Verschillen In Virulentie Bij Nectria Cinnabarina (Tode) Fr.

Samenvatting Door inoculatieproeven met reinculturen vanNectria cinnabarina (Tode) Fr. opAcer platanoides L. werd aangetoond, dat uitbreiding van de aantasting plaats heeft gedurende het groeiseizoen van de boomen. Dit is in overeenstemming met resultaten van vroegere proeven. Daaruit bleek nl. datN. cinnabarina een tamelijk hoog temperatuur-optimum heeft van ± 22 1/2°. De twee voor de inoculatie gebruikte isolaties waren afkomstig van één tak vanAcer pseudoplatanus L., elk uit één enkele spore gekweekt. Beide isolaties veroorzaakten bij de proef de typische symptomen van schorsbrand. Zij verschilden echter in de mate, waarin zij zich in de bast uitbreidden. Het gevolg hiervan was, dat in het eene geval van isolatiea bij een beperkte aantasting, een kanker-achtig ziektebeeld ontstond, in het andere van isolatiec de aantasting zich in denzelfden tijd zoover uitstrekte, dat bij 42 % van het aantal inoculaties taksterven optrad. Elkaar tegensprekende mededeelingen over het parasitisme vanN. cinnabarina in oudere publicaties kunnen worden verklaard door de hier aangetoonde verschillen in virulentie binnen deze soort. Voor phytopathologisch onderzoek in het algemeen moet uit het resultaat van de proef worden afgeleid, dat het werken met enkele willekeurige isolaties van zwammen, die van pathogeniteit worden verdacht, niet voldoende is. Het is noodig, eerst een groot aantal isolaties op hun pathogeniteit te onderzoeken, waaruit men daarna een keuze moet doen voor het eigenlijke onderzoek.

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Isolations of nectria cinnabarina (Tode) Fr. with different vir ulence

Summary Inoculation experiments withN. cinnabarina onAcer platanoides L. proved that the fungus makes rapid growth during the growing season of the trees. This is in accordance with results of earlier experiments about the influence of temperature on the vegetative growth of the fungus. The optimum temperature ofN. cinnabarina is about 22 1/2°. The two isolations used in the inoculation experiments have been taken from one branch ofAcer pseudoplatanus L., each cultured from one single spore. Both isolations caused in the experiment the typical symptoms of canker („schorsbrand”). But they differed greatly in their growth within the bark. This resulted in the case of isolationa (from one ascospore) in relatively small cankers, in the case of isolationc (from one conidiospore) the attack extended to such a degree, that 42% of the inoculations caused a dieback. Mutually discrepant earlier reports on the parasitism ofN. cinrzabarina may be explained by the existence of strains in this species. With regard to phytopathological research in general the result leads to the conclusion, that experiments with a few arbitrarily chosen isolations of fungi, suspected to be pathogenic, cannot be conclusive. A great number of them has to be tested in order to make the final experiment possible.

     

The occurrence of coral spot of Japanese persimmon caused by <Emphasis Type="Italic">Nectria cinnabarina</Emphasis> (Tode: Fries) Fries

A twig canker disease of Japanese persimmon with characteristic coral spots was found in Tottori Prefecture, Japan. The causal fungus was identified as Nectria cinnabarina, which causes coral spot disease on many host plants. This is the first report of the disease caused by N. cinnabarina on Japanese persimmon in Japan.     

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.     

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.     

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.     

Protective Effects Against Erwinia amylovora Induced by hrp Mutants in the Whole Plant are Only Partially Mimicked in Cultivated Cells

A virulent strain of Erwinia amylovora, the causal agent of fire blight of Maloideae, and two of its non-virulent hrp mutants (a secretory and a regulatory mutant) were inoculated into apple cell suspensions either alone or in mixed inoculations. In single inoculations, death of 4- to 5-day-old apple cells occurred only when the concentration of the virulent strain of E. amylovora reached a threshold inoculum concentration of 10⁴CFUml^–1, while high concentrations of the hrp mutants were unable to kill apple cells. When mixed inoculated with the virulent parental strain, both hrp mutants protected apple cells from death caused by the virulent strain. The protective effect was associated with a decrease in the population level of the virulent strain and it was dependent on the non-virulent to virulent inoculum concentration suggesting a competition between the non-virulent mutant and the virulent strain. However, no differential protective ability between the two types of mutants could be noticed, contrary to previous results obtained with apple seedlings or apple flowers in which the regulatory mutant was significantly more effective than the secretory mutant. In conclusion, inoculation of apple cell cultures with E. amylovora does not seem to be a model suitable for investigating mechanisms leading to protection.     

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).     

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     

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.     

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.     

Early investigations into the infection courts used by <Emphasis Type="Italic">Neonectria fuckeliana</Emphasis> to enter <Emphasis Type="Italic">Pinus radiata</Emphasis> stems

Nectria flute canker is a disease of Pinus radiata stems caused by the pathogen Neonectria fuckeliana occurring in the southern parts of New Zealand. In Northern Hemisphere countries where N. fuckeliana is endemic, it is commonly found in Picea and Abies spp. Open wounds, dead attached branches and branch stubs have been identified as the primary infection courts. Although in New Zealand the development of Nectria flute canker disease is associated with pruned branch stubs, recent studies suggest that this is not the only possible entry method as the fungus has been found in trees prior to pruning. Three field trials were established to examine the potential infection mechanisms for N. fuckeliana in P. radiata in New Zealand; including stem wounds and branch stubs. The difference between inoculations into the stem and into branch wood was clear. Inoculation of deep stem wounds resulted in the greatest fluting with 76% of trees inoculated developing cankers. Inoculation directly into stubs resulted in only small stem depressions that occurred in 17% of cases and the fungus was largely contained within the branch trace. Tree response to inoculation with either ascospores or conidia of the Acremonium anamorph gave similar results in terms of canker development and fungal spread within the stem. Tree response to inoculation was highly variable however: in one study 6% of trees did not respond to inoculation at all, while 26% produced severe cankers regardless of inoculation method. A more thorough understanding of the infection mechanisms of N. fuckeliana will contribute to the development of better disease management protocols to prevent infection and disease development in future plantation stock.     

First report of southern blight of common barley in Puerto Rico

In 1990–91, 96% of the test plants in a barley (Hordeum vulgare L.) winter nursery in Puerto Rico was lost toSclerotium rolfsii. Small necrotic lesions (1–3 mm long) developed at the base of the stem, followed by wilting and general chlorosis as the lesions progressed and eventually girdled the base of the stem. Sclerotia then developed on the plants at the stem base. Two morphologically different strains ofS. rolfsii that were mycelial incompatible were isolated. This is the first report of a destructive blight due toS. rolfsii on field barley in the Caribbean. The apparent rate of disease increase (r) was estimated to be 12.2% per day using the logistic model, with an initial disease incidence of 0.042% (R²=0.89, p<-0.001).     

Multiplication of Erwinia amylovora in fruit-trees. 2. A simulation study on sensitivity to weather

The sensitivity of an output variable of a model to changes of an input parameter value can be analyzed in various ways. Some methods of sensitivity analysis are described, and applied to a simulation model which has daily minimum and maximum temperatures (T _min andT _max, respectively), and daily global radiation as input parameters, and standardized relative multiplication rate ofErwinia amylovora in shoots in fruit-trees, averaged over a 24 hours' period, as output variable. Values of the input parameters were obtained from a weather station near Wageningen, the Netherlands, and refer to the second half of June, 1974–1988.According to the model, the output variable was twice as sensitive toT _max as toT _min. Because of this difference in sensitivity, and because the standard deviation ofT _max was larger than that ofT _min, the variation of the output variable due toT _max was three times larger than that due toT _min. The sensitivity to daily global radiation was negligible when the soil was moist.     

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).     

Inheritance and Mechanisms of Resistance to Tebuconazole, a Sterol C14-Demethylation Inhibitor, inNectria haematococca

Genetic control and mechanisms of resistance to tebuconazole, a sterol C14-demethylation inhibitor, were investigated in the phytopathogenic fungusNectria haematococca. Resistant mutants have been selected from the laboratory, following UV irradiation. They have been characterized through genetic crosses and mutations in at least three genes were found to be responsible for resistance. The genesTeb1, Teb2, andTeb3were clearly identified, a fourth gene calledTeb4could be hypothesized. Mutations at lociTeb2andTeb3induced pleiotropic effects such as reduced sporulation and growth rate, mycelium pigmentation (Teb2), or altered ascospore viability (Teb3). The resistance levels determined by mutations in the different genes were relatively low (below 10). When associated in double mutants, the additive effect was recorded. Cross-resistance toward other sterol C14-demethylation inhibitors was observed in all the resistant strains, except in theTeb4-carrying strain; moreover, for some C14-demethylation inhibitors hypersensitivity was expressed. A constitutive energy-dependent efflux seemed implicated in the mechanism of resistance for theTeb1-carrying strain and probably also for theTeb2andTeb3-carrying strains. However, theTeb4-carrying strain exhibited a kinetic of fungicide uptake similar to that of the wild-type strain. The sterol profile of theTeb4-carrying strain was similar to that of all the other resistant mutants and wild-type strains. Thus the resistance mechanism induced by mutation at theTeb4locus has not been found yet.     

Over enige insecten in lisdodden

Summary Observations on the biology ofLimnaecia phragmitella Stt. (fam. Momphidae, Lepid.) — made in the Netherlands — are mentioned.The species was previously considered as being rare but now is known to be numerous in a few areas. The caterpillars live in the heads of Typha where they feed on the seeds and later on the core. They hibernate when halfgrown, develop further in the spring and early summer and pupate in June; the moths appear during July.The species has a worldwide distribution: England, Central and Southern Europe, Northern Africa, Australia, New Zealand and the United States of America. In the latter country it was studied byP. W. Claassen together with a number of other Typha-insects occurring in the U.S.A. (Cornell Un. Memoir 47, Oct. 1921).The present author has found an hemipteron,Chilacis typhae Perris (Lygaeidae), in Typha heads occurring together with the caterpillars ofLimnaecia. This insect has also been reported in the literature as being rare in the Netherlands. It is suspected of living on the caterpillars but this has not been shown.     

A study of the development of Ophiostoma ulmi in elms with immunological techniques

The indirect immunofluorescence technique (IIF) and the indirect immunoperoxidase technique (IIP) were used to detect specificallyOphiostoma ulmi in inoculated elm branches. A strong cross-reaction was observed between the hyperimmune serum to the non-aggressive strain E2 ofO. ulmi and the aggressive strain H6. No reactions were found withVerticillium albo-atrum orFusarium oxysporum.During pathogenesisO. ulmi was never observed outside the vessels. The hyphae of the pathogen penetrated the pit membrane during growth from vessel to vessel; no direct cell wall penetration was observed.Samenvatting De indirecte immunofluorescentietechniek (IIF) en de indirecte immunoperoxidasetechniek (IIP) werden toegepast omOphiostoma ulmi (Buisman) Nannf. in geïnfecteerd iepehout aan te tonen. Er bleek een sterke kruisreactie op te treden tussen het hyperimmuun serum tegen respectievelijk de niet-agressive stam (E2) en de agressieve stam (H6) vanO. ulmi. Geen reactie trad op metVerticillium albo-atrum ofFusarium oxysporum.Gedurende de pathogenese kon de schimmel nooit buiten de houtvaten aangetoond worden. Bij de groei van het pathogeen van vat naar vat werd nooit directe celwandpenetratie waargenomen; deze vond altijd plaats via de hofstippels.     

Effects of pesticides on mite predators (Acari: Phytoseiidae) and colonization of apple trees byTetranychus urticae

A 2-year survey of mite populations and pesticide use was carried out in Nova Scotia, Canada, in apple orchards where the two-spotted spider mite (Tetranychus urticae Koch) was the dominant phytophagous mite. Fungicides were the only class of pesticides that affected cumulative number ofT. urticae-days per leaf in tree canopies and colonization success — the ratio ofT. urticae-days to number of immigratingT. urticae caught in sticky bands on tree trunks. In 2000, increased numbers ofT. urticae-days in the tree canopy were associated with more frequent applications of ethylene bis-dithiocarbamate (EBDC) fungicides and with higher fungicide toxicity scores, which indicate cumulative level of suppression of the phytoseiid predatorTyphlodromus pyri Scheuten by all fungicide applications. Higher rates of colonization success were also associated with higher toxicity scores. EBDC’s applied in 2000 promotedT. urticae immigration as indicated by their counts on sticky bands. In 2000 and 2001, number ofT. pyri-days in the tree canopies was decreased by more frequent EBDC applications and by higher fungicide toxicity scores. Promotion ofT. urticae in tree canopies by EBDC’s was attributed to their toxicity toT. pyri. BothT. pyri and another phytoseiid,Amblyseius fallacis (Garman), were found in ground cover vegetation. Hence, increased immigration from the ground cover attributed to the toxicity of EBDC’s toT. pyri and, especially, toA. fallacis, which is a specialist predator of spider mites and an effective natural enemy ofT. urticae. http//www.phytoparasitica.org posting Sept. 13, 2006. Formerly, Atlantic Food and Horticulture Research Centre, now retired.     

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.     

Distribution of streptomycin-resistant strainsof Erwinia amylovora in Israel and occurrence of blossom blight in the autumn

Following failure in control of fire blight with streptomycin, the distribution of streptomycin-resistant strains ofErwinia amylovora in Israel was surveyed. During 1994–1997 109 pear, apple, loquat and quince orchards were monitored. Streptomycin-resistant strains ofE. amylovora were recovered from flowers and from infected branches collected at 18 locations in the Sharon, Galilee and Golan Heights regions. In the Sharon region all the isolated strains ofE. amylovora were streptomycin-resistant, whereas in the Galilee and Golan Heights, resistant as well as sensitiveE. amylovora strains were recovered at different locations. In the southern coastal plain no resistance could be detected. Streptomycin-resistant strains ofE. amylovora did not hybridize with the DNA probe SMP3, and resistance could not be transferred by mating to a sensitive strain, suggesting that streptomycin resistance in Israel is not plasmid-mediated. Fire blight symptoms were observed, for the first time, on pear blossoms during the autumn of 1994. A high population of 2x 10⁶-6x 10⁷ CFU/flower in the autumn of 1995 and of 1996 was correlated with the appearance of blossom blight symptoms.