La monoculture du blé d'automne entraîn des baisses de rendement qui ne semblent pas dues uniquement à des causes sanitaires. Ces diminutions de rendement peuvent être atténuées par l'application de différentes mesures culturales. Un renforcement de la fumure azotée et, dans les parcelles exposées au piétin-verse, un traitement au bénomyl au début de la montaison, constituent les mesures les plus efficaces. Les effets négatifs de la monoculture ont été plus marqués aprés labour qu'en semis direct. 相似文献
Based on the time that symptoms of blackleg become evident in the field and the various ways of inoculation, it is concluded that the spread of symptom expression is due to the depth at which the bacteria penetrate into the interior of the tubers. Moreover, it is demonstrated that it is not the closed lenticels which prevent penetration, but the absence of a waterfilm in the intercellular spaces of the tuber tissue. 相似文献
As it is difficult to detect ring rot in its latent form as well as in badly decayed tubers and in potato haulm, a diagnostic technique has been developed. With the help of a Turmix blender and a little water, a suspension is made of the suspected material. The suspension is inoculated into eggplants. Gram-staining of bacteria in sap from petioles of leaves showing symptoms is used to confirm the diagnosis. Some results obtained with this method applied on potatoes and potato haulm are described. 相似文献
Experimental work and a survey of literature gave data on the effects of 175 Compositate on populations ofPratylenchus penetrans in the soil. Nearly 70 Compositae effectively suppress populations ofP. penetrans. It is shown that a close relationship exists between this suppressing feature and the chemotaxonomy of the Compositae.Samenvatting Eigen onderzoek aangevuld met gegevens uit de literatuur gaf informatie over de invloed van 175 Composieten op populaties vanPratylenchus penetrans in de grond. Bijna 70 soorten verlaagden deze dichtheden (Tabel 1). Het betreft soorten van de geslachtenGrindelia, Solidago, Coreopsis, Eclipta, Rudbeckia, Verbesina, Melampodium, Parthenium, Iva, Ambrosia, Milleria, Baeria, Schkuhria, Eriophyllum, Chaenactis, Helenium, Gaillardia, Tagetes, Arctotis, Gazania, Berkheya, Didelta, Echinops enUrospermum. Er is een duidelijk verband tussen de taxonomische indeling van Composieten en deze eigenschap. Bijna alle getoetste soorten van de subtribus Ambrosiinae, Heleniinae, Arctotinae, Gorteriinae en Echinopinae reduceerden populaties vanP. penetrans. In sommige geslachten zoalsSolidago, Coreopsis, Rudbeckia enMelampodium veroorzaakten slechts een of enkele getoetste soorten dit effect.Van de 16 Composieten, waarvan bekend is dat zij -terthienyl in hun wortels bevatten, verlaagden er 15 dichtheden vanPratylenchus. Vrijwel hetzelfde geldt voor Composieten met 5-(3-buteen-1-ynyl)-2,2-bithienyl in hun wortels (Tabel 1). Ook de aanwezigheid in een aantal andere Composieten van een groep rode dithio-acetyleen-verbindingen met waarschijnlijk nematicide eigenschappen in vitro, komt goed overeen met de eigenschap om dichtheden vanP. penetrans in de grond te verminderen. 相似文献
L'étude faunistique des ravageurs des pruneaux stockés a permis de faire l'inventaire des différentes espèces présentes et d'établir une évaluation quantitative de leurs populations à partir de 2 méthodes de prélévement (piégeage, tri d'échantillons). Par ordre d'importance on peut citer: les acariens: Carpoglyphus lactis L. (Glycyphagidae), les coléopteres: Carpophilus ligneus Murr., C. hemipterus L. (Nitidulidae) et Henoticus californicus Mann. (Cryptophagidae) et les lépidopteres Nemapogon granella L. (Tineidae), Plodia interpunctella Hübn. (Pyralidae). Les ravageurs primaires s'attaquent aux pruneaux sains: ils sont responsables des principaux dégáts et comprennent Carpophilus ligneus, C. hemipterus et N. granella . L'autre groupe est formé des ravageurs secondaires, qui s'installent sur des pruneaux déjá attaqués par des insectes ou des micro-organismes. On trouve dans cette catégorie Carpoglyphus lactis et H. calilornicus . Les conditions optimales au développement de ces insectes et de ces acariens sont réunies, lorsque la teneur en eau de la pulpe du pruneau est égale ou supérieure à 20 %, la température ambiante clans l'entrepôt supérieure à 15°C et l'hygrometrie relative variant suivant Ies espéces entre 50 et 85 %. 相似文献
Biological characteristics of the varieties of Gaeumannomyces graminis Arx & Olivier and Phialophora radicicola Cain are reviewed. They include: 1) pathogenicity to roots of cereals; 2) growth on living stem tissues; 3) type of fungal growth-cessation structure formed on or in the host. Together, these provide a simple means of characterizing isolates and standard methods for assessing them are presented. The role of pigmented cells and tissues (growth-cessation structures) in host penetration is questioned, since they are seldom associated with a progressive infection by G. graminis or P. radicicola . However, they are a taxonomic aid, especially as they are now known to form on cellophane overlying agar. New evidence is presented on factors affecting conidiation by these fungi. Flooding colonies with distilled water induced formation of conidia by G. graminis var. tritici Walker, P. radicicola var. radicicola (British isolates but not the type) and P. radicicola var. graminicola Deacon, whereas none formed on corresponding unflooded agar plates. Conidia were usually much larger and germinated readily when they formed in response to flooding; many of these fungi therefore have 2 conidial types, distinct in both morphology and behaviour. Preliminary results suggest that biotin and the form of nitrogen also affect the type of conidium formed by P. radicicola var. radicicola . 相似文献
1. Eggs from hens of three strains were dropped on to a heavy, stiff, smooth, plane body with impact at the equator of the shell; the height of drop, hc, just sufficient to produce shell failure was measured and the corresponding impact velocity, vc, calculated.
2. A small but commercially important percentage of the well‐formed eggs of one strain cracked when hc was as low as 3–3 mm and vc 250 mm/s.
3. Characteristics of the egg found to affect hc and vc included the overall thickness of its shell, thickness of its weak inner shell layer and average shell curvature, all measured at the point of impact, and its weight; its age also had a small effect (additional to that mediated through loss of weight); so did the degree of shell ridging.
4. No effect of shell colour was found.
5. Shell damage was typically a single hair‐crack that ran either round the equator or towards a pole. 相似文献
A method for the separation of leucocytes from bovine blood and its separation into lymphocyte and granulocyte fractions is described. The method, involving flash lysis of the erythrocyte population, was found to yield large numbers of viable cells suitable for maintenance in tissue culture medium and hence of value in immunological studies. 相似文献