Observation en Hollande de la forme parfaite du champignonGloeosporium perennans Zeller et Childs

Summary In October 1956 apothecia, belonging toPezicula malicorticis (Jackson)Nannfeldt (=Neofabraea malicorticis (Cordley) Jackson), the perfect stage of the parasite known in plant pathology literature asGloeosporium perennans, have been found on naturally infected appletrees in Druten and near Deest (Land van Maas en Waal) and on appletrees at Wageningen, which had been inoculated with mycelium ofG. perennans in October 1955. The apothecia occurred as well on the surface of the bark as in old conidial fructifications; they were sessile, clearly convex, bright-yellow under moist conditions and brownish when old or dry. The diameter of the apothecia was 0,4–1,6 mm. As many as 100 apothecia were found on a square cm. It is put forward that the formation of the apothecia has been favoured by the very wet weather of the preceding summer.

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Ingénieur agronome aux Stations fédérales d'essais agricoles, Lausanne (Suisse).     

Adaptation of native syrphid flies to new exotic plant (Impatiens spp.)-aphidant associations in Central Europe (Dipt., Syrphidae; Hom., Aphididae; Hym., Formicidae)

Impatiens parviflora andI. glandulifera, two invasive touchme-not species of exotic origin were found to be associated with two aphid groups in Central Europe: a) Exotic species subsequently following their invasive plant hosts (Impatientinum asiaticum Nevsky), b) native species secondarily adapted to the new exotic hosts (Aphis fabae cirsiiacanthoidis Scop.). The species number (listed) of associated syrphid flies in the newly developed guilds was rather high, consisting of broadly oligophagous species. The plant phenology and adaptation of the aphids have resulted in associations which apparently represent seasonally significant sources of prey, their importance apparently increasing with the decreasing season. Antattendance was determined in both aphid species, and no adverse interference with the preying syrphid larvae was observed. In spite of an overall classification of the target plants as expansive weeds, they are classified positively as contributing to the enhancement of syrphid fly populations in the biocorridors in the cultivated landscape.     

Hymenopterous parasitoids of the cherry bark tortrix, Enarmonia formosana (Scopoli) in central-east Europe (Hymenoptera, Ichneumonoidea; Lepidoptera, Tortricidae)

Strategies targeting the biological control of the cherry bark tortrix (=CBT), Enarmonia formosana (Scopoli) in North America have also included the search for potentially useful native hymenopterous parasitoids of the pest in Europe. The search for such agents undertaken in the central-east Europe (Czech Republic, Slovak Republic, Hungary) resulted in determination of several ichneumonid species (Campoplex cf. dubitator Horst., Liotryphon sp., Lissonotus sp., Pimpla spuria (Grav.), Pimpla turionellae (L.), and some others, and a braconid (Apanteles britannicus Wilk.) in 2001–2002.     

Hymenopterous parasitoids of the cherry bark tortrix, Enarmonia formosana (Scopoli) in central-east Europe (Hymenoptera, Ichneumonoidea; Lepidoptera, Tortricidae)

Strategies targeting the biological control of the cherry bark tortrix (=CBT), Enarmonia formosana (Scopoli) in North America have also included the search for potentially useful native hymenopterous parasitoids of the pest in Europe. The search for such agents undertaken in the central-east Europe (Czech Republic, Slovak Republic, Hungary) resulted in determination of several ichneumonid species (Campoplex cf. dubitator Horst., Liotryphon sp., Lissonotus sp., Pimpla spuria (Grav.), Pimpla turionellae (L.), and some others, and a braconid (Apanteles britannicus Wilk.) in 2001–2002.     

山东省樱桃主产区果蝇的调查与鉴定

为了解山东省樱桃主产区果蝇的发生情况,本研究选择了山东省主要樱桃产区的7个地点进行调查,并通过形态学特征和分子鉴定法对果蝇的种类进行鉴定。结果发现,山东省樱桃主产区有4种果蝇,通过形态特征与分子鉴定法最终确定4种果蝇,分别为斑翅果蝇Drosophila suzukii、黑腹果蝇D.melanogaster、海德果蝇D.hydei和伊米果蝇D.immigrans。这4种果蝇对樱桃的为害程度与种植地区、果实腐烂程度和樱桃的品种均有关系;莱芜和泰安地区果蝇分别有4种和3种;烟台和威海地区则只有斑翅果蝇和黑腹果蝇2种。烟台地区果蝇为害率最高,且数量最多,其中烟台丁家夼村樱桃为害率高达45.16%,在第2次采集中烟台薛家村每100粒樱桃中斑翅果蝇和黑腹果蝇的数量最多。美早和先锋2个品种樱桃对果蝇的吸引力较强;采摘后期腐烂的果实可吸引大量的果蝇产卵。因此,应对烟台地区进行重点预防、早期防治,并减少美早和先锋品种樱桃在山东省的种植。     

Insights into the genetic diversity and evolution of Little cherry virus 1

Little cherry virus 1 (LChV‐1), a member of the recently proposed genus Velarivirus, is a sweet cherry pathogen that has been recently reported to infect other Prunus species and is associated with various plant disorders. In this work the incidence of the virus on its putative hosts and possible mechanisms driving its evolution were investigated. Due to problems encountered with LChV‐1 detection, a new nested RT‐PCR assay was developed and applied. The virus was found to be prevalent in cherry plantations in Greece and only occasionally detected in other Prunus species. Sequences corresponding to the partial RNA‐dependent RNA polymerase (RdRp), heat‐shock protein homologue (HSP70h) and coat protein (CP) genes were determined from Greek LChV‐1 isolates originating from different hosts; these were analysed, along with published homologous genomic regions from other isolates. Phylogenetic analysis of the three genes revealed the segregation of four evolutionary distinct groups showing no host or geography‐based clustering. Mean genetic distances among the four groups were high with the CP region showing the highest divergence, although intragroup variability levels were low. Nevertheless, estimations of the mean ratio of nonsynonymous substitutions per synonymous site to synonymous substitutions per synonymous site (dN/dS) for the partial RdRp, HSP70h and CP indicated that these genomic regions are under negative selection pressure. Interestingly, a recombination event was identified at the 3′ end of RdRp on a Greek virus isolate, thus highlighting the role of this mechanism in the evolutionary history of LChV‐1.     

Grain protectants for the control of malathion-resistant insects in stored sorghum

Duplicate experiments were carried out on bulk sorghum stored in South Queensland and in Central Queensland. Bioassays of treated grain, conducted during 6 months' storage, established that fenitrothion (12 mg kg^?1)+ bioresmethrin (1 mg kg^?1), and pirimiphos-methyl (4 mg kg^?1)+ carbaryl (8 mg kg^?1), controlled typical malathionresistant strains of Sitophilus oryzae (L.), Rhyzopertha dominica (F.), Tribolium castaneum (Herbst), and Ephestia cautella (Walker). Chlorpyrifos-methyl (10 mg kg^?1)+ pyrethrins (1.5 mg kg^?1)+ piperonyl butoxide (12 mg kg^?1), and fenitrothion (12 mg kg^?1)+ (1R)-phenothrin (1 mg kg^?1), also controlled the strains of S. oryzae, T. castaneum and E. cautella, but were only partly effective against R. dominica. Methacrifos (15 mg kg^?1) controlled all the tested species except E. cautella. Chemical assays established that the residues and rates of breakdown of these grain protectants on sorghum conformed to the general pattern for other cereal grains; residues from the above treatments were below the individual Maximum Residue Limits recommended by the Codex Alimentarius Commission.     

Schurft op Pyrancantha

Summary Spilocaea pyracanthae (Otth) v. Arx comb. nov. (Syn.:Fusicladium pyracanthae (Otth) Viennot-Bourg.), the scab fungus ofPyracantha coccinea, overwinters in its conidial stage on the living leaves and on twigs. No perithecial stage could be found the last three years on overwintered fallen leaves.     

Assessment of the inheritance of resistance and tolerance in cherry (Prunus sp.) to Blumeriella jaapii,the causal agent of cherry leaf spot

Cherry leaf spot (CLS), caused by Blumeriella jaapii, is a serious fungal disease of sour cherry (Prunus cerasus). Cultivar Montmorency, the major cultivar grown in the United States, is highly susceptible to CLS. As many as 10 fungicide sprays can be required each growing season to combat this disease; therefore, developing CLS‐resistant cultivars is a top breeding priority. Germplasm previously reported to be resistant or tolerant to CLS was acquired and incorporated into the sour cherry breeding programme at Michigan State University (MSU) and included three cherry species: sour cherry, sweet cherry (P. avium), and the wild species P. canescens. This study aimed to: (i) compare the CLS disease progression profile of the susceptible cultivar Montmorency with those of the resistant and tolerant germplasm; and (ii) gain an understanding of the inheritance of these resistance and tolerance traits by evaluating the host response of progeny individuals belonging to families derived from this germplasm. Significant differences were observed between the susceptible Montmorency and the tolerant and resistant accessions in their response to CLS and its progression during the growing season. Evaluation of the CLS host responses of progeny individuals derived from this germplasm supported a dominant two‐gene model for P. canescens‐derived resistance and a recessive gene model for sweet cherry‐derived tolerance. These insights into disease progression and trait inheritance improve the efficiency and potential success of breeding sour cherry cultivars with durable resistance to CLS.     

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.     

Identification and Discrimination of Pseudomonas syringae Isolates from Wild Cherry in England

A survey of wild cherry (Prunus avium) woodland plantations and nurseries was carried out in 2000/01. Trees with symptoms of bacterial canker were found in 20 of the 24 plantations visited and in three of seven nurseries. Fifty-four Pseudomonas syringae isolates from wild cherry together with 22 representative isolates from sweet cherry and 13 isolates from other Prunus spp., pear and lilac were characterised by physiological, biochemical, serological and pathogenicity tests. Isolates from wild cherry were predominantly P. syringae pv. syringae (Pss), but P. syringae pv. morsprunorum (Psm) races 1 and 2 were also found. Physiological and biochemical tests discriminated Psm races 1 and 2 from other P. syringae isolates. Agglutination and indirect-enzyme-linked immunosorbent assay tests with three different antisera showed that Psm race 1 and race 2 were very uniform and indicated high variability amongst other P. syringae isolates. However, pathogenic Pss isolates could not be distinguished from non-pathogenic isolates of P. syringae on the basis of physiological, biochemical or serological tests. Pathogenicity tests on rooted lilac plants and on micropropagated plantlets of lilac and two wild cherry clones differentiated Pss and Psm isolates and demonstrated a range of aggressiveness amongst Pss isolates. Serological tests could be used as an alternative to the classical physiological and biochemical tests to increase the speed of detection and discrimination of isolates, but pathogenicity tests are still necessary to discriminate the pathogenic Pss isolates.     

Identifying resistance in wild and ornamental cherry towards bacterial canker caused by Pseudomonas syringae

Bacterial canker is a major disease of stone fruits and is a critical limiting factor to sweet cherry (Prunus avium) production worldwide. One important strategy for disease control is the development of resistant varieties. Partial varietal resistance in sweet cherry is discernible using shoot or whole tree inoculations; however, these quantitative differences in resistance are not evident in detached leaf assays. To identify novel sources of resistance to canker, we used a rapid leaf pathogenicity test to screen a range of wild cherry, ornamental Prunus species and sweet cherry × ornamental cherry hybrids with the canker pathogens, Pseudomonas syringae pvs syringae, morsprunorum races 1 and 2, and avii. Several Prunus accessions exhibited limited symptom development following inoculation with each of the pathogens, and this resistance extended to 16 P. syringae strains pathogenic on sweet cherry and plum. Resistance was associated with reduced bacterial multiplication after inoculation, a phenotype similar to that of commercial sweet cherry towards nonhost strains of P. syringae. Progeny resulting from a cross of a resistant ornamental species Prunus incisa with susceptible sweet cherry (P. avium) exhibited resistance indicating it is an inherited trait. Identification of accessions with resistance to the major bacterial canker pathogens is the first step towards characterizing the underlying genetic mechanisms of resistance and introducing these traits into commercial germplasm.     

The Problem of Protecting Crops Against Harmful Birds in Poland

From the point of view of Polish agriculture, the rook (Corpus frugilegus L.) causes the most damage. Jackdaws (C. monedula L.) usually forage together with rooks and are equally abundant as a breeding species in the southern and central regions of Poland. Fields under spring oats, barley, wheat, maize, peas and winter wheat are the main feeding grounds of rooks and jackdaws. Unlike the corvine birds, starlings (Sturnus vulgaris L.), in Poland, only cause damage to cherry orchards, although in certain areas they also attack strawberries and currants. The house sparrows (Passer domesticus L.) cause considerable damage to ripening crops of wheat, barley, and sunflowers. Domestic pigeons cause considerable damage to crops of peas, wheat and maize grown within a 50 km radius of a town.     

Over het verband tussen de aantasting door de koolzaadgalmug,Dasyneura brassicae Winn. (Diptera,Itonididae) en de Koolzaadsnuitkever,Ceuthorrhynchus assimilis Payk. (Coleoptera,Curculionidae)

Samenvatting De tegenstrijdige meningen, die bestaan over de vraag of de koolzaadga Imug (Dasyneura brassicae Winn.) voor zijn ei-afzetting is aangewezen op beschadigde hauwen, gaven aanleiding dit punt nader te onderzoeken. Uit infectieproeven, waarbij de galmug òf planten met uitsluitend gave òf planten met beschadigde hauwen kreeg aangeboden om zijn eieren te leggen, bleek, dat deze eieren uitsluitend in de van te voren beschadigde hauwen werden gevonden. Ook waarnemingen over het gedrag van de mug in het veld ondersteunden de opvatting, dat de eieren uitsluitend door reeds bestaande boorgaten in de hauw worden afgezet. De koolzaadsnuitkever (Ceuthorrhynchus assimilis Payk.) zal ongetwijfeld de belangrijkste veroorzaker van deze beschadigingen zijn. De bestrijding van de kever zal in de regel niet in staat zijn het aantal beschadigde hauwen zo sterk te verminderen, dat de eerste galmugvlucht geen gelegenheid tot ei-afzetting meer heeft. Door de vermindering van het aantal keverlarven als gevolg van de effectieve keverbestrijding, kan een vermindering van het a antal uitkruipgaten der larven bereikt worden, die wèl belangrijk is, daar de tweede galmugvlucht voor ei-afzetting vooral op deze gaten is aangewezen.

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On the relation between the infestation by the cabbage seed pod midge, Dasyneura brassicaeWinn. and the seed pod weevil, Ceuthorrhynchus assimilisPayk

Summary The controversy of whether or not the cabbage seed pod midge (Dasyneura brassicae Winn.) uses only damaged pods for depositing its eggs was reason for further investigation. Experiments with potplants were started. Midges were caged on colza-plants which had only undamaged pods as well as on plants which had pods artificially damaged by prickling with a needle. Eggs were only found in the damaged pods. The behaviour of the midge in the field, when it is intending to oviposite, also shows its need for damaged places as the midges were observed continuously walking on the pods, trying with their ovitubus to find a hole in the wall of the pod. The cabbage seed pod weevil (Ceuthorrhynchus assimilis Payk.) is undoubtedly the chief contributor to the number of damaged pods. Economic control of this weevil will only have a limited indirect effect on infestation by the first midge flight. However as it reduces the number of pods with weevil larvae, it reduces the number of exit holes in the pods. These exit holes are especially used by the second midge flight which therefore is controlled indirectly to some extent.

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Destijds werkzaam bij het Instituut voor Plantenziektenkundig Onderzoek (I.P.O.) te Wageningen; thans werkzaam bij het Laboratorium voor Entomologie van de Landbouwhogeschool te Wageningen.     

Losses in grain yield of winter crops from Lolium rigidum competition depend on crop species, cultivar and season

The competitive abilities of eight winter crops were compared against Lolium rigidum Gaud, (annual ryegrass), an important weed of southern Australia, as a potential strategy to suppress weeds and reduce dependence on herbicides. Two cultivars of each species were chosen to represent the range of competitive ability within each crop and grown in field experiments in 1992 and 1993. The order of decreasing competitive ability (with the ranges of percentage yield reduction from L. rigidum at 300 plants m^?2 in parenthesis) was as follows: oats (Avena sativa L.), 2–14%; cereal rye (Secale cereale L.), 14–20%; and triticale (×Triticosecale), 5–24%; followed by oilseed rape, (Brassica napus L.), 9–30%; spring wheat (Triticum aestivum L.), 22–40%; spring barley (Hordeum vulgare L.), 10–55%; and, lastly, field pea (Pisum sativum L.), 100%, and lupin (Lupinus angustifolius L.), 100%. Differences in competitive ability of cultivars within each species were identified, but competition was strongly influenced by seasonal conditions. Competition for nutrients (N, P and K) and light was demonstrated. L. rigidum dry matter and seed production were negatively correlated with grain yield of the weedy crops. More competitive crops offer the potential to suppress grass weeds while maintaining acceptable grain yields. Ways of improving the competitive abilities of grain legume crops are discussed.     

“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.     

Is verrijking van de mycoflora mogelijk?

Samenvatting Van verrijking der mycoflora is slechts dan sprake, als nieuwe elementen in een gebied verschijnen door invoer van elders, door nieuwe kruisingen of door nieuwe mutaties van zwammen. Het ontdekken van een vroeger onbekende zwam is nog geen bewijs voor een verrijking der mycoflora. Het kan zijn dat de onbekende vroeger alleen aan de aandacht is ontsnapt.Voorbeelden van verrijking der flora door het overbrengen van parasitaire zwammen van het eene werelddeel naar een ander zijn gemakkelijk te geven. Uit de verspreiding van de populierenroesten over de aarde blijkt, dat het gevaar van overbrengen van Noord-Amerikaansche soorten van Melampsora naar Europa en van Europeesche soorten naar Noord-Amerika niet denkbeeldig is (Afb. 1).Bij proeven aan het Laboratorium voor Mycologie en Aardappelonderzoek te Wageningen over de vatbaarheid van populieren voor eenige soorten van Melampsora, traden in 1941 verschillende rassen en een witte variant vanMelampsora Larici-populina Kleb. op (Afb. 4, 5 en 6), die in de eerste twee jaren zeker niet voorkwamen (Tabel 1). De physiologische rassen zijn met behulp van een speciale laboratorium-methode te onderscheiden door de verschillende reactietypen van een sortiment van populieren (Afb. 2 en 4). Het optreden van de rassen wordt toegeschreven aan het feit, dat in het najaar van 1940Larix sp. tusschen de populieren van het proefveld werden geplant. Op deze Larix kunnen nl. door kruising nieuwe combinaties van genetische factoren tot stand komen.Ook bij andere parasitaire zwammen o.a. bijPhytophthora infestans de Bary (de aardappelziekte) en bijSynchytrium endobioticum (Schilb.) Perc. (de wratziekte) op aardappel, zijn onverwachte complicaties van het resistentie-onderzoek ontstaan door het verschijnen van voordien onbekende rassen van deze parasieten. Of door deze de mycoflora werkelijk met iets nieuws werd verrijkt, is moeilijk te beslissen. Zij kunnen er reeds zijn geweest, maar in een zoo gering percentage, dat de kans op een isolatie practisch nul was. Pas de vermeerdering door het gebruik van speciale rassen van hun waardplanten brengt hun bestaan aan het licht.Met het oog op de roesten van populieren is een verrijking van de mycoflora mogelijk door invoer van elders en door nieuwe rassen, die uit kruising ontstaan. Beide kansen ontnemen aan het resistentie-onderzoek zijn absolute waarde. Dat zulke teleurstellingen groot kunnen zijn, blijkt uit de hevige aantasting vanPopulus candicans Aiton door één der nieuwe rassen en de witte variant vanM. Larici-populina, die alles overtreft, wat bij jarenlange observatie werd waargenomen.Summary Only the appearance of new elements by introduction from abroad, by new hybrids or by new mutations of fungi may be called an enrichment of the mycoflora. Discovery of formerly unknown fungi is no proof of such an enrichment. It may be that till then the unknown fungus merely escaped attention.Examples of enrichment of the mycoflora by transport of parasitic fungi from one continent to another are easy to give. From the distribution of poplar rust fungi on earth it is evident, that the danger of introducing North-American Melampsora's on poplar into Europe and European species into North-America is not imaginary (Afb. 1).Experiments on the susceptibility of poplars to infection by some species of Melampsora, carried out at the Laboratorium voor Mycologie en Aardappelonderzoek at Wageningen, proved the appearance in 1941 of several physiologic races and one white variety ofM. Larici-populina Klebahn (Afb. 4, 5, 6). These were certainly not present during the first two years of the experiments, 1939 and 1940 (Tabel 1). The physiologic races can be distinguished with the aid of a special laboratory-method by the reaction-types of a collection of poplars (Afb. 2, 4).The appearance of the races is supposed to be due to the planting in the autumn of 1940 of larches between the poplars of the experimental plot. The formation of new races has become possible by hybridizing on these larches, on whichM. Larici-populina forms its 0 and I stages.Unexpected complications in breeding of potatoes for resistance have been raised by the appearance of formerly unknown races ofPhytophthora infestans de Bary (potato blight) andSynchytrium endobioticum (Schilb.) Perc. (wart-disease). It is, however, difficult to decide, whether in these cases the mycoflora has been enriched by some new races. They may have existed already before, but in such a low percentage that practically there was no chance to isolate them. It is only by using special races of hostplants that their existence can be stated.In relation to the rusts of poplars the possibility exists of an enrichment of the mycoflora by introduction from abroad and by the formation of new races by hybridization. Both possibilities make the results of breeding for resistance less absolute. To what extent such disappointments may develop is evident from the heavy attack ofPopulus candicans Aiton by one of the new races and by the white variety ofM. Larici-populina. This attack surpasses all earlier ones observed during several years.Voordracht gehouden op 4 Maart 1944 voor de Nederl. Plantenziektenkundige Vereeniging.     

Pseudomonas syringae pv. avii (pv. nov.), the Causal Agent of Bacterial Canker of Wild Cherries (Prunus avium) in France

Bacterial strains isolated from cankers of wild cherry trees (Prunus avium) in France were characterized using numerical taxonomy of biochemical tests, DNA–DNA hybridization, repeat sequence primed-PCR (rep-PCR) based on REP, ERIC and BOX sequences, heteroduplex mobility assay (HMA) of internal transcribed spacer (ITS) as well as pathogenicity on wild cherry trees and other species of Prunus. They were compared to reference strains of Pseudomonas syringae pathovars isolated from wild and sweet cherry and various host plants. Wild cherry strains were closely related to P. syringae (sensu lato) in LOPAT group Ia (+ - - - +). Wild cherry strains were pathogenic to wild cherry trees and produced symptoms similar to those observed in orchards. They were pathogenic also, but at a lesser extent, to sweet cherry trees (cv. Napoléon). The wild cherry strains were collected from five different areas in France and appeared to constitute a very homogeneous group. They showed an homogenous profile of a biochemical and physiological characteristics. They were closely related by DNA–DNA hybridization and belonged to genomospecies 3 `tomato'. Rep-PCR showed that wild cherry strains constitute a tight group distinct from P. s. pv. morsprunorum races 1 and 2 and from other P. syringae pathovars. HMA profiles indicated that the ITS of all wild cherry strains were identical but different from P. s. pv. persicae strains since the two heteroduplex bands with reduced mobility were generated by hybridization with the P. s. pv. persicae pathotype strain CFBP 1573. The 8 genomospecies of Gardan et al. (1999) have not been converted into formal species as they cannot be differentiated by biochemical tests. Therefore, the pathovar system within P. syringae was currently used. P. syringae pv. avii is proposed for this bacterium causing a wild cherry bacterial canker and strain CFBP 3846 (NCPPB 4290, ICMP 14479) is designated as the pathotype.     

Tachinidae parasitoids of<Emphasis Type="Italic">Traumatocampa ispartaensis</Emphasis> from Turkey

Tachinid parasitoids ofTraumatocampa ispartaensis Doğanlar & Avcı (Lepidoptera, Thaumetopoeidae), which was found to be a new species, were collected from the cedar forests around Isparta-Kapıdağ. The species found wereBlondelia nigripes (Fall.),Compsilura concinnata (Meig.),Pales processioneae (Ratz.),Phryxe caudata (Rond.),Exorista segregata (Rond.) andCarcelia iliaca (Ratz.). Within the six species of Tachinidae,B. nigripes was the most common one, parasitizing up to 4.6% ofT. ispartaensis pupae. http://www.phytoparasitica.org