Resistance response of the tomato rootstock SC 6301 to <Emphasis Type="Italic">Meloidogyne javanica</Emphasis> in a plastic house

Nematode reproduction on the nematode-susceptible tomato cv. Durinta grafted onto the Mi-resistance gene tomato rootstock SC 6301 was compared to the Mi-resistance gene tomato cv. Monika in a plastic house infested with Meloidogyne javanica. The ungrafted susceptible cv. Durinta was included as a control for reference. Final soil population densities were lower (P ≤ 0.05) on the resistant than susceptible cultivar but intermediate values were recorded on the rootstock SC 6301. The lowest numbers of eggs per gram root were recorded on the resistant cultivar followed by those on the rootstock; in both cases, they were lower (P < 0.05) than on the susceptible control. Cumulative yield (kilogram per square meter) was higher (P < 0.05) on the resistant than susceptible cultivar whether or not it had been grafted. The rootstock SC 6301 provided an intermediate resistance response to M. javanica and was less effective than the resistant cultivar in suppressing nematode populations and plant damage under the experimental conditions of this study.     

Quantitative approach for the early detection of selection for virulence of Meloidogyne incognita on resistant tomato in plastic greenhouses

Resistant tomato cultivars are an important tool to control Meloidogyne spp., which cause the highest yield losses attributed to plant‐parasitic nematodes. However, the repeated cultivation of Mi resistant cultivars can select virulent populations. In the present study, the susceptible tomato cv. Durinta and the resistant cv. Monika were cultivated from March to July in a plastic greenhouse for 3 years to determine the maximum multiplication rate, maximum nematode density, equilibrium density, relative susceptibility and population growth rate of M. incognita; these were used as proxy indicators of virulence and yield losses. The values of population dynamics and growth rate on the resistant tomato increased year by year and were higher when it was repeatedly cultivated in the same plot compared to when it was alternated with the susceptible cultivar and the level of resistance decreased from very to moderately resistant. The relationship between the nematode density at transplanting (P_i) and the relative yield of tomato fitted to the Seinhorst damage model for susceptible, but not resistant, cultivars. The tolerance limit and the relative minimum yield were 2–4 J2 per 250 cm³ of soil and 0.44–0.48, respectively. The tomato yield did not differ between cultivars at low P_i, but it did at higher P_i values, at which the resistant yielded 50% more than the susceptible. This study demonstrates the utility of population dynamics parameters for the early detection of selection for virulence in Meloidogyne spp., and that three consecutive years were not sufficient to select for a completely virulent population.     

Analysis of head and leaf reaction towards <Emphasis Type="Italic">Microdochium nivale</Emphasis>

This research examined the variation in the response of eight commercial wheat cultivars to Microdochium nivale isolates using both in vivo FHB tests (AUDPC and RHW measurements) and in vitro detached leaf assays (LGR). Irrespective of fungal variety, the two Italian cvs Fortore and Norba exhibited the greatest amount of visual disease symptoms (mean AUDPC=2.2 and 2.3, respectively), being significantly more susceptible than the other six cultivars (AUDPC 1.24) (P < 0.05). Irrespective of fungal variety, the Italian cv. Norba and the Irish cv. Falstaff were more susceptible than the other cultivars (except Fatima 2) in terms of RHW (P < 0.05), while the cvs Fortore, GK Othalom and Consort were more resistant than the other five cultivars (P < 0.05). In the detached leaf assay, the Hungarian cv. GK Othalom and the Italian cv. Norba were more susceptible (mean LGR=0.79 and 0.81 mm day^–1, respectively) to M. nivalethan the other six cultivars (mean LGR=0.51–0.72) (P < 0.05). Analysis of the relationship between head and leaf reaction to M. nivaleinfection revealed no significant correlation.     

Resistance of wheat to Mycosphaerella graminicola involves early and late peaks of gene expression

Large-scale cDNA-AFLP profiling identified numerous genes with increased expression during the resistance response of wheat to the Septoria tritici blotch fungus, Mycosphaerella graminicola. To test whether these genes were associated with resistance responses, primers were designed for the 14 that were most strongly up-regulated, and their levels of expression were measured at 12 time points from 0 to 27 days after inoculation (DAI) in two resistant and two susceptible cultivars of wheat by real-time quantitative polymerase chain reaction. None of these genes was expressed constitutively in the resistant wheat cultivars. Instead, infection of wheat by M. graminicola induced changes in expression of each gene in both resistant and susceptible cultivars over time. The four genes chitinase, phenylalanine ammonia lyase, pathogenesis-related protein PR-1, and peroxidase were induced from about 10- to 60-fold at early stages (3 h–1 DAI) during the incompatible interactions but were not expressed at later time points. Nine other genes (ATPase, brassinosteroid-6-oxidase, peptidylprolyl isomerase, peroxidase 2, 40S ribosomal protein, ADP-glucose pyrophosphorylase, putative protease inhibitor, methionine sulfoxide reductase, and an RNase S-like protein precursor) had bimodal patterns with both early (1–3 DAI) and late (12–24 DAI) peaks of expression in at least one of the resistant cultivars, but low if any induction in the two susceptible cultivars. The remaining gene (a serine carboxypeptidase) had a trimodal pattern of expression in the resistant cultivar Tadinia. These results indicate that the resistance response of wheat to M. graminicola is not completed during the first 24 h after contact with the pathogen, as thought previously, but instead can extend into the period from 18 to 24 DAI when fungal growth increases dramatically in compatible interactions. Many of these genes have a possible function in signal transduction or possibly as regulatory elements. Expression of the PR-1 gene at 12 h after inoculation was much higher in resistant compared to susceptible recombinant-inbred lines (RILs) segregating for the Stb4 and Stb8 genes for resistance. Therefore, analysis of gene expression could provide a faster method for separating resistant from susceptible lines in research programs. Significant differential expression patterns of the defense-related genes between the resistant and susceptible wheat cultivars and RILs after inoculation with M. graminicola suggest that these genes may play a major role in the resistance mechanisms of wheat.     

Regulation of defense-related enzymes associated with bacterial spot resistance in Tomato

Twenty tomato (Solanum lycopersicon) cultivars were screened for resistance against bacterial spot disease incited byXanthomonas axonopodis pv.vesicatoria under field conditions with and without pathogen infection. Screening was done by artificially inoculating aX. axonopodis pv.vesicatoria suspension to 4-week-old tomato seedlings and observing them for typical symptoms of the disease. Seedlings were categorized into highly resistant, resistant, susceptible and highly susceptible cultivars on the basis of disease incidence. Tomato cultivars were screened for defense-related enzymes, total phenols and lignin contents. The temporal patterns of all these enzymes were estimated with a moderately susceptible tomato cultivar. Native PAGE analysis of both peroxidase (POX) and polyphenol oxidase (PPO) was carried out for the time course of enzyme activities and also by selecting three different tomato cultivars, following infection with the pathogen. Based on the inducible amounts of these enzymes upon pathogen infection, the tomato cultivars were correlated with the disease incidence under field conditions. A significant (P≤0.05) correlation was observed between the degree of host resistance and the enzyme levels. In highly resistant tomato cultivars the enzyme levels, total phenols and lignin contents were increased in comparison with highly susceptible tomato cultivars. Isoform analysis of POX and PPO enzymes indicated a clear difference between resistant and susceptible tomato cultivars in the number of isoforms and also in the intensity of each isoform in the presence of pathogen infection. The possible regulation of defense-related enzymes in imparting host resistance is discussed. http://www.phytoparasitica.org posting March 11, 2008.     

Infectivity of a Japanese isolate of <Emphasis Type="Italic">Oidium neolycopersici</Emphasis> KTP-01 to a European tomato cultivar resistant to <Emphasis Type="Italic">O. lycopersici</Emphasis>

The infectivity of a Japanese isolate of tomato powdery mildew, Oidium neolycopersici KTP-01, to tomato cultivars was examined using a resistant cultivar Grace bred in The Netherlands to O. lycopersici, which was recently proposed to be renamed O. neolycopersici. Grace was severely infected with KTP-01, and its susceptibility was similar to that on susceptible tomato cultivars Moneymaker and Ponderosa, suggesting that KTP-01 differs in pathogenicity on tomatoes from those of European and American isolates.     

Significance of PWT4–Rwt4 interaction in the species specificity of Avena isolates of Magnaporthe oryzae on wheat

We examined whether PWT4, an avirulence gene of Avena isolates of Magnaporthe oryzae toward wheat, corresponded to Rwt4, a resistance gene identified in wheat cultivar Norin 4, in a one-to-one manner. Twelve wheat cultivars were inoculated with 65X1, an F₁ culture with PWT4 derived from a cross between an Avena isolate (Br58) and a Triticum isolate (Br48). Three wheat cultivars (Norin 26, Shin-chunaga, Cheyenne) were resistant and therefore selected as possible carriers of Rwt4. The three cultivars were then inoculated with a population derived from a backcross of 61M2 carrying PWT4 with Br48 carrying pwt4. Segregation analyses revealed that PWT4 operates against the three cultivars. If PWT4 corresponds to Rwt4 in a one-to-one manner, all three cultivars should carry Rwt4. To test if this is the case, the three cultivars were crossed with Chinese Spring (a noncarrier of Rwt4) and Norin 4. When F₂ seedlings from Chinese Spring × Norin 26, Chinese Spring × Shin-chunaga, and Chinese Spring × Cheyenne were inoculated with 61M2, resistant and susceptible seedlings segregated in a 3 : 1 ratio. On the other hand, crosses between the three cultivars and Norin 4 yielded no susceptible F₂ seedlings. These results indicate that all three cultivars carry Rwt4. Considering all results, we concluded that PWT4 corresponds to Rwt4 in a one-to-one manner. An inoculation test with Chinese Spring–Cheyenne chromosome substitution lines indicated that Rwt4 is located on chromosome 1D.     

Ultrastructural and immunocytochemical investigation of pathogen development and host responses in resistant and susceptible wheat spikes infected by Fusarium culmorum

Pathogen development and host responses in wheat spikes of resistant and susceptible cultivars infected by Fusarium culmorum causing Fusarium head blight (FHB), were investigated by means of electron microscopy as well as immunogold labelling techniques. The studies revealed similarities in the infection process and the initial spreading of the pathogen in wheat spikes between resistant and susceptible cultivars. However, the pathogen’s development was obviously more slow in the resistant cultivars as in comparison to a susceptible one. The structural defence reactions such as the formation of thick layered appositions and large papillae were essentially more pronounced in the infected host tissues of the resistant cultivars, than in the susceptible one. β -1,3-glucan was detected in the appositions and papillae. Furthermore, immunogold labelling of lignin demonstrated that there were no differences in the lignin contents of the wheat spikes between susceptible and resistant cultivars regarding the uninoculated healthy tissue, but densities of lignin in host cell walls of the infected wheat spikes differed distinctly between resistant and susceptible cultivars. The lignin content in the cell walls of the infected tissues of the susceptible wheat cultivar increased slightly, while the lignin accumulated intensely in the host cell walls of the infected wheat spikes of the resistant cultivars. These findings indicate that lignin accumulation in the infected wheat spikes may play an important role in resistance to the spreading of the pathogen in the host tissues. Immunogold labelling of the Fusarium toxin DON in the infected lemma showed the same labelling patterns in the host tissues of resistant and susceptible cultivars. However, there were distinct differences in the toxin concentration between the tissues of the susceptible and resistant cultivars. At the early stage of infection, the labelling densities for DON in resistant cultivars were significantly lower than those in the susceptible one. The present study indicates that the FHB resistant cultivars are able to develop active defence reactions during infection and spreading of the pathogen in the host tissues. The lower accumulation of the toxin DON in the tissues of the infected spikes of resistant cultivars which results from the host’s defence mechanisms may allow more intensive defence responses to the pathogen by the host.     

Response of tomato rootstocks carrying the <Emphasis Type="Italic">Mi</Emphasis>-resistance gene to populations of <Emphasis Type="Italic">Meloidogyne arenaria,M. incognita and M. javanica</Emphasis>

The response of four Mi-resistance gene tomato rootstocks to seven populations of Meloidogyne was determined in pot tests conducted in a glasshouse. Rootstocks PG76 (Solanum lycopersicum × Solanum sp.) and Brigeor (S. lycopersicum × S. habrochaites) and resistant cv. Monika (S. lycopersicum) were assessed against one population of M. arenaria, three of M. incognita, and three of M. javanica. Rootstocks Beaufort and Maxifort were assessed against one population of M. arenaria, two of M. incognita and two of M. javanica. Rootstock PG76 was highly resistant (reproduction index <10%) to all the populations, whereas rootstock Brigeor and cv. Monika were highly to moderate resistant. Rootstocks Beaufort and Maxifort showed reduced resistance or inability to suppress nematode reproduction, and their responses varied according to the population tested. Beaufort and Maxifort were susceptible to the two populations of M. javanica as Maxifort was to one of M. incognita. The reproduction index of the nematode was higher (P < 0.05) on Maxifort than Beaufort for all root-knot nematode populations.     

Role of stilbenes in the resistance of grapevine to powdery mildew

Stilbene phytoalexins are identified as defence response in pathogen–grapevine interactions, but little information is available on the role of stilbenes on Erysiphe necator, causal agent of grapevine powdery mildew. Analysis of stilbenes in artificially infected leaf discs from susceptible to highly resistant cultivars was performed and compared to the development of the pathogen. Results indicate that stilbene synthesis is confined in infected cells, penetrated by an appressorium–peg. Stilbene amounts expressed by infection site allow discriminating susceptible and resistant cultivars. Highest viniferins concentrations on resistant cultivars are in correspondence with the observed inhibition of the pathogen growth. The analysis of stilbenes at the infection site and viniferins accumulation in grapevine defence reaction is discussed.     

A new aggressive strain of Verticillium albo-atrum in Verticillium resistant cultivars of tomato in the Netherlands

In 1991 serious losses caused byVerticillium wilt were found on two holdings in the Westland glasshouse district in the Netherlands in which theVerticillium resistant tomato cultivars Calypso and Criterium were grown in soilless systems. Isolates from diseased plants were identified asVerticillium albo-atrum.In inoculation experimentsVerticillium resistant tomato cultivars were seriously affected by the new isolates but not by a control isolate. Moneydor, a susceptible cultivar without the Ve gene, was the most seriously diseased by all isolates. The isolates from theVerticillium resistant tomato cultivars were less virulent on the susceptible cultivar than the control isolate.     

Distribution and multiplication of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> in tomato plants with resistance derived from different origins

The distribution and multiplication of Ralstonia solanacearum in tomato plants of 11 resistant cultivars derived from different genetic sources and susceptible cultivar Ponderosa were examined. Bacterial multiplication in stems of resistant tomato plants was suppressed owing to the limitation of pathogen movement from the protoxylem or the primary xylem to other xylem tissues. The limitation was most conspicuous in Hawaii 7996. Grafting experiments indicated that the percentage of wilting of Ponderosa scions was less on Hawaii 7996 rootstocks than that on the most resistant rootstock (LS-89) used in Japan. Hawaii 7996 could be an alternative genetic source for breeding for resistance to bacterial wilt.     

Spread of potato virus Y in potato cultivars (Solanum tuberosum L.) with different levels of sensitivity

The aim of this work was to correlate the appearance of the symptoms, multiplication and spread of virus after mechanical inoculation of potato (Solanum tuberosum L.) cultivars showing different levels of susceptibility and sensitivity to Potato virus Y^NTN (PVY^NTN). The potato cultivars used were the resistant cultivar Sante and susceptible cultivars Igor, Pentland squire and Désirée. The spread of the virus PVY^NTN in infected plants was monitored using different methods: DAS-ELISA, tissue printing, immuno-serological electron microscopy and real-time PCR. In all three susceptible cultivars, the virus was detected in the inoculated leaves 4–5 days after inoculation. From there virus spread rapidly, first into the stem, then more or less simultaneously to the upper leaves and roots. Real-time PCR was shown to be very sensitive and enabled viral RNA to be detected in non-inoculated leaves of susceptible cultivar Igor earlier than other methods. Therefore, for exact studies of plant–virus interaction, a combination of methods which detect viruses on the basis of their different properties (coat protein, morphology or RNA) should be used to monitor the spread of viruses.     

Factors Influencing Transmission of Didymella rabiei (Ascochyta Blight) from Inoculated Seed of Chickpea Under Controlled Conditions

Ascochyta blight of chickpea (Cicer arietinum), caused by the fungus Didymella rabiei, has the potential to cause 100% crop loss in severe epiphytotics. Management of this disease often involves reducing sources of inoculum. The influence of sowing depth, host resistance, seed infection level and soil temperature on disease transmission was investigated in a series of glasshouse and growth room trials using seed artificially inoculated with D. rabiei. A positive correlation (R²=0.9992) was observed between rate of seed infection and the incidence of disease on seedlings. Disease transmission to seedlings was not significantly influenced by sowing depth (1, 3 and 6 cm) in separate trials on two cultivars. Susceptibility of the host showed no obvious influence on the frequency of disease transmission in two trials conducted using four cultivars ranging from highly susceptible to moderately susceptible/moderately resistant. Trials conducted in controlled conditions showed that there was no obvious relationship between soil temperature (5, 9, 14 and 19 °C) and the incidence of disease on seedlings.     

Phytotoxicity on cotton ex-plants of an 18.5 kDa protein from culture filtrates of Verticillium dahliae

A phytotoxic protein that evokes the typical symptoms of Verticillium wilt disease in seedlings of Gossypium hirsutum L. (Upland cotton) was isolated from culture filtrates of Verticillium dahliae. The protein was purified by ammonium sulfate precipitation, Sephadex-G100 fractionation, and native PAGE. The 18.5 kDa protein, designated VD18.5, appears to be a single subunit protein with an isoelectric point between 3 and 5. VD18.5 induces symptoms of leaf dehydration, chlorosis, necrosis and stem discoloration in seedlings of the disease susceptible cotton cultivar Siokra 1–4. The LD₅₀ of VD18.5 on protoplasts of Siokra 1–4 was 18 μg mL⁻¹. VD18.5 had no noticeable effect on Pima S-7, which is a disease resistant cultivar. Phytotoxic activity was partially destroyed at high temperature and was abolished by digestion with proteinase K. Mass spectrometry fingerprinting and protein sequence data from VD18.5 yielded no significant matches when submitted to the Mascot search engine and NCBI non-redundant protein databases, respectively. These results suggest that VD18.5 is a novel protein that may be involved in the development of some of the symptoms associated with Verticillium wilt disease in the cotton plant.     

Variability in infection and reproduction of Meloidogyne javanica on tomato rootstocks with the Mi resistance gene

The response of 10 commercial or experimental tomato rootstocks with the Mi resistance gene to an initial inoculum of a Mi‐avirulent population of Meloidogyne javanica was determined in pot tests conducted in spring and summer. In a field test, the rootstocks were subjected to continuous exposure to high initial population densities (2050 ± 900 second‐stage juveniles (J2) per 250 cm³ soil) of the nematode. The presence of the Mi locus in the resistant rootstocks and cultivars was confirmed using the PCR co‐dominant markers REX‐1 and Mi23. Nematode infectivity (egg masses) and reproduction (eggs g^?1 root) were highly variable in the spring tests. Rootstocks PG76, Gladiator and MKT‐410 consistently responded as highly resistant, with nematode multiplication rate (Pf/Pi) < 1 and reproduction index (RI) < 10%, and they were as efficient as standard resistant tomato cultivars at nematode suppression. The relative resistance levels of rootstocks Brigeor, 42851, 43965, Big Power and He‐Man varied depending on the susceptible standard used for reference or the duration of the test. Rootstocks Beaufort and Maxifort were susceptible to M. javanica (Pf/Pi > 50 and RI > 50%). Rootstocks PG76 and He‐Man, and the resistant tomato cv. Caramba showed high levels of resistance in the test conducted in summer, whereas MKT‐410 and 42851 and the resistant tomato cv. Monika were moderately resistant. In the field, seven rootstocks showed high levels of resistance and one (He‐Man) showed an intermediate level, whereas Beaufort and Maxifort were susceptible.     

Common resistance to different <Emphasis Type="Italic">Fusarium</Emphasis> spp. causing <Emphasis Type="Italic">Fusarium</Emphasis> head blight in wheat

Different sets of wheat genotypes were tested under field conditions by spraying inocula of isolates of seven Fusarium spp. and Microdochium nivale (formerly F. nivale) in the period 1998–2002. The severity of Fusarium head blight (FHB), Fusarium-damaged kernels (FDK), the yield reduction and the deoxynivalenol (DON) contamination were also measured to describe the nature of the resistance. The degrees of FHB severity of genotypes to F. graminearum, F. culmorum, F. avenaceum, F. sporotrichioides, F. poae, F.␣verticillioides, F. sambucinum and M. nivale were very similar, indicating that the resistance to F.␣graminearum was similar to that for other Fusarium spp. listed. This is an important message to breeders as the resistance relates not only to any particular isolate of F. graminearum, but similarly to isolates of other Fusarium spp. This holds true for all the parameters measured. The DON contamination refers only to DON-producers F. graminearum and F. culmorum. Highly significant correlations were found between FHB, FDK, yield loss and DON contamination. Resistance components such as resistance to kernel infection, resistance to DON and tolerance were identified in the more susceptible genotypes. As compared with western European genotypes which produced up to 700 mg kg⁻¹ DON, the Hungarian genotypes produced only 100 mg kg⁻¹ at a similar FDK level. This research demonstrates the importance of measuring both FDK and DON in the breeding and selection of resistant germplasm and cultivars.     

Effect of solarization and fumigant applications on soilborne pathogens and root-knot nematodes in greenhouse-grown tomato in Turkey

A study was conducted in two greenhouses with a history of Fusarium crown and root rot (Fusarium oxysporum f.sp.radicis-lycopersici, Forl) and root-knot nematodes (Meloidogyne javanica andM. incognita). During the 2005–06 growing season, the effectiveness of soil disinfestation by solarization in combination with low doses of metham-sodium (500, 750, 1000 and 1250l ha⁻¹) or dazomet (400 g ha⁻¹), was tested against soilborne pathogens and nematodes in an attempt to find a suitable alternative to methyl bromide, which is soon to be phased out. Solarization alone was not effective in the greenhouse with a high incidence ofForl. In the greenhouse with a low level ofForl, all the treatments tested reduced disease incidence, and were therefore considered to be applicable for soil disinfestation. In addition, root-knot nematode density decreased with all the treatments tested in both of the greenhouses.     

Nematicidal potential of materials from <Emphasis Type="Italic">Medicago</Emphasis> spp.

The nematicidal effect of soil amendments with dry top and root material from Medicago sativa and/or Medicago arborea was evaluated on the root-knot nematode Meloidogyne incognita and on the cyst nematode Globodera rostochiensis in potting mixes. All amendments suppressed root and soil population densities of both nematode species compared to non-treated and chemical controls. The suppressiveness of M. sativa differed between top and root material and among the amendment rates. In field conditions soil amendments with 20 or 40 t ha⁻¹ of a pelleted M. sativa meal increased tomato crop yield and reduced soil population densities and root galling by M. incognita. It is suggested that saponins were at least partly responsible for the nematicidal activity.