion of alatae was produced in all regions of the plants and on all cultivars, regardless of population density at the site of eclosion. This was thought to be due to the rapid state of flux in the entire population.Pronounced varietal differences developed in the size and distribution of populations, Tuneful supporting six times as many aphids as Princess Anne. Vertical distribution of aphids on the plants differed not only with cultivar, but also according to the population density and the developmental stage of the plant. A complete redistribution occurred as the density stabilized, revealing further varietal characteristics. The youngest leaves were always the most attractive to the aphids, and preference was frequently shown for their upper surface, particularly on Princess Anne.Short days had little direct effect on the behaviour of the aphids. The induced flowering, however, brought inevitable changes in aphid distribution; populations tended to move upwards towards the flowers, resulting in small, damaged and infested bloom

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01262.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYAir temperature is one of the most important factors influencing the spread of potato viruses in Poland. High correlations of leaf‐roll infection with accumulated air temperatures for the period I January‐30 April, and of infection with virusYwith accumulated air temperatures for the period 1 January‐10 July were obtained. On this basis the expected areas of different incidence of potato virus diseases were delimited in Poland. The correlation of mean infection for 4 years and mean accumulated temperatures for 15 years was higher than for the particular years, and the proportion of the total variance accounted for by regression exceeded 60%.The differences in the spread of both the viruses are disc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1965.tb01263.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY