<Emphasis Type="Italic">Alternaria</Emphasis> species associated with early blight epidemics on tomato and other <Emphasis Type="Italic">Solanaceae</Emphasis> crops in northwestern Algeria

Clubroot, caused by the protozoan parasite Plasmodiophora brassicae Woronin, is one of the most damaging diseases of Brassica napus worldwide. Resistant plant material is valuable for cultivation in all areas of high incidence of the disease and intensive growth of oilseed rape. We have evaluated clubroot resistance, plant morphology and seed quality in 15 lines of an F₄ generation and selected six lines of F₅ generation of interspecific hybrids obtained from a cross between a male sterile line of B. napus ‘MS8’, selected from resynthesized oilseed rape (B. rapa ssp. chinensis × B. oleracea var. gemmifera) and an ecotype of B. rapa ssp. pekinensis. Clubroot resistance was evaluated using a bioassay with P₁-P₅ pathotypes of P. brassicae (according to the classification of Somé et al. 1996). The resistance to the pathotype P₁ was successfully fixed in the F₅ generation, and improved in some lines in respect to the pathotypes P₂-P₄. The resistance to P₁ and the other tested pathotypes was not linked. Characterization of plant material included recent techniques of FISH and BAC-FISH with a special focus on the analysis of ribosomal DNA (rDNA) of selected individuals. Two hybrid lines combined high levels of resistance with appropriate plant morphology, good seed quality traits and a stable chromosome number and arrangement. Recent techniques of ‘chromosome painting’ provided good insight into chromosome organization in the hybrids obtained, and offered opportunities of further improvement of the breeding process.     

Characterization of a unique copper resistance gene cluster in <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">campestris</Emphasis> isolated in Trinidad,West Indies

Whole genome sequencing of a copper resistant (Cu^R) black rot strain of Xanthomonas campestris pv. campestris (Xcc) isolated from a broccoli plant in Trinidad revealed a unique operon for copper resistance. The cop genes of strain Xcc-BrA1 were determined to be present on a 160 to 180 kb plasmid shown to be non-conjugative with other xanthomonads. While nucleotide comparison of a putative 8.0 Kbp copLABMGF gene cluster identified in Xcc-BrA1 genome did not reveal any homologous region with other known Cu^R Xanthomonas strains from diverse origins, the comparison of the translated amino acid sequence indicated similarity with X. citri, X. c. pv. citrumelonis and X. vesicatoria Cop proteins. Cloning of the copLAB gene cluster from Xcc-BrA1 conferred copper resistance to other copper-sensitive xanthomonads. Although Xcc-BrA1 harbors copLAB genes with similar sizes and organization and is able to grow on Cu-amended medium as other Cu^R xanthomonads, the phylogenetic analysis of nucleotide sequences indicates that the cop cluster in Xcc-BrA1 is unique and distantly related to other copLAB genes from Xanthomonas and Stenotrophomonas. The origin of copper resistance genes in Xcc-BrA1 is likely a result of horizontal gene acquisition from a still unknown phylloplane cohabitant. The findings of this study have implications for the management of crop diseases caused by Cu^R xanthomonads. Future studies could focus on and determining the distribution, overall importance and appropriate control measures for strains harbouring these unique genes.     

Identification of blast resistance genes in 358 rice germplasms (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) using functional molecular markers

Rice blast, caused by the fungus Magnaporthe oryzae, is one of the most devastating diseases of rice (Oryza sativa L.), and neck blast is the most destructive phase of this disease. Although neck blast causes tremendous yield loss, little is known about the molecular mechanisms underlying the neck blast resistance. To address this issue, we collected 358 rice varieties from different ecotypes in China and assessed them for the neck blast resistance under natural conditions favoring disease development in Jining, Shandong Province. Our results showed that 124 (34.6%) and 234 (65.4%) varieties were resistant and susceptible to M. oryzae under natural field conditions, respectively. Among the 358 rice varieties that were screened for the presence of 13 major blast resistance (R) genes against M. oryzae by using functional markers, 259 varieties contained one to seven R genes. In addition, the relationship between the presence of R genes and the disease reactions was also investigated by integrative analysis of phenotyping and genotyping based on functional markers. Our results showed that the rice blast resistance gene Pi2 was significantly correlated with neck blast resistance. Furthermore, any of the 13 major blast R genes was absent from 32 rice varieties exhibited obvious neck blast resistance, which would be the potential materials for identifying novel neck blast R genes. Taken together, our findings provide insight into the distribution of the 13 major blast R genes in the tested Chinese rice germplasm resources, which will serve as a basis for developing rice blast resistant. Furthermore, 32 rice varieties exhibited neck blast resistance, but they did not harbor any of the 13 major blast R genes. In the future, these varieties may be used to identify novel neck blast R genes.     

Temperature and plant age drive downy mildew disease epidemics on oilseed <Emphasis Type="Italic">Brassica napus</Emphasis> and <Emphasis Type="Italic">B. juncea</Emphasis>

Studies were undertaken on the effects of temperature (14/10 °C and 22/17 °C day/night) and plant age (15, 23, 31 and 40 day-old-plants) on the severity of downy mildew (Hyaloperonospora parasitica) on oilseed Brassica cultivars (temperature: Brassica juncea Montara, B. napus Atomic, ATR-Hyden, Hyola 432, Hyola 450 TT, Thunder TT; plant age: B. juncea Dune, B. napus Surpass 402 and Hyola 450 TT). For temperature studies, there were significant (P?<?0.001) effects of temperature, cultivar, and cultivar x temperature interaction. On cotyledons of susceptible cultivars (B. napus Hyola 450 TT and Thunder TT), plants were symptomatic at 22/17 °C by 48 h post inoculation (hpi) and with abundant sporulation evident by 72 hpi, and with all cotyledons of B. napus Thunder TT collapsed by 7 days post inoculation (dpi). However, at 14/10 °C, there were no symptoms on the same cultivars until 5 dpi, and sporulation only observed at 7 dpi. Percent disease index values (DI%) at 22/17 °C of B. juncea Montara and B. napus ATR-Hyden, Hyola 432, Atomic, Hyola 450 TT and Thunder TT were 4.5, 49.0, 51.4, 65.8, 86.3 and 96.0, respectively, with all except B. juncea Montara having significantly lower (P?<?0.001) disease at 14/10 °C with DI% values of 2.8, 30.4, 27.9, 31.1, 44.4 and 76.4, respectively. For plant age studies, there were significant (P?<?0.001) effects of plant age, cultivar, and cultivar x plant age interaction. DI% was significantly higher at 15 compared to 40 day-old-plants (dop) across all cultivars. B. juncea Dune showed greatest resistance, particularly on 40 dop, with DI% values of 25.8, 24.6, 22.9 and 7.5, for 15, 23, 31 and 40 dop, respectively. B. napus Surpass 402 showed high susceptibility on cotyledons of 15 dop but moderate resistance on leaves of other ages, with DI% values of 59.0, 31.2, 27.1 and 26.2 for 15, 23, 31 and 40 dop, respectively. B. napus Hyola 450 TT showed very high susceptibility at the cotyledon stage on 15 dop, but some resistance on 23 dop and more so on 31 and 40 dop, with DI% values of 84.0, 41.2, 35.4 and 32.9 for 15, 23, 31 and 40 dop, respectively. Together, these findings explain for the first time why development of downy mildew epidemics on susceptible cultivars occurs early in the growing season when warmer seasonal temperatures in autumn coincide with presence of seedlings; in contrast to later in the growing season on less susceptible older plants coinciding with cooler and less favourable winter temperatures. Increasing maximum and minimum temperatures associated with climate change have likely fostered the increased severity of downy mildew over the past 15 years.     

Genotypic and phenotypic variability of <Emphasis Type="Italic">Pectobacterium</Emphasis> strains causing blackleg and soft rot on potato in Turkey

Pectinolytic bacteria were isolated from 48 potato plants showing the symptoms of blackleg and collected in different fields of commercial potato production areas at Samsun, Amasya, Corum and Yozgat provinces in Turkey in 2015. The survey resulted in the isolation of 26 pectinolytic strains that belonged to P. atrosepticum, P. carotovorum subsp. brasiliense, P. carotovorum subsp. carotovorum and P. parmentieri species based on molecular identification with species-specific PCR and phenotypic characterization. The identified strains indicated typical biochemical characteristics of the assigned species. For 16 representative Pectobacterium isolates 10 unique rep-PCR band patterns were obtained. The 16S rRNA and recA and gapA gene fragment sequencing confirmed the species identity of the isolates. The phenotypic characterization of the strains revealed that for all assays but one (cellulase, protease activity, swimming but not swarming), the tested Pectobacterium species were significantly different from each other proving the diversity of the strains belonging to these genera. Recent outbreaks of blackleg and/or soft rot in potato production areas in Turkey may pose a threat on other crops, as tomato, pepper, cucumber, onion, cabbage, broccoli and sugar beet are cultivated in the same provinces.     

Characterization of <Emphasis Type="Italic">Dickeya</Emphasis> and <Emphasis Type="Italic">Pectobacterium</Emphasis> strains obtained from diseased potato plants in different climatic conditions of Norway and Poland

Soft rot and blackleg of potato caused by pectinolytic bacteria lead to severe economic losses in potato production worldwide. To investigate the species composition of bacteria causing soft rot and black leg of potato in Norway and Poland, bacteria were isolated from potato tubers and stems. Forty-one Norwegian strains and 42 Polish strains that formed cavities on pectate medium were selected for potato tuber maceration assays and sequencing of three housekeeping genes (dnaX, icdA and mdh) for species identification and phylogenetic analysis. The distribution of the species causing soft rot and blackleg in Norway and Poland differed: we have demonstrated that mainly P. atrosepticum and P. c. subsp. carotovorum are the causal agents of soft rot and blackleg of potatoes in Norway, while P. wasabiae was identified as one of the most important soft rot pathogens in Poland. In contrast to the other European countries, D. solani seem not to be a major pathogen of potato in Norway and Poland. The Norwegian and Polish P. c. subsp. carotovorum and P. wasabiae strains did not cluster with type strains of the respective species in the phylogenetic analysis, which underlines the taxonomic complexity of the genus Pectobacterium. No correlation between the country of origin and clustering of the strains was observed. All strains tested in this study were able to macerate potato tissue. The ability to macerate potato tissue was significantly greater for the P. c. subsp. carotovorum and Dickeya spp., compared to P. atrosepticum and P. wasabiae.     

Host-delivered RNAi-mediated root-knot nematode resistance in <Emphasis Type="Italic">Arabidopsis</Emphasis> by targeting <Emphasis Type="Italic">splicing factor</Emphasis> and <Emphasis Type="Italic">integrase</Emphasis> genes

Root-knot nematodes (RKNs) are one of the most important biotic factors limiting crop productivity in many crop plants. The major RKN control strategies include development of resistant cultivars, application of nematicides and crop rotation, but each has its own limitations. In recent years, RNA interference (RNAi) has become a powerful approach for developing nematode resistance. The two housekeeping genes, splicing factor and integrase, of Meloidogyne incognita were targeted for engineering nematode resistance using a host-delivered RNAi (HD-RNAi) approach. Splicing factor and integrase genes are essential for nematode development as they are involved in RNA metabolism. Stable homozygous transgenic Arabidopsis lines expressing dsRNA for both genes were generated. In RNAi lines of splicing factor gene, the number of galls, females and egg masses was reduced by 71.4, 74.5 and 86.6%, respectively, as compared with the empty vector controls. Similarly, in RNAi lines of the integrase gene, the number of galls, females and egg masses was reduced up to 59.5, 66.8 and 63.4%, respectively, compared with the empty vector controls. Expression analysis revealed a reduction in mRNA abundance of both targeted genes in female nematodes feeding on transgenic plants expressing dsRNA constructs. The silencing of housekeeping genes in the nematodes through HD-RNAi significantly reduced root-knot nematode infectivity and suggests that they will be useful in developing RKN resistance in crop plants.     

Biochemical,physiological, and molecular characterization of <Emphasis Type="Italic">Dickeya dianthicola</Emphasis> (formerly named <Emphasis Type="Italic"> Erwinia chrysanthemi</Emphasis>) causing potato blackleg disease in Japan

The taxonomic assignment of Japanese potato blackleg isolates of Dickeya spp. has not been confirmed after the changes in their former name, Erwinia chrysanthemi. Therefore, we investigated and identified 23 representative isolates of Dickeya spp. from symptomatic stems of potatoes in Japan, with biochemical tests and phylogenetic sequence analysis using recA, dnaX, rpoD, gyrB, and 16S rDNA sequences. Results of our biochemical tests showed that all isolates can be assigned to phenon 5 and biovar 1, which are associated with D. dianthicola. Based on the recA, dnaX, rpoD, gyrB, and 16S rDNA sequences, all isolates are in the same clade with D. dianthicola and were clearly distinguished from D. chrysanthemi, D. dadantii, D. dadantii subsp. dieffenbachiae, D. solani, D. zeae, and D. paradisiaca. Therefore, we conclude that Dickeya spp. isolated from potatoes with blackleg symptoms in Japan are D. dianthicola.     

Suppression subtractive hybridization and microarray analysis reveal differentially expressed genes in the <Emphasis Type="Italic">Lr39/41</Emphasis>-mediated wheat resistance to <Emphasis Type="Italic">Puccinia triticina</Emphasis>

Wheat leaf rust caused by Puccinia triticina (Pt) is one of the most severe fungal diseases threatening the global wheat production. The use of leaf rust resistance (Lr) genes in wheat breeding programs is the major solution to solve this issue. Wheat isogenic line carrying the Lr39/41 gene has shown a moderate to high resistance to most of the Pt pathotypes detected in China. In the present study, a typical hypersensitive response (HR) was observed using microscopy in leaves of the Lr39/41 isogenic line inoculated with the avirulent Pt pathotype THTT from 48 h-post inoculation. Two Lr39/41 resistance-associated suppression subtractive hybridization (SSH) libraries with a total of 6000 clones were established. Microarray hybridizations were performed on all obtained SSH clones using RNAs extracted from leaves of the Pt-inoculated and non-inoculated Lr39/41 isogenic lines, and leaves of the Pt-inoculated and non-inoculated Thatcher susceptible lines. Differentially expressed clones were analyzed by significance analysis of microarrays (SAM), followed by further sequencing. A total of 36 Lr39/41-resistance-related differentially expressed genes (DEGs) were identified, many of which had been previously reported to be involved in the plant defense response. The expression levels of eight selected DEGs during different stages of the Lr39/41-mediated resistance were further quantified by a qRT-PCR assay. Several pathogenesis-related (PR) and HR-related genes seem to be crucial for the Lr39/41-mediated resistance. In general, a brief profile of DEGs associated with the Lr39/41-mediated wheat resistance to Pt was drafted.     

Evaluation of oilseed rape seed yield losses caused by <Emphasis Type="Italic">Leptosphaeria biglobosa</Emphasis> in central China

Phoma stem canker of oilseed rape (Brassica napus), caused by Leptosphaeria maculans/L. biglobosa is a globally important disease. Severe phoma stem canker symptoms have been observed on winter oilseed rape in China but the seed yield loss caused by this disease remains unknown. In May 2012 and May 2013, 17 and 13 crops were surveyed, respectively, in seven counties of Hubei Province, central China. Stems with phoma stem canker disease symptoms were sampled for pathogen isolation and identification. Only L. biglobosa was identified by culture morphology and species-specific PCR; no L. maculans was found. To evaluate the yield losses, yield components (number of branches per plant, number of pods per plant, 1000-seed weight, number of seeds per pod) were assessed on healthy and diseased plants sampled from crops in four counties and on plants from inoculated pot experiments (plants of three cultivars were inoculated at the green bud stage by injecting L. biglobosa conidia into the stem between the first and second leaf scars). Results of the field surveys showed that diseased plants had 14–61% less branches and 32–83% less pods than healthy plants, respectively. The estimated seed yield loss varied from 10% to 21% and from 13% to 37% in 2012 and 2013, respectively. In the pot experiments, there were no differences in numbers of branches or pods but there were differences in number of seeds per pod between inoculated and control plants. For the three cultivars tested, the inoculated plants had yield losses of 29–56% compared with the control. This study indicates that L. biglobosa could cause substantial seed yield loss in China.     

Rice <Emphasis Type="Italic">OsPBL1</Emphasis> (ORYZA SATIVA ARABIDOPSIS PBS1-LIKE 1) enhanced defense of <Emphasis Type="Italic">Arabidopsis</Emphasis> against <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> DC3000

The receptor-like cytoplasmic kinases (RLCK family VII) are required for plant defense against various pathogens. Previously, OsPBL1 (ORYZA SATIVA ARABIDOPSIS PBS1-LIKE 1) was isolated from rice as a potential RSV (rice stripe virus) resistant factor, but its physiological roles in plant defense are yet to be investigated. In this study, we demonstrated that OsPBL1increased defense against P. syringae in transgenic Arabidopsis. To ascertain the role of OsPBL1 gene in plant defense, OsPBL1 tagged with HA (i.e. Hemagglutinin) was overexpressed in Arabidopsis and examined for the resistance against Pseudomonas syringae pv. tomato DC3000 (i.e. Pst DC3000). At 3 dpi of Pst DC3000, transgenic Arabidopsis lines exhibited the reduced chlorotic lesion and propagation of P. syringae, compared to wild type. Elevated pathogen resistance of transgenic lines was correlated with increased H₂O₂ accumulation and callose deposition on the infected leaves. It was also revealed that expression levels of salicylic acid dependent genes such as PR1, PR2, and PR5, were induced higher in transgenic lines than wild type. Taken together, our data suggested that OsPBL1 exerted the role in defense against pathogen attacks in plant via mainly facilitating salicylic acid dependent pathway.     

A myosin passenger protein gene (<Emphasis Type="Italic">FaSmy1</Emphasis>) is an essential regulator of cell development,pathogenicity, DON biosynthesis,and resistance to the fungicide phenamacril in <Emphasis Type="Italic">Fusarium asiaticum</Emphasis>

Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) are important viruses of wheat (Triticum aestivum L.) in the Great Plains of United States. In addition to agronomic practices to prevent damage from these viruses, temperature sensitive resistance genes Wsm1, Wsm2 and Wsm3, have been identified. However, threshold temperatures for Wsm1 and Wsm3 have not been clearly defined. To better understand these two resistance genes, wheat lines C.I.15092 (Wsm1), KS96HW10–3 (Wsm1), and KS12WGGRC59 (Wsm3) were evaluated for WSMV resistance at 27, 30, 33 and 35 °C and for TriMV resistance at 18, 21, 24, 27, 30, 33 and 35 °C. The results showed that only C.I.15092 remained resistant at 30 °C for both viruses. This line also tolerated TriMV at 33 and 35 °C with less sever symptom and lower infection rates. Wheat lines KS96HW10–3 and KS12WGGRC59 hold resistance to TriMV up to 21 °C. Molecular marker results suggested that the resistance in C.I.15092 is most probably conditioned by the resistance gene Wsm1 and additional gene(s) other than Wsm2 and Wsm3.     

Virulence profiling of <Emphasis Type="Italic">Xanthomonas oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis> isolates,causing bacterial blight of rice in India

Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo), remains a major production constraint in rice cultivation especially in irrigated and rainfed lowland ecosystems in India. The pathogen is highly dynamic in nature and knowledge on pathotype composition among the Xoo population is imperative for designing a scientific resistance breeding program. In this study, four hundred isolates of Xoo collected from diverse rice growing regions of India were analyzed for their virulence and genetic composition. Virulence profiling was carried out on a set of differentials consisting of 22 near isogenic lines (NILs) of IR24 possessing different BB resistance genes and their combinations along with the checks. It was observed that different NILs possessing single BB resistance gene were susceptible to about 59–94% of the Xoo isolates except IRBB 13 (containing BB resistance gene xa13), which showed susceptibility to about 35% of the isolates. Based on the reaction of the Xoo isolates on the differentials, they were categorized into 22 pathotypes. Among the 22 pathotypes, IXoPt-1 and IXoPt-2 were least virulent and IXoPt # 18–22 were highly virulent. Pathotype IXoPt-19 which was virulent on all single BB resistance genes except xa13 constituted the major pathotype (22.5% isolates) and was widely distributed throughout India (16 states). This was followed by pathotype IXoPt-22 (17.25%) which was virulent on all the NILs possessing single BB resistance genes. Molecular analysis was carried out using two outwardly directed primers complementary to sequence of IS1112, a repetitive element of Xoo. A high level of genetic polymorphism was detected among these isolates and the isolates were grouped into 12 major clusters. The data indicated complex nature of evolution of the Xoo pathotypes and there was no strong correlation between pathotypes and genetic clusters as each genetic cluster was composed of Xoo isolates belonging to different pathotypes. The study indicated that none of the single BB resistance genes can provide broad spectrum resistance in India. However, two-gene combinations like xa5 + xa13 and different 3 or 4 genes combination like Xa4 + xa5 + xa13, Xa4 + xa13 + Xa21, xa5 + xa13 + Xa21 and Xa4 + xa5 + xa13 + Xa21 are broadly effective throughout India.     

<Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> upregulates marker genes of the salicylic acid and ethylene signaling pathways but not those of the jasmonic acid pathway in leaflets of <Emphasis Type="Italic">Solanum</Emphasis> lines during early stage of infection

Real-Time PCR assay was used to quantify the expression of marker genes of the salicylic acid, jasmonic acid and ethylene signaling pathways in seven Solanum lines after inoculation with a Ralstonia solanacearum phylotype I strain, R008. Four Solanum lycopersicum lines (CRA 66, Hawaii 7996, MST 32/1, Quatre carrées), one S. tuberosum line (Spunta), the wild Lycopersicon cerasiforme and Solanum commersonii were used for this investigation. Results revealed very little activation of the jasmonic acid pathway marker genes, lipoxygenase A (LoxA) and protease inhibitor II (Pin2), with no significant difference (p > 0.05) in fold change expression among the Solanum lines. In contrast the salicylic acid pathway marker genes, glucanase A (GluA) and PR-1a, and the ethylene pathway marker genes, osmotin-like (Osm) and PR-1b, were expressed at higher levels with a statistically significant difference (p < 0.05) in fold change expression among the Solanum lines. The resistant lines L. cerasiforme, CRA 66, Hawaii 7996 and S. commersonii showed stronger activation of the salicylic acid and ethylene marker genes than the moderately resistant cultivar (MST 32/1) and the susceptible lines (Quatre carrées and Spunta). The marker genes reached their highest expression levels earlier (4 h.p.i) in the resistant and moderately resistant lines than in the susceptible lines (48 h.p.i.). These results indicate that salicylic acid and ethylene signaling pathways have a significant role in defense against R. solanacearum. The timing and magnitude of the upregulation of gene expression may determine the plant ability to put up a defense response against the pathogen.     

Identifying seedling and adult plant resistance of Chinese Brassica napus germplasm to Leptosphaeria maculans

Blackleg disease of canola/rapeseed (Brassica napus), caused by the devastating fungal pathogen Leptosphaeria maculans, can significantly influence B. napus production worldwide, except for China, where only the less aggressive L. biglobosa has been found associated with the disease. The aim of this study was to characterize both seedling resistance (major gene resistance, R gene resistance) and adult plant resistance (APR) from a collection of Chinese B. napus varieties/lines (accessions) to L. maculans. Evaluation of seedling resistance was carried out under a controlled environment, using 11 well‐characterized L. maculans isolates as differentials. The identification of APR was performed under multiple field environments in western Canada. R genes were detected in more than 40% of the accessions tested. Four specific R genes, Rlm1, Rlm2, Rlm3 and Rlm4 were identified, with Rlm3 and Rlm4 being the most common genes, while Rlm1 and Rlm2 were detected only occasionally. Results of field evaluation indicated significant variations among field locations as well as accessions; a large portion of the B. napus accessions, regardless of the resistance level observed at the seedling stage, showed high to moderate levels of APR under all environments tested. This study highlights that both R gene resistance and APR are present in Chinese B. napus germplasm and could be potential sources of resistance against blackleg caused by L. maculans if the pathogen ever becomes established in China.     

Chitin elicitor receptor kinase 1 (CERK1) is required for the non-host defense response of <Emphasis Type="Italic">Arabidopsis</Emphasis> to <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. Sp. <Emphasis Type="Italic">cubense</Emphasis>

Banana wilt disease is a typical vascular disease caused by the fungal pathogen Fusarium oxysporum f. sp. cubense 4 (Foc 4). Pattern recognition receptors in the plant cell membrane can recognize pathogen-associated molecular patterns (PAMPs) to activate multi-layer defense responses, including defense gene expression, stomatal closure, reactive oxygen species (ROS) burst and callose deposition, to limit pathogen growth. In the present study, we found that chitin elicitor receptor kinase 1 (CERK1) was required for the non-host resistance of Arabidopsis thaliana to Foc B2 (a strain of Foc 4). The cerk1 mutant had weaker defense responses after Foc B2 treatment, including lower expression of PAMP- and salicylic acid-responsive genes, no stomatal closure, lower ROS level and less callose deposition, than that of the wild-type plant. Consistent with this, the cerk1 mutant plants exhibited higher susceptibility to non-host pathogen Foc B2. These results suggest the crucial importance of CERK1 in Foc B2-triggered non-host resistance.     

Resistance evaluation of differentials and commercial wheat cultivars to stripe rust (<Emphasis Type="Italic">Puccinia striiformis</Emphasis>) infection in hot spot regions of Canada

Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases of wheat in Canada. This study presents the results from resistance evaluation of Yr genes and western Canadian wheat cultivars from different milling classes, to natural infection in southern Alberta and British Columbia which are considered hot spots of stripe rust occurrence in Canada, due to proximity to Pacific Northwest of the United States where stripe rust epidemics are frequent. Genes Yr1, Yr5, Yr15, and YrSP were effective in all environments; Yr17 and Yr28, which were earlier reported ineffective to existing stripe rust races at the seedling stage in Canada, were effective at adult plant stages in most of the environments because of warmer climates in southerly locations, a favourable condition for expression of the genes. Yr17 is common in winter wheat cultivars and only reported spring wheat cultivar carrying it is CDC Stanley, which can serve as donor parent in breeding programs. Gene Yr24/26 was not very effective in western prairies although reported as effective in eastern prairies. Residual resistance from combination of defeated genes (Yr3, Yr7, Yr9, Yr27) in some supplementary differentials was observed. Most cultivars carry slow-rusting, pleiotropic adult-plant resistance gene Yr18 and some Yr29, which were effective in some locations. These genes failed to provide complete protection under high disease pressure. Seedling and adult plant resistance genes Yr5, Yr15, Yr17 and Yr18, Yr36, respectively could be good targets for resistance breeding. Stacking adult plant resistance genes with seedling resistance genes can provide durable resistance to stripe rust.     

Biochemical changes in the <Emphasis Type="Italic">Brassica juncea-fruticulosa</Emphasis> introgression lines after <Emphasis Type="Italic">Lipaphis erysimi</Emphasis> (Kaltenbach) infestation

Insect damage leads to changes in biochemical profile of plants. Response of three Brassica juncea-fruticulosa introgression lines (already reported resistant to Lipaphis erysimi) in terms of changes in biochemical constituents after aphid infestation was studied along with B. fruticulosa (resistant parent), B. juncea var. PBR ?210 (susceptible parent) and B. rapa ecotype brown sarson BSH-1 (susceptible check). These six genotypes were grown under aphid infested and uninfested conditions and were sampled at peak aphid infestation to analyze the biochemical changes caused by aphid feeding from top 10 cm central twig of plant. A significant reduction in glucosinolates content in aphid infested plants of three introgression lines (I₈, I₇₉ and I₈₂) was observed while opposite was observed in B. fruticulosa, PBR-210 and BSH-1. Exactly opposite trend was observed for total phenols where aphid infestation resulted in significant increase in phenols content in the three introgression lines while a decrease was observed in B. fruticulosa, PBR-210 and BSH-1. A general trend of decline in flavonols, total sugars and free amino acids content was observed after aphid infestation in all the genotypes. Glucosinolates and total phenols served as biochemical bases of resistance in the three introgression lines since there was downregulation of glucosinolates and upregulation of total phenols as against opposite trend observed in BSH-1 and PBR-210.     

The effect of temperature on the phenotypic features and the maceration ability of <Emphasis Type="Italic">Dickeya solani</Emphasis> strains isolated in Finland,Israel and Poland

Pectinolytic bacteria from the genus Dickeya (former Erwinia chrysanthemi), belonging to Dickeya dianthicola and Dickeya solani species, are causative agents of blackleg and soft rot diseases in Europe. Recently, D. solani have been isolated most frequently from potato plants with the symptoms of blackleg and soft rot. D. solani strains were shown to cause more severe disease symptoms on potato plants than D. dianthicola especially at the higher temperature. They are also able to develop blackleg disease from lower inoculum levels. In the presented study we not only compared phenotypic features of fifteen D. solani strains isolated in countries having different climatic conditions, Poland, Finland and Israel, but also we examined three D. dianthicola strains. The comparison was performed to determine the influence of the strain origin and the temperature of incubation on the ability of the strains to macerate potato tissue and on their major virulence factors such as: pectinolytic, cellulolytic and proteolytic activities, siderophore production and motility. Polish D. solani strains showed higher activities of cell wall degrading enzymes than the Finnish and Israeli strains at all the tested temperatures: 18, 27, 37 °C. This observation is correlated with the higher ability of Polish D. solani strains to cause soft rot. In addition, D. solani strains exhibited higher activity of the above mentioned enzymes and caused more severe potato tuber maceration in laboratory tests than the tested D. dianthicola strains. The collected results indicate that although D. solani strains from different climatic conditions have identical Pulse Field Gel Electrophoresis (PFGE) profiles in addition to the same fingerprint profiles obtained by the repetitive sequence-based polymerase chain reaction (REP, ERIC and BOX repetitive sequences), they differ in the examined phenotypic features, especially in the activities of pectinolytic, cellulolytic and proteolytic enzymes and their capacity to macerate potato tuber tissue.     

Response of sorghum stalk pathogens to <Emphasis Type="Italic">brown midrib</Emphasis> plants and soluble phenolic extracts from near isogenic lines

Sorghum [Sorghum bicolor (L.) Moench] has drawn attention as potential feedstock for lignocellulosic biofuels production, and reducing lignin is one way to increase conversion efficiency. Little research has been previously conducted to assess the response of reduced lignin sorghum lines to the Fusarium stalk rot pathogens Fusarium verticillioides and Fusarium proliferatum and the charcoal rot pathogen, Macrophomina phaseolina. Loss of function mutations in either the Brown midrib (Bmr) 6 or 12 gene that both encode a monolignol biosynthetic enzyme in the pathway that produces subunits of the lignin polymer, results in reduced lignin content. Near-isogenic bmr6, bmr12, and bmr6 bmr12 lines had previously been developed, which were shown to have significantly reduced lignin content and increased levels of soluble phenolics. In the current study, these lines in two backgrounds were shown to not be more susceptible to F. verticillioides, F. proliferatum and M. phaseolina inoculations, and some bmr lines exhibited increased resistance to F. proliferatum and M. phaseolina, compared to wild-type lines. When the Fusarium stalk rot pathogen, Fusarium thapsinum, was grown on methanol soluble stalk extracts from bmr6 and wild-type plants, it grew significantly faster on medium with bmr6 extract than on wild-type extract or controls. This result suggested that factors other than soluble phenolics from the extract, such as cell wall bound phenolics or inducible defense compounds, contributed to increased resistance observed in bmr6 plants.