Occurrences of Ceratocystis ulmi in Norway1

Norway (in contrast to Denmark and Sweden) has so far had only a few outbreaks of Dutch elm disease, all in the southern part of Norway (cities of Oslo and Drammen) on one or a few Ulmus glabra trees in city parks, not far from harbours and railways. Scolytus laevis endemic to Norway is the only potential vector found in the diseased trees. Transmission of the fungus through root grafts cannot be disregarded. The fungus is currently considered a dangerous foreign organism in Norway, subject to treatment according to the Norwegian phytosanitary regulations. Control measures, aiming at eradication, have been applied in all known cases of attack. Removal and destruction of diseased trees, stump treatment with herbicide, and covering of stumps with soil, have apparently been successful measures.     

Sanitation campaign against Ceratocystis ulmi in The Netherlands1

The introduction and rapid spread of the aggressive strain of Ceratocystis ulmi in The Netherlands led to development of a 100% subsidised nationwide felling campaign. Since 1978, all elms have been assessed twice a year for health and viability, and diseased trees have been destroyed within a month. This limited losses to 1% of the important elm clones planted along roads, but at high annual cost (6 million F1) because of the need also to destroy diseased field elms. In future, long-term costs will be reduced by destruction of the less important field elms in the west of the country. In the east, the campaign has been abandoned (with some exceptions round cities).     

The control in vitro of Ceratocystis ulmi by amine cations

Of 60 amine cations tested in vitro for activity against Ceratocystis ulmi, that of methyl benzimidazol-2-ylcarbamate (carbendazim) showed the highest activity, this being constant with three different associated anions. Some guanidines, 2-nitro-morpholine and 2-(thiazol-4-yl)benzimidazole (thiabendazole) showed considerable activity but a large group of alkylamines, 1-methylalkylamines and poly-amines were relatively inactive.     

Structure—activity relationships of organotin biocides and Ceratocystis ulmi

The effect of organotin compounds on the growth of Ceratocystis ulmi, the causative agent of Dutch elm disease, was studied in shake culture. Triphenyltin, (C₆H₅)₃SnX, tricyclohexyltin, (C₆H₁₁)₃SnX, and tributyltin, (C₄H₉)₃SnX, compounds were all effective in the inhibition of C. ulmi in vitro. The anionic group, X, did not play a major role in the inhibitory activities of these compounds, suggesting that the species involved in the inhibition is R₃Sn⁺ or the hydrated cation.     

Formation of perithecia of Ceratocystis ulmi on natural and synthetic nutrient media

Ceratocystis ulmi formed fertile perithecia on 17 of 37 culture media tested, including many of the (autoclaved) natural substrates, but not on Saboraud's media or White's medium and not on potato dextrose agar (Table 1). Later, perithecia formed abundantly on four of eight variants of Zentmyer-Tchernoff agar medium (Table 2). This appears to be the first report on perithecia ofC. ulmi on an agar medium to which only synthetic nutrients were added. Both normal-strength and 110 diluted media gave perithecia. If only the sugar or only the asparagine-plus-salts were diluted, none or very few perithecia formed. Tenfold dilution of the vitamins did not affect results. Light did not prevent formation of perithecia.Samenvatting Ceratocystis ulmi vormde rijpe peritheciën op 17 van de 37 getoetste voedingsbodems, maar in het begin alleen op enkele van de (gesteriliseerde) natuurlijke voedingsbodems, niet op Sabourauds of Whites agar en evenmin op aardappel-dextrose-agar (Table 1). In latere proeven werden rijkelijk peritheciën gevormd op 4 van de 8 varianten op Zentmyer-Tchernoff-agar (Tabel 2).Waarschijnlijk is dit de eerste vermelding van vorming van peritheciën vanC. Ulmi op agar waaraan uitsluitend synthetische voedingsstoffen zijn toegevoegd. Zowel op de standaard-concentratie als op een tienvoudige verdunning van de voedingsstoffen werden peritheciën gevormd. Als alleen de glucose of alleen de asparagine-plus-zouten verdund waren, werden er geen of zeer weinig peritheciën gevormd. Tienvoudige verdunning van de vitaminen beïnvloedde de resultaten niet. Licht remde de vorming van peritheciën niet.A contribution of the Massachusetts Agricultural Experiment Station.     

Tylose formation in elms after inoculation with Ceratocystis ulmi,a possible resistance mechanism

After inoculation of elms withCeratocystis ulmi tylose formation in vessels of the susceptible clone Belgica appeared to be delayed in comparison with tylose formation in the resistant clone 390. It is suggested that tylose formation may be a resistance mechanism in elms to Dutch elm disease.Samenvatting Na inoculatie van iepen metCeratocystis ulmi bleek de thyllenvorming te zijn vertraagd in de vaten van de vatbare kloon Belgica in vergelijking met de thyllenvorming in de resistente kloon 390 (Fig. 1). Thyllenvorming zou een resistentie mechanisme kunnen zijn tegen de iepziekte.     

Length and diameter of xylem vessels as factors in resistance of elms to Ceratocystis ulmi

Conductivity of the vascular system of 2-year-old shoots as regards air and water was higher in susceptible than in resistant elms. The xylem vessels of resistant elms were relatively shorter and the percentage of short vessels was greater than in susceptible elms. The percentage of vessels with a large diameter was smaller in resistant elms than in susceptible ones. These results might explain the limited spreading of the spores in the new annual ring of resistant elms.Samenvatting Tweejarige scheuten van resistente iepen bleken lucht en water minder snel door te laten dan vergelijkbare scheuten van vatbare iepen. De vaten bij resistente iepen waren relatief kort en het percentage korte vaten was groter dan bij vatbare iepen. Het percentage grote vaten was kleiner bij resistante iepen dan bij vatbare. Dit zou een verklaring kunnen zijn voor de relatief geringe verspreiding van de sporen in de nieuwe jaarring van de resistente iepen.     

Infection of Norway spruce (Picea abies (L.) Karst.) seedlings with Pythium irregulare Buism. and Pythium ultimum Trow.: histological and biochemical responses

We have studied the reaction of Picea abies seedlings to infection with Pythium. The highly virulent species Pythium ultimum and the less virulent species Pythium irregulare germinated on the root and hypocotyl surface, formed appressoria and penetrated through the stomata as well as through the epidermis. No major differences in the growth of both fungal species were observed during the early events of colonization. The less virulent species formed about 25% more appressoria suggesting that the fungus experienced difficulties with penetration. Differences were observed in the response of the host plant to infection. Autofluorescence, possibly related to deposition of lignin or lignin-like materials increased more in cortical and endodermal tissue colonized with the highly virulent P. ultimum than with the less virulent P. irregulare. Chitinase activity was highest in the tissues most extensively colonized by the fungus. In addition, a systemic increase of chitinase activity was also detected. Interestingly, chitinase activity increased systemically in cotyledons which were never in contact with the pathogen, indicating the translocation of a systemic signal. Salicylic acid was also detected in spruce seedlings; its level increased in roots during infection with the less virulent P. irregulare.     

Virulence inCeratocystis ulmi

Single-ascospore cultures ofCeratocystis ulmi from the progeny of a cross between a culture of compatibility type A from Belford, Massachusetts, U.S.A., and one of type B from Rotterdam, Netherlands, were morphologically heterogeneous and varied widely in virulence towards young elms inoculated in the greenhouse. Some cultures regularly caused typical wilt in callus cuttings ofUlmus hollandica Belgica (susceptible) but none in those ofU. carpinifolia Christine Buisman (resistant). Some cultures cuased wilt in trees of both clones; others in neither. All isolates produced abundant yeast-like cells in liquid culture. All isolated induced typical vascular discoloration except in the terminal inch of twigs. Similar progeny from a cross between cultures of types A and B, both from Naarden, Netherlands, however, were morphologically homogeneous and caused a fairly uniform level of symptoms in young trees ofU. hollandica Belgica (susceptible) and Commelin (moderately resistant), and in seedlings ofU. americana after inoculation in the nursery.Samenvatting Eén-ascosporecultures vanCeratocystis ulmi, verkregen uit de nakomelingen van een kruising tussen een cultuur van het compatibiliteitstype A uit Bedford, Massachusetts, V.S., en een type B uit Rotterdam, Nederland, waren morfologisch heterogeen en vertoonden grote verschillen in virulentie ten opzichte van jonge iepen, die in de kas waren geïnoculeerd. Enkele cultures veroorzaakten bij herhaling een typische verwelking bij callusstekken van de kloonUlmus hollandica Belgica (vatbaar), maar zij brachten geen verwelking teweeg bijUlmus carpinifolia Christine Buisman (resistent). Andere cultures veroorzaakten verwelking bij bomen van beide klonen, weer andere bij geen van beide. In alle gevallen ontstond na inoculatie de typische houtverkleuring, die echter uitbleef in de toppen van de twijgen (ca. 3cm). Alle cultures produceerden in een voedingsvloeistof een overvloed van gistachtige cellen.Eén-ascosporecultures, verkregen uit een kruising tussen de twee compatibiliteitstypen, beide afkomstig uit Naarden, Nederland, waren daarentegen morfologisch homogeen. Zij vertoonden bovendien vrijwel geen verschillen in virulentie na inoculatie in de kwekerij in jonge bomen vanU. hollandica Belgica en Commelin (respectivelijk vatbaar en matig resistent) en in zaailingen vanU. americana (vatbaar).A contribution of the Massachusetts Agricultural Experiment Station.     

European Forestry and Ceratocystis Species1

Ceratocystis spp. are responsible for some serious tree diseases. Vascular mycosis of oak, oak wilt, Dutch elm disease, and canker stain of plane are discussed in the context of the information required by a plant protection organisation concerned with the risks created by specific pathogens.     

8种杀螨剂对苹果树红蜘蛛田间防效评价

对8种不同作用机理杀螨剂防治苹果树红蜘蛛的效果进行了田间试验。结果表明：三唑锡、炔螨特、哒螨灵、阿维菌素、唑螨酯、螺螨酯、双甲脒、甲氰菊酯均是防治苹果树红蜘蛛的有效药剂,以螺螨酯的总体防效最好。