Occurrence of Passalora Leaf Spot Caused by Passalora ampelopsidis on Virginia Creeper in Korea

A previously unknown leaf spot disease was observed on Virginia creeper (Parthenocissus quinquefolia) vines in Seoul, Korea. Affected plants exhibited leaf spots and discoloration, resulting in leaf blight and premature defoliation. The causal agent of the disease was identified as Passalora ampelopsidis by comparing morphological characteristics and analyzing the internal transcribed spacer region of the rDNA. Pathogenicity tests were conducted twice with the same results, fulfilling Koch's postulates. Passalora leaf spot on Virginia creeper vines was first recorded in the United States in 1878. Recent reports of Passalora leaf spots on Virginia creeper vines in 2005 in Germany, in 2012 in China and now in Korea indicate the prevalence of the disease.     

First Report of Pseudomonas lurida Causing Bacterial Leaf Spot on Miscanthus sinensis

Miscanthus spp. are large perennial wetland grasses that are receiving considerable attention as bioenergy crops. In late summer 2011, leaf spot symptoms were observed in a field of Miscanthus sinensis in Jeongseon, Gangwon province, Korea. Bacterial strains that belonged to the γ‐Proteobacteria genus Pseudomonas were isolated from the affected leaves. By phylogenetic analysis and phenotypic characterization, the representative strain MDM‐03 was identified as Pseudomonas lurida. Healthy M. sinensis leaves inoculated with MDM‐03 developed leaf spots similar to those observed in field. Bacteria re‐isolated from the leaf lesions were identical to the original strain MDM‐03 based on their cultural characteristics and 16S rDNA sequencing. This is the first report of bacterial leaf spot in Miscanthus sinensis.     

Powdery Mildew Caused by an Erysiphe sp. on Korean Ginseng

In August and September 2014, Korean ginseng (Panax ginseng) plants showing symptoms of powdery mildew infection were found in a polyethylene film‐covered greenhouse in Suwon, Korea. The mildew was initially observed to occur in circular to irregular white colonies, which subsequently developed into abundant mycelial growths on both leaf surfaces. No chasmothecia were observed. Based on its morphological characteristics, the fungus was determined to be a species of Erysiphe. Phylogenetic analysis of the sequence of the internal transcribed spacer region of the ribosomal DNA obtained from the isolate placed the powdery mildew fungus in the genus Erysiphe. Here, we describe this Erysiphe sp. found growing on Korean ginseng using both illustrations and molecular data. A comparison of the Korean isolate and three previous records of powdery mildews known to grow on Panax plants is also provided. This is the first report of powdery mildew on Korean ginseng in Korea.     

First Report of Cercospora Leaf Spot of Burcucumber Caused by Cercospora citrullina in Korea

Burcucumbers (Sicyos angulatus) showing necrotic leaf spots were found in several locations in Korea during 2008–2012. The causal agent was a fungus that was identified as Cercospora citrullina, based on morphological characteristics as well as sequences of the ribosomal DNA internal transcribed spacer region. Although C. citrullina has been known to attack various cucurbitaceous plants, this is the first report of this fungus on S. angulatus.     

Epidemiological and molecular study on ‘Candidatus Phytoplasma prunorum’ in Austria and Hungary

The epidemiology of ‘Candidatus Phytoplasma prunorum’ was studied in Austria and Hungary from 2014 to 2018. Testing of root samples showed average infections rates of 61 and 40% of the Austrian Prunus spinosa and Prunus domestica spp. insititia samples, respectively. In Hungary, on average 21% of the P. spinosa and 13% of the feral Prunus cerasifera samples were infected. The pathogen was found in 18 out of 19 apricot orchards and PCR positive Cacopsylla pruni were observed at 11 out of 17 sampling locations in both countries. In cage experiments with C. pruni remigrants successful pathogen transmission to Prunus armeniaca, P. domestica and P. spinosa seedlings in budding and foliated developmental stages was recorded, an inoculation access period of 4 hr was sufficient for transmission. A field experiment with ungrafted apricot seedlings planted in 2012 and 2014 indicated a prominent role of the insect vectors for disease spread. In 2017, 40 and 28% of the trees planted in 2012 and 2014, respectively, were infected. Molecular characterisation based on the genes aceF and imp allowed the discrimination between 10 phytoplasma types in apricots. Around 70% of the phytoplasma types in apricots were also common in P. spinosa, in P. domestica spp. insititia and in remigrant C. pruni pointing to a possible pathogen exchange by insects between wild and cultivated Prunus spp. For disease control, vector management over the entire flight period of the remigrants seems necessary; when selecting active compounds, the short inoculation access period of not more than 4 hr should be considered.     

First Report of Anthracnose of Ledebouriella seseloides Caused by Colletotrichum gloeosporioides in Korea

In 2012, dark brown spots were observed on leaves of Ledebouriella seseloides (Fang Feng) in several research plots located at the Goseong Agricultural Research Extension services in Gyeongam Province, Republic of Korea. A fungus was isolated from the infected plants which produced pink‐coloured spores in mucilage on PDA and conidial morphology suggested that the causal agent was Colletotrichum gloeosporioides. Internal transcribed spacer sequences of the pathogen showed 99% identity to those of C. gloeosporioides. Pathogenicity of the isolate was proved by Koch's postulates. This is the first report of anthracnose in L. seseloides caused by C. gloeosporioides.     

Pythium aphanidermatum Causing Pythium Rot on Lampranthus spectabilis in Korea

Pythium aphanidermatum was found to be associated with rotting of leaves and stems in Lampranthus spectabilis in the summers of 2013 and 2014. Infected plants were initially characterized by water‐soaked and discoloured tissue, which are soon covered with cottony aerial hyphae. Subsequently, infected tissues wilted, leaves and stems appeared desiccated, and infected plants died. Pathogenicity of a representative isolate was proved, fulfilling Koch's postulates. Sequence of the internal transcribed spacer region of ribosomal DNA from the isolate shared 100% identity with that of P. aphanidermatum. To our knowledge, this is the first report of P. aphanidermatum causing leaf and stem rot on L. spectabilis in Korea.     

European Stone Fruit Yellows: A Mark,Release and Recapture Experiment Tracking the Dispersal of its Vector Cacopsylla pruni (Hemiptera: Psyllidae) in a Model Apricot Orchard and Epidemiological Studies in Lower Austria

During the last 15 years, European stone fruit yellows (ESFY) has become a major concern in Austrian fruit production. Therefore, presence and temporal dynamics of its vector Cacopsylla pruni were investigated using a beating tray method and yellow sticky traps on Prunus armeniaca, Prunus domestica, Prunus spinosa and P. cerasifera nigra. Infection rates of C. pruni and Prunus spp. trees were assessed by direct, nested and real‐time PCR. Movement of remigrants in a model apricot orchard was tracked by aid of a mark, release and recapture study. Insects were marked by fluorescent dyes. Movement of the marked insects and presence of naturally occurring insects were monitored by yellow sticky traps. In 2011, remigration of C. pruni to Prunus spp. started in calendar week 10 (8th of March) and in 2012, in calendar week 12 (18th of March). Remigrants were observed until calendar week 20 (middle of May), significant numbers of the springtime generation adults were present until week 26 (end of June). The phytoplasma was ascertained in 0–11.5% of the remigrants and in 0–3.44% of the springtime generation insects. About 9.8–63.3% of the apricot samples, 20–40% of the plum samples and single blackthorn samples were infected. The mark, release and recapture study proved a fast and frequent tree‐to‐tree movement of remigrated C. pruni adults. Insects easily covered distances from row to row or even farther (ca. 13 m) within 24 h after release and were present in a large part of the model orchard after 8 days (up to 24 m from release point).     

Rapid Detection and Identification of Six Tomato yellow leaf curl virus Isolates from Different Regions Using Polymerase Chain Reaction and Restriction Enzyme Analysis

The combinational analysis of polymerase chain reaction and restriction enzyme analysis (PCR‐RE) to distinguish six Tomato yellow leaf curl virus (TYLCV) isolates from five countries was developed. Tomato yellow leaf curl virus has spread from the Middle East to Western Europe, Central America and Eastern Asia, and occurs on infected crops such as tomatoes, peppers, cucurbits and beans. Tomato yellow leaf curl virus isolates from Jordan (TYLCV‐Mld[Jo:Cuc] and TYLCV‐IL[Jo:Cuc]), Israel (TYLCV‐IL[IL:Reo:86]), Spain (TYLCV‐Mld[ES72/97]), USA (TYLCV‐IL[US:F10:04]) and Korea (TYLCV‐KR) were collected, and the sequences of the six isolates were analysed to distinguish them by PCR‐RE combination analysis. Oligonucleotide primers for the six TYLCV isolates were designed to amplify approximately 740 base pairs including the intergenic region (IR) and parts of V1 and V2 ORF. Unique restriction enzyme sites were analysed to identify isolate‐specific restriction enzyme sites on the PCR products of each isolate. Three enzymes (DdeI, FauI and BssSI) were selected by in silico analysis, and then, the PCR products following the serial digestion of each restriction enzyme were separated by agarose gel electrophoresis to distinguish the TYLCV isolates. Taken together, the PCR‐RE combination analysis by serial digestion with three restriction enzymes could be a useful method for distinguishing the six isolates.     

Description and identification of two new diseases of guariroba palm (Syagrus oleraceae) in Brazil

Guariroba is a palm species native to central Brazil. Seedlings of guariroba with leaf spots of unknown aetiology were found in Patos de Minas, Minas Gerais, Brazil. The leaf spots were manifest as two different symptom types: the first lesion type consisted of necrotic spots with a rounded to elongate shape, with a light colour and dark edges; the second lesion type had a rounded shape, was dark brown in colour with a light brown edge. The objective of this study was to elucidate the aetiology of both diseases. The likely causal agents were isolated and Koch's postulate fulfilled. Subsequently, the ITS region of rDNA from both micro‐organisms were amplified and sequenced. According to the morphological characteristics and molecular analyses, the fungal species were identified as Pestalotiopsis adusta (causing necrotic spots with a rounded to elongate shape, with a light colour and dark edges), and Alternaria tenuissima (causing lesions with a rounded shape, dark brown in colour with a light brown edge). Identification of the causal organisms of these two diseases will help guide management approaches that might be tested to reduce impact of the disease on Guariroba, including the use of fungicides and cultural approaches.     

Cage and field experiments as basis for the development of control strategies against Cacopsylla pruni,the vector of European Stone Fruit Yellows

The efficacy and the instant effect of 13 insecticides and antifeedants towards Cacopsylla pruni, the vector of ‘Candidatus Phytoplasma prunorum’ were examined in cage studies (no choice experiments with 10 field‐collected overwintered adults per experiment) on potted apricot trees (budding trees under outdoor conditions in early spring and foliated seedlings kept at 21°C). Cypermethrin caused 100% insect mortality within 2–4 h, thiacloprid 90–100% mortality within 24 h both on foliated and on budding trees. On budding trees spinosad led to 70–90% mortality within 24 h, thixotropic white trunk paint to 90% mortality within 48 h. On foliated seedlings flonicamid gave 70–100% mortality within 1 day, abamectin, spinosad, acetamiprid and spirotetramat 70–100% within 72 h. Field studies monitoring the effects of thiacloprid on remigrants of C. pruni by yellow sticky traps were carried out in two apricot orchards. Additionally the influence of the insecticide on insect dispersal was examined by mark, release and recapture trials. As compared to the control thiacloprid significantly reduced the catches of naturally occurring and released insects, decreased the number of trees on which released insects were recaptured (by 25–100%) and shortened the migration distances of the released insects by more than half. Our results suggest that appropriate insecticide treatments both reduce C. pruni populations and have a direct effect on pathogen transmission. Application of Cypermethrin before bloom and thiacloprid after bloom seem best suited to achieve these objectives. Thixotropic white trunk paint could, a formulation for spray application provided, eventually be a sustainable alternative or complement for treatments before bloom.     

First Report of Frosty Mildew on Salix koreensis Caused by Mycopappus alni in Korea

A frosty mildew was observed on leaves of Salix koreensis in two localities of Korea during 2011 and 2012. The main signs and symptoms were expressed as conical white to cream coloured tufts of the causal fungus on the brown lesions, followed by premature defoliation. Based on morphological observations, cultural characteristics and phylogenetic analyses of rDNA‐ITS, the fungus was identified as Mycopappus alni, which has been known to be associated with frosty mildews on Alnus spp., Betula spp., Crataegus chlorosarca and Pyrus pyrifolia. Pathogenicity test was conducted twice with the same results, fulfilling Koch's postulates. This is the first case of Salix–Mycopappus association as well as the first report of frosty mildew on S. koreensis.     

New Host Record of Myrothecium roridum Causing Leaf Spot on Abutilon megapotamicum from China

During September 2010, Abutilon megapotamicum plants with dark‐brown concentric spots on leaves were observed in a commercial glasshouse located in Beijing, China. This study was carried out to identify the causal agent of this disease based on Koch's postulates and morphological characteristics. Pathogenicity tests in the glasshouse showed that Myrothecium roridum Tode ex Fr. caused the leaf spot on A. megapotamicum plants, which were the same as those observed in naturally infected plants in the field. Moreover, to confirm the pathogen to species, the rDNA internal transcribed spacer (ITS) of isolate was PCR‐amplified using ITS1 and ITS4 primer pairs and sequenced. DNA analysis revealed a 100% species identity index for M. roridum. To the best of our knowledge, this is the first report of M. roridum on A. megapotamicum in China.     

Verticillium wilt of pea (Pisum sativum)

A wilt disease of garden pea (Pisum sativum) caused by Verticillium dahliae is described and the range of pathogenicity of the isolate investigated. It is pathogenic to potato, sweet pea, antirrhinum and broad bean and isolates of V. dahliae from potato, lucerne and sweet pea and V. albo-atrum from lucerne are pathogenic to pea. Since the most common disease symptoms, acropetal progression of chlorosis and necrosis of the leaves followed by premature defoliation are indistinguishable from natural senescence, it is probable that disease and senescence symptoms are confused in the field. The premature defoliation results in marked reduction in green leaf area, leaf dry weight and pod yield.     

Identification of a major QTL for Xanthomonas arboricola pv. pruni resistance in apricot

Xanthomonas arboricola pv. pruni causes bacterial spot of stone fruit resulting in severe yield losses in apricot production systems. Present on all continents, the pathogen is regulated in Europe as a quarantine organism. Host resistance is an important component of integrated pest management; however, little work has been done describing resistance against X. arboricola pv. pruni. In this study, an apricot population derived from the cross “Harostar” × “Rouge de Mauves” was used to construct two parental genetic maps and to perform a quantitative trait locus analysis of resistance to X. arboricola pv. pruni. A population of 101 F1 individuals was inoculated twice for two consecutive years in a quarantine greenhouse with a mixture of bacterial strains, and disease incidence and resistance index data were collected. A major QTL for disease incidence and resistance index accounting respectively for 53 % (LOD score of 15.43) and 46 % (LOD score of 12.26) of the phenotypic variation was identified at the same position on linkage group 5 of “Rouge de Mauves.” Microsatellite marker UDAp-452 co-segregated with the resistance, and two flanking microsatellites, namely BPPCT037 and BPPCT038A, were identified. When dividing the population according to the alleles of UDAp-452, the subgroup with unfavorable allele had a disease incidence of 32.6 % whereas the group with favorable allele had a disease incidence of 21 %, leading to a reduction of 35.6 % in disease incidence. This study is a first step towards the marker-assisted breeding of new apricot varieties with an increased tolerance to X. arboricola pv. pruni.     

Identification and Characterization of Paraphoma chrysanthemicola Causing Leaf Spot Disease on Atractylodes japonica in China

Atractylodes japonica is a perennial herb in Compositae family, which is used for stomach disorders as a traditional Chinese medicine (Guo et al. 2006 ). In 2013, a leaf spot disease was first observed on plants of A. japonica in a production field of Fushun County, Liaoning Province, China. The disease had a speckled appearance initially. Lesions with grey–white centre and brown margin gradually developed and enlarged. Eventually, infections usually caused yellowing of the leaves and premature defoliation. The causal agent of infection on plants was identified as Paraphoma chrysanthemicola based on morphological and cultural characteristics, pathogenicity tests and phylogenetic analysis. To our knowledge, this is the first report of a leaf spot disease on A. japonica caused by P. chrysanthemicola in China.     

<Emphasis Type="Italic">Periconiella lecythidis</Emphasis> sp. nov., the causal agent of a zonate leaf spot disease of the Brazilian tree <Emphasis Type="Italic">Lecythis pisonis</Emphasis>

A new defoliating disease was observed on 20-year-old trees of Lecythis pisonis in Viçosa, Minas Gerais, Brazil. The disease is characterized by forming one or more large zonate epiphyllous leaf spots with a light brown to white center, followed by two to three zones gradually varying from brown to red-brown. On the corresponding abaxial leaf surface, the spots are lighter with a profuse greenish gray coloration caused by the fungal colonies. In PDA culture, the fungus is characterized by a slow growth of the colonies with brown-violet pigmentation at the reverse. Inoculation tests carried out on healthy plants of L. pisonis confirmed the pathogenicity of this fungus. Periconiella lecythidis sp. nov., the causal agent of the zonate leaf spot disease of L. pisonis is described, illustrated, discussed and compared with the other species of the genus Periconiella. The intricate generic affinity within a complex of morphologically similar hyphomycete genera consisting of Metulocladosporiella, Parapericoniella, Penidiella and Periconiella is discussed in detail.     

Microbial secondary metabolite induction of abnormal appressoria formation mediates control of rice blast disease caused by Magnaporthe oryzae

Okinawa, the only subtropical area in Japan with numerous island ecosystems, is expected to have diverse microbial resources. Recently, we reported the construction of a culture filtrate library with microbes originally isolated from soils in Okinawa, including the Yaeyama Archipelago, and validated its phylogenetic diversity. In the present study, we investigated the inhibitory effect of the cell extract (CE) from microbial isolate 3–45 against Magnaporthe oryzae in rice (Oryza sativa). Abnormal appressorium formation by M. oryzae was induced in the presence of the CE from isolate 3–45. Additionally, melanization of appressoria was inhibited in the presence of CE from isolate 3–45. Sequence analysis of the 16S rDNA region of isolate 3–45 indicated that it shared similarities with Streptomyces erythrochromogenes. When rice leaves were inoculated with M. oryzae in the presence of CE from isolate 3–45, blast lesion formation was inhibited compared to leaves treated with M. oryzae in the absence of CE from isolate 3–45. In addition, M. oryzae infective activity was significantly inhibited in rice leaf sheaths treated with CE from isolate 3–45. Furthermore, abnormal appressorium formation was observed in the presence of heat‐treated CE from isolate 3–45. These results suggest that CE from isolate 3–45 can protect rice from blast disease caused by M. oryzae. Further studies are required to identify the active compounds present in 3–45‐CE and to clarify its mechanism of inhibition in full detail. The present study on isolate 3–45 might contribute to the development of a new fungicide for controlling rice blast disease caused by M. oryzae.     

Sooty Mould on Hibiscus rosa‐sinensis Caused by Leptoxyphium kurandae is Associated with Extrafloral Nectaries

In August 2013, sooty mould was observed on Chinese hibiscus (Hibiscus rosa‐sinensis) in a propagation nursery in Seoul, Korea. The sooty mould initially developed at the junction between the leaf blade and leaf petiole and then dispersed along the vein on the abaxial surface. The fungal growth pattern on the plants was quite different from general sooty moulds growing on honeydew secreted by insects on the plants. On the basis of the morphological characteristics and phylogenetic analysis using the internal transcribed spacer rDNA, this fungus was identified as Leptoxyphium kurandae. A pathogenicity test was carried out to fulfil Koch's postulates. Through field observation and a pathogenicity test, we found an association between the sooty mould and extrafloral nectaries. To our knowledge, this is the first report of sooty mould caused by L. kurandae on the extrafloral nectaries of H. rosa‐sinensis.