ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03686.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYYeoman wheat, in the six‐course rotation experiment (potatoes, rye, sugar beet, barley, clover, wheat) at Rothamsted between 1937 and 1960 averaged 34% of straws at harvest infected, 19% severely, withCercosporella herpotrichoides, the cause of eye‐spot. In different years infected straws ranged from 2 to 99%, which included 1–81% with severe lesions. Straws severely infected increased by about 7% in each succeeding 6‐year cycle, presumably because the amount of infectious material steadily increased. The small amount of eyespot at the beginning of the experiment can be explained by the few cereal crops taken on the land before the experiment began.The fungus survived 5 years between wheat crops partly on spring‐sown barley and autumn‐sown rye, which (1952‐60) each averaged 8% infected straws, only 2% severely, while wheat had 45 % infected, 27 % severely.Other factors that probably influenced yield in some years include lodging (which occurred in 10 years, when straw yield or severe eyespot were above average), other diseases and pests, notably wheat bulb fly, weeds and differences in cultivations and treatments.Mean yield of grain in the 30 years was 28·5 cwt./acre, the maximum 41·1, minimum 18·7. In a neighbouring field, Yeoman wheat, unharmed by soil‐borne diseases and pests and given the same amount of nitrogen (0·6 cwt./acre) yielded about 40 cwt./acre with a year‐to‐year variance of only 5 cwt./acre compared with a range of 19·1 cwt./ acre in the six‐course wheat in the same period (1952‐58), the same weather having different effects on healthy and diseased wheat.The number of straws per foot row (adjusted to 7 in. spacing) averaged annually 21·3 (maximum 28·0, minimum 14·8). Regression analyses showed that 18% of the variance in grain yield was accounted for by the number of straws and that when the number with severe eyespot lesions was included as a depressing factor, together they accounted for 48%. These figures further indicate that severe infection of all straws would almost halve the yield, and that the mean loss attributable to severe eyespot lesions at

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03687.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYWeighed amounts of lightly pulverized soil were drawn through a perforated aluminium plate and impacted on agar media in Petri dishes. This was done by placing the dishes in an Andersen air sampler, through which air was drawn at 14 l./min. The sampler was operated so that the soil was dispersed uniformly into 400 equally sized units/dish, each unit weighing 0·125 mg. These were transferred either to water‐agar medium to detectPythiumspp., or to Dox‐yeast‐agar medium forFusarium oxysporum.The amount of each fungus in the soil was estimated from the frequency it was recovered from the transferred soil units. Results were more reproducible than by the usual soil‐dilution methods, and the method gave more uncontaminated cultures of Fusaria an

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03688.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYIn Petri‐dish trappings in parsnip crops during the wet seasons of 1958 and 1960, ballistospores ofItersonilia pastinacaewere first obtained in August and increased in number to a peak in October or November. In the dry seasons of 1959 and 1961 the spores were much fewer and appeared later. There was a diurnal periodicity in the numbers of spores trapped, the maximum concentration occurring around dawn and the minimum during the afternoon. The fungus occurred to only a small extent in the air over bare ground. The numbers of ballistospores of I.perplexanswere lower than those of I.pastinacae, but showed somewhat similar seasonal and diurnal fluctuations.I.pastinacaewas isolated from parsnip leaves either at the same time as, or shortly after, the earliest trappings from the air.Attempts to prevent the ballistospores ofI. pastinacaereaching the roots, by raising ridges of soil or peat over them or by defoliating the plants, resulted in reductions in black canker on the root

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03689.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYMycelium developing from germinating spores ofVerticillium tricorpus, supplied with an adequate source of carbohydrate, penetrated healthy but not wounded tomato leaves, whereasV. dahliae, originally isolated from Brussels sprouts, invariably failed to enter a living leaf. Colonization byV. tricorpusceased when the lamina became chlorotic and was followed quickly by premature leaf‐fall. Whereas leaves killed by immersing in boiling water were quickly invaded byV. tricorpusandV. dahliae, fallen leaves which had died naturally appeared to have on their surfaces a substance which had an inhibiting effect upon the germination of conidia of both fungi.Expressed sap from living leaves contained a water‐soluble thermolabile substance which inhibited the germination of, but was not lethal to, conidia suspended in distilled water, but its action was suppressed by the presence of sucrose.It is suggested that this inhibitor, probably in a bound state in the living leaf, on death passed out through the now completely permeable cell membranes on to the surface in a sufficient concentration to prevent the germination of the coni

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03690.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYIn field trials aimed at developing a successful control for withertip disease of limes, applications of fungicides containing phenylmercuric salts, copper, captan, zineb and nickel were compared. Of these, the organo‐mercurial fungicides were the most effective. A light mineral oil as a carrier for this type of fungicide proved less satisfactory than water.Timing of the spraying programme should be determined by two particular periods of flowering—that associated with showers at the end of August and that with thevulirains (November‐December). These flowering periods provide the greater part of the crop in the following year.The number of spray applications necessary to obtain good disease control was found to depend mainly on rainfall during periods of new growth. In one trial, however, regular applications every 5th day, irrespective of rainfall, gave good co

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03691.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYAbacá mosaic virus (AMV), which is readily transmissible between maize seedlings by inoculation with sap, has properties suggesting that it is a strain of sugar‐cane mosaic virus. Antisera to AMV precipitated specifically with sap from plants infected with the strain of sugar‐cane mosaic virus found, in Puerto Rico. Partially purified preparations of AMV contained flexuous rods 680 mμ long similar to those recorded for sugar‐cane mosaic virus.No evidence was found to support the widely held view that AMV is a strain of cucumber mosaic virus. Cucumber mosaic may infect abacá, but it is certain that other viruses can cause typical symptoms of abac

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03692.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYWater‐culture experiments with six concentrations of zinc between a trace and 20 p.p.m. showed that the symptoms of clover phyllody were ameliorated by zinc. The proportion of symptomless flower‐heads increased with higher concentration, and when pollinated these set viable, virus‐free seed. Infected plants produced approximately twice as many inflorescences as uninfected plants at each concentration, but the addition of zinc decreased the number produced. Leaf‐bronzing typical of the phyllody syndrome was greater in infected plants and increased with higher concentration, but necrotic spotting attributable to zinc toxicity was more marked in uninfected plants. Zinc at 20 p.p.m. was generally toxic. The dry weight of shoot and root decreased at the higher levels of zinc, and at a lower level with infected than with uninfected plants. Zinc content of root and shoot increased with greater concentrations in the culture solution, being higher in the roots of infected plants than of uninfected ones but less in the shoots. Stolons of infected plants bearing symptomless inflorescences reverted to the full phyllody condition when transplanted into normal soil.The relationship of zinc to normal metabolic processes in the host, including earlier work on hormone levels, is discussed. It is considered that the technique would be of practical value to the legume

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03693.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYIn the examination of a soil sample for the cysts of potato‐root eelworm subjective errors are liable to occur at three particular stages of the technique, especially when large numbers of samples are being examined as a routine. Three pieces of equipment have been developed to mechanise these stages as far as practicable: (1) A centrifugal divider was adapted to obtain mechanically a uniform aliquot subsample from the full soil sample taken from the field; (2) A turntable was developed so that if cyst numbers are large the total may be estimated without picking off all the cysts present; (3) A magnetic stirrer was used to ensure that a reliable aliquot subsample is taken from the suspension of eggs for counting in the Fenwick slide. The inherent errors associated with each of these stages of the technique are examine

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03694.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

SUMMARYForty‐seven British populations of potato‐root eelworm (Heterodera rostochiensis) were tested for ability to form cysts on plants with resistance derived fromSolanum tuberosumssp.andigena, S. multidissectum, S. vernei, S. sanctae‐rosae, S. famatinaeandS. × juzepczukii, and onS. nigrum, S. sarachoidesandNicotianaspp.The potato variety Arran Banner was used as the standard susceptible host and the number of cysts formed on the resistant plants in pot tests was expressed as a percentage of those formed on Arran Banner or assessed visually from the cysts observed on the outside root mat. Cyst production onandigenahybrids ranged from less than 1% of those on Arran Banner to slightly over 100%. About half of the populations produced 10% or less, and populations of this type, against whichandigenaresistance would be effective, were especially common in south‐east England and Northern Ireland. Cyst production onfamatinaehybrids, a race ofS. nigrumfrom East Germany,S. miniatumandS. sarachoides, resembled that onandigenahybrids. Cyst production onmultidissectumhybrids varied less and only a few populations produced less than 10% and none less than 3% of the number on Arran Banner.S. verneiwas highly resistant to all but about 5% of populations and a race ofS. nigrumfrom Rothamsted was resistant to all tested.In selection experiments the proportion of females able to complete development increased whenandigenahybrids,S. verneiorS. nigrum, were grown repeatedly in the same inoculum. Increase onS. verneiwas slow, the pattern of increase onandigenahybrids suggested recessive inheritance but this could not be confirmed and increase onS. nigrumwas more rapid, suggesting that the genetic mechanisms concerned in plant resistance and those concerned in the production of resistance‐breaking nematode biotypes differ for the three types of plant.The tests revealed much variability between populations of potato‐root eelworm from different localities despite the fact that they have undergone much selection on one type of host plant, cultivatedSolanum tuberosumssp.tuberosum.No cysts were seen onNicotianaspp. Nevertheless,H. tabacummay prove to be little more than a recognizable biotype ofH. r

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1963.tb03695.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY