First Report of Powdery Mildew Caused by Podosphaera xanthii on Cuphea hyssopifolia (Lythraceae) in Mainland China

Cuphea hyssopifolia (Mexican heather) is a popular evergreen perennial shrub used for ornamental and medicinal purposes. Due to its high ornamental value, it is often used as a ground cover in parks and gardens in China. During February and March 2019 & 2020, powdery mildew was observed on C. hyssopifolia in the districts of Minhou and Jinshan of Fuzhou, China. Disease incidence was 70% but of low severity with only a few older leaves showing yellowing and wilting. Sparse irregular patches of white superficial powdery mildew observed on both sides of mature and young leaves. The powdery mildew fungal appressoria that occurred on epigenous hyphae, were indistinct to nipple-shaped, hyaline, and smooth. Conidiophores were erect, smooth, 80 to 210 × 10 to 12 µm, and produced two to eight crenate-shaped conidia in chains. Foot-cells of conidiophores were straight, cylindric, and 30 to 65 × 10 to12 µm. Conidia were hyaline, smooth, ellipsoid-ovoid to barrel-shaped, 25 to 38 × 16 to 20 µm with distinct fibrosin bodies. Germ tubes were simple to forked and produced from the lateral position of the germinating conidia. No chasmothecia were observed on the surface of infected leaves. Based on the morphology of the imperfect state, the powdery mildew fungus was identified as Podosphaera xanthii (Castagne) U. Braun & N. Shishkoff (Braun and Cook 2012). To confirm fungal identification, total DNA was extracted (Mukhtar et al., 2018) directly from epiphytic mycelia on infected leaves collected from both districts. Internal transcribed spacer (ITS) regions and the partial large subunit (LSU) rDNA were amplified using primers ITS1/ITS4 and LSU1/LSU2 (Scholin et al. 1994, White et al. 1990), respectively. The sequences were deposited in GenBank (ITS: MW692364, MW692365; LSU: MW699924, MW699925). The ITS and LSU sequences were 99 to 100 % identical to those of P. xanthii in GenBank, (ITS: MT568609, MT472035, MT250855, and AB462800; LSU: AB936276, JX896687, AB936277, and AB936274). Koch’s postulates were completed by gently pressing diseased leaves onto leaves of five healthy potted C. hyssopifolia plants that were held in a greenhouse at 24 to 30°C without humidity control. Five non-inoculated plants served as controls. Inoculated plants developed symptoms after 6 to 10 days, whereas the controls remained symptomless. The morphology of the fungus on the inoculated leaves was identical to that observed on the originally diseased leaves. Previously, Podosphaera sp. has been reported on C. rosea in the United Kingdom (Beales & Cook 2008) and P. xanthii on C. hyssopifolia in Taiwan (Yeh et al. 2021). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on C. hyssopifolia in mainland China. Our field observations suggest that the P. xanthii infections would be a potential threat to the health of C. hyssopifolia in China. References: Beales, P. A., and Cook, R. T. A. 2008. Plant Pathol. 57:778. Braun, U., Cook, R. T. A. 2012. The Taxonomic Manual of the Erysiphales (Powdery Mildews). CBS Biodiversity Series 11: CBS. Utrecht, The Netherlands. Mukhtar, I., et al. 2018. Sydowia.70:155. Scholin, C. A., et al. 1994. J. Phycol. 30:999. White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. Yeh, Y. W., et al. 2021. Trop. Plant Pathol. 46:44.

First Report of Fusarium wilt of Coleus forskohlii Caused by Fusarium oxysporum in China

Coleus forskohlii (Wild) Briq. is an aromatic plant in the Lamiaceae family cultivated primarily in India, Sri Lanka, Nepal and China (Yunnan Province). This herb is considered to have medicinal properties and the whole plant can be used to treat asthma, cancer and other diseases with remarkable efficacy. Due to the high medicinal and economic value of C. forskohlii, it has been introduced to Tongcheng (N29°18′12.24″, E113°53′59.36″), Hubei Province for cultivation. However, severe Fusarium wilt disease of C. forskohlii has been epidemic in Tongcheng since 2018 with a disease incidence of 5 to 30% in surveyed fields. This disease is characterized typically by root rot, vascular discoloration and leaf wilting of C. forskohlii (Fig 1), resulting in progressive plant death. Ten diseased plants were collected from the fields and the roots and stems were rinsed in 70% ethanol for 5 min and samples at the junction of disease and healthy tissues (0.5 × 0.5 cm2) were cutted and placed on potato dextrose agar (PDA) for fungal isolation in a dark chamber at 28°C. Eventually, ten pure isolates were obtained from hyphal-tip followed by single-spore purification on PDA. Seven of the purified isolates showed white aerial mycelium initially and secreted orange-brown pigment 8 days after incubation. Macroconidia were falciform, hyaline, three to five septate, ranging from 2.02 to 4.17 (mean 2.98 µm) × 10.05 to 21.90 µm (mean 12.04 µm) in size (n = 30) (Fig 2). These morphological characteristics resembled Fusarium oxysporum. (Leslie and Summerell 2006) and we selected one of them for molecular identification. Genome DNA was extracted from isolate (RS-4) using the CTAB method (Mahadevakumar et al. 2018). The translation elongation factor 1 alpha (EF-1α) DNA sequence was amplified using primers EF1/EF2 (Geiser et al. 2004), and the second largest subunit of RNA polymerase II (RPB2) DNA sequence was amplified using primers fRPB2-5F/fRPB2-7cR (Liu et al. 1999). The obtained EF-1α sequence of RS-4 (MW219142) showed 100% identity with that of F. oxysporum (FD_01376) (FUSARIUM-ID database). RPB2 sequences of RS-4 (MW219143) showed 100% identity with F. oxysporum (FD_01679) (FUSARIUM-ID database). Moreover, a phylogenetic tree of the EF-1α gene sequence of RS-4 was constructed based on the Neighbor-Joining method in MEGA7 software (Tamura et al. 2013) and revealed that strain RS-4 was closest to F. oxysporum (Fig 2). To test the pathogenicity of RS-4, six healthy leaves of C. forskohlii were collected and inoculated either with the colonized PDA discs (diameter, 5 mm) of RS-4 or control PDA discs, in a moist chamber at 25 ± 2°C. Five days later, brown-black lesions were observed on all inoculated leaves. However, the non-inoculated leaves were maintained asymptomatic. For in vivo pathogenicity test, twenty-day-old C. forskohlii plants (n=3) were inoculated with 106 spores/ml of the RS-4 at a position approximately 1 cm above the soil. Three seedlings treated with sterile water were used as controls. These inoculated and control seedlings were incubated in a moist chamber (25 ± 2 °C, RH 85%). Three days later, typical Fusarium rot symptoms were observed on all inoculated seedlings with rotten stems and withering leaves (Fig 2). Fungal pathogens were re-isolated from the inoculated sites of in vitro and in vivo inoculations by repeating the above isolating operation, and were reconfirmed through morphological features. This is the first report of F. oxysporum causing root rot on C. forskohlii in China. F. oxysporum is one of the most economically important fungal pathogens causing vascular wilt on a wide range of plants worldwide (Dean et al. 2012). The identification of F. oxysporum as the causal agent of the observed Fusarium wilt on C. forskohlii, is critical to the prevention and control of this disease in the future. Acknowledgement This research was supported by funding from the Key project at the central government level titled, “The ability to establish sustainable uses for valuable Chinese medicinale resources” (2060302) Reference Dean, R., et al. 2012. Mol. Plant. Pathol. 13: 414. https://doi.org/10.1111/j.1364-3703.2011.00783.x. Geiser, D. M., et al. 2004. Eur. J. Plant Pathol. 110: 473. https://doi.org/10.1023/B:EJPP.0000032386.75915.a0. Leslie, J. F. and Summerell, B. A. 2006. The Fusarium Laboratory Manual. Blackwell Publishing, Oxford, U.K. Liu, Y. J., et al. 1999. Mol. Biol. Evol. 16: 1799. https://doi.org/10.1093/oxfordjournals.molbev.a026092 Mahadevakumar, S. et al. 2018. Eur. J. Plant Pathol. 151:1081. https://doi.org/10.1007/s10658-017-1415-2. Tamura, K., et al. 2013. Mol. Biol. Evol. 30: 2725. https://doi.org/10.1093/molbev/msw054.

First Report of Bacterial Leaf Spot Disease of Broussonetia papyrifera Caused by Pseudomonas syringae pv. actinidiae in China

Broussonetia papyrifera (paper mulberry) is a deciduous tree with a number of uses and is native to northeastern Asia. Because of its fast-growing nature and high tolerance to dust, smoke, and high temperatures, paper mulberry is regarded as an important and economically-valuable component of a biologically diverse community and is used extensively in several areas including medicine, animal husbandry, paper making, weaving, afforestation and light industry (Mei et al. 2016). From June to August of 2019, symptoms on paper mulberry trees were observed in Shiniushan village, Sanhua town, Xishui County, Hubei province of China. Typical symptoms on leaves included small, angular, brown spots surrounded by yellow haloes. These spots coalesced into necrotic areas. The incidence was around 30%, which threatened the survival and reduced the yield of paper mulberry. In order to identify the causal pathogenic organism, leaf samples from 10 different infected trees were collected every two weeks and isolations made over three months. Several circular, flat, granulated colonies with entire margins were isolated on King’s B medium (KB). The biochemical and physiological characteristics of thirty typical strains were tested and listed as following: gram negative, aerobic, rod shaped, and non-fluorescent on King’s B medium; positive for carbohydrate utilization (sucrose, glucose, fructose and arabinose), levan production, hypersensitive on tobacco, potato and tomato; and negative for oxidase, arginine dehydrolase, tyrosinase and urease activity, gelatin liquefaction, and reduction of nitrate. Psa pathovar-specific primers PsaF1/PsaR2 (280bp product ) identified two representative strains as Psa (Rees-George et al. 2010). BLAST analysis further confirmed that the 16S rDNA region amplified by primers 27F/1492R (NCBI accession nos. MT472100 and MT472101) shared 99.84% and 99.77% identity with the Psa type strain ICMP 18884 (CP011972) respectively (Weisburg et al. 1991). For ten typical strains, pathogenicity was confirmed by spraying a bacterial suspension (108 cfu/mL) onto fifty one-year seedlings of B. papyrifera, five seedlings repetitions for each strain. Symptoms of infection similar to those observed initially in the field were detected within 7 days after incubation at 25°C with 80–85% humidity. No symptoms were observed on control plants. The pathogen was re-isolated from symptomatic leaves and re-identified as Psa by morphological characteristics and sequencing. To our knowledge, this is the first report of Psa causing bacterial leaf spot disease on B. papyrifera, China. Psa has been reported as a pathogen causing bacterial canker of kiwifruit worldwide, resulting in severe economic losses to kiwifruit growers (McCann & Li, 2017). As a host of Psa, B. papyrifera may be a source of inoculum for nearby kiwifruit orchards, and consequently effective control measures should be taken to manage this disease. Funding: This study was supported by the National Natural Science Foundation of China (31701974; 31901980), Science and technology program funded by Wuhan Science and Technology Bureau (2018020401011307). References: Mei et al. 2016. Eur J Plant Pathol. 145: 203. McCann & Li et al. 2017. Genome Biol Evol. 9: 932. Rees-George et al. 2010. Plant Pathol. 59: 453 Weisburg et al. 1991. J Bacteriol. 173: 697.

First Report of Grapevine Pinot gris virus (GPGV) in grapevine in France

Grapevine Pinot gris virus (GPGV), belonging to the genus Trichovirus of the family Betaflexiviridae, was first identified by siRNA sequencing in northern Italy in 2012, in the grapevine varieties Pinot gris, Traminer, and Pinot Noir, which exhibited mottling and leaf deformation (1), and in asymptomatic vines, with a lower frequency. Since 2012, this virus has also been reported in South Korea, Slovenia, Greece (3), Czech Republic (2), Slovakia (2), and southern Italy (4). In 2014, GPGV was identified by Illumina sequencing of total RNAs extracted from leaves of the Merlot variety (Vitis vinifera) grafted onto Gravesac rootstock originated from a vineyard in the Bordeaux region of France. This Merlot plant exhibited fanleaf-like degeneration symptoms associated with Tomato black ring virus (TBRV) infection. Cuttings were collected in 2010 and maintained thereafter in a greenhouse. The full-length genome was assembled either de novo or by mapping of the Illumina reads on a reference GPGV genome (GenBank FR877530) using the CLC Genomics workbench software (CLC Bio, Qiagen, USA). The French GPGV isolate “Mer” (7,223 nucleotides, GenBank KM491305) is closely related to other European GPGV sequences; it exhibits 95.4% nucleotide identity with the reference Italian isolate (NC_015782) and 98 to 98.3% identity with Slovak isolates (KF134123 to KF134125). The higher divergence between French and Italian GPGV isolates was mainly due to differences in the 5′ extremity of the genome, as already shown with the Slovak GPGV isolates. RNA extracted from phloem scrapings of 19 cv. Merlot vines from the same plot collected in 2014 were analyzed by RT-PCR using the specific primer pair Pg-Mer-F1 (5′-GGAGTTGCCTTCGTTTACGA-3′) and Pg-Mer-R1 (5′-GTACTTGATTCGCCTC GCTCA-3′), designed on the basis of alignments of all available GPGV sequences from GenBank. The resulting amplicon of 770 bp corresponded to a fragment of the putative movement protein (MP) gene. Seven (35%) of the tested plants gave a strong positive amplification. Three RT-PCR products were directly sequenced and showed 99.3 to 99.5% identity within the MP gene of the GPGV-Mer isolate. Given the mixed viral infection status of the vines found infected by GPGV, it was not possible to associate a specific symptomatology with the presence of GPGV. Furthermore, similar RT-PCR tests were also performed on RNA extracts prepared from two plants of cv. Carignan that originated from a French grapevine collection, exhibiting fanleaf-like symptoms without any nepovirus detection. These samples similarly gave a strong positive amplification. The sequences obtained from the two Carignan vines showed 98.4 and 97.8% identity with the GPGV-Mer isolate. To our knowledge, this is the first report of GPGV in France. GPGV has been discovered in white and red berry cultivars, suggesting that its prevalence could be important in European vineyards (2). Further large-scale studies will be essential to determine the world prevalence of GPGV and to evaluate its potential effects on yield and on wine quality, as well as to shed light on GPGV epidemiology. Of particular concern is whether, like the other grapevine-infecting Trichovirus, Grapevine berry inner necrosis virus (GPGV) can be transmitted by the eryophid mite Colomerus vitis. References: (1) A. Giampetruzzi et al. Virus Res. 163: 262, 2012. (2) M. Glasa et al. Arch. Virol. 159: 2103, 2014. (3) G. P. Martelli, J. Plant Pathol. 96: S105, 2014. (4) M. Morelli et al. J. Plant Pathol. 96:431, 2014.

First Report of Puccinia psidii (Myrtle Rust) in Eucalyptus Plantations in Australia

Puccinia psidii Winter (myrtle rust, eucalyptus rust) is a significant pathogen of Eucalyptus plantations in Brazil, causing reduced growth, stem malformation, and in severe cases, tree death (3). It has a wide host range in the Myrtaceae, with over 445 species in more than 72 genera (4). As such, P. psidii has long been a threat to Australia, where many ecosystems are dominated by Myrtaceae and industries are reliant on myrtaceous hosts, including almost 1 million hectares of eucalypt plantations. In April 2010, P. psidii was detected in Australia (2) and is now established along the east coast from southern New South Wales to far north Queensland (1,5). Although known to cause severe damage to eucalypt seedlings and coppice in native forests (5), it had not been found affecting eucalypt plantations in Australia. Surveys for P. psidii were thus initiated in eucalypt plantations in NSW from the central coast (33°06′40.0″ S, 151°18′13.8″ E) to the NSW–Queensland border, encompassing 55 plantations. Two to four 100-tree transects were conducted per plantation, during spring and summer. Symptoms were first detected in December 2011 in a 6-month-old Eucalyptus agglomerata Maiden plantation on the central coast. Further surveys until summer 2014 identified P. psidii on E. pilularis Sm., E. cloeziana F. Muell., and E. grandis (Hill) Maiden in young plantations from the central coast to the north coast (30°24′20.2″ S, 152°55′57.9″ E) of NSW. Necrotic lesions and yellow pustules typical of P. psidii were present on immature leaves and shoots, often causing leaves to buckle and die. Urediniospores were globose to subglobose, yellowish brown, 15 to 20 × 18 to 23 μm, single-celled, and finely echinulate, with a prominent tonsure on the majority of spores. Teliospores were cylindrical to ellipsoidal with a rounded apex, tan brown, 25 to 45 × 15 to 25 μm, and two-celled, with remnants of a pedicel. These morphological characteristics are consistent with those of P. psidii from Australia and elsewhere (5). Simple Sequence Repeats developed from genome sequencing of an Australian isolate of P. psidii revealed no variation among 15 isolates of P. psidii from Australia and Hawaii, including an isolate from an E. pilularis plantation in NSW (K. S. Sandhu and R. F. Park, unpublished), corroborating the morphological identification. This is the first report of this significant pathogen in eucalypt plantations in Australia. P. psidii was found in only five plantations during the current surveys, in trees 6 months to 2 years old, with only a low incidence (1%) per plantation. Repeat surveys revealed no ongoing disease in the same plantations after trees were three years of age. Moreover, P. psidii was found only in plantations surrounded by native forest stands, which harbor a large reservoir of susceptible hosts, such as Rhodamnia rubescens (Benth.) Miq. The strain of P. psidii that entered Australia is currently not causing serious disease in eucalypt plantations. However, there is a need to continue quarantine restrictions to reduce the chance of another, more aggressive strain of P. psidii entering Australia. References: (1) A. J. Carnegie and J. R. Lidbetter. Australas. Plant Pathol. 41:13, 2012. (2) A. J. Carnegie et al. Australas. Plant Pathol. 39:463, 2010. (3) T. A. Coutinho et al. Plant Dis.82:819, 1998. (4) F. Giblin and A. J. Carnegie. Puccinia psidii (myrtle rust)—Global host list. Retrieved 2 October 2014 from http://www.anpc.asn.au/resources/Myrtle_Rust.html . (5) G. S. Pegg et al. Plant Pathol. 63:1005, 2014.

First Report of Broad bean wilt virus 2 in Leonurus sibiricus in Korea

Leonurus sibiricus L. (family Lamiaceae) has been used as a traditional herbal remedy to treat various gynecologic diseases. Although it is a widely distributed subtropical weed in Southeast Asia, L. sibiricus have been commercially cultivated on a small scale in many geographic areas of Korea. In August 2012, field-grown L. sibiricus plants showing mosaic, yellowing, and stunting symptoms were collected near a pepper field in Andong, Korea. Since L. sibiricus is only consumed as a raw material of traditional medicine in Korea, symptomatic plants lose commercial value entirely. To identify the causal agent(s) of the virus-like symptoms, total RNA was extracted from the symptomatic leaves, and a transcriptome library was generated using the TruSeq Stranded Total RNA with Ribo-Zero plant kit (Illumina, San Diego, CA) according to the standard protocol. Next-generation sequencing (NGS) was performed using an Illumina HiSeq2000 sequencer. De novo assembly of the quality filtered NGS reads (101-bp paired-end reads) were performed using the Trinity pipeline and the assembled contigs (92,329 contigs) were analyzed against the viral reference genome database in GenBank by BLASTn and BLASTx searches (3). The entire NGS procedure was performed by Macrogen Inc. (Seoul, South Korea). Among the analyzed contigs, only two large contigs were clearly of viral origin. Nucleotide blast searches showed that the first and second contigs (5,914 and 3,534 bp, respectively) have maximum identities of 91 and 95% to RNA1 of the isolate RP3 (GenBank Accession No. JX183225) and RNA2 of the isolate RP7 (JX183234) of Broad bean wilt virus 2 (BBWV-2), which were isolated from pepper in Korea. The NGS results were confirmed by analyzing the sequences of the fragments covering the entire BBWV-2 genome amplified by RT-PCR using specific primers for BBWV-2 as described previously (1). To obtain the complete genome sequence, terminal sequences of both RNA segments were analyzed by the 5′ and 3′ rapid amplification of cDNA ends (RACE) method as described previously (1). The assembled full-length sequences of BBWV-2 RNA1 and RNA2 isolated from L. sibiricus were 5,951 and 3,575 nucleotides in length, respectively, and deposited in GenBank under the accessions KM076648 and KM076649, respectively. BBWV-2 belongs to the genus Fabavirus in the family Secoviridae and it is known to have a wide host range. To investigate the host range of the BBWV-2 isolated from L. sibiricus, sap from the symptomatic leaves of L. sibiricus was inoculated to the test plants including Nicotiana benthamiana, Capsicum annuum (red pepper), and C. annuum var. gulosum (Paprika). RT-PCR detection and sequencing of the amplicons showed that all the inoculated test plants were infected with the BBWV-2 isolated from L. sibiricus. Currently, BBWV-2 is epidemic in pepper fields in Korea (1,2). Because BBWV-2 is easily transmitted by various aphids, and L. sibiricus is widely distributed in both wild and cultivated fields in Korea, this host might serve as a potential source of BBWV-2 to other crops such as pepper. To the best of our knowledge, this is the first report of BBWV-2 in L. sibiricus. References: (1) H.-R. Kwak et al. Plant Pathol. J. 29:274, 2013. (2) H.-R. Kwak et al. Plant Pathol. J. 29:397, 2013. (3) S.-E. Schelhorn et al. PLoS Comput. Biol. 9:e1003228, 2013.

First Report of Asiatic Brown Rot Caused by Monilinia polystroma on Peach in Italy

Monilinia spp. are well-known pathogens causing brown rot of fruit trees in many fruit production areas worldwide. In Italy, three Monilinia species are particularly significant with regard to fruit trees, causing blossom and twig blight and brown rot in fruits: Monilinia laxa (Aderhold and Ruhland) Honey, M. fructicola (Winter) Honey, and M. fructigena (Aderhold and Ruhland). In 2009, a new species, M. polystroma, was distinguished from M. fructigena based on morphological and molecular characteristics in Europe (3). M. polystroma is not known to occur in Italy and to date has been reported from the Czech Republic (1), Hungary (3), Poland (4), Serbia (5), and Switzerland (2). In July 2013, during a survey for fungal postharvest pathogens, stored peaches (Prunus persica (L.) Batsch) belonging to different cultivars showing brown rot symptoms were observed in the Emilia Romagna and Sardinia regions of Italy. Typical decay spots were circular and brown, tending toward black, and 5% of peaches presented a large number of yellowish or buff-colored stromata and firm decayed tissues, the symptoms originated by M. polystroma. The pathogen was isolated on V8 agar (V8A) and culture plates were incubated at 25°C in darkness for 5 days. A conidial suspension was spread on malt extract agar (MEA) and single spores were selected. M. polystroma colonies grown on potato dexstrose agar (PDA) were yellowish in color. Irregular black stromatal crusts occurred on the edges of the colonies after 10 to 12 days of incubation and on the margin was present sporogenous tissue slightly elevated above the colony surface, color buff/pale luteous (1). The conidia were one-celled, ovoid or limoniform, smooth and hyaline, and 12 to 20 × 8 to 12 μm in distilled water when grown on V8A at 22°C. The ribosomal ITS1-5.8S-ITS2 region was PCR-amplified from genomic DNA obtained from mycelium using primers ITS1 and ITS4. A BLAST search in GenBank revealed the highest similarity (99%) to M. polystroma sequences (GenBank Accession No. GU067539). Pathogenicity was confirmed using surface-sterilized mature ‘Red Heaven’ peaches. The fruits were wounded (2 × 2 × 2 mm) twice with a sterile needle and inoculated with 2-mm plugs of 7-day-old mycelia from fungal colony margins. The sample unit was represented by 10 fruits. Control fruits were inoculated with PDA. After 7 days of incubation at 20°C in plastic containers with high humidity, typical symptoms of brown rot developed on both the wounds of all inoculated fruits, while control fruits remained symptomless. By the 14th day, all fruits had rotted and the yellowish exogenous stromata appeared on the surface of infected peaches. The fungus isolated from inoculated fruit exhibited the same morphological and molecular features of the original isolates; the molecular analysis performed using the primers by Petroczy (3) confirmed the result of the PCR with ITS1 and ITS4 primers. To our knowledge, this is the first report of M. polystroma on peach in Italy. This is relevant because the new pathogen could spread into other European countries that are main peach producers (such as Spain), causing economic losses. Bringing it to the attention of the scientific community allows the arrangement of research studies for assessing potential resistances with a significant impact on disease control management. Further studies are necessary to determine geographic distribution, prevalence, and economic importance of this organism in Italy. References: (1) EPPO Reporting Service. 2011/134: First reports of Monilinia polystroma in Hungary and the Czech Republic. No. 6, 2011. (2) M. Hilber-Bodmer et al. Plant Dis. 96:146, 2012. (3) M. Petroczy and L. Palkovics. Eur. J. Plant Pathol. 125:343, 2009. (4) A. Poniatowska et al. Eur. J. Plant Pathol. 135:855, 2013. (5) M. Vasic et al. Plant Dis. 97:145, 2013.

First Report of Pseudomonas syringae pv. actinidiae, the Causal Agent of Bacterial Canker of Kiwifruit in Slovenia

In May 2013, 20 plants in a production orchard of kiwifruit (Actinidia deliciosa) cv. Hayward in the seaside area of Primorska showed small, angular, coalescing necrotic leaf spots and cankers on green shoots. In the following 2 weeks, disease progressed to wilting and shoot dieback with exudates. Symptoms were consistent with Pseudomonas syringae pv. actinidiae. Circular, flat, granulated colonies with entire margins were isolated from leaf spots on King's medium B (KB) and on sucrose nutrient agar with boric acid, cephalexine, and cycloheximide. Strains were purified on KB and showed weak fluorescence upon a prolonged incubation (>10 days) and belonged to P. syringae LOPAT group Ia (+---+). DNA was extracted from strains and plant extracts with Chelex 100 resin and Bio-Nobile QuickPick Plant Kit (Turku, Finland), respectively. PCR products of expected sizes were generated by PCR assays (2,4) from all strains and plant extract, supporting the strains as being P. syringae pv. actinidiae. Two strains (NIB Z 1870 and 1871) were further identified by cytochrome C oxidase (negative), glucose metabolism (oxidative), aesculine (negative), and nitrate (negative). Their partial rpoD gene sequences (GenBank Accession Nos. KJ724117 and KJ724118) (3) were identical to the sequence of the P. syringae pv. actinidiae pathotype strain NCPPB 3739 (FN433222, 100% coverage) and to the sequence of P. syringae pv. theae at 96% coverage (FN433271). BOX-PCR fingerprinting and multilocus sequence analysis (MLSA) based on four housekeeping genes gapA (KJ733923 and KJ733924), gltA (KJ733925 and KJ733926), gyrB (KJ733927 and KJ733928), and rpoD identified both strains as biovar 3, a highly virulent biovar of P. syringae pv. actinidiae (5). The pathogenicity of the two strains was confirmed on four plants of A. deliciosa ‘Hayward’ for each strain. Six-month-old plants were sprayed on the abaxial sides of leaves with 30 ml cell suspension prepared from a 72-h-old culture of the appropriate strain (~8 × 106 CFU/ml in 0.01 M MgSO4), covered with plastic bags for 24 h, and incubated under high relative humidity (80%) with 14 h daylight and 24/21°C day/night temperature. Three positive and three negative control plants were inoculated with the Italian P. syringae pv. actinidiae virulent strain K9 (kindly provided by Dr. Gian Luca Bianchi of the Plant Health Service of Friuli Venezia Giulia region) and 0.01 M MgSO4, respectively. After 7 days, water-soaked brown spots with pale green halos were observed on all plants inoculated with bacteria. Re-isolated bacteria were identical to the original strains in their morphology, PCR products, and rpoD sequences. Negative control plants did not develop symptoms, and no growth was observed on media. This is the first laboratory confirmation of bacterial canker of kiwifruit in Slovenia. Visual inspections carried out by the plant health authorities in 2013 and laboratory analysis confirmed additional infection with P. syringae pv. actinidiae in a single, nearby orchard. The pest status of P. syringae pv. actinidiae in Slovenia is officially declared as present, subject to official control (1). References: (1) EPPO Reporting Service. Online publication: http://archives.eppo.int/EPPOReporting/2014/Rse-1402.pdf . No. 02 2014/026, 2014. (2) A. Gallelli et al. J. Plant Pathol 93:425, 2011. (3) N. Parkinson et al. Plant Pathol. 60:338, 2011. (4) J. Rees-George et al. Plant Pathol. 59:453, 2010. (5) J. L. Vanneste et al. Plant Dis. 97:708, 2013.