Enkele gegevens omtrent sclerospora in Indonesië

Samenvatting De gevoelige periode van de maisplant voor infectie doorSclerospora maydis (Rac.) Butler werd bepaald, alsmede de incubatietijd (grafieken 1 en 2). Behalve deze soort komt sinds 1947 op Noord CelebesSclerospora philippinensis Weston voor, die daar aanzienlijke schade aan mais toebrengt. De verschillen van deze schimmel metSclerospora sacchari zijn slechts gering en een nader onderzoek dienaangaande is dan ook zeer gewenst.De eerste oögoniën-vorm vanSclerospora in Indonesië werd gevonden en wel vanSclerospora northii Weston op eenErianthus spec. op het eiland Soemba.Summary The nomenclature ofSclerospora maydis (Rac.) Butler is discussed. The susceptible period of the host and the time of incubation of this fungus (graphs 1 and 2) were determined.Since 1947 a species ofSclerospora has caused considerable damage on maize in North Celebes. It is stated to beSclerospora philippinensis Weston. The differences between this fungus andSclerospora sacchari T. Miyake are very slight. AsSclerospora sacchari is still unknown in Indonesia, it is very important for the culture of sugarcane on Java to investigate by means of inoculation trials, ifSclerospora philippinensis can attack sugarcane. Sclerospora northii Weston has been found onErianthus spec. on the isle of Sumba; it is the only knownSclerospora species in Indonesia which forms oögonia.Vroeger verbonden aan het Instituut voor Plantenziekten te Bogor, Indonesia, thans aan het Inst. v. Plantenziektenkundig Onderzoek (I.P.O.) te Wageningen.     

Het optreden van plaatselijke rassen bij Helopeltis antonii Sign. op Java

Summary Helopeltis antonii was bred at different constant temperatures at the experimental station at Semarang in 1939 and 1940. Some of the results concerning the duration of development from hatching of the egg untill the imaginal stage are recorded in the table and the graph. By comparing these data with those published byLeefmans (1916) (Helopeltis bred on tea in West Java) andZehntner (1901) (Helopeltis bred on cocoa in Central Java) we find that the time of development mentioned by these authors is shorter. In accordance with the experiments ofBonnemaison (1946) this probably can be attributed to the breeding ofHelopeltis at alternating temperatures (day and night). The duration of development at 19°C, mentioned byLeefmans (19 days), however, differs so much from the duration found in this investigation (32–34 days) that this explanation seems improbable. Other experiments at constant temperature, that will be published elsewhere, show that the population used for breeding was well adapted to the average temperature at the estate, Djati Rungo, from where this population came. This extreme adaptation suggests that this may also occur at other localities. Therefore it is probable that the populations ofH. antonii from different localities do not have the same genetical composition. The differences mentioned above can probably be attributed therefore to this fact. Data are given to strengthen this supposition. The existence of genetically different populations has already been suggested by ProfessorRoepke in 1909. He called them biological races. The occurrence of the varietybradyi ofH. antonii is probably caused by such a difference too and thus could better be considered as a subspecies.Helopeltis theobromae Mill. is without doubt only a subspecies ofH. theivora.Thus we suggest:Helopeltis antonii subspec.bradyi Wat. new comb. Helopeltis theivora subspec.theobromae Mill. new comb.

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Deventer     

Solanum dulcamara L. (Bitterzoet) als mogelijke bron voor bladrolvirus

Summary Dijkstra (1933) demonstrated thatSolanum dulcamara (Bittersweet, Woody Nightshade) can be a host plant of potato leaf-roll virus. It was, however, not known whether this wild growing plant in nature contains the virus. AsS. dulcamara is the only common perennial Solanacea in the Netherlands its role as a virus reseroir was investigated.At 25 localities plants ofS. dulcamara were collected, and tested for the presence of leaf-roll virus by transferring virus-freeMyzus persicae (Sulz.) after 24 hrs feeding to groups ofPhysalis floridana, where they fed for 24 hrs before being killed. All plants ofS. dulcamara appeared to contain leafroll virus, though they did not show symptoms. Also seedlings ofS. dulcamara from seed of a leafroll infested plant showed no symptoms before or after infection with leafroll bij transmission withMyzus persicae (Sulz.).The virus could be transmitted fromS. dulcamara to potato (var. Bintje) byMyzus persicae (Sulz.) and by graftingS. dulcamara on potato.Seedlings, grown from seed obtained from a plant which was shown to have leaf-roll, all appeared to be infected with leaf-roll. As so far no plants were found or obtained which had no leaf-roll virus, it is possible that inS. dulcamara leaf-roll virus is invariably transmitted with seed. But as the virus does not appear to be pathogenic inS. dulcamara, one might assume that what in potatoes and other plants is called leaf-roll virus, inS. dulcamara is an integral, natural component of the organism.     

De rijpingsvraat van de eikensp intkever,scolytus intricatus ratzeb

Summary The oak barkbeetle,Scolytus intricatus Ratz., is, in normal times, a rather uncommon insect in the Netherlands. After the outbreak of the war, however, it developed in large numbers in oak trees, damaged bij direct war action. The presence of the beetle is indicated bij its maturation feeding, consisting in affecting and killing a large number of spur shoots during May. Bij their boring activity the young beetles nearly cut off these shoots near their base, soon they wither and fade becoming clearly visible in the green canopy. Stormy weather causes them to drop off green so that the ground may become densily covered with these shoots.A rectification is added concerning the maturation feeding ofSc. laevis Bechst., as described formerly by the same author. The identification of the beetle in question proved to be wrong. The maturation feeding described refers to the commonSc. rugulosus Ratz.     

Influence of altitude on adult emergence and dynamics ofKaltenbachiola strobi (Winnertz) (Diptera: Cecidomyiidae) populations and its parasites in the Tatra National Park, Poland

A field study onKaltenbachiola strobi (Winnertz) (Diptera: Cecidomyiidae), was carried out between 1987 and 1993 in the highest mountain range in the Western Carpathians located within the Tatra National Park, in southern Poland. Rearing and analysis of 5 780 cones ofPicea abies (L.)Karst., collected from trees growing at different altitudes, yielded 30,478 individuals ofKaltenbachiola strobi, which infested 89.10% of the cones. In case of 29.81% of cones there were more than 20 larvae ofK. strobi per cone. It was shown thatK. strobi in the Tatra Mts. is more abundant in spruce stands of the upper mountain forest zone. Significant connections between the time of cone infestation byK. strobi and its parasitoids and characteristic phenophases in spruce foliage and cone development, and also the development of selected vegetation of the forest floor at different heights above sea level were determined. It was shown that the population dynamics ofK. strobi had tendency to alternate the increase and decrease in numbers every two years. It was also discovered that every two years spruce cones were inhabited by the population ofK. strobi with increased percentage of individuals having prolonged diapause. In total, the parasitoids reduced the population ofK. strobi by about 16–22.63%. Parasitism ofK. strobi in the lower mountain forest zone was higher than in the upper zone.Triplatygaster contorticornis Ratz. (Hymenoptera: Platygasteridae),Torymus azureus Boheman (Hymenoptera: Torymidae) andTetrastichus strobilanae Ratz. (Hymenoptera: Eulophidae) were most effiecient in reduction of the population ofK. strobi, and in the lower mountain forest zoneT. azureus was the dominant parasitoid species, while in the upper zoneT. contorticornis andT. strobilanae. It was shown that a considerable part of the populations ofT. azureus, T. contorticornis andT. strobilanae have their diapause prolonged and highly synchronized with the diapause of their host.     

The occurrence of Rhizoctonia solani on subterranean parts of wild plants in potato fields

The subterranean parts of 1585 wild plants (weeds) belonging to 52 species, found in potato fields in the northern part of the Netherlands were examined for the presence ofRhizoctonia solani. The fungus could be isolated from 30 plants belonging to 12 species. Of these isolates 62% proved to be pathogenic to potato sprouts.Some species seemed more frequently colonized byR. solani than others, particularlySolanum nigrum, Elytrichia repens andMatricaria recutita. On some common weeds, viz.Chenopodium album andPoa annua, noR. solani was observed, while about 1% of allPolygonum persicaria were infected.Disease symptoms were only observed once onElytrichia repens as sharp eyespots, presumably caused byR. cerealis.The incidence ofR. Solani on weeds increased markedly towards the end of the growing season.

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Samenvatting Wortels, wortelstokken en ondergrondse stengeldelen van onkruiden voorkomend in aardappelakkers in Groningen, Friesland en Drenthe zijn onderzocht op de aanwezigheid vanRhizoctonia solani. Van 1585 planten, behorend tot 52 soorten, herbergde bijna 2%, d.w.z. 29 planten behorend tot 12 soorten,R. solani op de ondergrondse delen. Van dezeRhizoctonia-isolaten bleek 62% aardappelspruiten aan te tasten.Bepaalde onkruidsoorten bleken vaker drager te zijn vanR. solani dan andere. Dit was het geval met kweek, zwarte nachtschade en echte kamille. Op enkele algemene onkruiden als witte ganzevoet en straatgras is geenRhizoctonia waargenomen. Van het algemeen op zandgronden voorkomende perzikkruid bleek ongeveer 1%Rhizoctonia op de wortels te herbergen.Typische ziektesymptomen — scherpe oogvlekken — zijn alleen waargenomen op stengels van kweek. Het voorkomen vanR. solani op onkruiden neemt sterk toe tegen het eind van het groeiseizoen (eind augustus en september).

     

Over de cicadellidenfauna van de kers

Summary In connection with the investigation of a possible vector of the Eckelrader virus disease of sweet cherry in the Netherlands, an examination was made of the leaf hopper fauna of cherry. Five species were found breeding regularly on this hostplant viz.Typhlocyba quercus (F.),Erythroneura alneti (Dhlb.),Erythroneura flammigera (Geoffr.),Empoasca flavescens (F.), andEupteroidea stellulata (Burm.). Some details about their biology are given. Other leafhopper species found on cherry, but which are probably only there by accident, are mentioned.      

“Zwartbenigheid” bij tulp en iris,veroorzaakt doorSclerotium wakkerii nov. spec.

Samenvatting Aansluitend op een vorige publikatie over de z.g. zwartbenigheid bij tulpen (Boerema, 1960) zijn in dit artikel nadere gegevens medegedeeld over deze ziekte en de veroorzakende schimmel. Een 23-tal bloembolgewassen zijn door uitplanting op zwaar besmette grond getoetst op hun gevoeligheid voor deze ziekte. Daarbij kon het typische ziektebeeld van de zwartbenigheid alleen worden verkregen bij tulpen en bolirissen. De uit de praktijk afkomstige stelling dat ook krokussen voor deze ziekte gevoelig zijn (Silver & Slootweg, 1959), kon niet worden bewezen.De kenmerkende eigenschappen van de sclerotiën vormende schimmel die deze zwartbenigheid veroorzaakt, zijn uitvoerig besproken. Daar de schimmel onbekend blijkt te zijn, is deze beschreven als een nieuwe soort:Sclerotium wakkerii. Deze schimmel is nauw verwant aanSclerotium denigrans Pape, die een zwarte verkleuring vanConvallaria-kiemen veroorzaakt (Pape, 1943).Summary After reference to an earlier paper on black leg of tulips (Boerema, 1960) the present paper gives further data on the disease and the causal fungus. Besides affecting tulips, the disease is also found in the field on bulbous irises. The disease symptoms are shown in figs. 1, 2, 3 and 4.The susceptibility to black leg of 23 bulb species was tested in heavily contaminated soil. In agreement with experience in practice, only tulips and irises developed the typical black leg symptoms. In other bulb species a black discoloration of the dead membraneous bulb or tuber tunic was sometimes found, but no disease symptoms appeared above ground. This applied also to crocus, for which susceptibility to black leg in the field has been claimed (Silver & Slootweg, 1959).The black leg-fungus is easily isolated on cherry agar at 20 °C (fig. 5a), after treating the attacked tissue with a detergent and rinsing with tap water. Growth of the fungus was studied on malt agar, as this medium favours good and rapid growth. The relation between the growth rate on malt agar in the dark and temperature is shown in fig. 6. In the early stage a white flat mycelium is formed; later this turns brownish-black, secreting a typical dark pigment in the medium (fig. 7a and 7b). The hyphae (fig. 5d) vary in width from 1.8 to 7.5 , the walls being rather thick, 0.4 to 0.8 . The hyphae are often anastomosed and branched. After 2 or 3 weeks in culture the fungus develops brownish-black round or flattened irregular sclerotia 2–5 mm in diameter and 0.5–1.5 mm thick, consisting of a compact mass of hyaline hyphae surrounded by thick-walled dark coloured cells (fig. 5a and 5c). When the fungus is grown at low temperatures sclerotia sometimes develop in the aerial mycelium. These are always somewhat spherical and at first white in colour (fig. 5b). In an old culture of the fungus grown on malt agar microconidia formed in phialides were found in 1960 (Boerema, 1960). This has not been observed again, however, so possibly a contamination was concerned.The black leg fungus differs from all other known sclerotia producing fungi.¹ It is therefore described as a new species,viz. Sclerotium wakkerii Boerema & Posthumus nov. spec. We take pleasure in naming this species after Dr.J. H. Wakker (1859–1927), originator of scientific work on bulb diseases. Living cultures of the fungus have been placed at the disposal of the Centraalbureau voor Schimmelcultures at Baarn (type culture) and at the Commonwealth Mycological Institute at Kew. Dried plate cultures were sent to the Commonwealth Mycological Institute at Kew and the Rijksherbarium at Leyden. Sclerotium wakkerii closely resemblesSclerotium denigrans Pape, the cause of a black discoloration of the shoots of lily of the valley (Pape, 1943). However, the sclerotia ofSclerotium denigrans are considerably smaller than those ofSclerotium wakkerii.     

Aantasting van bladeren van rhododendron DoorChaetapiospora rhododendri (Tengw.) v. Arx

Summary Two fungi were isolated from diseased leaves ofRhododendron ponticum: Botryosphaeria foliorum (Sacc.)v. Arx etMüll enChaetapiospora rhododendri (Tengw.) v. Arx. With the latter inoculation-experiments were performed. It became clear that this fungus can only invade the leaves ofRhododendron ponticum through wounds, causing dead areas. These spots enlarged quickly when the leaves were detached from the branches. Perithecia developed in the dead tissues.     

Het parasitaire karakter van Septotinia populiperda Waterman & Cash

Summary Mature apothecia ofSeptotinia populiperda Waterman andCash are formed in spring and early summer on leaves shed the previous autumn. The ascospores ofS. populiperda produce an infection in the form of leafblotches only when an injury of the leaf is present.P. candicans Ait. is more susceptible to the parasite thanP. marilandica Bosc. andP. brabantica Houtz. Leafblotches are produced in equal numbers when the ascospores are sprayed with an atomizer upon the upper or the lower leafsurface. The germination of the ascospores is inhibited in vitro at a concentration of 7 to 8 mg copper per liter, when copper is used as Bordeaux mixture, or as coppersulfate (CuSO₄5H₂O).     

First report of Rhizomonas sp. causing corky root of lettuce in Europe

Typical symptoms of corky root were observed on iceberg lettuce (Lactuca sativa L.) in the Netherlands and England, on prickly lettuce (Lactuca serriola L.) in Spain, and on sowthistle (Sonchus oleraceus L.) in Greece. Slow-growing bacteria with similar colonies as strains ofRhizomonas suberifaciens or otherRhizomonas species were isolated from soil surrounding plants with corky root symptoms using lettuce seedlings as bait. Crude lysate from all strains was tested for DNA homology with DNA fromR. suberifaciens strain CA1 (R. sub. CA1) andRhizomonas sp. strain WI4 (R. sp. WI4). Strains that had homology values higher than that ofR. sp. WI4 orR. sub. CA1 were tested for pathogenicity on 1-wk-old lettuce seedlings, cv. Salinas, Two strains from the Netherlands induced typical symptoms of corky root on lettuce. These strains tested negative with monoclonal antibody MAb-Rs1 specific forRhizomonas suberifaciens in an enzyme-linked immunosorbent assay (ELISA). They had low DNA homology withR. sub. CA1 (4–9%) and low to moderate DNA homology withR. sp. WI4 (4–17%). Some nonpathogenic strains had moderate to high levels of DNA homology withR. sub. CA1 orR. sp. WI4 (19–84%). All strains had fatty acid profiles similar to those ofRhizomonas species. This is the first report ofRhizomonas sp. causing corky root of lettuce in Europe.     

Een virus inAtropa belladonna

Summary In a bgarden at Baarn, The Netherlands,Atropa belladonna plants, grown from seed, showed symptoms similar to those described bySmith (1946, 1957) for Belladonna mosaic. After inoculation of solanaceous test plants with sap from diseased plants, the following species showed symptoms:Atropa belladonna L.,Capsicum annuum L.,Hyoscyamus niger L.,Nicandra physaloides Gaertn.,Nicotiana glutinosa L.,Nicotiana tabacum L. var. Samsun,Petunia hybrida andPhysalis floridana Rydb. The symptoms suggest that the virus may be identical with that described bySmith. A high virus concentration was found inHyoscyamus niger. Nicandra physaloides, Petunia hybrida, Physalis floridana, in the roots and the pericarp of diseasedAtropa plants, and also inSolanum nigrum L. andDatura stramonium L. The latter two species showed hardly any symptoms. A. low virus concentration was found inCapsicum annuum, though this plant showed severe symptoms.The dilution end point of the virus was between 10^–3 and 10^–4; virusinactivation occurred between 70° and 80°C.In electron micrographs the rod-shaped virus particles appeared similar to those of rattle virus.Virus could be detected in the roots of tobacco plants after the leaves had been inoculated with sap of diseasedAtropa-plants (Table 1). The reverse did not occur. Following immersion of the roots of tobacco plants in virus-containing sap these plants were potted in steamed soil. Subsequently the roots proved to be infected but the stems and leaves contained no virus. However,Atropa plants treated in the same way, did show leaf symptoms.It appeared, that the roots of young, healthy tobacco plants could become infected with virus, when grown in naturally infested soil for only tow days (Table 2). Fungus cultures isolated from diseased roots did not show any infectivity. Nematodes are probably the vectors of this virus (Sol, Van Heuvel & Seinhorst, 1960).Met medewerking van Merr.J. M. Dekhuyzen-Maasland, Dr. S. Gayed (Karthoum), Mej.C. van Heuven, C. de Vooys en Mej.R. van Wessem.     

Massenvermehrung von phyllophagen Schmetterlingen in Laubw?ldern des Rheinlands

Zusammenfassung  In den Jahren 1996 und 1997 wurde in ausgew?hlten Gebieten des Rheinlands die Populationsdichte von Schmetterlingsraupen erfa?t, die an Eichen (Quercas robur undQ. petraea) und an Hainbuchen (Carpinus betulus) Kahlfra?, an Rotbuchen (Fagus sylvatica) erheblichen Fra?schaden verursachten. An dem Blattfra? waren insgesamt 63 Schmetterlingsraupen beteiligt. An Eichen erfolgte Kahlfra? gleichzeitig durch mehrere Arten (Operophtera brumala, O. fagata, Erannis defoliaria undTortrix viridana), w?hrend an Hainbuche und RotbucheOperophtera fagata für den hohen Fra?schaden verantwortlich war. Standorte, an denen Massenvermehrungen nachgewiesen wurden, waren gut mit N?hrstoffen versorgt und best?tigen so die Hypothese zur Ressourcenverfügbarkeit. Die Populationsdichten der Schmetterlingsraupen waren an Eichen so gro?, da? es zu inter- und intraspezifischer Konkurrenz (scramble competition) kam. In Eichenbest?nden, die mit Rotbuchen unterbaut waren, wurde die Konkurrenzsituation unter den Schmetterlingsraupen vermindert. Somit k?nnen waldbauliche Ma?nahmen, besonders bei einer Massenvermehrung vonOperophtera fagata, zu einer Verl?ngerung der Gradation beitragen.

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Mass occurrence of phyllophagous caterpillars in the deciduous forests of the Rhineland

We investigated species assemblages of Lepidoptera which fed onQuercus petraea, Carpinus betulus andFagus sylvatica trees growing in commercial forests in the Rhineland (Germany). In total we found 63 different species of caterpillars. Several species (Operophtera fagata, O. brumata, Tortrix viridana, Agriopis leucophaearia, A. aurantiaria andErannis defoliaria) appeared in high abundances on oak trees, which they together defoliated. Defoliation ofCarpinus betulus as well as high feeding damages onFagus sylvatica were caused mainly by a single species,Operophtera fagata. From our observations of individual caterpillars and their extraordinarily high feeding damages (=45%) onFagus sylvatica trees which were growing in the shade of oak trees, in comparison to individualF. sylvatica trees not growing beneath oak trees (feeding damage= 7%), we made the following conclusions: Firstly, in the case of mass occurrence a severe influence of scramble competition occurs between caterpillars. Secondly, a prolongation of gradation of polyphagous caterpillars is caused when stratification byFagus sylvatica living as undergrowth of oak trees occurs. Defoliated trees occurred in sites with enhanced nutrient availability. This supports the resource availability hypothesis. Although there was a surplus of nutrients in the soil and within the roots we found a deficiency of P in the leaves.

     

Enkele waarnemingen over het opreden van de verwelkingsiekte bij luzerne in Zeeland in 1957

Summary Some observations have been made on lucerne wilt disease during the growing season in 1957, and in experimental inoculation tests in a glasshouse in 1958. In the province of Zeeland the disease does harm to the crop and prevents many farmers from keeping their crops longer than two years.In a survey data have been collected on soil type, preceding crops, green manuring and manuring with stable dung, pH, structure and weeds. No correlations between these factors and the degree of attack by the disease could be proved, except that on heavy soils the disease was less severe than on lighter soils (as a mean of all observations).Development of the disease is facilitated by damage caused by mechanical equipment to the crop. Damage to the crown of the plants should be avoided as much as possible. The disease is distributed extensively after frequent mowing. On attacked leaves left behind on the mowed stalks, and on decayed leaves dropped to the soil, masses of spores ofVerticillium albo-atrum are produced, which form a potential source of infection in a weakened crop.It seems that the disease is more air-borne than soil-borne, since one year old crops are seldom attacked.From attacked lucerne plants in the field the following fungi have been isolated:Verticillium albo-atrum Reinke & Berth.,Gliocladium roseum Bain andFusarium avenaceum (Fr.) Sacc. (table 1).Isolations have been made from 50 different species of weeds, out of which the following fungi were obtained:Verticillium albo-atrum Reinke & Berth. fromCapsella bursa-pastoris Med. andPlantago major L.,V. dahliae Kleb. fromPrunella vulgaris L.,Capsella bursa-pastoris Med. andThlaspi arvense L., andV. lecanii (Zimm.) Viegas fromPlantago major L.In inoculation experiments with all these isolates, in roots, stalks and on cut plants of lucerne, onlyV. albo-atrum, both from lucerne and weeds, andV. lecanii proved to be able to cause wilting of leaves and stalks. WithGliocladium, Fusarium andVerticillium dahliae no such symptoms could be obtained. The results were the same whatever method of inoculation was used.     

Verticillium albo-atrum as a parasite ofSenecio vulgaris

Many weeds, includingSenecio vulgaris, are virtually symptomless hosts ofVerticillium albo-atrum. Plants ofSenecio vulgaris were inoculated with spore suspensions ofV. albo-atrum by two different methods: root-dipping or injection. Infected plants rarely wilted but were stunted, their lower leaves died prematurely and numbers of lateral shoots were decreased.V. albo-atrum was isolated from all parts of the host including achenes. When placed on agar, infected achenes germinated more rapidly than healthy ones. Only small amounts of mycelium developed in the vessels. Severe wilting was possibly avoided because there is insufficient time for damaging amounts of mycelium to develop inSenecio which has a short period of vegetative growth. On the other hand its tolerance to infection may be attributed to the morphology of its vascular system with its narrow vessels and sparse parenchyma cells.In co-operation withH. van Geest, J. P. Overdulve andC. J. J. Richter.     

Het toetsen van stammen vanNectria cinnabarina (Tode) fr. op levende takken in vitro

Summary Some types of elm hybrids resistent to the Dutch elm disease turned out to be susceptible toNectria cinnabarina (Tode) Fr. This fungus may behave as a parasite, killing branches. Virulent and non-virulent strains are known. A method is described for cultivatingNectria-strains in vitro on living desinfected branches ofAcer and ofUlmus. Three weeks after inoculation with a virulent strain the branches were killed. They were covered all over by a thick layer of mycelium. The mycelium of non-virulent strains could not kill the branches. It developed only sparsely. By this method it will be possible to select the most virulent strains out of a collection of isolates in order to use them for testing elm hybrids on their resistence toNectria cinnabarina.     

Grondonderzoek op phytophthora sabdariffae

Summary For the successful cultivation ofHibiscus sabdariffa for fiberproduction in Java a preceding determination is necessary whether either soil or organic manure are contaminated byPhytophthora sabdariffa or not. To this end a method has been elaborated analogous to the method to determined soil contamination byPhytophthora nicotianae.According toGarrett's scheme ofWaksman's classification of soil fungi into soil inhabitants and soil invaders,Phytophthora sabdariffa has to be classified as soil invader.To test the presence of this fungus in soil or in organic manure leaves ofRicinus communis prove to be useful as a detector, since leaves ofHibiscus sabdariffa are too small and too quickly given tot decay. A method is to spread a paste of the soil or of the organic manure on the leaves and to keep these leaves contaminated during 24 hours (spreading method). Afterwards the paste is washed away and the leaves are kept in humid conditions during another 24 hours or 2×24 hours.The number of spots caused by Phytophthora is a measure of soil- or manureinfection (Table I). A more sensitive method is obtained by making a suspension of the soil or of the manure and by streaming this suspension (submersion method) during two hours over Ricinus leaves (Thung, 3). Afterwards the leaves are kept in humid air to give the fungus occasion to form spots (Table 2). Since Ricinus leaves are also susceptible to tobacco- and Ricinus-Phytophthora, these fungi will also be detected by these leaves. Owing to the fact that these fungi are also a parasite ofHibiscus sabdariffa, these method prove to be useful to detect suspected soil or manure regarding the cultivation of this fiberplant.     

Oriënteerend onderzoek omtrent physiologiese specialisatie van Puccinia triticina Eriks. In Nederland

Summary Physiologic specialization inP. triticina, the organe leaf rust of wheat, was discovered byMains andJackson (8, 9, 10), who, in the United States, found 12 physiologic forms.Scheibe (11), in Germany, found form 11 and three new forms: 13, 14 and 15. The present author found forms 11, 14 and 15 to occur among five isolations ofP. triticina from different regions of the Netherlands (cp. table I on p. 7). The wheat-varieties, usually grown in Holland, were all found to be equally susceptible to all three forms of the rust. Foreign varieties, however, exist which are highly resistant to the three froms, so that improvement of the dutch wheat-varieties can be accomplished by crossing with such resistant varieties. (vroeger: Wageningen, Holland; thans: Buitenzorg, Java)     

On biotypes of the cereal-root eelworm (Heterodera Avenae) and resistance in oats and barley

In the Netherlands four biotypes of cereal-root eelworm have been recognized by usingAndersen's series of test varieties. Three forms ofAvena sterilis and 14 varieties of oats were found to be resistant to the four biotypes. In barley two varieties showed resistance to four biotypes and many varieties were found to be resistant to one, two or three biotypes.     

Een ziekte in erwten,veroorzaakt door het aaltje hoplolaimus uniformis thorne

Summary In some gardens on light sandy soil in Ede a poor growth and yellowing of the leaves beginning with the lowermost ones was observed in peas together with root rot and reddish discoloration of the vascular bundles. The soil was heavily infected withHoplolaimus uniformis Thorne,Pratylenchus penetrans (Cobb)Sher andAllen,P. minyus Sher andAllen and aTylenchorhynchus species.The disease symptoms described above were reproduced experimentally by growing peas in soil inoculated withHoplolaimus uniformis.The other species mentioned above did not damage peas grown in soil inoculated with numbers five times as high as in the original soil.