Occurrence of Leaf Spot Disease on Watermelon Caused by Pseudomonas syringae pv. syringae

Typical bacterial symptoms, water-soaking brown and black leaf spots with yellow halo, were observed on watermelon seedlings in nursery and field of Gyeongnam and Jeonnam provinces. Bacterial isolates from the lesion showed strong pathogenicity on watermelon and zucchini. One of them was rod-shaped with 4 polar flagella by observation of transmission electron microscopy. They belonged to LOPAT group 1. The phylogenical trees with nucleotide sequences of 16S rRNA and multi-locus sequencing typing with the 4 house-keeping genes (gapA, gltA, gyrB, and rpoD) of the isolates showed they were highly homologous to Pseudomonas syringae pv. syringae and grouped together with them, indicating that they were appeared as P. syringae genomospecies group 1. Morphological, physiological, and genetical characteristics of the isolates suggested they are P. syringae pv. syringae. We believe this is the first report that P. syringae pv. syringae caused leaf spot disease on watermelon in the Republic of Korea.

Two new species of Cladosporium from leaf spots of Paris polyphylla in north-western Yunnan Province, China

During the survey of pathogenic fungi on medicinal plant leaves in Yunnan Province, China, two Cladosporium-like taxa were isolated from leaf spots of Paris polyphylla. Based on morphological characteristics and phylogenetic analysis of combined ITS, TEF1-α and ACT genes, two new species were discovered. Two new species Cladosporium yunnanensis and C. paris are introduced, the detailed descriptions and illustrations are provided. Morphology of the two new species is compared with other related Cladosporium species. This study widens the host diversity of the genus Cladosporium.

A New Leaf Blight Disease Caused by Alternaria jacinthicola on Banana in China

A leaf blight disease with an incidence level of about 50% was found on Robusta banana in Guangdong province of China in September 2020. The early symptom appeared as pale gray to black brown, irregular, small, necrotic lesions mainly on the top 3–5 leaves. Severely infected leaves were withered and necrotic. Two representative fungus strains, strain L1 and strain L2, were isolated from affected banana leaves, and morphological and molecular identification analysis confirmed that the two fungi were both Alternaria jacinthicola. Many Alternaria species have been reported to cause wilting, decay, leaf blight and leaf spots on plants and lead to serious economic losses in their production, including A. alternata, causing leaf blight and leaf sport diseases on banana. The Koch’s postulates of A. jacinthicola causing the leaf blight disease was further fulfilled, which confirmed that it is the causal agent of this disease. To our knowledge, this is the first report of A. jacinthicola causing leaf blight on banana in China.

Achievements in breeding and main directions for improving black currant adssortment in Federal Horticultural Research Center for Breeding, Agrotechnology and Nursery

The article presents the main results of twenty years of research carried out at the Federal Horticultural Research Center for Breeding, Agrotechnology and Nursery (Kokino Base Station) on the search and creation of various genetic origin genotypes and the possibility of their use in further breeding work on black currants. The created genetic sources of resistance to American powdery mildew, leaf spots (canker, septoria, cercosporosis), large-fruited, berries’ high vitamin С content, fruit strength, plant productivity are presented: 7-37-2 (Litvinovskaya × Dar Smolyaninovoy), 37-27-4/05 (Debryansk, free pollination), 63-35-1 (Lentyay × Debryansk), 68-03-1 (Charodey × Yadryonaya), 5-66-5 (Dobrynya, free pollination), 13-51-1 (Shalunya, free pollination), 33-27-1 (Strelets × Selechenskaya 2) etc. As a result of breeding research, 12 black currant varieties have been created, eight of which (Bryanskiy Agate, Debryansk, Mif, Vera, Gamayun, Strelets, Charodey, Barmaley) are included in the State Register of Breeding Achievements, approved for using.

Polyphasic Analysis of Isolates from Kiwifruit Reveal New Genetic Lineages of Pseudomonas syringae pv. actinidifoliorum Look-Alike

Currently, kiwifruit cultivation arouses great economic interest in the agricultural sector in several countries of the European Union due to high consumer demand and good results achieved in terms of production potential and fruit quality. One of the main bacterial species that cause yield losses in kiwifruit plants is Pseudomonas syringae. Diseases such as bacterial canker, caused by pathovar (pv.) actinidiae; floral bud necrosis caused by pv. syringae and leaf spots caused by pv. actinidifoliorum (Pfm) are clear examples. Between 2014 and 2017, in the main kiwifruit producing areas in the north and east of Spain, several surveys were carried out in search of these pathogens. Analyses realized from symptomatic and asymptomatic plants of Actinidiadeliciosa revealed the existence of new bacterial isolates close to Pfm. These new isolates werelow virulence pathogens similar to Pfm but belonging to a new group of P. syringae that affected the leaves of A. chinensis var. deliciosa. This study focused on the characterization and classification of these new isolates by a polyphasic approach in order to provide more information for understanding how the different populations of P.syringae affecting kiwifruit. They had the phenotypic characteristics of Pfm but by molecular approaches, they constituted a supported genetic lineage closely-related to Pfm independent of the five lineages described so far. This work revealed the great diversity found in P. syringae species affecting kiwifruit plants and supports the hypothesis that Pfm is a low virulence pathogen which is long established in Europe.

Detection of the Phoma pathogens Plenodomus biglobosus subclades ‘brassicae’ and ‘canadensis’ on wasabi, and ‘canadensis’ in Europe

Phoma stem canker / blackleg is an internationally important disease of Brassicas including B. napus (oilseed rape, OSR), caused by multiple genetic subclades of the fungi Plenodomus lingam (formerly Leptosphaeria maculans) and P. biglobosus (L. biglobosa). In Spring 2021, Phoma-like disease symptoms were observed on leaves and stems of Eutrema japonicum (wasabi) crops at three UK sites (Northern Ireland, Southern England and the West Midlands). Fungal isolation from wasabi leaf spots yielded colonies with two distinct phenotypes on potato dextrose agar (PDA). Isolates from the Northern Ireland and Southern England sites had white colonies with abundant pink cirri that were confirmed (based on ITS rDNA, beta tubulin and actin sequences) as P. biglobosus subclade ‘canadensis’ (Pbc). Those from the West Midlands site, however, had yellow pigmented colonies and were confirmed by sequencing as P. biglobosus subclade ‘brassicae’ (Pbb). Greenhouse pathogenicity testing showed that Pbb and Pbc wasabi isolates were pathogenic not only to this host but also OSR, B. oleracea (cabbage), and B. rapa (pak choi). Re-isolation of the fungi was attempted and confirmed from lesions that developed on inoculated OSR and wasabi, thus completing Koch’s postulates. These findings represent new discoveries for both Pbb and Pbc on wasabi, plus for Pbc in Europe. The crop health implications of these results are briefly considered.

Neopestalotiopsis rosae Causing Black Spot on Leaf and Fruit of Pecan (Carya illinoinensis) in China

Pecan (Carya illinoinensis K. Koch) is very productive and brings good economic returns for mountain dwellers. In recent years, symptoms were observed on both leaves and fruits of pecan in orchards, Fuyang, Anhui Province, and Jiande, Zhejiang Province. On the leaf, spots, rust-colored, long shuttle to irregular shaped, and 1–3 mm in size, firstly appeared between veins. The color of area around the spot gradually changed from green to yellow making a yellow halo. Then, some spots often merged in to a big lesion. On the fruit, symptoms firstly appear as irregular and black spots. The spots gradually spread to most part of the fruit and the core of the fruit turned black at the late stage of pathogenesis. Normally, the leaf infection rate was less than 10%, whereas infection rate of fruit could reach 5–15% which leads to drastic quality reduction and significant yield losses. To isolate the pathogens, fresh infected tissues were cut from samples, disinfected and cultured at 2% water agar at 28 oC till colony could be spotted. Fungal isolates were obtained by mycelia tip transferring. Similar cultural and morphological characters showed on 39 of the total 45 isolates. The mycelia grew rapidly in PDA plates, and colony diameter could reach 8.0 cm after culture at 25 oC in dark for 5 days. Mycelia on surface of the colony were cotton-like and showed obvious growth rings, and turn yellow from the middle on aged cultures. Pycnidia, brown to dark in color, began to form on PDA after 15 days’ culture in the dark. Conidia were fusoid, straight to slightly curved, 4-septate, 23.5–26.3×7.6–9.0μm, average 24.9×8.3μm (n=60) in size. The basal cell was hyaline, conic with a truncate base and thin-walled, average 4.4–5.1μm long (n=60). The three median cells were doliiform and brown with darker septa. The apical cell was hyaline, cylindrical, with 2–3 tubular apical appendages arising from the apical crest, unbranched, filiform, average 21.7–29.2 μm(n=60) long. The cultural and morphological characters of the strains matched the previous descriptions of Neopestalotiopsis sp. (Maharachchikumbura et al., 2014). Their 3 partial genes, ITS, β-tubulin (TUB) and translation elongation factor 1-alpha (TEF1-α), were amplified and sequenced with primers (Lee et al., 2006; Maharachchikumbura et al., 2014). These sequences were submitted in GenBank with accession number of MW504791 (ITS), MW633956 (TEF1-α), and MW633958 (TUB2), seperately. The BLAST results against the GenBank database showed more than 99% identity with sequences claimed from Neopestalotiopsis sp. The multilocus phylogenetic analysis of the three genes showed the isolate was closest with N. rosae. The strains were finally identified as N. rosae by morphological and molecular analysis. Pathogenicity testing was performed by spreading 20μl conidia suspension drop (1 × 106 conidia ml-1) on surface of wounded or unwounded leaves and fruits. The pecan variety MaHan was used for inoculation. Wounds were made by scratching with sterile needles, and then a drop of 20μl conidia suspension was spread on the wounded area. For unwounded inoculation, a drop of 20μl conidia suspension was spread without wound procedure. The same amount of water drops were spread on the surface of wounded and unwounded tissues as controls. The plant parts were wrapped with PE films to keep moisture after drop spreading. Ten trees were selected for inoculation, and 10 leaves and fruits were randomly selected separately for wounded and unwounded inoculation and corresponding controls in each tree. The similar symptoms appeared from 3 dpi on leaves and 9 dpi on fruits, and finally showed on more than 90% wounded inoculated leaves or fruits and on less than 50% after unwounded inoculation, while controls remained symptomless. N. rosae was consistently re-isolated from inoculated parts with symptoms, while not from the control. Therefore, N. rosae was confirmed as the pathogen causing black spot on leaf and fruit of pecan (C. illinoinensis). To the best of our knowledge, this is the first report of N. rosae causing black spot disease of pecan (C. illinoinensis). In recent years, both the infection area and severity of this disease grow rapidly, which means the potential of the disease to become a big problem in local orchards.

Detection of Ramularia collo-cygni DMI- and SDHI-resistant field populations in Austria and the effect of fungicides on the population and genetic diversity

Winter barley (Hordeum vulgare L.) is the third most cultivated crop after corn and wheat in Austria but one of the most challenging for disease control. The foliar pathogen Ramularia collo-cygni B. Sutton and J.M. Waller, causing Ramularia leaf spots (RLS), is one of the most important diseases in barley. In the recent years, control has only been achieved using fungicide mixtures including the multi-site inhibitor chlorothalonil, however this compound is totally banned in the EU. The objective of this study was to assess fungicide dose-rates and spray mixtures for RLS control. Furthermore, a field monitoring within the main barley growing areas of Austria was carried out, to analyse the current resistance situation to DMI and SDHI fungicides, which are still the backbone in RLS control. The results indicate that only the mixture with chlorothalonil achieved a good RLS control. Prothioconazole or benzovindiflupyr (alone or additively) decrease the severity of RLS but increase the local frequency of Cyp51 and sdhC mutations, especially the high dose rates. Based on a low Cyp51 mutation frequency of 16% in untreated control this frequency increased over 3.8 times following an application with 300 g ha−1 prothioconazole. The cumulative-sdhC mutations were even more increased after an application with benzovindiflupyr. This study showed that Ramularia collo-cygni is present in 91% of barley fields presented in this field survey. Widespread use of chlorothalonil fungicide maintained a low to moderate mutation frequency (Cyp51-I325T, Cyp51-I328L, sdhC-H146R and sdhC-H153R) in Austrian barley regions with no increase between 2017 and 2019.