Suppression of the in vitro growth and development of Microdochium nivale by phosphite

The ascomycete fungus Microdochium nivale is a major pathogen of many species of the gramineae. Control measures rely heavily on chemical fungicides, making alternative means of disease reduction desirable. Phosphite (PO₃^3?), has proven efficacy in reducing susceptibility of different species of gramineae to oomycetes, and has adverse effects on the in vitro growth of numerous other pathogens. The effect of phosphorous acid (H₃PO₃), phosphoric acid (H₃PO₄), dihydrogen potassium phosphite (KH₂PO₃), dihydrogen potassium phosphate (KH₂PO₄) and potassium hydroxide (KOH) on the in vitro mycelial growth and development of M. nivale was determined. Radial growth on amended potato dextrose agar (PDA) was used to calculate mean daily growth and percentage inhibition. PO₃^3? had a significant inhibitory effect on mycelial growth, with EC₅₀ values ranging between 35.9 and 40.99 μg mL^?1, whilst PO₄^3? and KOH had no significant inhibitory effect. Microscopic examination of mycelia showed morphological deformities in hyphae growing on PO₃^3? amended PDA, whilst hyphal growth was normal on PO₄^3? and KOH amended PDA. Conidial germination of M. nivale was significantly reduced following immersion in solutions of 50, 100 and 250 μg mL^?1 of PO₃^3?, while PO₄^3? and KOH at the same concentrations induced no inhibitory affect. These results show that PO₃^3? is a significant inhibitor of the growth of M. nivale and may have the potential to be used as a chemical control agent in the field.     

Poacic acid suppresses dollar spot and snow mould in amenity turfgrass

Plant-based antifungal agents offer an alternative to synthetic fungicides in amenity turfgrass disease management. Poacic acid is a by-product of the biofuel production process that has exhibited antifungal activity, and the objective of this research was to determine its ability to serve as an effective management tool for economically important turfgrass diseases such as dollar spot and snow moulds. In vitro and field tests were conducted in Wisconsin and Michigan, USA from 2015 to 2017 to determine the efficacy of poacic acid in suppressing the economically important turfgrass pathogens Clarireedia jacksonii and Microdochium nivale. Poacic acid demonstrated strong antifungal activity against both pathogens in vitro, inhibiting growth of C. jacksonii and M. nivale by 93% and 74% relative to nonamended media, respectively. Poacic acid reduced dollar spot in the field in one of two years, but failed to suppress snow mould when applied alone. Poacic acid was an effective mix partner for snow mould control when combined with a synthetic fungicide, an important attribute because no single fungicide currently on the market provides acceptable snow mould control under heavy disease pressure. Future research should focus on improving poacic acid field efficacy so that it can be incorporated into plant-based disease management strategies for amenity turfgrass.     

The effect of a mixture of seed-borne Microdochium nivale var. majus and Microdochium nivale var. nivale infection on Fusarium seedling blight severity and subsequent stem colonisation and growth of winter wheat in pot experiments

Greenhouse experiments were conducted in order to determine the impact of seed-borne Microdochium nivale var. nivale and var. majus inoculum, and seed treatment with a carboxin+thiram mixture, on the development of seedling blight, and on subsequent stem colonisation and growth of winter wheat (cv. Cadenza). Experiments were conducted at temperatures favourable (3°C) and unfavourable (22°C) to M. nivale. Seed-borne inoculum resulted in seedling blight symptom development when plants were grown at 3°C, but not when plants were grown at 22°C. For seedlings grown at 3°C, plants arising from heavily blighted seedlings developed more severe symptoms of stem colonisation, when compared with those arising from seedlings from carboxin+thiram treated seeds. In addition, the vigour of such plants (assessed by determining the number of tillers and ears per plant, stem length, green leaf area, dry weight and yield) was also significantly lower than for plants arising from carboxin+thiram treated seeds. Microdochium nivale var. majus and var. nivale appeared to have little effect on plant vigour from seedlings grown at 22°C. This is the first recorded incidence of seedling blight affecting subsequent plant growth. Microdochium nivale var. majus and var. nivale stem colonisation increased from growth stage (GS) 40–49 to harvest in plants raised from seedlings grown at both temperatures. Microdochium nivale var. majus and var. nivale were isolated from the second node at GS 40–49 and the third node at harvest of plants from seedlings grown at 3°C. For plants from seedlings raised at 22°C, M. nivale var. majus and var. nivale were isolated from the first node at GS 40–49 and the second node at harvest. Carboxin+thiram seed treatment decreased the extent and severity of stem colonisation on plants from seedlings grown at 22°C.     

Silicon-enhanced resistance to rice blast is attributed to silicon-mediated defence resistance and its role as physical barrier

A series of experiments were performed to study the effects of silicon (Si) on rice blast development, H₂O₂ accumulation and lipid peroxidation in a controlled rice—Magnaporthe grisea pathosystem. Rice plants supplied with Si as a single dose immediately after pathogen inoculation (−/+Si) exhibited the same high protection against disease as plants treated continuously with Si for the whole growth period (+/+Si), with disease severity indices of 20.8% and 19.6%, respectively, which were significantly lower than that for the control treatment with no Si supplied (63.7%). A single application of Si to rice plants before inoculation (+/−Si) conferred partial protection (disease severity index of 33.3%) compared with the control treatment. Silicon induced a rapid but transient burst of H₂O₂ at 24 h after inoculation. The addition of Si to rice plants significantly altered the activities of catalase and lipoxygenase and the concentration of malodialdehyde (indicative of lipid peroxidation) in rice plants. We propose that rice plants may respond to Si by increased H₂O₂ accumulation and lipid peroxidation. In turn, these responses are linked to host defence mechanisms such as lignin production, oxidative cross-linking in the cell wall, phytoalexin production, and the hypersensitive reaction. Thus, the mechanisms of Si-stimulated plant disease protection may extend beyond its established role in physically strengthening cell walls.     

Salicylic acid alleviates growth inhibition and oxidative stress caused by zucchini yellow mosaic virus infection in Cucurbita pepo leaves

The effects of zucchini yellow mosaic virus (ZYMV) infection and pretreatments with salicylic acid (SA) on biomass accumulation of pumpkin (Cucurbita pepo cv. Eskandarani) were investigated. The response of photosynthesis, transpiration and the activities of antioxidant enzymes in leaves was also considered. Significant reductions in growth parameters (i.e. leaf area, biomass and shoot height), photosynthesis and chlorophyll a and b content were detected in ZYMV-infected leaves in comparison to healthy controls. Antioxidant enzyme activities were increased up to 3-fold for peroxidase (POD), 2-fold for ascorbate peroxidase (APX) and catalase (CAT) activities and 1.3-fold for SOD activity by virus infection. ZYMV infection also caused increases in H₂O₂ and malondialdehyde (MDA) contents. These results suggest that ZYMV infection causes oxidative stress in pumpkin leaves leading to the development of epidemiological symptoms. Interestingly, spraying pumpkin leaves with SA led to recovery from the undesirable effects of ZYMV infection. Leaves treated with 100 μM SA three days before inoculation had the appearance of healthy leaves. No distinct disease symptoms were observed on the leaves treated with 100 μM SA followed by inoculation with ZYMV. In non-infected plants, SA application increased activities of POD and superoxide dismutase (SOD) and inhibited APX and CAT activities.In contrast, SA treatment followed by ZYMV inoculation stimulated SOD activity and inhibited activities of POD, APX and CAT. In addition, MDA displayed an inverse relation, indicating inhibition of lipid peroxidation in cells under SA treatment. It is suggested that the role of SA in inducing plant defense mechanisms against ZYMV infection might have occurred through the SA-antioxidant system. Such interference might occur through inhibition or activation of some antioxidant enzymes, reduction of lipid peroxidation and induction of H₂O₂ accumulation following SA application.     

<Emphasis Type="Italic">Sunflower Chlorotic Mottle Virus</Emphasis> in Compatible Interactions with Sunflower: ROS Generation and Antioxidant Response

Sunflower chlorotic mottle virus (SuCMoV) is a recently described potyvirus that causes systemic infections in sunflower plants leading to chlorotic mottling and important growth reductions and yield losses. Oxidative damage is expressed after symptom development in this host-pathogen combination. The involvement of antioxidant enzyme activities in disease susceptibility was studied in two sunflower lines differing in the intensity and rate of development of SuCMoV infections: L2 is more susceptible than L33. A transient superoxide production peak was detected in leaves of both lines before symptom development. H₂O₂ accumulation increased before symptom expression in infected plants of L33 but in L2 such increase was registered only after symptoms became evident. In healthy plants of both lines, superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) showed similar activity levels. In inoculated plants of line L2, but not in L33, SOD and CAT activities increased significantly before the appearance of symptoms, and APX increases were detected later. A 1 mM SA treatment effectively decreased SuCMoV accumulation in plants of L2 but it did not affect it in L33. This treatment increased H₂O₂ accumulation and prevented the increase in antioxidant enzyme activities in infected plants of L2. It is suggested that increases in antioxidant enzyme activities interrupted the signals generated by the increase in ROS, which may have otherwise triggered defence reactions in the host and thus, resulted in a compatible interaction.     

Mycorrhizal protection of chili plants challenged by <Emphasis Type="Italic">Phytophthora capsici</Emphasis>

Hydrogen peroxide (H₂O₂) has been implicated in many stress conditions. Control of H₂O₂ levels is complex and dissection of mechanisms generating and relieving H₂O₂ stress is difficult, particularly in intact plants. Here the role of the mycorrhizal inoculation in chili plants challenged with Phytophthora capsici was investigated to study the effect on hypersensitive response. In the treatment without mycorrhiza (treatment T3) and with mycorrhiza (considered treatment T4) visible disorders were detected two days after inoculation with P. capsici, but in the next days T3 plants rapidly developed 25% more necrotic lesions on the leaves than T4 plants. Leaf necrosis correlated with H₂O₂ accumulation and the greater damage observed in T3 plants coincided with larger accumulation of H₂O₂ after 12 h of inoculation accompanied with an increase in POX (peroxidase) and SOD (superoxide dismutase) activity. T4-infected and mycorrhizal plants exhibited an earlier accumulation of H₂O₂ starting 6 h after inoculation with lower levels compared to T3 plants. Correlated with observed damage, POX and SOD activity measured in T4 plants indirectly suggest a smaller accumulation of ROS (reactive oxygen species) leading to a decrease in the wounds observed and slightly diminishing the advance of the pathogen. According to these findings, we conclude that mycorrhizal colonization contributes significantly in maintaining the redox balance during oxidative stress, but the exact mechanism is still uncertain.     

Spatiotemporal patterns of oxidative burst and micronecrosis in resistance of wheat to brown rust infection

The accumulation of H₂O₂ (oxidative burst) and the progress of pathogen development were studied in compatible and incompatible wheat‐brown rust interactions. The accumulation of H₂O₂ was detected in 98·7% of guard cells with appressoria 8 h post inoculation (hpi). The reaction in both susceptible and resistant plants declined 2–3 days post inoculation (dpi). The second phase of the oxidative burst was observed in the mesophyll and/or epidermis. In susceptible plants it began 4–5 dpi and was detected only in the epidermis. In resistant plants the response was observed in the mesophyll. In moderately resistant plants it was induced 1–3 dpi, and the percentage of infection units reached 80–90% 8 dpi. This corresponded with severe necrotic symptoms. In highly resistant plants, the oxidative burst was short and transient. The percentage of infection units with H₂O₂ accumulation reached its highest level (60–70%) 2 dpi, and decreased thereafter. Four days later, the low percentage and weak DAB staining indicated very low H₂O₂ accumulation. The localization and the time‐course changes of the oxidative burst correlated with the profiles of the micronecrotic response, haustorium mother cell formation and pathogen development termination. An early and localized induction of oxidative burst followed by its rapid quenching correlated with high resistance and almost no disease symptoms. The possible correlation of the oxidative burst and pathogen development patterns with the level and durability of resistance conferred by Lr genes are discussed.     

The effect of potential resistance inducers on development of <Emphasis Type="Italic">Microdochium majus</Emphasis> and <Emphasis Type="Italic">Fusarium culmorum</Emphasis> in winter wheat

The effect of potential resistance inducing chemicals on disease development of Fusarium head blight was studied in winter wheat (Triticum aestivum L.). As a pre-screening test, the effect of different treatments on development of Microdochium majus (syn. Microdochium nivale var. majus) was studied in detached leaves. Based on these tests, DL-3-aminobutyric acid, Bion (benzo-(1,2,3) thiadiazole-7-carbothioic acid S-methyl ester), and a foliar fertilizer containing potassium phosphite were selected for further studies. Greenhouse-grown winter wheat was sprayed with aqueous solutions of the potential resistance inducers 7 days prior to Fusarium culmorum point inoculation of the heads. Disease development was registered as number of bleached spikelets per inoculated spike. Spraying plants with the foliar fertilizer reduced the disease severity of F. culmorum by up to 40%. A reduced disease development of M. majus was also observed in detached leaves pre-treated with the foliar fertilizer. When the foliar fertilizer was added to the growth medium, a reduced in vitro growth of M. majus and F. culmorum was observed, indicating that the effect on disease development is at least partly due to a fungistatic effect. No significant reduction in disease development was observed in wheat pre-treated with DL-3-aminobutyric acid or Bion, although these compounds tended to reduce disease development, especially when applied in combination with other potential resistance inducers. We conclude that spraying winter wheat with a solution containing potassium phosphite can reduce development of M. majus and F. culmorum.     

Application of energy-filtering electron microscopy (EFEM) for analysis of hydrogen peroxide and lignin in epidermal walls of cucumber leaves triggered by acibenzolar-S-methyl treatment prior to inoculation with Colletotrichum orbiculare

Hydrogen peroxide (H₂O₂) and lignin induced by acibenzolar-S-methyl (ASM) during the expression of systemic acquired resistance (SAR) of cucumber plants against the fungus Colletotrichum orbiculare was analysed with electron microscopy and energy-filtering electron microscopy (EFEM). ASM pretreatment consistently led to the blockage of appressorial penetration pegs into leaves at early stages after inoculation, whereas the fungus was able to grow into the vascular tissue after distilled water pretreatment. The blocked pegs, seen frequently at epidermal pectin layers in leaves of ASM-treated plants, were surrounded by abundant electron-dense amorphous material and dots. These were identified as lignin, based on their appearance and high reactivity with KMnO₄. Lignin first appeared as an amorphous material at pectin layers, and then as dots in some areas of the material. The results showed that ASM caused SAR in leaves via faster formation of lignin within 1 day after inoculation. After CeCl₃ treatment to detect H₂O₂, H₂O₂-reactive products (cerium perhydroxides) were seen near ASM-induced lignin formation sites in pectin layers. EFEM analysis showed that Ce and O were located at the same sites as the lignin dots, suggesting that lignin was associated with sources of H₂O₂ generation. The results indicate that the faster H₂O₂ generation and lignification induced by ASM were the potential causes of SAR.     

Ultrastructural Localization of Hydrogen Peroxide in Host Leaves Treated with AK-toxin I Produced by Alternaria alternata Japanese Pear Pathotype

The rapid generation of reactive oxygen species (ROS), called the oxidative burst, is one of the earliest host responses to pathogen infection or elicitor treatments. Therefore, we looked for the induction of ROS generation in Japanese pear leaves by the host-specific toxin, AK-toxin I using a cytochemical method for detecting H₂O₂. A small amount of non-specific generation of H₂O₂ was found in the cell walls in toxin- and water-treated susceptible and resistant leaves. Thus, the generation of H₂O₂ at cell walls appears to be caused by wounding stress during sampling. Specific generation of ROS, however, was found only in the membrane fragments and extended desmotubules characteristic of modified sites of the plasma membrane in the toxin-treated susceptible leaves. In addition, generation of H₂O₂ at plasma membranes was observed with higher frequency in toxin-treated susceptible leaves. This result indicates that the H₂O₂ generation was associated with damaged sites in the plasmalemma after toxin treatment and perhaps with the formation of membrane fragments from altered portions of the invaginated plasma membrane. Received 21 September 2001/ Accepted in revised form 25 October 2001     

Induction of oxidants in tomato leaves treated with <Emphasis Type="SmallCaps">DL</Emphasis>-β-Amino butyric acid (BABA) and infected with <Emphasis Type="Italic">Clavibacter michiganensis</Emphasis> ssp. <Emphasis Type="Italic">michiganensis</Emphasis>

Bacterial canker is an economically important disease of tomato. Resistance induced by DL-β-Amino butyric acid against bacterial canker caused by Clavibacter michiganensis ssp. michiganensis in tomato plants was investigated. Different doses of DL-β-Amino butyric acid (250–1000 μg ml⁻¹ doses) were tested on 3-week old plants inoculated with a 10⁸ CFU ml⁻¹ bacterial suspension, and disease development was evaluated after inoculation and treatment. Although in vitro growth of the bacteria was not affected by DL-β-Amino butyric acid treatment, foliage sprays of 500 μg ml⁻¹ DL-β-Amino butyric acid significantly suppressed disease development up to 54% by day 14 after inoculation at the four different doses tested. Bacterial populations were reduced by 84% in BABA-treated plants compared to water-treated plants by day 4 after inoculation. Inoculated BABA-treated plants showed significantly higher phenylalanine ammonia-lyase activity, peroxidase activity, and H₂O₂ concentration than inoculated water-treated plants during day 1 after treatment. These findings suggest that the DL-β-Amino butyric acid treatment resulted in an increase of these enzymes and in H₂O₂ concentration in planta, and was associated with induction of resistance to bacterial canker.     

Salicylic acid alleviates growth inhibition and oxidative stress caused by zucchini yellow mosaic virus infection in Cucurbita pepo leaves

The effects of zucchini yellow mosaic virus (ZYMV) infection and pretreatments with salicylic acid (SA) on biomass accumulation of pumpkin (Cucurbita pepo cv. Eskandarani) were investigated. The response of photosynthesis, transpiration and the activities of antioxidant enzymes in leaves was also considered. Significant reductions in growth parameters (i.e. leaf area, biomass and shoot height), photosynthesis and chlorophyll a and b content were detected in ZYMV-infected leaves in comparison to healthy controls. Antioxidant enzyme activities were increased up to 3-fold for peroxidase (POD), 2-fold for ascorbate peroxidase (APX) and catalase (CAT) activities and 1.3-fold for SOD activity by virus infection. ZYMV infection also caused increases in H₂O₂ and malondialdehyde (MDA) contents. These results suggest that ZYMV infection causes oxidative stress in pumpkin leaves leading to the development of epidemiological symptoms. Interestingly, spraying pumpkin leaves with SA led to recovery from the undesirable effects of ZYMV infection. Leaves treated with 100 μM SA three days before inoculation had the appearance of healthy leaves. No distinct disease symptoms were observed on the leaves treated with 100 μM SA followed by inoculation with ZYMV. In non-infected plants, SA application increased activities of POD and superoxide dismutase (SOD) and inhibited APX and CAT activities.In contrast, SA treatment followed by ZYMV inoculation stimulated SOD activity and inhibited activities of POD, APX and CAT. In addition, MDA displayed an inverse relation, indicating inhibition of lipid peroxidation in cells under SA treatment. It is suggested that the role of SA in inducing plant defense mechanisms against ZYMV infection might have occurred through the SA-antioxidant system. Such interference might occur through inhibition or activation of some antioxidant enzymes, reduction of lipid peroxidation and induction of H₂O₂ accumulation following SA application.     

The Oxidants and Antioxidant Enzymes in Tomato Leaves Treated With O-Hydroxyethylorutin and Infected with Botrytis cinerea

Application of o-hydroxyethylorutin restricted the development of Botrytis cinerea in tomato leaves. Superoxide anion and hydrogen peroxide generation rates and changes in superoxide dismutase, peroxidase and catalase activities were studied in uninfected tomato plants, in plants infected with B. cinerea, and in plants treated with o-hydroxyethylorutin and infected with pathogen. About two times higher hydrogen peroxide concentration were found in plants treated with o-hydroxyethylorutin and infected with the pathogen at the early infection stages compared with untreated infected plants. In vitro tests showed that germination of B. cinerea conidia was significantly inhibited by H₂O₂. Higher H₂O₂ concentrations were needed to inhibit mycelial growth. The results indicate that o-hydroxyethylorutin triggers hydrogen peroxide production in tomato plants and suggest that enhanced levels of H₂O₂ are involved in restricted B. cinerea infection development.     

褐飞虱与白背飞虱为害诱导水稻防御反应的比较

为探究2种稻飞虱——褐飞虱Nilaparvata lugens(St?l)和白背飞虱Sogatella furcifera(Horváth)诱导的水稻防御反应差异,于室内测定了水稻在分别受褐飞虱或白背飞虱产卵雌成虫为害时,其茉莉酸、水杨酸、乙烯、H_2O_2以及挥发物含量的变化。结果表明,尽管褐飞虱和白背飞虱产卵雌成虫的为害均可以诱导水稻茉莉酸、水杨酸、乙烯和H_2O_2等防御相关信号分子以及一些水稻挥发物含量的增加,但是二者的诱导作用存在差异。水稻在受白背飞虱产卵雌成虫为害时,茉莉酸的含量在3 h时就显著升高,12 h时含量达到最高;而受褐飞虱产卵雌成虫为害时,6 h时茉莉酸含量才显著升高,72 h时含量达最高;并且在2种稻飞虱为害的3～48 h内,白背飞虱为害诱导的茉莉酸含量始终显著高于褐飞虱为害诱导的。水稻受白背飞虱产卵雌成虫为害24 h后诱导的水杨酸含量、为害48 h后诱导的乙烯含量、为害72 h后诱导的H_2O_2含量及为害24 h后诱导的挥发物释放量分别是褐飞虱产卵雌成虫为害诱导的1.28、1.45、4.10和1.77倍。表明水稻能识别褐飞虱和白背飞虱的为害,从而做出针对害虫种类特异性的防御反应;并且水稻对白背飞虱产卵雌成虫为害所做出的防御反应比对褐飞虱的更强烈。     

Silicon induced resistance against powdery mildew of roses caused by Podosphaera pannosa

Powdery mildew, caused by Podosphaera pannosa, is a very common disease in greenhouse potted roses, resulting in poor marketing value and hence economic losses. Alternatives to chemical control are necessary, and therefore the ability of silicon (Si) applied to roots to control the disease was investigated, as well as the mechanisms behind the observed disease reductions. Four genotypes of miniature potted roses representing different genetic backgrounds and susceptibility to disease were studied. Plants were watered with a nutrient solution containing either 3·6 mm Si (100 ppm) supplied as K₂SiO₃ (Si+) or no Si (Si?) before inoculation with P. pannosa. Si application increased leaf Si content two‐ to four‐fold compared to control plants. Confocal microscopy showed that Si deposition was larger in Si+ than in Si? plants and that deposition mainly occurred in the apoplast, particularly in epidermal cell walls. Si application delayed the onset of disease symptoms by 1–2 days and disease severity was reduced by up to 48·9%. The largest reduction was found in the two most resistant genotypes, which also had the highest increase in Si uptake. The Si‐induced disease protection was accompanied by increased formation of papillae and fluorescent epidermal cells (FEC) as well as deposition of callose and H₂O₂, especially at the sites of penetration and in FEC, which are believed to represent the hypersensitive response. Si treatment reduced powdery mildew development by inducing host defence responses and can therefore be used as an effective eco‐friendly disease control measure.     

Microscopic detection of reactive oxygen species generation in the compatible and incompatible interactions of Alternaria alternata Japanese pear pathotype and host plants

 Reactive oxygen species (ROS) generation was examined in the interaction of Alternaria alternata Japanese pear pathotype and host plants using three methods: nitro blue tetrazolium (NBT) method for microscopic detection of O₂ ⁻, diaminobenzidine (DAB) methods for microscopic detection of H₂O₂, and cerium chloride methods for ultrastructural detection of H₂O₂. ROS generation was detected by NBT and DAB methods at appressoria on leaves of susceptible cultivars and heat-shocked leaves of resistant cultivars but not in leaves of resistant cultivars. Ultrastructural detection by the cerium chloride method identified ROS generation at cell walls of appressoria and penetration pegs in susceptible, resistant leaves and heat-shocked leaves. These differences in the ultrastructural and microscopic data in resistant areas were due to the restriction of ROS generation in limited areas, the side facing the plant surface, of appressoria and penetration pegs. Therefore, ROS generation was apparently induced regardless of the resistance or susceptibility of the cultivar with the difference being in the volumes generated. After evaluating the pathological role of ROS generation in fungal structures, such generation was found to be associated with early penetration of cell walls in pear plants. Additionally, ROS generation in plants was also found in degrading pectin layers near infected hyphae and in plasma membrane modification sites in susceptible leaves but not in resistant leaves. ROS generation in susceptible leaves might be accompanied with plasma membrane damage, although the role of ROS generation in the pectin layers is not clear. ROS generation in both fungal and plant cells during their interaction was likely associated with the expression of susceptibility. Received: June 3, 2002 / Accepted: July 31, 2002