Occurrence and inheritance of resistance to powdery mildew (Oidium lycopersici) in Lycopersicon species

Among 146 accessions of Lycopersicon pimpinellifolium , 132 of L. esculentum var. cerasiforme and 53 of L. peruvianum screened for resistance to powdery mildew, caused by Oidium lycopersici , a wide variation in reactions was found. Two plants of L. esculentum var. cerasiforme accession LA-1230 were resistant. One resistant symptomless plant of accession LA-1230, designated LC-95, produced homozygous resistant progenies. LC-95 was crossed with cv. Marmande (susceptible parent) and F₁, F₂ and backcrosses to the resistant and the susceptible parents were derived. These genotypes were grown in glasshouses at 23°C and 95–100% RH and inoculated with O. lycopersici . The F₁ plants were susceptible. F₂ and backcross segregations fitted the hypothesis of a single recessive gene which is here designated ol-2 .     

Selection of virulent populations of Meloidogyne javanica by repeated cultivation of Mi resistance gene tomato rootstocks under field conditions

Field trials were conducted in a plastic house artificially infested with an avirulent population of Meloidogyne javanica to determine the durability of the resistance mediated by the Mi gene in tomato rootstocks after repeated cultivation for three consecutive years. Treatments included an experimental rootstock cv. PG76 ( Solanum lycopersicum  ×  Solanum sp.), a commercial rootstock cv. Brigeor ( S. lycopersicum  ×  S. habrochaites ), a resistant tomato cv. Monika ( S. lycopersicum ), and a susceptible cv. Durinta ( S. lycopersicum ). Based on the reproduction index (RI: number of eggs per g root on the resistant cultivar divided by number of eggs per g root on the susceptible cultivar × 100), rootstock cv. PG76 responded as highly resistant (RI = 7%) after the first cropping cycle (3·4 nematode generations), showed intermediated resistance (RI = 33%) after the second cropping cycle (3·3 generations), and was fully susceptible (RI = 94%) after the third cycle (3·3 generations). In contrast, rootstock cv. Brigeor and resistant cv. Monika retained intermediate resistance levels (RI = 41 and 25%, respectively) after the third cropping cycle. Virulent nematode populations were rapidly selected from an avirulent one after repeated cultivation of resistant tomatoes under field conditions. Bioassays conducted under controlled conditions confirmed that selection for virulence occurred more rapidly in plots with cv. PG76 followed by Brigeor and Monika. The nematode population in the field not exposed to Mi resistance remained avirulent to Mi genotypes. The genetic background of the resistant rootstocks and the frequency of cropping were critical factors for the appearance of virulent nematode populations. Irrespective of nematode infection, all resistant tomatoes yielded more than the susceptible cultivar.     

Influence of drought, salt stress and abscisic acid on the resistance of tomato to Botrytis cinerea and Oidium neolycopersici

Abiotic stress may affect plant response to pathogen attack through induced alterations in growth regulator and gene expression. Abscisic acid (ABA) mediates several plant responses to abiotic stress. The effects of drought, salt stress and ABA on the interaction of tomato ( Lycopersicon esculentum ) with the biotrophic fungus Oidium neolycopersici and the necrotrophic fungus Botrytis cinerea were investigated. Drought stress resulted in a twofold increase in endogenous ABA as well as a 50% reduction in B. cinerea infection and a significant suppression of O. neolycopersici on tomato cv. Moneymaker. Salt stress did not affect B. cinerea infection, but significantly reduced infection by O. neolycopersici , with no obvious increase in endogenous ABA. Compared with the wild type, the ABA-deficient sitiens mutant was more resistant to O. neolycopersici and B. cinerea . Exogenous ABA resulted in increased susceptibility of sitiens to both pathogens, but did not increase the basal susceptibility of wild-type plants. It is concluded that, in tomato, drought and salt stress stimulate different, but possibly overlapping, pathogen-defence pathways which may not necessarily involve ABA. Meanwhile, basal endogenous ABA levels suppress the resistance of tomato to O. neolycopersici and B. cinerea , but an ABA increase above the basal level, resulting from exogenous application, does not increase susceptibility to these pathogens.     

Biochemical aspects of reactive oxygen species formation in the interaction between Lycopersicon spp. and Oidium neolycopersici

Three Lycopersicon spp. accessions differing in the level of resistance to Oidium neolycopersici L. Kiss (tomato powdery mildew) were studied. Defence reactions occurring in tissue of Lycopersicon esculentum cv. Amateur (susceptible control), Lycopersicon hirsutum f. glabratum (LA 2128) (highly resistant) and Lycopersicon chmielewskii (LA 2663) (moderately resistant) were investigated during the first 120 h post-inoculation (hpi). A hypersensitive reaction was detected after 48 hpi in both resistant tomato accessions. Changes in accumulation of hydrogen peroxide and enzymes involved in its metabolism (catalase, peroxidases, superoxide dismutase) were monitored. In resistant accessions, intensive H₂O₂ production correlated with increased activity of cytosolic guaiacol peroxidase, syringaldazine peroxidase and ascorbate peroxidase. Catalase activity increased especially in moderately resistant L. chmielewskii. A similar degree of lipid peroxidation occurred in all Lycopersicon accessions. An increase in the concentration of free phenols but no change in the level of cell-wall-bound phenols were observed during the first 120 hpi in all Lycopersicon spp. accessions. Spermidine represented the major part of the total polyamine content. Pathogen-induced lignification was not observed in any of the studied accessions.     

The haustorial interface in a resistant interaction of Erysiphe pisi with Pisum sativum

The interface between Erysiphe pisi and pea cv. JI 1049 was studied at the ultrastructural and cytochemical levels and compared with those in two susceptible cultivars. Haustorial efficiencies, as indexed by the length of mycelium associated with each haustorium, and growth rates on the resistant and one susceptible cultivar were also compared.The interaction in the resistant cultivar differed from those in the susceptible cultivars in the following ways: (i) there was no contact between the host plasmalemma and the A neckband region; (ii) papillae were contiguous with the surface of the neck and thus were probably formed before haustoria and (iii) there appeared to be less polysaccharide in the extrahaustorial membrane. The extrahaustorial membrane in the resistant cultivar lacked ATPase activity, whereas the rest of the host plasmamembrane had normal activity.Each haustorium supported a significantly greater total hyphal length in the resistant than in the susceptible cultivars. Growth rates of superficial hyphae were very similar on the susceptible and resistant cultivars but there was a delay in the onset on hyphal growth on the resistant cultivar which correlated with the previously reported delay in formation of the first haustorium. In contrast to hyphal growth rates, the rate of haustorium production was significantly less in the resistant cultivar. It is proposed that resistance in cv. JI 1049 operates at the stages prior to haustorium formation, similarly to that in some non-host and partial resistance systems. Once formed, however, the function of the haustorium seems to be unimpaired, despite the observed interfacial differences.     

Sources of verticillium wilt resistance in wild olive germplasm from the Mediterranean region

Fifty-seven wild olive accessions collected from the Mediterranean basin were screened under greenhouse conditions for their resistance to verticillium wilt. Plants were root-dip inoculated. One defoliating and one non-defoliating isolate of Verticillium dahliae , both obtained from diseased plants in southern Italy, were used. Plants of the highly susceptible cv. Cima di Mola, frequently used as a rootstock in Apulia, were also included in this test. Disease reactions were evaluated on the basis of external symptoms, vascular browning and by calculating areas under disease progress curves ( audpc ). On the basis of audpc values and external symptom severity, accessions were grouped into four phenotypic groups: highly resistant, moderately resistant, susceptible and highly susceptible. Three accessions showed high resistance to both V. dahliae pathotypes. Forty resistant plants were selected from accessions that had shown the highest levels of resistance. Clones were obtained from each of these plants by in vitro micropropagation for further testing. Ten clones showed the resistance characteristics of their original mother plants, while others suffered greater levels of disease severity than their mother plants. Several new olive rootstocks were identified that were highly resistant to verticillium wilt and could be included in breeding programmes for resistance of olive to V. dahliae .     

Characterization of Resistance Mechanisms to Erysiphe pisi in Medicago truncatula

ABSTRACT In this work, we studied the resistance of 277 Medicago truncatula accessions against powdery mildew and further characterized the defense mechanisms of resistant plants. Ten resistant accessions were selected according to macroscopic assessment. Histological studies showed a range of defense mechanisms, acting alone or combined, that impeded fungal development at different stages. Some accessions allowed a reduced spore germination frequency compared with that of the susceptible control. In others, the fungus was arrested at penetration stage due to papilla formation. Epidermal cells of several accessions were penetrated by the fungus but then hypersensitive response (HR) leading to cell death hampered fungal development. In some cases, cell death was very fast and no haustorium could be observed in epidermal cells, whereas in others, haustoria and secondary hyphae indicated a slow HR. Finally, in some accessions in which no HR was observed, colony growth was restricted through posthaustorial defense mechanisms. Characterization of defense mechanisms will be useful for further cellular and molecular studies to unravel the bases of resistance in this species in particular and in legume-powdery mildew interaction in general.     

The salicylic acid-dependent defence pathway is effective against different pathogens in tomato and tobacco

The role of salicylic acid (SA) was investigated in basal defence and induced resistance to powdery mildew ( Oidium neolycopersici ) and grey mould ( Botrytis cinerea ) in tomato ( Lycopersicon esculentum ) and tobacco ( Nicotiana tabacum ). A comparison of NahG transgenic tomato and tobacco (unable to accumulate SA) to their respective wild types revealed that in tomato, SA was not involved in basal defence against O. neolycopersici but NahG tobacco showed an enhanced susceptibility to O. neolycopersici infection, the effect becoming more obvious as the plants grew older. In contrast, SA played no role in the basal defence of tobacco against B. cinerea , but seemed to contribute to basal defence of tomato against B. cinerea. Activation of the SA-dependent defence pathway via benzothiadiazole (BTH) resulted in induced resistance against O. neolycopersici in tobacco but not in tomato. Microscopic analysis revealed that BTH treatment could prevent penetration of the Oidium germ tube through tobacco leaves, whereas penetration was successful on tomato leaves irrespective of BTH treatment. In contrast, soil or leaf treatment with BTH induced resistance against B. cinerea in tomato but not in tobacco. It is concluded that the SA-dependent defence pathway is effective against different pathogens in tomato and tobacco.     

Systemic Potato virus YNTN infection and levels of salicylic and gentisic acids in different potato genotypes

Endogenous levels of free and conjugated salicylic (SA) and gentisic (GA) acids, both putative signal molecules in plant defence, were analysed in order to investigate their involvement in the resistance of four potato ( Solanum tuberosum ) genotypes with different susceptibilities to Potato virus Y^NTN (PVY^NTN) infection: the highly susceptible cv. Igor and its extremely resistant transgenic line, the extremely resistant cv. Sante and the tolerant cv. Pentland Squire. The lowest levels of free and conjugated SA were observed in the extremely resistant cv. Sante, while free GA, which was detected in all the other varieties, was absent. The extremely resistant transgenic cv. Igor contained the highest basal total SA level and the lowest level of total GA of all four cultivars. In susceptible cv. Igor, but not in resistant transgenic cv. Igor, a systemic increase of free SA was measured 1 day postinfection (dpi). Even more significant increases of free and conjugated SA and GA were detected 11 dpi when systemic symptoms appeared. In inoculated but not in upper noninoculated leaves of resistant transgenic cv. Igor, significant increase of SA conjugates occurred, but not before 11 dpi. The increase of SA and GA in susceptible cv. Igor could contribute to the general elevated levels of phenolic compounds as a response to stress caused by virus infection. It appears that basal levels of SA and GA do not correlate with resistance to PVY^NTN in potato plants.     

Resistance to <Emphasis Type="Italic">Rice yellow mottle virus</Emphasis> in rice germplasm in Madagascar

Rice yellow mottle virus (RYMV) is a recent and major threat to rice production in Madagascar. A large scale screening of resistance to RYMV in rice germplasm in Madagascar was conducted by visual symptom scoring and virus-assessment through ELISA tests. The response to virus inoculation of 503 local or introduced rice accessions was assessed. Most of them were susceptible to RYMV. A few cultivars expressed partial resistance at a level similar to the partially resistant Oryza sativa japonica cv. Azucena. Only one O. sativa cultivar expressed high resistance characterised by a lack of symptoms and an undetectable level of virus. It was a Malagasy traditional indica cultivar, named Bekarosaka, which originated from the northwest of the country. It was selected by farmers for its field resistance to RYMV. The response of cv. Bekarosaka to four pathotypes of RYMV was similar to that of cv. Gigante, the only other highly resistant indica cultivar. The sequence of the middle domain of the eIF(iso)4G, the genetic determinant of Rymv1 resistance on chromosome 4, of cv. Bekarosaka was similar to that of cv. Gigante. Subsequently, cvs Bekarosaka and Gigante probably carried the same resistance allele Rymv1-2. Rymv1-2 resistance was efficient against isolates of the major strains of RYMV, but was readily overcome by a pathotype from the northwest of Madagascar.     

Interaction between powdery mildew and barley with mlo5 mildew resistance

Powdery mildew infection of barley with the mlo5 barley powdery mildew resistance gene was examined, using near-isogenic barley lines, with and without mlo5 resistance, and two near-isogenic powdery mildew isolates, HL3/5 and GE3 with high (virulent) or low (avirulent) penetration efficiency on the resistant barley line. In all isolate–host combinations (except GE3 on the resistant barley line), frequency of haustorium formation increased significantly from zero at 11 h after inoculation to a maximum by 13 h, and there was no subsequent increase up to 24 h. In the susceptible barley line, 27% of appressoria from both isolates formed haustoria. Although this was significantly higher than the frequency of haustorium formation (18%) of HL3/5 on the resistant barley line, HL3/5 was much more successful than GE3 (frequency of haustorium formation less than 1%). The fact that HL3/5 did not possess a generally higher ability to penetrate successfully to form haustoria on the susceptible barley line, indicates that HL3/5 did not overcome the mlo5 resistance by being generally more vigorous. In the resistant barley line, papillae were larger than in the susceptible line; however, both isolates were associated with papillae of the same diameter at the time of penetration. We suggest that the mlo5 resistant barley line confers two different forms of resistance: isolate-specific and isolate-nonspecific.     

Host Range of Oidium lycopersici Occurring in the Netherlands

Nine accessions of three cucurbit species, ten of eight legume species, three of lettuce (Lactuca sativa) and 34 of 14 Solanaceae species were inoculated with a Dutch isolate of the tomato powdery mildew fungus (Oidium lycopersici) to determine its host range. Macroscopically, no fungal growth was visible on sweet pepper (Capsicum annuum), lettuce, petunia (Petunia spp.) and most legume species (Lupinus albus, L. luteus, L. mutabilis, Phaseolus vulgaris, Vicia faba, Vigna radiata, V. unguiculata). Trace infection was occasionally observed on melon (Cucumis melo), cucumber (Cucumis sativus), courgette (Cucurbita pepo), pea (Pisum sativum) and Solanum dulcamara. Eggplant (Solanum melongena), the cultivated potato (Solanum tuberosum) and three wild potato species (Solanum albicans, S. acaule and S. mochiquense) were more heavily infected in comparison with melon, cucumber, courgette, pea and S. dulcamara, but the fungus could not be maintained on these hosts. All seven tobacco (Nicotiana tabacum) accessions were as susceptible to O. lycopersici as tomato (Lycopersicon esculentum cv Moneymaker), suggesting that tobacco is an alternative host. This host range of the tomato powdery mildew differs from that reported in some other countries, which also varied among each other, suggesting that the causal agent of tomato powdery mildew in the Netherlands differ from that in those countries. Histological observations on 36 accessions showed that the defense to O. lycopersici was associated with a posthaustorial hypersensitive response.     

Differences in the responses of melon accessions to fusarium root and stem rot and their colonization by Fusarium oxysporum f. sp. radicis‐cucumerinum

Fusarium root and stem rot caused by the fungus Fusarium oxysporum f. sp. radicis‐cucumerinum is a major disease in greenhouse cucumbers. Over the past decade, the disease has been documented in melon greenhouses in Greece, and recently it has been sporadically recorded in greenhouse melons in Israel. Variations in disease response were found among 41 melon accessions artificially inoculated with the pathogen: 10 accessions were highly susceptible (90–100% mortality), 23 exhibited an intermediate response (20–86%) and eight were resistant (0–4%). Two melon accessions – HEM (highly resistant) and TAD (partially resistant) – were crossed with the susceptible accession DUL. The responses of the three accessions and F₁ crosses between the resistant and susceptible parents were evaluated. HEM contributed higher resistance to the F₁ hybrid than TAD. Roots of susceptible and resistant accessions were 100 and 79% colonized, respectively, following artificial inoculation. However, only susceptible plants showed colonization of the upper plant tissues. Microscopic evaluation of cross sections taken from the crown region of the susceptible DUL revealed profuse fungal growth in the intercellular spaces of the parenchyma and in xylem vessels. In the resistant cultivar HEM, very little fungal growth was detected in the intercellular spaces of the parenchyma, and none in the xylem or any other vascular tissue. Finding resistant accessions may create an opportunity to study the genetics of resistance inheritance and to develop molecular markers that will facilitate breeding resistant melon cultivars.     

Identification of Lentil Germ Plasm Resistant to Colletotrichum truncatum and Characterization of Two Pathogen Races

ABSTRACT A total of 1,771 lentil accessions from the U.S. lentil collection (U.S. Department of Agriculture-Agricultural Research Service, Pullman, WA) and the Institut für Pflanzengenetik und Kulturpflanzenforschung (Gatersleben, Germany) were screened for resistance to Colletotrichum truncatum, the cause of anthracnose. About 95% of the accessions were susceptible when inoculated with a single isolate in the field. Retesting, under controlled conditions, of accessions rated as resistant or moderately resistant in the field resulted in identification of anthracnose resistance in four accessions from the U.S. collection (PI 320937, PI 320952 [cv. Indianhead], PI 345629, and 468901), and 12 accessions from the German collection (Lens 3, 102, 104, 106, 107, 119, 122, 134, 135, 177, 195, and 209). Seven of the accessions were used as host differentials to characterize pathogenic variability of 50 single-spore isolates collected in Manitoba and Saskatchewan, Canada. The presence of two distinct races was demonstrated. Isolates of C. truncatum avirulent on cv. Indianhead, PI 320937, PI 345629, PI 468901, Lens 102, Lens 104, and Lens 195 were designated race Ct1. Isolates that were virulent on these seven entries were designated race Ct0, indicating their lack of avirulence genes. Race Ct0 was isolated more frequently from commercial seed samples than race Ct1, but the two races were isolated with similar frequency from plants in commercial fields planted to susceptible cultivars. Race Ct0, to which no resistance has yet been identified, presents a high risk to lentil production in Canada and potentially worldwide.     

Response of Cucurbita spp. to tomato leaf curl New Delhi virus inoculation and identification of a dominant source of resistance in Cucurbita moschata

Tomato leaf curl New Delhi virus is an emerging whitefly-borne species of begomovirus in Mediterranean regions that poses a severe threat to cucurbit crops of the genus Cucurbita. Until now, only two sources of resistance have been identified in Cucurbita spp., these being PI604506 (cv. Large Cheese) and PI381814 (Indian landrace), both of C. moschata. The resistance of cv. Large Cheese is conferred by a single recessive gene located on chromosome 8. The objective of the present investigation was to screen for tomato leaf curl New Delhi virus (ToLCNDV) resistance among 105 accessions drawn from five species of Cucurbita and, if high resistance was found in any of them, determine the mode of inheritance. Screening was conducted using whitefly-mediated inoculation on all 105 accessions. The accessions showing some resistance were further screened by mechanical inoculation as well as by quantitative PCR-based diagnostics. The results showed that, overall, the accessions of C. pepo and C. maxima were the most susceptible, those of C. argyrosperma and C. ecuadorensis intermediate, and those of C. moschata most resistant to ToLCNDV. Only one accession of C. moschata, BSUAL-252, originating from Japan, was highly resistant to ToLCNDV, showing no symptoms after either method of inoculation, and absence of virus accumulation. Upon crossing BSUAL-252 with a susceptible accession of C. moschata, BSUAL-265, the resistance was observed to be conferred by a single dominant gene. This gene is not linked to the genomic region on chromosome 8 where the locus of the previously identified recessive gene for ToLCNDV resistance resides.     

Characterization of acetolactate synthase from sulfonylurea herbicide‐resistant Schoenoplectus juncoides

Ten accessions of sulfonylurea‐resistant Schoenoplectus juncoides were collected from paddy fields in Japan. In order to characterize acetolactate synthase from sulfonylurea‐resistant S. juncoides, acetolactate synthase amino acid substitutions, whole‐plant growth inhibition and acetolactate synthase enzyme inhibition were examined. Schoenoplectus juncoides has two acetolactate synthase genes (ALS1 and ALS2). The sulfonylurea‐resistant accessions harbored amino acid substitutions at Pro197 or Trp574 in either ALS1 or ALS2 (the amino acid number is standardized to the Arabidopsis thaliana sequence). The whole plants of all the sulfonylurea‐resistant accessions showed resistance to imazosulfuron. The resistance level depended on the altered amino acid residues in acetolactate synthase. The acetolactate synthase enzyme that was partially purified from all the sulfonylurea‐resistant accessions was less sensitive to imazosulfuron, compared to the susceptible accession, suggesting that the resistance is related to the altered acetolactate synthase enzyme. In addition, the concentration–response inhibition of acetolactate synthase activity by imazosulfuron in the sulfonylurea‐resistant accessions was remarkably different with the presence of an amino acid substitution in either ALS1 or ALS2. Furthermore, the concentration–response inhibition of acetolactate synthase activity in the sulfonylurea‐resistant accessions with a P197S, P197T or W574L mutation showed a double‐sigmoid curve. The regression analysis of enzyme inhibition suggested that the abundance ratio of ALS1 to ALS2 enzymes was approximately 70:30%, with a range of ±15%. Taken together, these results suggest that the resistance of sulfonylurea‐resistant accessions of S. juncoides is related to altered acetolactate synthase in either ALS1 or ALS2, although the abundance of the altered acetolactate synthase in the plants is different among the sulfonylurea‐resistant accessions.     

Resistance to Botrytis cinerea in Solanum lycopersicoides is Dominant in Hybrids with Tomato, and Involves induced Hyphal Death

Botrytis cinerea causes gray mold disease and affects hundreds of plant species, including tomato (Lycopersicon esculentum). The wild nightshade, Solanum lycopersicoides, is cross compatible with tomato and is more resistant to B. cinerea, thus representing a potential source for crop improvement. Tests involving droplet inoculation of detached leaves and spray inoculation of entire seedlings demonstrated that resistance to B. cinerea varies among S. lycopersicoides accessions, with S. lycopersicoides LA2951 being the most resistant accession tested. Expression of resistance in the intergeneric hybrid (L. esculentum cv. 'VF36' × S. lycopersicoides LA2951) suggested that resistance is at least partially dominant in tomato. A green fluorescent protein-tagged B. cinerea strain was used for confocal microscopic comparison of infection in leaves of S. lycopersicoides and tomato. Even though S. lycopersicoides supported spore germination, there was evidence for hyphal lysis and death 3 days after inoculation, at a time when lesions were expanding on susceptible tomato plants. The reduced frequency of B. cinerea lesion spread on S. lycopersicoides explains why this fungus produced fewer spores in this wild nightshade than in tomato.     

Tomato Breeding Lines Resistant and Tolerant to Tomato Yellow Leaf Curl Virus Issued from Lycopersicon hirsutum

ABSTRACT Two tomato yellow leaf curl virus (TYLCV)-resistant plants from accessions LA1777 and LA386 of the wild tomato species Lycopersicon hirsutum have been crossed. The resulting resistant F1 plants were crossed with the domesticated tomato L. esculentum, and a series of selfing was performed. At each generation, individuals were selected for resistance (no symptoms and undetectable viral DNA) and tolerance (no symptoms but with detectable viral DNA) following controlled massive and repeated inoculations with viruliferous whiteflies. A stable BC1F4 line (denominated 902) that does not segregate for resistance was obtained. This line does not support virus accumulation, even upon extensive whitefly-mediated inoculation of young seedlings, and does not need protection with nets or insecticides. Another stable BC1F4 line (denominated 908) was tolerant to the virus. Both lines have good horticultural characteristics and bear 80- to 120-g red fruits. Analysis of segregation of susceptibility, tolerance, and resistance during the BC1F1 to BC1F4 crosses indicated that tolerance is controlled by a dominant major gene and resistance by two to three additive recessive genes. The resistant and tolerant lines do not need to be protected by insecticides or nets.     

Induction of transient ethylene and reduction in severity of tomato bacterial wilt by Pythium oligandrum

Pythium oligandrum (PO) is a mycoparasite on a wide range of fungi and suppresses diseases caused by fungal pathogens when colonizing the rhizosphere. PO and its cell wall proteins (CWPs) have elicitor activity that induces defence responses in plants. The potential of a mycelial homogenate of PO to suppress bacterial diseases was studied in roots of tomato ( Lycopersicon esculentum cv. Micro-Tom) inoculated with Ralstonia solanacearum . PO-treated plants showed enhanced resistance to R. solanacearum and reduction in severity of wilt symptoms. As ethylene often acts as one of the signal molecules for induced resistance, its production following treatment of tomato roots with the mycelial homogenate or CWP of PO was measured. The level of ethylene in PO- and CWP-treated plants was transiently elevated six- to 11-fold at 4–8 h after treatment, followed by high expression of three basic ethylene-inducible defence-related genes ( PR-2b , PR-3b and PR-5b ). Analysis of PR-5b gene expression in the leaves of PO- and CWP-treated plants suggested that PR gene expression was induced systemically. The expression of LeERF2 and LeETR4 , which confer an ethylene-dependent signalling pathway, was also significantly accelerated by such treatments. These results indicate that PO has the potential to control bacterial wilt disease and that CWP may play an important role in the induction of resistance to R. solanacearum accompanying the activation of the ethylene-dependent signalling pathway.