Does <Emphasis Type="Italic">Puccinia hemerocallidis</Emphasis> regularly host-alternate between <Emphasis Type="Italic">Hemerocallis</Emphasis> and <Emphasis Type="Italic">Patrinia</Emphasis> plants in Japan?

Daylily rust fungus, Puccinia hemerocallidis, was proven to host-alternate between a wild daylily, Hemerocallis fulva var. longituba, and a patrinia, Patrinia villosa. No proof was obtained for the early belief that the fungus is pathogenic to plantainlilies, Hosta species, in addition to daylilies, Hemerocallis species. The fungus seems to alternate regularly between daylilies and patrinias in Japan because most daylily species are deciduous, and a vegetatively reproducing stage of the pathogen does not seem capable of successfully overwintering free of the living host tissue.     

Modelling pathogen competition and displacement– <Emphasis Type="Italic">Phytophthora infestans</Emphasis> in Scandinavia

Populations of Phytophthora infestans have displaced less fit populations in a number of regions, but not in Scandinavia. In order to study this process, a simple epidemic model was developed, based on the Lotka-Volterra model for competition. The model contains two epidemics, each with logistic growth of two separate populations that interact with each other in that they compete for the same resource base (the plant). In Scandinavia, epidemics from suspected oospore infections are thought to start earlier than those originating from tubers, so routines were added to allow the epidemics to start at different time points. A numerical solution to the model was developed using the deSolve package of the open-source statistical program ‘R’. The resulting model allows examination of the relative importance of different values for the apparent infection rates and starting parameters for the two sub-epidemics. If epidemics from oospore infections start earlier than those from tuber infections, the delay for epidemic initiation via tuber infection would require extremely high values of r in order for this population to dominate at the end of the season. This could be one reason for the lack of persistent clones in the Scandinavian Phytophthora infestans population.     

First report of ‘<Emphasis Type="Italic">Candidatus</Emphasis> Phytoplasma malaysianum’ associated with <Emphasis Type="Italic">Elaeocarpus</Emphasis> yellows of <Emphasis Type="Italic">Elaeocarpus zollingeri</Emphasis>

“Elaeocarpus yellows” (ELY) is a widely reported phytoplasma disease of Elaeocarpus zollingeri trees in Japan. The phytoplasma associated with ELY (ELY phytoplasma) had not been identified at the species level because its 16S rRNA sequence had yet to be reported. Here, we report the results of a sequence analysis based on 16S rRNA and secA gene sequences, which showed that the ELY phytoplasma is related to ‘Candidatus Phytoplasma malaysianum’. To our knowledge, this is the first report showing the occurrence of ‘Ca. P. malaysianum’ outside Malaysia and the infection of E. zollingeri by the phytoplasma.     

Effect of polyploidisation on the response of apple (<Emphasis Type="Italic">Malus</Emphasis> × <Emphasis Type="Italic">domestica</Emphasis> Borkh.) to <Emphasis Type="Italic">Venturia inaequalis</Emphasis> infection

Spinach is one of the most nutritious green-leaf vegetables. In the spinach production, diseases cause a significant loss in both yield and quality. Improving disease resistance is one of the major challenges in spinach breeding. Arabidopsis nucleoporin CONSTITUTIVE EXPRESSER OF PATHOGENESIS-RELATED GENES 5 (CPR5) functions as a negative regulator of plant cell death and immunity as cpr5 mutant exhibits spontaneous cell death and heightened immunity. In addition, CPR5 play a role in trichome development as the majority of cpr5 mutant trichomes are branchless whereas wild type trichomes are often three-branched. In the spinach genome, we identified a homolog of Arabidopsis CPR5, referred to as Spinacia oleracea CPR5 (SoCPR5). To investigate the function of SoCPR5, we introduced SoCPR5 into Arabidopsis cpr5 mutant. Our data showed that both spontaneous cell death and heightened immunity were suppressed in the SoCPR5-transgenic cpr5 mutants, verifying that SoCPR5 functions as its Arabidopsis counterpart in plant cell death and immunity. SoCPR5 also fully restored wild type trichome phenotype of the cpr5 mutant. Our study therefore indicates that the function of SoCPR5 is conserved between plant species and SoCPR5 can be applied for genetic manipulation of plant immunity in spinach.     

Evaluation of PCR markers for <Emphasis Type="Italic">Phytophthora infestans</Emphasis> mating type determination

Late blight is a devastating potato disease caused by Phytophthora infestans. This organism can reproduce asexually and sexually between the strains of two mating types named A1 and A2. Mating type is an important strain characteristic affecting the pathogen’s population structure. We validate different PCR markers for P. infestans mating type determination by comparison of the results obtained with the markers (W16, S1, PHYB) with the pairing test results for 26 isolates collected worldwide and for a group of 146 Polish isolates. This study identifies an interesting feature of the isolates of genotype US-1. For all these A1 mating type isolates, the product specific for A2 isolates is amplified using the marker W16. Analysis of sequences of W16 PCR products indicates high similarity of the US-1 isolates with modern A2 mating type isolates. When US-1 isolates are excluded from analysis, 95 and 96% of isolates are correctly assigned by markers W16 and S1, respectively, when compared with the pairing test results. Marker PHYB produces 14% of discrepant results with the pairing test. Our results show that molecular markers can be useful tools for P. infestans mating type determination, but their application should be preceded by validation in each local population since their efficiency may vary depending on a pathogen’s genotype.     

Activity of <Emphasis Type="Italic">ß</Emphasis>-1,3-glucanase and <Emphasis Type="Italic">ß</Emphasis>-1,4-glucanase in two potato cultivars following challenge by the fungal pathogen <Emphasis Type="Italic">Alternaria solani</Emphasis>

Early blight of potato, caused by Alternaria solani, is a ubiquitous disease in many countries around the world. Our previous screening of several Iranian potato cultivars found that variation in resistance exists between two cultivars: ‘Diamond’ and ‘Granula’. Cultivar Diamond is more resistant to multiple isolates of A. solani when compared to cv. Granula. Furthermore, we have found that different pathogen isolates have varying degrees of infection. We monitored the activities of two pathogen-related (PR) glucanase proteins in Diamond and Granula in response to two isolates of A. solani with different degrees of virulence. ß-1,3-glucanase and ß-1,4-glucanase activities were recorded in healthy and diseased leaves of potatoes up to 10 days after inoculation. Their activities were found to be higher in diseased leaves when compared to those of uninfected leaves. Our data suggest that significantly reduced activities of theses enzymes in potato could be related to a lower degree of resistance or an increased ability of a more aggressive isolate to suppress PR protein expression.     

<Emphasis Type="Italic">In planta</Emphasis> multiplication and graft transmission of ‘<Emphasis Type="Italic">Candidatus</Emphasis> Liberibacter asiaticus’ revealed by Real-Time PCR

The bacterium Candidatus Liberibacter asiaticus (CLas) is associated with huanglongbing (HLB) in citrus in many countries. Despite the fact that many characteristics of the disease are known, the rate of multiplication of the bacterium within an infected tree is still poorly understood. To study this feature, we used the quantitative Real-Time polymerase chain reaction (Q-PCR) assay to follow and to quantify the multiplication of CLas in grafted infected young sweet orange plants. The rate of infection by grafting reached 100% at 120 days post-inoculation (dpi) showing that grafting could easily transmit CLas. A well-adjusted linear regression equation describing the bacterial growth in planta was obtained independently with measurements taken using repeated sampling in the same plant or different plants through the analysed period. The bacterial population, measured as copy number (CN) of the 16S rDNA target gene g⁻¹ of tissue, increased 10,000 times from 10³ at 30 dpi to approximately 10⁸ CN at 240 dpi indicating that CLas multiplication was fastest in young citrus plants. We observed a direct relationship between the concentration of pathogen and the expression of symptoms. Yellowed leaves or shoots, are commonly the first observed symptom of HLB, and were present in trees with a low amount of bacteria (10⁵ CN g⁻¹). Blotchy mottle symptoms were observed in trees with 10⁷ CN g⁻¹ of bacteria after 180 dpi. Buds taken from infected, but non-symptomatic branches were grafted on Rangpur lime and resulted in transmission rates ranging from 10 to 60%.     

Pathogenicity and Fungicide Sensitivity of <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> and <Emphasis Type="Italic">R. cerealis</Emphasis> Isolates

The Rhizoctonia solani species consists of multinucleate isolates that belong to anastomosis groups AG1–AG3 and differ in virulence and host affinity. R. cerealis is a binucleate species of anastomosis group AG-D which causes sharp eyespot, a common plant disease in Poland. Rhizoctonia spp. is a ubiquitous soil pathogen that poses a significant threat for global crop production due to the absence of effective crop protection products. The aim of this study was to determine the virulence of R. solani and R. cerealis isolates towards Beta vulgaris, Zea mays, Triticum spelta and T. aestivum seedlings, to confirm the presence of endopolygalacturonase genes pg1 and pg5 in the genomes of the tested isolates and to evaluate the tested isolates’ sensitivity to triazole, strobilurin, imidazole and carboxamide fungicides. All tested isolates infected B. vulgaris seedlings. but none of them were virulent against Z. mays plants. R. solani isolates AG4 PL and AG2-2IIIB PL were characterized by the highest virulence (average infestation score of 2.37 and 2.53 points on a scale of 0–3 points) against sugar beet seedlings. The prevalence of infections caused by most of the analysed isolates (in particular R. solani AG4 J—11.8, and R. cerealis RC2—0.78) was higher in spelt than in bread wheat. The virulence of the analysed isolates was not correlated with the presence of pg1 and pg5 genes. The efficacy of the tested fungicides in controlling Rhizoctonia spp. infections was estimated at 100% (propiconazole + cyproconazole), 98.8% (penthiopyrad), 95.4% (tebuconazole) and 78.3% (azoxystrobin).     

Transgenic citrus expressing the antimicrobial gene <Emphasis Type="Italic">Attacin E</Emphasis> (<Emphasis Type="Italic">attE</Emphasis>) reduces the susceptibility of ‘Duncan’ grapefruit to the citrus scab caused by <Emphasis Type="Italic">Elsinoë fawcettii</Emphasis>

Citrus scab, caused by Elsinoë fawcettii (anamorph Sphaceloma fawcettii), is a common foliar fungal disease affecting many citrus cultivars, including grapefruit. No commercial grapefruit cultivar is resistant to scab, and the disease results in severely blemished fruit which reduces its marketability. Transgenic ‘Duncan’ grapefruit trees expressing the antimicrobial attE gene were produced via Agrobacterium-mediated transformation. In in vitro leaf and greenhouse assays, several transgenic-lines had significantly lower susceptibility to E. fawcettii compared to the non-transformed control (P?P?P?attE mRNA was inversely related to the number of copies detected by Southern blot. The least susceptible line had a single inserted copy of the attE transgene whereas more susceptible lines had multiple copies. Since the attacin mode of action was thought to be specific to Gram-negative bacteria, it was unexpected to find that there was a significant activity against E. fawcettii.     

First report of pileus rot disease on cultivated <Emphasis Type="Italic">Morchella importuna</Emphasis> caused by <Emphasis Type="Italic">Diploöspora longispora</Emphasis> in China

In March 2013, pileus rot disease was first observed on cultivated Morchella importuna. Infected ascomata were covered by white, velvety mycelia mainly on the pileus, and the infection resulted in malformed fruiting bodies. The causal pathogen was identified as Diploöspora longispora based on its morphology and the internal transcribed spacer of its ribosomal DNA sequences. After inoculation of young ascomata with the isolates, the original symptoms were reproduced, and the same pathogen was reisolated from diseased ascomata. This is the first report of pileus rot disease on morels caused by D. longisporain China.     

<Emphasis Type="Italic">Talaromyces wortmannii</Emphasis> FS2 emits <Emphasis Type="Italic">β</Emphasis>-caryphyllene,which promotes plant growth and induces resistance

A plant-growth-promoting fungus (PGPF), Talaromyces sp. was isolated from an agricultural field in southwestern Japan. We found that this fungus emitted several terpenoid-like volatiles including β-caryophyllene. Then we investigated the effect of β-caryophyllene on promoting the growth and inducing resistance of Brassica campestris L. var. perviridis. The compound significantly enhanced the growth of seedlings and their resistance to Colletotrichum higginsianum. On the basis of these results, we discuss the role of β-caryophyllene in the activities of PGPF.     

<Emphasis Type="Italic">Spiraea salicifolia:</Emphasis> a new plant host of “<Emphasis Type="Italic">Candidatus</Emphasis> Phytoplasma ziziphi”-related phytoplasma

Spiraea salicifolia is widely grown in China as an ornamental plant, and its roots and young leaves have many medical uses. On the campus of Northwest A&F University, we observed diseased S. salicifolia plants that had yellowed, dwarfed, deformed leaves and other symptoms resembling diseases caused by phytoplasma. This study was aimed at determining the causal agent of the disease. On the basis of phytoplasma-specific DNA amplification by PCR, a phytoplasma infection of S. salicifolia was confirmed. The phytoplasma was related to “Ca. Phytoplasma ziziphi” according to RFLP and phylogenetic analyses. This report is the first of phytoplasma infection of S. salicifolia in China.     

Mechanisms of induced resistance in lettuce against <Emphasis Type="Italic">Bremia lactucae</Emphasis> by DL<Emphasis Type="Bold">-</Emphasis>β<Emphasis Type="Bold">-</Emphasis>amino<Emphasis Type="Bold">-</Emphasis>butyric acid (BABA)

BABA induced local and systemic resistance in lettuce (Lactuca sativa) against the Oomycete Bremia lactucae. Structure-activity analysis showed no induced resistance by related amino-butanoic acids or β-alanine. The R-enantiomer of BABA induced resistance whereas the S-enantiomer did not, suggesting binding to a specific receptor. Other compounds known to be involved in SAR signaling, including abscisic acid, methyl-jasmonate, ethylene, sodium-salicylate and Bion® (BTH) did not induce resistance. Systemic translocation of ¹⁴C-BABA and systemic protection against downy mildew were tightly correlated. BABA did not affect spore germination, appressorium formation, or penetration of B. lactucae into the host. Epifluorescence and confocal microscopy revealed that BABA induced rapid encasement with callose of the primary infection structures of the pathogen, thus preventing it from further developing intercellular hyphae and haustoria. Invaded host cells treated with BABA did not accumulate phenolics, callose or lignin, or express HR. In contrast, cells of genetically-resistant cultivars accumulated phenolics, callose and lignin and exhibited HR within one day after inoculation. The callose synthesis inhibitor DDG did not inhibit callose encasement nor compromised the resistance induced by BABA. PR-proteins accumulated too late to be responsible for the induced resistance. DAB staining indicated that BABA induced a rapid accumulation of H₂O₂ in the penetrated epidermal host cells. Whether H₂O₂ stops the pathogen directly or via another metabolic route is not known.     

Characterisation of <Emphasis Type="Italic">Phytophthora infestans</Emphasis> isolates collected from potato in Estonia during 2002–2003

A collection of 101 isolates of Phytophthora infestans, obtained from seven sampling sites representing central, east and south-east Estonia during 2002 and 2003 were assessed for several phenotypic and genotypic markers. All 101 isolates were assessed for virulence and resistance to metalaxyl. Virulence to each of the 11 classic resistance genes was found among the tested isolates. The mean number of virulences per isolate was 6.3, with a very low frequency of virulence against resistance genes R5 (5%) and R9 (14%). The most common pathotypes were 1.3.4.7.8.10.11 and 1.3.4.7.10.11, representing altogether 12% of the studied strains. In terms of metalaxyl resistance, 30 resistant, 52 intermediate and 19 sensitive isolates were found. A subgroup of 50 isolates was assessed for mating type, allozymes [glucose-6-phosphate isomerase (Gpi) and peptidase (Pep)], DNA fingerprints with probe RG57 and mtDNA haplotype. Of this subset, 30 were A1 and 20 were A2. Collections from three of the seven fields contained both mating types. Allozyme analysis did not reveal any polymorphism. However, 19 diverse RG57 fingerprints were detected, and two mitochondrial DNA haplotypes, Ia and IIa, were detected. By combining the mating type, mtDNA haplotype and RG57 fingerprint data, 26 multilocus genotypes were identified, of which 18 were detected only once. Genotypic diversity measured by the normalised Shannon diversity index was high (0.76). The large number of multilocus genotypes and the presence of both mating types in some fields indicate that sexual reproduction may take place in Estonian populations of P. infestans.     

PCR-mediated Detection of <Emphasis Type="Italic">Xanthomonas oryzae </Emphasis>pv. <Emphasis Type="Italic">oryzae </Emphasis>by Amplification of the 16S–23S rDNA Spacer Region Sequence

A detection method specific for Xanthomonas oryzae pv. oryzae, the pathogen responsible for bacterial blight of rice, was based on the polymerase chain reaction (PCR) and designed by amplifying the 16S–23S rDNA spacer region from this bacterium. The nucleotide sequence of the spacer region between the 16S and 23S rDNA, consisting of approximately 580-bp, from X. oryzae pv. oryzae, X. campestris pv. alfalfae, X. campestris pv. campestris, X. campestris pv. cannabis, X. campestris pv. citri, X. campestris pv. cucurbitae, X. campestris pv. pisi, X. campestris pv. pruni and X. campestris pv. vitians, was determined. The determined sequences had more than 95% identity. Therefore, a pair of primers, XOR-F (5′-GCATGACGTCATCGTCCTGT-3′) and XOR-R2 (5′-CTCGGAGCTATATGCCGTGC-3′) was designed and found to specifically amplify a 470-bp fragment from all strains of X. oryzae pv. oryzae isolated from diverse regions in Japan. No PCR product was amplified from X. campestris pathovars alfalfae, campestris, cannabis, carotae, cucurbitae, dieffenbachiae, glycines, pisi, pruni, vitians or zantedeschiae, except for pathovars citri, incanae and zinniae. The method could also detect the pathogen in infected rice leaves within 3 hr, at a detection limit of 4×10¹ cfu/ml. Received 17 December 1999/ Accepted in revised form 10 April 2000     

Influence of Stigmatic Morphology on Flower Colonization by <Emphasis Type="Italic">Erwinia amylovora</Emphasis> and <Emphasis Type="Italic">Pantoea agglomerans</Emphasis>

The morphology of apple and pear stigma was investigated with confocal laser scanning microscopy and scanning electron microscopy. The floral colonization process by Erwinia amylovora was studied with gfp-labelled bacteria and confocal laser scanning microscopy to allow the in vivo observation of the pathogen colonization on intact, viable plant tissues without any kind of staining of the specimens. The interaction on the stigma between Erwinia amylovora and Pantoea agglomerans, both labelled with genes encoding for fluorescent proteins (DsRed-GFP), was also investigated. A stylar groove, covered by papillae and dwelling from the stigma along the style, was visualized. In laboratory conditions, this groove was shown to be an important way for E. amylovora migration towards the nectarthodes. Due to its anatomical structure the groove can sustain bacterial multiplication and thus may play an important role on the interactions between the pathogen and the bacterial antagonist P. agglomerans.     

Diversity of defence mechanisms in plant–oomycete interactions: a case study of <Emphasis Type="Italic">Lactuca</Emphasis> spp. and <Emphasis Type="Italic">Bremia lactucae</Emphasis>

Plant pathogenic oomycetes, including biotrophic downy mildews and hemibiotrophs/necrotrophs such as Phytophthora and Pythium, cause enormous economic losses on cultivated crops. Lettuce breeders and growers face the threat of Bremia lactucae, the causal agent of lettuce downy mildew. This pathogen damages leaf tissues and lettuce heads and is also frequent on wild Asteraceae plants. The interactions of Lactuca spp. with B. lactucae (abbr. lettuce–Bremia) display extreme variability, due to a long co-evolutionary history. For this reason, during the last 30 years, the lettuce–Bremia pathosystem has been used as a model for many studies at the population, individual, organ, tissue, cellular, physiological and molecular levels, as well as on genetic variability and the genetics of host–parasite interactions. The first part of this review summarizes recent data on host–parasite specificity, host variability, resistance mechanisms and genetics of lettuce–Bremia interactions. The second part focuses on the development infection structures. Phenotypic expression of infection, behaviour of B. lactucae on leaf surfaces, the process of penetration, development of primary infection structures, hyphae and haustoria are discussed in relation to different resistance mechanisms. In the third part, the components of host resistance and the variability of defence responses are analysed. The role of reactive oxygen species (ROS), antioxidant enzymes, nitric oxide (NO), phenolic compounds, reorganization of cytoskeleton, electrolyte leakage, membrane damage, cell wall disruption, hypersensitive reaction and plant energetics are discussed in relation to defence responses. In general, the extreme variability of interactions between lettuce and Bremia, and their phenotypic expression, results from diversity of the genetic background. Different mechanisms of resistance are conditioned by an orchestra of defence responses at the tissue, cell, and molecular levels. The various events responsible for defence involve a complex interaction of the processes and reactions mentioned above. This review also provides an overview on the timing of pathogen development, host pathological anatomy, cytology and physiology of lettuce–Bremia associations. The significance of these factors on the expression of different resistance mechanisms (non-host and host resistance, race-specific and race non-specific resistance, field resistance) is discussed.