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Conditions affecting germination and growth of Fusarium mangiferae, causal agent of mango malformation disease, were studied in vitro. Both conidial germination and colony growth required temperatures >5°C and reached a peak at 28 and 25°C, respectively. A minimum 2-h wetness period was required for conidial germination, reaching a peak after 8 h of wetness. High incidence of fungal colonization in buds, predominantly the apical buds, was detected compared with inoculated leaves. The pathogen was detected in the roots of inoculated soil 19 weeks postinoculation but not in aboveground parts of the plants, and symptoms of the disease were not observed, either. Dry, malformed inflorescence debris serving as a source of inoculum caused significantly higher colonization (52 and 20%) of inoculated buds, compared with that (0%) of the untreated controls. Incidence of sampled leaf disks bearing propagules of F. mangiferae from an infected orchard peaked in June and July and decreased during the following months, whereas airborne infections on 1-month-old branches was the highest in May and June, corresponding with inoculum availability released from infected inflorescences. Colonization pattern, determined in naturally infected vegetative and woody branches, was significantly higher in node sections than in the internode sections. This study sheds light on infection dynamics, colonization patters, and the disease cycle of F. mangiferae in mango.

The role of the mango bud mite, Aceria mangiferae, in carrying conidia of Fusarium mangiferae, vectoring them into potential infection sites, and assisting fungal infection and dissemination was studied. Following the mite's exposure to a green fluorescent protein-marked isolate, conidia were observed clinging to the mite's body. Agar plugs bearing either bud mites or the pathogen were placed on leaves near the apical buds of potted mango plants. Conidia were found in bud bracts only when both mites and conidia were co-inoculated on the plant, demonstrating that the mite vectored the conidia into the apical bud. Potted mango plants were inoculated with conidia in the presence or absence of mites. Frequency and severity of infected buds were significantly higher in the presence of mites, revealing their significant role in the fungal infection process. Conidia and mite presence were monitored with traps in a diseased orchard over a 2-year period. No windborne bud mites bearing conidia were found; however, high numbers of windborne conidia were detected in the traps. These results suggest that A. mangiferae can carry and vector conidia between buds and assist in fungal penetration but does not play a role in the aerial dissemination of conidia between trees.

The effects of several spray and climate treatments on Leveillula taurica were tested under controlled and commercial greenhouse conditions either alone or combined with a climate treatment. Ampelomyces quisqualis AQ10 inhibited the germination of conidia on leaves, but not on glass. Trichoderma harzianum T39 inhibited germination on both surfaces. Neither the examined biological control agents (BCAs) nor the two tested mineral oils (AddQ and JMS Stylet-Oil) affected the viability of conidia. Sulphur drastically limited the germination and viability of L. taurica. In experiments at 15–25°C, AQ10 alone reduced hyphal leaf colonisation at 25°C. T. harzianum T39 significantly reduced leaf colonisation at all temperatures but significantly reduced disease only at 20–25°C. The oils significantly reduced leaf colonisation and sulphur reduced both leaf colonisation and disease at all temperatures. Results were confirmed in an experimental greenhouse. In a field experiment, azoxystrobin, polyoxin AL, neem extract, and T39 were effective; sulphur was superior to them. Under severe epidemic conditions the disease had a negative impact on yield; late fungicide treatments at spring-time were found unnecessary. Chemical sprays applied in alternation was compared with the ‘friendly’ spray regime (alternation of Heliosoufre, T. harzianum T39 + JMS Stylet oil, A. quisqualis AQ10+AddQ oil and Neemgard) in two climates i.e. (i.) day warm climate and (ii.) regular (cool) day climate regimes. In the warm climate, there was no significant difference in the performance of the ‘friendly’ spray regime and the chemical spray regime. However, in the cooler climate, the ‘friendly’ spray programme was not as effective as the chemical spray programme. It was concluded that a change in the greenhouse climate may affect the development of powdery mildew and, at the same time, promote the activity of BCAs and render a pathogen more vulnerable to these control agents, allowing for better disease suppression.

The effect of colored shade nets with different shade intensities and qualities of irradiation transmittance on pepper powdery mildew was tested in mini-plots and field experiments. Leaf coverage byLeveillula taurica and leaf shedding due to the disease were more severe in the shade, by up to 275% and 70%, respectively, than in the open field. Leaf coverage byL. taurica symptoms and leaf shedding from plants grown under 25% shade black nets were higher, by up to 70% and 180%, respectively, than under 40% shade nets. The color of the shade nets affected the intensity of photosynthetically active (PAR), ultra-violet (UV), blue, red and far red radiations, the UV/blue light ratio, and percent PAR and UV transmitted. The various nets suppressed the disease differently. Black, blue-silver, green and red nets were associated with lower levels of disease in the field experiments. The red net was also superior in the mini-plots. The other results from the mini-plots were not similar to those from the field, probably reflecting more intensive epidemic development in the mini-plots. No interaction between net type and cultivar was found when two cultivars were grown under the nets. Yield was higher under nets than in the open; nevertheless, the yield from plants grown under the 40% shade black net was not higher than that of the plants under the 25% black net, despite the significantly lower levels of disease at the higher shade intensity. B-quality pepper yield was significantly higher in the plots covered by 25% shade. Yield differences between the different colored nets were also not well correlated with disease levels, probably due to factors negating the direct effect of the nets on the plants and their yield. Implementation of either ‘friendly’ (Ampelomyces quisqualis AQ10/Trichoderma harzianum T39/ sulfur/ neem seed extract) or chemical (sulfur/ pyrifenox/ Polyoxin AL/ myclobutanil/ azoxystrobin) spray regimes successfully reduced disease severity under the different nets. There was no interaction between net type and spray regime. Thus, growing sweet pepper under shade nets results in increased yields and also in higher powdery mildew severity. Disease is negatively associated with the rate of shading and is variably affected by the quality of light filtered through the different colored shade nets.

Mango malformation, caused by the fungus Fusarium mangiferae, is one of the major diseases of this crop occurring worldwide. This study was conducted to investigate aspects of the epidemiology, survival and spread of the pathogen in general and specifically in seedlings, the majority of which are cultivated in infected orchards in Egypt. Survival of conidia of a representative isolate (506/2) declined very rapidly in soil under summer conditions (1·6 weeks for 50% population decline), but significantly less in controlled and winter conditions (17·9 and 15·0 weeks, respectively, for 50% population decline). Likewise, inoculum survival in naturally infected panicles on the soil surface declined faster than in those buried at 30-cm depths. Natural infections were evaluated on fruits and seeds in a heavily infected and a healthy orchard. In infected trees, the skins of all sampled fruits within a 2-m radius of infected panicles were infected, but the pathogen was not detected in the seeds, seed coats or flesh. The pathogen was not detected in any parts of fruits from a healthy orchard. Vegetatively malformed mango seedlings, growing under infected trees bearing infected panicles, were sampled in two locations in Egypt to determine whether infection in seedlings was systemic (evenly distributed within plant tissue) or whether the pathogen originated from malformed panicles. According to PCR-specific primer amplification, the pathogen was detected in 97% of seedling apical meristems, declining gradually to 5% colonization in roots. It was concluded that inoculum of the pathogen originates from infected panicles and affects seedlings from the meristem, with infections descending to lower stem sections and roots. Minor infections of roots may occur from inoculum originating from infected panicles, but the pathogen is not seedborne.

Scytalidium wilt, caused by Scytalidium lignicola, has become prevalent on ‚Star Ruby’ grapefruit in orchards in the Jordan Valley, an area with a warm climate in the north of Israel. It occurs in the summer in certain years, soon after extreme hot and dry weather conditions have prevailed for several consecutive days, but not in other years with regular summer temperatures. The effect of temperature conditions before and after inoculation with S. lignicola on disease development on ‚Star Ruby’ was studied in greenhouse chambers with three day/night temperature regimes: ‚Very Hot’ (47 °C/34 °C); ‚Hot’ (36 °C/28 °C); and ‚Moderate’ (30 °C/20 °C). Among the pre-inoculation regimes, ‚Very Hot’ was most conducive to infection, whereas the ‚Hot’ regime sustained canker development only when followed by a ‚Very Hot’ post-inoculation regime. The moderate pre-inoculation conditions appeared to have a negligible, if any, effect on canker development, even with a ‚Very Hot’ post-inoculation regime. Wilt developed in infected saplings if they were exposed to the ‚Very Hot’ temperature regime either pre- or post-inoculation, but did not develop under the cooler conditions. Saplings of ‚Star Ruby’ exposed to a ‚Very Hot’ regime developed heat-stress symptoms, similar to those observed on ‚Star Ruby’ in the Jordan Valley. Under a constant ‚Very Hot’ regime, both canker expansion and subsequent foliar wilt developed on ‚Flame’, but not on ‚Marsh Seedless’ or ‚Rio Red’ grapefruit. The study confirmed an hypothesis that predisposition induced by extremely hot temperature is a prerequisite for infection of susceptible hosts by S. lignicola.

Powdery mildew of strawberry is caused by the obligate pathogenic fungus Sphaerotheca macularis f. sp. fragariae. The disease affects the leaves, flowers and fruit of this crop. This study examined the effects of different environmental factors on disease cycle components (germination, conidiation and survival) in strawberry to determine which conditions limit the progress of the disease. The optimal environmental conditions for conidial germination and conidial germ tube length ranged between 15 and 25 °C with relative humidity (RH) higher than 75%, but less than 98%. High light intensity reduced germination and hyphal growth. The viability of conidia on infected leaves was examined at temperatures ranging from 15 to 35 °C at 80–85% RH. Conidia survival declined over time, but a certain percentage of conidia remained active after 5 months incubation. The rate of conidial germination was significantly higher on young leaves than on older leaves. This observation was consistent across all four tested cultivars. Conidiation at 70–75% RH was similar to that at 80–85%, but greater than that at ≥95% RH. The shortest time from inoculation to appearance of the first disease symptoms was 4 days, at 20 and 30 °C with RH above 75%. In growth chambers, temperatures of 10 and 30 °C, RH above 95%, radiation of 7000 lux and the use of a more tolerant cultivar were all detrimental to disease development. In general, the environmental conditions required for germination and dispersal of powdery mildew are conducive to disease progress under strawberry production conditions in Israel. Furthermore, viability and survival of the pathogen during and between seasons appears to be dependent on asexual inoculum production.

Apricot gummosis pathogens — the fungi Hendersonula toruloidea, a Cytosporina sp. and a Cytospora sp., produce cellulase (endo-1,4-β-glucanase, carboxymethylcellulase, CMCase) in culture. Cytospora sp. produced significantly lower amounts of cellulase than H. toruloidea and Cytosporina sp. The tendency of cellulase accumulation inside apricot stems infected with either H. toruloidea or Cytosporina sp. is similar: most of the cellulase was found in the necrotic area, whereas comparatively small amounts accumulated at the advancing edge of the disease symptom. H. toruloidea produces cellulase with a molecular mass of 76 kDa.

Two antifungal terpenoids, 6-isopropyltropolone β-glucoside and 5-(3-hydroxy-3-methyl- trans -1-butenyl)-6-isopropyl-tropolone β-glucoside, named by us cupressotropolone A and B, respectively, were isolated from the bark of Italian cypress, in response to infection by the fungus Diplodia pinea f. sp. cupressi . These tropolone glucosides inhibited in vitro germination of spores of Diplodia pinea f. sp. cupressi, Seiridium cardinale, Alternaria alternata and Verticillium dahliae .

Inoculum availability and conidial dispersal patterns of Fusarium mangiferae, causal agent of mango malformation disease, were studied during 2006 and 2007 in an experimental orchard. The spatial pattern of primary infections in a heavily infected commercial mango orchard corresponded with a typical dispersal pattern caused by airborne propagules. Malformed inflorescences were first observed in mid-March, gradually increased, reaching a peak in May, and declined to negligible levels in August. The sporulation capacity of the malformed inflorescences was evaluated during three consecutive months. Significantly higher numbers of conidia per gram of malformed inflorescence were detected in May and June than in April. Annual conidial dissemination patterns were evaluated by active and passive trapping of conidia. A peak in trapped airborne conidia was detected in May and June for both years. The daily pattern of conidial dispersal was not associated with a specifically discernable time of day, and an exponential correlation was determined between mean relative humidity (RH) and mean number of trapped conidia. Higher numbers of conidia were trapped when RH values were low (

A cold-tolerant strain of the mycoparasite Fusarium proliferatum was isolated following UV mutagenesis of the G6 strain, which is a biocontrol agent of grape downy mildew. The isolated strain (designated 1505) exhibited radial growth two to threefold that of the parent strain when grown at 13 degrees C, which is generally suboptimal for growth of Fusarium spp., but desirable for its host, Plasmopara viticola. This rapid growth was correlated with improved biological control of P. viticola, determined by a detached-leaf assay. Even though radial growth of strain 1505 at higher temperatures was slower than that of G6 and the strain failed to conidiate, there was no reduction in biocontrol efficacy. Significantly higher levels of extracellular beta-glucosidase and endo-1,4-beta-glucanase activity were measured in the culture filtrate of strain 1505 relative to that of strain G6. A DNA-mediated transformation procedure that included the introduction of antibiotic resistance and a GUS reporter gene system was adapted for F. proliferatum. Using the GUS-engineered strains, we demonstrated that both G6 and 1505 exhibit the characteristic coiling and penetration of host structures.

Ampelomyces quisqualis, a mycoparasite of fungi causing powdery mildews, exhibited high levels of extracellular exo-beta-1,3-glucanase activity in culture compared with Neurospora crassa and Gliocladium roseum. A. quisqualis culture filtrates affected powdery mildew caused by Sphaerotheca fusca in a manner indicative of cell wall degradation, as determined by microscopic examination. A gene encoding an exo-beta-1,3-glucanase in A. quisqualis, designated exgA, was isolated and sequenced. The predicted polypeptide deduced from exgA had 46, 42, and 30% identity with amino acid sequences of Trichoderma harzianum exo-beta-1,3-glucanase and Cochliobolus carbonum EXG1 (both encoding exo-beta-1,3-glucanase) and T. harzianum bng13.1 (encoding an endo-beta-1,3-glucanase), respectively. The exgA gene had a predicted molecular mass of 84 kDa and a pI of 4.79. The gene was expressed during the late stages of growth in culture, and transcription was induced by fungal cell wall components. Transcript levels for exgA were present during late stages of hyperpar-asitism and were abundant along A. quisqualis mycelium and were slightly less abundant in A. quisqualis pycnidia.

Sweet pepper-Leveillula taurica microclimate relations were studied under controlled conditions and in commercial greenhouses. Conidial germination occurred at 10 to 37 degrees C and was optimal at 20 degrees C. Conidial viability declined as temperatures increased to 40 degrees C for 6 h. Leaf colonization was optimal at 15 to 25 degrees C. Severe leaf infections occurred at 15 to 20 degrees C and conidiation was suppressed at 20 to 25 degrees C. Highest germination rates were observed at 75 to 85% relative humidity (RH). Severity of leaf coverage by symptoms was high for plants which were subjected to longer periods of temperatures between 10 to 15 degrees C and daytime RH between 85 to 95%, and positively correlated with nighttime RH. Disease severity was negatively correlated with lengthy periods of temperatures >25 degrees C, day and night average temperatures, and average daytime RH. Conversely, leaf shedding was relatively high under conditions characterized by long periods of temperatures >20 degrees C and

The rate of water flow through segments of cypress branches infected by either Diplodia pinea f.sp. cupressi or Seiridium cardinale was markedly lower than in healthy branches. Xylem flow resistance was enhanced more by diplodia canker than by seiridium canker. Water flow rate in wounded control branches was similar to that in healthy unwounded ones. Histological study of branches infected by these pathogens revealed that hyphal colonization of tracheids and parenchyma rays of sapwood tissue was sparse and could not be related to water blocking. Neither tyloses nor resin deposition were observed in the affected zone. Tannin accumulation was occasionally observed in tracheids and parenchyma rays of sapwood. Scanning electron microscope examinations of tracheids from branches affected by seiridium or diplodia cankers, revealed heavy plugging of pit membranes with dense material, while pit membranes of intact wounded or healthy branches were well perforated. We suggest that mortality of cypress due to these pathogens results from obstruction of water flow in the xylem, caused by plugging of pit membranes.

A range of microorganisms, with previously identified antagonistic properties towards a variety of plant pathogens, were screened for their biological control activity against the foliar necrotroph Botrytis cinerea. On detached, senescing strawberry leaves the most successful isolate, Trichoderma atroviride LU132, was able to inhibit B. cinerea lesion development and significantly reduce sporulation compared to the control treatment. T. atroviride LU132 was further evaluated under field conditions and, over a 2-year period, on three different strawberry cultivars, was able to significantly suppress B. cinerea sporulation on leaves and flower parts giving a similar level of disease control as the fungicide fenhexamid. The mechanisms of action of T. atroviride LU132were postulated to be a combination of competition for sugars, production of non-volatile compounds and possible mycoparasitism. The strategic approach described in this paper demonstrates an efficient way of screening microorganisms for biocontrol activity and validates the notion that certain microorganisms can be antagonistic to a variety of plant pathogens.

Postinfection applications of microconidial suspensions of Fusarium proliferatum G6 reduced sporangial production of Plasmopara viticola on grape leaf disks by 97% and prevented resporulation. Microscopic examination of the hyphal interaction in vitro showed hyphae of F. proliferatum G6 coiled around and inside sporangiophores of P. viticola. In the field from 1992 to 1995, where substantial natural grape downy mildew developed, weekly applications of F. proliferatum G6 microconidia reduced disease development on leaves and fruit clusters of Vitis interspecific hybrid cultivars Chancellor and Lakemont. Severity of downy mildew on Chancellor clusters was reduced by 77% in 1992, 80% in 1993, and 53% in 1994 and was reduced on leaves by 71% in 1992. On Lakemont, disease severity on clusters was reduced by 99% in 1993, 94% in 1994, and 81% in 1995 and was reduced on leaves by 79% in 1992, 67% in 1994, and 60% in 1995. Fumonisin mycotoxins, which are produced by F. proliferatum, including F. proliferatum G6, were not found in grape berries or juice made from berries sprayed with microconidia in the field. Agar tests with fungicides showed sulfur, copper, and metalaxyl to be minimally detrimental to F. proliferatum G6. Biological control with F. proliferatum might be practical in conjunction with a management program in which sulfur and copper are used or in an antiresistance management program with metalaxyl, on moderately resistant cultivars, or in areas where downy mildew is not severe.

The effects of gamma irradiation and temperature of incubation on accumulation of the phytoalexin scoparone were investigated in citrus inoculated with the fungus Phytophthora citrophthora. In all the tested citrus species, scoparone concentration in the branches was higher and lesion length was shorter when the incubation temperature after inoculation with P. citrophthora was 28 rather than 20 C. The temperature effect was pronounced, especially in inoculated branches of rough lemon, which after 4 days at 28 C had a scoparone concentration of 290 μg/g fresh weight, compared with 42 μg/g fresh weight at 20 C. The comparable lesion length in this species was 5.2 mm at 28 C compared with 11.0 mm at 20 C [...]

(...) The lengths on seedlings of resistant species were 2.8 mm for Citrus macrophylla and 3.2 mm for Poncirus trifoliata; lengths on moderately-resistant species were 5.0 mm for C. aurantium and 5.2 mm for P. trifoliata × C. sinensis; lengths on susceptible species were 11.0 mm for both C. jambhiri and C. sinensis. Thirty-two hybrids (P. trifoliata × «poorman orange») were tested using this method. Of these, 14 hybrids were resistant, eight were moderately resistant, and 10 were susceptible

Different isolates ofTrichoderma harzianum andTrichoderma hamatum were isolated from naturally infected roots ofRosellinia necatrix. T. harzianum andT. hamatum isolates overgrew cultures ofR. necatrix placed simultaneously in petri dishes. Relative levels ofR. necatrix population were assessed by the avocado leaf colonization method.T. harzianum isolate T-8, significantly reducedR. necatrix colonization of avocado leaves in comparison to other isolates in artificially and naturally infested soils.R. necatrix inoculum decreased steadily over 4 and 6 week periods in artificially inoculated soil and naturally infested soil respectively when isolate T-8 was applied, to a point where noR. necatrix could be recovered. Disease incidence of almond seedlings was significantly reduced when isolate T-8 was added to naturally infested En-Zurim soil.

An isolate of Ampelomyces quisqualis obtained from a Oidium sp. infecting Catha edulis in Israel, proved to be infective to several powdery mildew fungi belonging to the genera Oidium, Erysiphe, Sphaerotheca, Podosphaera, Uncinula, and Leveillula. In field trials, A. quisqualis parasitized the powdery mildews of cucumber, carrot and mango and reduced the disease. Hyperparasitism on Oidium mangiferae is reported for the first time. A. quisqualis was tolerant to many fungicides currently used to control powdery mildews and/or other plant diseases. In one experiment, treating powdery mildew of cucumber (cv. Hazera 205) with spores of A. quisqualis alone, significantly decreased disease severity and increased cucumber yields by approximately 50%. However, a greater increase in yield was obtained by using the fungicide pyrazophos alone or in combination with the hyperparasite. In a second experiment, using cv. Dalila, all treatments increased the yield over the untreated control which did not produce fruits. Zusammenfassung Ampelomyces quisqualis in der biologischen und integrierten Bekampfung des Echten Mehltaus in Israel Festgestellt wurde, das ein Ampelomyces quisqualis-Stimm, der aus einer Oidium sp. an Catha edulis in Israel isoliert wurde, einige der Pilze des Echten Mehltaus der Gattungen Oidium, Erysiphe, Sphaerotheca, Podosphaera, Uncinula und Leveillula parasitisieren konnte. In Feldversuchen konnte A. quisqualis Gurken-, Mohren- und Mangomehltau parasitisieren und dadurch den Krankheitsbefall reduzieren. Der Hyperparasitismus an Oidium mangifera wird zum ersten Mal dokumentiert. Es wurde auch festgestellt, das A. quisqualis gegen einige Fungizide, die ihren Einsatz als Mehltaufungizide oder auch gegen andere Krankheiten finden, unempfindlich ist. In einem Versuch wurde ermittelt, das nach der Anwendung von A. quisqualis-Sporen gegen Gurkenmehkau (Sorte Hazera 205) eine deutliche Reduzierung der Befallsintensitat und eine Erhohung des Gurkenertrages um 50% erzielt wurde. Jedoch wurden noch hohere Ertrage erzielt, wenn entweder das Fungizid Pyrazophos alleine oder in Kombination mit dem Hyperparasit angewandt wurde. In einem zweiten Versuch mit der Sorte Dalila wurden bessere Ertrage mit allen Behandlungen erzielt als in der unbehandelten Kontrolle, wo keine Gurken wuchsen.

Dematophora necatrix, the causal agent of the white root rot disease in plants, produced large amounts of cellulase (Cx) and very small amounts of polygalacturonase (PG). Both tannins (100 mg/l) and phenols (200 mg/l) extracted from roots of plants showing resistance to the disease decreased Cx productionin vitro. PG production was affected only by tannin extracts. Exposure of the fungus for 2 days to the tannin (100 mg/l) but not to the phenol (200 mg/l) extracts decreased the subsequent rate of fungal growth in an agar medium free of these compounds.

Crops e. g., pecan, persimmon and passionflower, which show resistance to the fungus Dematophora necatrix, the causal agent of white root rot disease, contain phenolic compounds which inhibit its growth. Roots of resistant crops contain higher concentrations of phenolic compounds than those of suceptible crops, e. g., apple, almond and peach. The fungus contains active polyphenoloxidase (PPO). The oxidation of phenols to quinones may decrease the inhibitory effect. Catechol, methylcatechol, hydroquinone and 8-hydroxyquinoline significantly inhibited the growth of the fungus. In greenhouse experiments, seedlings were irrigated with, or dipped in, phenols. Catechol, methylcatechol and hydroquinone delayed the appearance of disease symptoms. Zusammenfassung Eine mogliche Rolle der phenolischen Substanzen in der Resistenz von Gartenbauerzeugnissen gegenuber Dematophora necatrix Hartig Pflanzenarten, wie z. B. Pekannus, Persimone oder Passionsblume, die eine Resistenz gegenuber dem Pilz Dematophora necatrix aufweisen, enthalten phenolische Substanzen, die ihren Wuchs hemmen. Die Wurzeln der resistenten Pflanzen enthalten hohere Konzentrationen der phenolischen Substanzen als diejenigen der empfindlichen Arten, z. B. Apfel-, Mandeloder Pfirsichibaume. Der Pilz, der die weise Wurzelfaule verursacht, enthalt Polyphenoloxidase (PPO). Die Oxidierung der Phenole zu Chinonen kann diese hemmende Wirkung herabsetzen. Katechin, Methylkatechin, Hydrochinon und 8-Dehydrochinolin uben signifikante Hemmung auf den Wuchs des Pilzes aus. In Gewachshausuntersuchungen wurden die Samlinge entweder mit Phenolen irrigiert oder in Phenole getaucht, Katechin, Methylkatechin und Hydrochinon verzogenten die Erscheinung der Krankheitssymptome.

Germination of Botrytis cinerea spores was inhibited on beetroot leaf was reformed on glass fibre. Wax was extracted by immersion of leaves in chloroform for periods of 1 to 60 s. There was some inhibition of spore germination on wax deposited for 6 h, and a marked inhibition after 18 h or longer. Inhibition of germination of spores on reformed wax was less than that on beetroot leaves. Inhibition was overcome by the addition of nutrients to spore suspensions on reformed wax. Continuous spraying of beetroot plants with water, or chemical treatment of plants with TCA or EPTC, caused a reduction in contact angles on leaves. Germination of B. cinerea spores was greatly increased on leaves of plants treated with water-spray or chemicals.

There was no consistent reduction in numbers of bacteria isolated from unwetted beetroot leaves following exposure to ultraviolet light. Bacteria increased in water droplets on leaves but were readily killed by short exposures to ultraviolet light. After prolonged exposures numbers of surviving bacteria were similar to those on unwetted leaves. Evidence suggested that the rapid recolonization of leaves after ultraviolet irradiation occurred from surviving bacteria either within the leaf or protected on the surface from direct exposure. The higher numbers of bacteria which developed in water droplets placed on leaves previously exposed to ultraviolet light may have been associated with increased leakage of electrolytes, amino acids and carbohydrates from leaves following irradiation. Germination of Botrytis cinerea spores was more strongly inhibited in vitro in droplets from leaves previously exposed to ultraviolet light. The spectrum of bacterial species on leaves was changed following exposure to ultraviolet light but isolates of bacteria from irradiated leaves were not more antagonistic against B. cinerea spores in vitro .

Rosellinia necatrix, the cause of white root rot in fruit trees, was efficiently controlled in an infested avocado orchard soil, by applying methyl bromide by deep injection (up to 90 cm) of cold gas and by surface application of hot gas, at a dosage (for heavy soil) of 1500 kg/ha and 1000 kg/ha, respectively. Efficiency of control was evaluated: 1) by testing pieces of naturally diseased avocado roots buried in the soil before treatment at different depths up to 100 cm; 2) by planting avocado and almonds in the treated field and in soil samples; 3) by burying avocado leaves in the soil samples. All the evaluaton tests showed that both treatments of methyl bromide were effective in controlling R. necatrix completely up to the depth of 100 cm, immediately and 9 months after treatment.

6,7-Dimethoxycoumarin was isolated from the bark of citrus trunks, branches and fruit peels following inoculation with the fungus Phytophthora citrophthora . The compound inhibited growth in vitro of Phytophthora citrophthora, Verticillium dahliae, Penicillium digitatum, P. italicum, Colletotrichum gloeosporioides, Diplodia natalensis and Hendersonula toruloidea.

In macrophylla, sour orange, and rough lemon, concentrations of scoparone were two- to fourfold greater in inoculated branches treated with 300 μg of fosetyl-Al or 125 μg of phosphorous acid (H 3 PO 3 ) per milliliter than in inoculated, untreated branches. Lesion length in these three species decreased more rapidly than in niva after treatments with 0-300 μg of fosetyl-Al or 0-125 μg of H 3 PO 3 per milliliter, whereas lesion length in niva decreased sharply only with treatments of more than 500 μg of fosetyl-Al or 200 μg of H 3 PO 3 per milliliter

On montre que la phenylalanine est le precurseur de la scoparone et que l'aminooxyacetique acide inhibe la production de scoparone en intervenant dans sa biosynthese chez les agrumes qui deviennent ainsi sensibles au Phytophthora