Races Of Phytophthora Infestans Research Articles

Nitric oxide modulates redox-mediated defense in potato challenged with Phytophthora infestans

In our experimental approach we investigated how post-infection nitric oxide-dependent signaling activated in potato leaves was related to defense against avirulent (avr) and virulent (vr) races of Phytophthora infestans. Results revealed that only in an incompatible response, early NO and superoxide (O2 •-) generation led to peroxynitrite (ONOO−) formation and together with hydrogen peroxide (H2O2) production synchronized with SOD activity induced effective defense against avr pathogen. Early oxidative and nitrosative bursts triggered an imbalance in redox homeostasis in inoculated tissue. To counteract that effect, a total antioxidative capacity, ascorbate and sulfhydryl (-SH) group compounds increased both synergistically and markedly, confirming the precise mechanism of redox re-adjustment in avr oomycete -potato interaction. Moreover, the NO-coded message was stored and converted into an enhanced total SNO pool and particular S-nitrosylation of targeted proteins. Overall, we identified 104 proteins typed for S-nitrosylation in mock- or P. infestans-inoculated potato leaves. The S-nitrosoproteome structure comprised a wide repertoire of proteins, i.e. defense- and redox-related. Finally, only in the incompatible interaction, NO-based signal was re-written on the rapid PR-1 gene and PR-2 protein activation and was tuned with a limitation of late blight disease symptoms.

RESISTANCE EVALUATION ON POPULATIONS OF CROSSES BETWEEN TRANSGENIC POTATO KATAHDIN RB AND NON-TRANSGENIC ATLANTIC AND GRANOLA TO LATE BLIGHT (Phytophthora infestans) IN CONFINED FIELD TRIAL

Late blight resistance gene (RB gene) isolated from Solanum bulbocastanum, is a broad resistance gene against all races of Phytophthora infestans. The gene was transformed into Katah-din event SP904 and SP951 using Agrobacterium tumefaciens and these transgenic plants have been crossed with susceptible potato cultivars Atlantic and Granola. Populations of the crosses have been molecularly characterized for the integration of the RB transgene. The study aimed to evaluate the resistance of the populations of crosses between transgenic Katahdin RB and susceptible non-transgenic parents (Atlantic and Granola) to late blight in a confined field trial at Pasir Sarongge, Cianjur, West Java. A total of 84 clones originated from four popula-tions were evaluated for resistance to late blight. These included 22 clones of Atlantic x transgenic Katahdin SP904, 16 clones of Atlantic x transgenic Katahdin SP951, 19 clones of Granola x transgenic Katahdin SP904, and 27 clones of Granola x transgenic Katahdin SP951. Observations of the late blight infection were conducted when late blight symptoms were detected, i.e. at 56, 60, 63, 70, and 77 days after planting (DAP). The result showed there were high variations in the resistance level of all the 84 clones tested. Clones of crosses between susceptible parents (Atlantic or Granola) and resistant parents (transgenic Katahdin SP904 or Katahdin SP951) showed a similar pattern based on the area under disease progress curve (AUDPC) value, i.e. 377.2 greater than the AUDPC of the resistant parents (180.1), but smaller than that of the susceptible parents (670.7). Observation at 77 DAP resulted four resistant potato clones having resistance score of 7.0-7.6, higher than the transgenic parents Katahdin SP904 (4.6) and Katahdin SP951 (6.8), i.e. clone B8 (Atlantic x transgenic Katahdin SP951) with resistance score of 7.6 and clones B26 (Atlantic x transgenic Katahdin SP951), C183 (Granola x transgenic Katahdin SP904), and D89 (Granola x transgenic Katahdin SP951) with resistance score of 7. These four transgenic potato resistant clones need to be further developed as promising potato clones to late blight.<br /><br />

Sgt1, but not Rar1, is essential for the RB-mediated broad-spectrum resistance to potato late blight.

BackgroundLate blight is the most serious potato disease world-wide. The most effective and environmentally sound way for controlling late blight is to incorporate natural resistance into potato cultivars. Several late blight resistance genes have been cloned recently. However, there is almost no information available about the resistance pathways mediated by any of those genes.ResultsWe previously cloned a late blight resistance gene, RB, from a diploid wild potato species Solanum bulbocastanum. Transgenic potato lines containing a single RB gene showed a rate-limiting resistance against all known races of Phytophthora infestans, the late blight pathogen. To better understand the RB-mediated resistance we silenced the potato Rar1 and Sgt1 genes that have been implicated in mediating disease resistance responses against various plant pathogens and pests. The Rar1 and Sgt1 genes of a RB-containing potato clone were silenced using a RNA interference (RNAi)-based approach. All of the silenced potato plants displayed phenotypically normal growth. The late blight resistance of the Rar1 and Sgt1 silenced lines were evaluated by a traditional greenhouse inoculation method and quantified using a GFP-tagged P. infestans strain. The resistance of the Rar1-silenced plants was not affected. However, silencing of the Sgt1 gene abolished the RB-mediated resistance.ConclusionOur study shows that silencing of the Sgt1 gene in potato does not result in lethality. However, the Sgt1 gene is essential for the RB-mediated late blight resistance. In contrast, the Rar1 gene is not required for RB-mediated resistance. These results provide additional evidence for the universal role of the Sgt1 gene in various R gene-mediated plant defense responses.

Involvement of mitogen-activated protein kinase in the induction of StrbohC and StrbohD genes in response to pathogen signals in potato

The respiratory burst oxidase homolog (rboh), a plant homolog of the catalytic subunit of phagocyte NADPH oxidase (gp91 phox ), has been implicated in O2 − generation. In the previous study, we reported that StrbohA is constitutively expressed at a low level, whereas StrbohB is upregulated after pathogen signals are perceived in potato tubers. To gain a better understanding about the role of rboh in the defense response in potato leaves, we investigated the regulatory mechanisms of the gene. StrbohB gene was activated in response to an avirulent race of Phytophthora infestans or to hyphal wall components (HWC) from the pathogen; however, levels of expression were very low. We isolated two novel rboh cDNAs, StrbohC and StrbohD, by virtue of the sequence information from the tomato whitefly-induced gene 1 (LeWfi1) and tomato TC121349, respectively. The expression of StrbohC and StrbohD was drastically upregulated in the potato leaves inoculated with P. infestans or treated with HWC elicitor. Mitogen-activated protein kinase (MAPK) is known to play a pivotal role in the oxidative burst. The transcript accumulation induced by HWC treatment was blocked by U0126, which is a specific inhibitor of MAPK kinase (MAPKK). Conversely, the StrbohC and StrbohD genes were upregulated, driven by a pathogen-inducible promoter, in transgenic potato leaves that carry a constitutively active mutant of the MAPKK, StMEK1DD, that activates defense-related MAPKs. These results suggest that a MAPK cascade is involved in the process leading to the expression of the StrbohC and StrbohD genes.

Comparative analysis of quantitative trait loci for foliage resistance toPhytophthora infestans in tuber-bearingSolanum species

Previously published data for potato foliage resistance to late blight were examined in a combined analysis to determine how the genetic backgrounds of the host and pathogen affect the occurrence of resistance QTLs. Data from 19 diploid populations and one tetraploid population that originated from at least 12 different tuber-bearingSolanum species were included. Comparative analysis across all populations revealed three highly active genomic regions on the distal parts of chromosomes 3,4, and 5. The region most consistently detected that conferred foliage resistance inSolanum was located on chromosome 5, near marker locus GP21. A previously identified cluster of three race-specific R-genes on chromosome 11 was not associated with polygenic resistance. Statistical examination of active QTLs indicates that congruence among QTLs is significantly affected by both genetic relatedness of mapping populations and race ofPhytophthora infestans used for resistance tests. The proportion of congruent QTLs for late blight resistance decreased from 0.52 detected in relatedSolanum populations tested with the same race ofPhytophthora infestans to 0.20 found in unrelated mapping populations tested with different races ofPhytophthora infestans. Analysis of resistance mapping tests provided statistical evidence for the occurrence of race-specific QTLs in tuber-bearingSolanum. The highly conserved genomic regions identified in the comparative analysis are likely to be good candidates for gene cloning or marker assisted selection in potato breeding programs.

Assessment of the field resistance of potato genotypes with major gene resistance to late blight (Phytophthora infestans (Mont.) de Bary) using inoculum comprised of two complementary races of the fungus

Two races ofPhytophthora infestans, differing in virulence against four major (R) genes for resistance, were used to assess the field resistance of differential (R) genotypes, both singly and mixed together in equal proportions. The mixed inoculum led to an over-estimation of the foliage resistance of genotypes with which only one of the races was compatible, by up to two scoring categories of a 1–9 scale in field trials and, to a lesser extent, in glasshouse tests depending on the differential and the test. Assessment of tuber resistance was not significantly affected. The R10 and R2 differentials showed a higher level of field resistance in the foliage and tubers, respectively, than the other genotypes. It is concluded that assessments of genotypes which may possess R genes, using mixed inoculum, should be interpreted with caution, and apparent high levels of field resistance confirmed through genetic studies of the inheritance of the resistance.

Heritability of resistance to foliar late blight in a diploid hybrid potato population of Solanum phureja×Solanum stenotomum

AbstractThe emergence of new races of Phytophthora infestans has necessitated the search for additional sources of potato germplasm with resistance to late blight. This study examined 281 clones, derived from 72 families of a diploid random‐mated hybrid population of Solanum phureja×Solanum stenotomum. The clones were evaluated in a replicated field trial for 2 years with the control cultivar ‘Atlantic’ in Pennsylvania, USA. The P. infestans US‐8 A2 mating type culture was used to inoculate spreader rows of susceptible S. tuberosum cv.‘Russet Burbank’. Percent defoliation caused by the late blight fungus was estimated visually in each plot three times near the end of the growing season. Area under the disease progress curve (AUDPC) was estimated and showed that late blight was more severe in 1997 than in 1996. Genetic differences among clones and significant, but small, clone–environment interaction were detected for AUDPC. Broad‐sense and narrow‐sense heritability estimates, over years, were 0.79 ± 0.05 (P = 0.05) and 0.78 ± 0.29, respectively. Seventy‐five percent of the diploid clones had a significantly lower mean AUDPC than Atlantic. These results support the idea that this diploid population is worthy of use in breeding for late blight resistance in tetraploid potato cultivars.

Reduction of lesion growth rate of late blight plant disease in transgenic potato expressing harpin protein

Using harpin protein gene from apple fire blight pathogen Erwinia amylovora and potato prp1-1 promoter as main DNA elements, the feasibility of using pathogen infection-induced hypersensitive response was explored as a new strategy of engineering fungal disease resistance. Three plant transformation vectors were constructed and 68 transgenic potato plants were produced through Agrobacterium mediated transformation method. Southern, Northern and Western blot analysis demonstrated the insertion, transcription and protein expression of harpin protein gene in transgenic plants. Disease resistance test using a complex race of Phytophthora infestans as challenging pathogen showed that both constitutive and pathogen infection-induced expression of harpin protein gene in transgenic potato reduced the lesion growth rate of fungus. Among plants where harpin protein gene expression was induced only by fungus infection, two plants were found to be highly resistant to P.infestans infection. Fungal hyphae were not produced on total of 30 inoculated leaves from the two resistant plants and necrotic lesion was limited to inoculation area. The results highlighted that engineered hypersensitive response in plants was a very promising approach to produce fungal disease resistant genotype.

Vertical resistance to late blight in wild potato species from Argentina

The possible presence of vertical resistance to late blight conferred by R genes in Argentine wild Solanum species, which presumably have not evolved under the pressure of the fungus, was investigated. Solanum microdontum, S. commersonii and S. chacoense clones were tested in the greenhouse and with detached leaves in the laboratory after inoculation with a complex race and a non-virulent race of Phytophthora infestans. Two progeny tests were carried out to assess the performance of contrasting parents in regards to their resistance. A varying frequency of incompatible clones was detected among the species, with S. microdontum having the higher proportion of clones yielding incompatible reactions both in the laboratory and in the greenhouse. S. chacoense and S. commersonii showed a small but still considerable frequency of incompatible clones. The progeny tests confirmed the presence of R genes in a S. commersonii cross and their absence in a S. chacoense cross. The unexpected presence of R genes, its evolutionary significance and the consequences on the use of these species in breeding is discussed.

Involvement of actin filament association in hypersensitive reactions in potato cells

In potato tissues after either penetration by an incompatible race ofPhytophthora infestans, the potato late blight fungus, or treatment with hyphal wall components (HWC) prepared fromP. infestans, cytoplasmic aggregation is observed as one of the earliest resistance reactions. In potato protoplasts, the number of aggregated protoplasts increased after treatment with HWC. The increase was repressed by treatment with cytochalasin D, staurosporine, verapamil, ophiobolin and quinacrine prior to HWC treatment, suggesting that cytoplasmic aggregation in potato protoplasts was connected with actin filament association, protein phosphorylation, Ca2+, calmodulin and phospholipase reactions. The ratio of monomer-actin in potato tissues was decreased by treatment with HWC, while the decrease was repressed by treatment with cytochalasin D, staurosporine, ophiobolin and quinacrine prior to HWC treatment. These inhibitors inhibited the accumulation of rishitin, a potato phytoalexin, which occurs in potato tissues treated with HWC. The results imply that the factors involved in signal transduction might be connected with the cytoskeleton, especially actin filament association, during the initiation of defence responses in potato cells.

Defence reactions in two potato cultivars following infection with two races ofPhytophthora infestans

The kinetics of accumulation of chitinases, glucanases and phytoalexins were studied in two potato cultivars, differing in their degrees of vertical and horizontal resistance, when infected with two races ofPhytophthora infestans. Tuber disks of cvs Kennebec (susceptible, low horizontal resistance) and Huinkul (tolerant, high horizontal resistance) were infected with either race “0” (avirulent) or “C” (complex, race 1.3.5.7.11) ofPhytophthora infestans. Extracts of tuber tissue (0–7 days) from cv. Kennebec infected with race “0” showed a strong increase in phytoalexin production and in chitinase and glucanase activities when compared with those infected with race “C”. These results indicate that race “C” is able to block defensive reactions. No significant differences were observed in cv. Huinkul infected with both races. The contribution of these reactions to horizontal resistance is unknown, and our results would not support a conclusive role for them in the interaction.

Effect of glucans from different races of Phytophthora infestans on defense reactions in potato tuber

It has been proposed that susceptibility of potato to Phytophthora infestanswould be a consequence of suppression and /or delaying of defense reactions by a soluble glucan which is released by compatible races of the fungus. In this report, the reaction of potato tuber slices ( Solanum tuberosum cv. Huinkul) infected with either race I (1,4,7,8,10,11) or C (1,4,10,11) of Phytophthora infestans was studied. Race C grew better on slices than race I. Glucans from both races were isolated and their effect on the accumulation of phytoalexins and glucanases in tuber slices was studied. The glucans from the less virulent race (I) did not affect the accumulation of phytoalexins and glucanases in tuber slices infected or elicited with eicosapentaenoic acid, whereas the glucans from race C produced 70% inhibition of phytoalexin accumulation and reduced by 50% the induction of glucanase activities. Purified glucanases from potato degraded the glucans from race C but not from race I. The results reported here show that, at least on this cultivar, glucans from both races affected defense responses in a different manner, which could reflect structural differences between these glucans. Abbreviations:EPA ‐ 5,8,11,14,17 eicosapentaenoic acid.

Race specific resistance against Phytophthora infestans in potato is controlled by more genetic factors than only R-genes

For RFLP mapping of R-genes, determining resistance to specific races of Phytophthora infestans in tetraploid potato, it is necessary to develop well segregating populations at the 2x level. During mapping studies, evidence was obtained that more genetic factor(s) are involved in the expression of R-genes than conventionally believed. Two experiments are described in which such an additional genetic factor was suppressing or enhancing the expression of unknown R nand R ifactors. R nand R iappeared to be present in the investigated plant material, containing R4 and R10, or in one of the susceptible crossing parents. In a third experiment, the expression and the segregation of the well known R1 gene was influenced by an additional genetic factor. In that case there were indications for a dominant suppressor. This was established by the selection of susceptible plants carrying a RFLP allele of probe GP21 closely linked to R1. In three of the four F1 populations, resulting from crosses between such susceptible plants and susceptible tester plants, resistnat progenies were found. The resistance appeared to be R1-specific. This clearly indicates that in three of the four investigated susceptible plants, the R1 gene was still present but not expressed.

Durable resistance to late blight (Phytophthora infestans) in old potato cultivars

Twenty-two R gene-free cultivars, introduced between 1900 and 1954, were field-tested for their level of partial resistance to a complex race ofPhytophthora infestans. Disease assessments, expressed as areas under the disease progress curve, appeared closely correlated to resistance ratings given between 1929 and 1954. This, and the stability in time since 1929 of the ratings in the Dutch Descriptive List of Varieties of Field Crops, suggest that the resistance concerned is durable. Lesion growth rate was found to be a very important component of resistance in these cultivars and also in more recently introduced ones, whereas latent period varied little between the cultivars. The most resistant cultivars were Robijn, Populair, Pimpernel, Libertas and Surprise, which were also among the latest maturing in the material. These five cultivars are closely related and may have the same resistance genes.

Suppression of Phenylalanine Ammonia-Lyase mRNA Accumulation by Suppressors from Phytophthora infestans.

The transient accumulation of phenylalanine ammonia-lyase (PAL) transcript was markedly induced in aged potato tuber slices 1 to 2hr after inoculation with an incompatible race of Phytophthora infestans, whereas the transcript in compatible interaction accumulated to lesser extent. A dramatic increase of PAL transcript accumulation occurred within 30min after treatment with hyphal wall components (HWC) of the pathogen, but the HWC-elicitor-stimulated increase was greatly suppressed by treatment with a suppressor from the compatible race. In contrast, treatment with HWC-elicitor in the presence of the suppressor from the incompatible race caused an acceleration of the accumulation of PAL mRNA compared with that with HWC-elicitor alone. These results for PAL transcript paralleled those based on the changes in PAL enzyme activity. Elicitation and suppression of induction of PAL transcript accumulation and PAL activity were discussed in relation to the race-cultivar specificity in potato late blight.

Races ofPhytophthora in festans in France, 1991–1993

Nineteen races were found among 116 isolates ofPhytophthora infestans recovered from French potato and tomato crops during 1991–1993. The most common races were 1.3.4.7.11. 1.3.4.7.8.11 and 1.3.4.7.10.11 in 1991, race 1.3.4.7.11 in 1992, and race 1.3.4.7.10.11 in 1993. None of the isolates was virulent to either R2 or R6, and only one to R5. The mean number of virulences per isolate was 5.78 in 1991, 4.35 in 1992 and 4.53 in 1993. TheP. infestans population from Brittany showed mainly quantitative changes in the frequencies of major races over the period investigated, but races identified were almost the same in all 3 years. No geographical substructure was apparent, since variation between locations accounted for only 13–22% of the total racial diversity within the Brittany population. This is interpretated as evidence for limited gene flow in this population, which is believed to have evolved from a few founding genotypes.

Effect of plant age and inoculum concentration on expression of major gene resistance to Phytophthora infestans in detached potato leaflets

Ten genotypes of a differential host series, each possessing different major (R) genes effective against races of Phytophthora infestans, were grown in a glasshouse to produce plants ranging between 3- and 10-wk-old at the time of inoculation. Detached leaflets were inoculated with a suspension of 2·5, 5, 10, 20 or 50 × 103 zoospores ml−1 applied as a single drop or a covering of fine droplets. Plants expected to show susceptibility uniformly gave spreading sporulating lesions, but resistance was variably expressed, with symptoms ranging from hypersensitive or symptomless reactions indicating immunity to spreading sporulating lesions covering all the leaf surface. Immune reactions were most prevalent on leaflets of flowering plants (8–10-wk-old). The incidence of immune reactions was greater with the drop than with the spray method of inoculation and decreased as spore concentration increased.

Wild tuber-bearing species ofSolanum and incidence ofPhytophthora infestans (Mont.) de Bary on the Western slopes of the volcano Nevado de Toluca. 3. Physiological races ofPhytophthora infestans

A survey of races ofPhytophthora infestans was made in 1985 and 1986 on the western slopes of the volcano Nevado de Toluca, Mexico. Isolates were collected from infected plants of wildSolanum species found in five long (7–10 km) and some short (300–500 m) transects. The study are of 15 000 ha was between 2900 and 3900 m altitude. Isolates were collected fromSolanum demissum (35 isolates),verrucosum (11),iopetalum (2),brachycarpum (7),stoloniferum (2), r-genotype (9) and from differential hosts (11). No isolate was identified as race 0. Ten virulence genes were identified with a set of differential hosts and the most common were numbers 2 and 4. Isolates with eight virulence genes were the most common and those with ten were found on eight occasions in the natural habitat and on three in the experimental fields.

Variation in resistance toPhytophthora infestans among 21Solanum verrucosum plant introductions

Detached leaflets of 21Solanum verrucosum plant introductions (PIs) were inoculated with two races ofPhytophthora infestans to evaluate levels of resistance present within this species. Inoculated leaflets were visually evaluated for the percentage area colonized byP. infestans and the intensity of sporulation over the colonized area. Disease reactions ranged from moderately susceptible to highly resistant (immune). Significant plant-to-plant heterogeneity for resistance was observed within many of the PIs, indicating that they may represent mixtures of different genotypes. Hypersensitive flecks were observed on some inoculated leaflets of all PIs tested. Adult plant reactions showed moderate agreement with those obtained by other workers on seedling populations of several PIs. These results support the hypothesis that R-genes and polygenes for resistance toP. infestans exist withinS. verrucosum accessions. This species thus may provide a useful source of novel late blight resistance genes.

Differential ethylene production by potato tuber tissue inoculated with a compatible or an incompatible race ofPhytophthora infestans

Synthesis of ethylene in Kennebec potato tuber discs was measured at various time intervals after inoculation with zoospores of race 0 (incompatible) or race 1,2,3,4 (compatible) ofPhytophthora infestans (Mont.) de Bary. A burst of ethylene production was observed within 6 hr after inoculation with race 0, but not with race 1,2,3,4. This response may have been due to recognition of the incompatible race 0 during host penetration. Additional ethylene was synthesized concomitant with symptom appearance in both compatible and incompatible combinations.