First Report of Olive Branch Dieback in Croatia Caused by Cytospora pruinosa Défago

Olive (Olea europaea L.) is a very important crop grown in the Mediterranean part of Croatia. Olive branch and fruit dieback symptoms were observed in two olive orchards in Istria, Croatia. The samples from symptomatic trees were collected and brought to the laboratory for analysis. Based on their morphological characterization, isolated fungi were identified as Cytospora sp. Two representative isolates (one per orchard) were taken for molecular analysis, and based on DNA sequence data of the ITS and TUB gene regions, and phylogenetic analysis of the sequences, the isolates were identified as Cytospora pruinosa Défago. To determine pathogenicity, pathogenicity tests were conducted on detached olive branches and two-year-old olive trees in the greenhouse. This is the first report of C. pruinosa causing olive branch and fruit dieback in Croatia.

Antifungal Activities of Fluorinated Pyrazole Aldehydes on Phytopathogenic Fungi, and Their Effect on Entomopathogenic Nematodes, and Soil-Beneficial Bacteria

Fluoro-substituted pyrazoles have a wide range of biological activities, such as antibacterial, antiviral, and antifungal activities. The aim of this study was to evaluate the antifungal activities of fluorinated 4,5-dihydro-1H-pyrazole derivatives on four phytopathogenic fungi: Sclerotinia sclerotiorum, Macrophomina phaseolina, Fusarium oxysporum f. sp. lycopersici, and F. culmorum. Moreover, they were tested on two soil beneficial bacteria-Bacillus mycoides and Bradyrhizobium japonicum-as well as two entomopathogenic nematodes (EPNs)-Heterorhabditis bacteriophora and Steinernema feltiae. The molecular docking was performed on the three enzymes responsible for fungal growth, the three plant cell wall-degrading enzymes, and acetylcholinesterase (AChE). The most active compounds against fungi S. sclerotiorum were 2-chlorophenyl derivative (H9) (43.07% of inhibition) and 2,5-dimethoxyphenyl derivative (H7) (42.23% of inhibition), as well as H9 against F. culmorum (46.75% of inhibition). Compounds were shown to be safe for beneficial soil bacteria and nematodes, except for compound H9 on EPN H. bacteriophora (18.75% mortality), which also showed the strongest inhibition against AChE (79.50% of inhibition). The molecular docking study revealed that antifungal activity is possible through the inhibition of proteinase K, and nematicidal activity is possible through the inhibition of AChE. The fluorinated pyrazole aldehydes are promising components of future plant protection products that could be environmentally and toxicologically acceptable.

First Report of Phaeoacremonium iranianum Causing Olive Twig and Branch Dieback

In an olive orchard on the western part of Istria, Croatia, twig and branch dieback was observed on several olive trees. In total, seven samples from symptomatic trees were collected. Samples were analyzed, and four fungal isolates showed morphological similarities to the species Phaeoacremonium. One isolate, chosen as a representative, was taken for molecular identification and pathogenicity tests. Based on the DNA sequence data of the ITS, TUB, and EF1α gene regions, the isolate was identified as P. iranianum. Pathogenicity tests were conducted on detached olive branches and olive trees in the greenhouse. To the best of our knowledge, this is the first report of twig and branch dieback on olive caused by Phaeoacremonium iranianum.

Influence of side-chain length on antifungal efficacy of N-alkyl nicotinamide-based compounds

This article presents fungicidal properties of 9 synthesized nicotinamide-bromides with different alkyl side chain lengths toward Fusarium graminearum, Sclerotinia sclerotiorum, and Botrytis cinerea which were examined. The fungicidal properties were determined by the measurement of the radial growth of fungi, followed by the calculation of the antifungal index. The obtained results were correlated with the descriptors from DFT calculations to determine structural features that affect the fungicidal properties of nicotinamides. Based on the experimental and theoretical results, it was confirmed that F. graminearum is most resistant to the change of lipophilicity of compounds, while S. sclerotiorum is most sensitive. For all investigated compounds, the growth rate decreased with the increase of carbon atoms in the side chain until tetradecylnicotinamidium bromide, [C14Nic][Br], while the further prolongation of the alkyl side chain increased the growth rate of fungus. This behavior was explained by the distinguished hydrophobic and hydrophilic surfaces in [C14Nic][Br] due to interactions between keto oxygen and bromide anion absent in the case of nicotinamides with a longer chain.

Oxidative Status and Antioxidative Response to Fusarium Attack and Different Nitrogen Levels in Winter Wheat Varieties

Abiotic and biotic stresses, such as mineral nutrition deficiency (especially nitrogen) and Fusarium attack, pose a global threat with devastating impact on wheat yield and quality losses worldwide. This preliminary study aimed to determine the effect of Fusarium inoculation and two different nitrogen levels on oxidative status and antioxidative response in nine wheat varieties. Level of lipid peroxidation, activities of antioxidant enzymes (catalase, ascorbate peroxidase, glutathione reductase), phenolics, and chloroplast pigments content were measured. In general, wheat variety, nitrogen, and Fusarium treatment had an impact on all tested parameters. The most significant effect had a low nitrogen level itself, which mostly decreased activities of all antioxidant enzymes and reduced the chloroplast pigment content. At low nitrogen level, Fusarium treatment increased activities of some antioxidative enzymes, while in a condition of high nitrogen levels, antioxidative enzyme activities were mostly decreased due to Fusarium treatment. The obtained results provided a better understanding on wheat defense mechanisms against F. culmorum, under different nitrogen treatments and can serve as an additional tool in assessing wheat tolerance to various environmental stress conditions.

Antifungal activities of silver and selenium nanoparticles stabilized with different surface coating agents

BACKGROUND

Extensive and growing use of different chemical pesticides that affect both the environment and human health raises a need for new and more suitable methods to deal with plant pathogens. Nanotechnology has enabled the use of materials at the nanoscale with exceptional functionality in different economic domains including agricultural production. This study aimed to evaluate antifungal potential of selenium nanoparticles (SeNPs) and silver nanoparticles (AgNPs) stabilized with different surface coatings and characterized by different surface charge on plant pathogenic fungi Macrophomina phaseolina, Sclerotinia sclerotiorum and Diaporthe longicolla.

RESULTS

AgNPs were coated with three different stabilizing agents: mono citrate (MC-AgNPs), cetyltrimethyl ammonium bromide (CTAB-AgNPs) and polyvinylpyrrolidon (PVP-AgNPs). SeNPs were coated with poly-l-lysine (PLL-SeNPs), polyacrylic acid (PAA-SeNPs), and polyvinylpyrrolidon (PVP-SeNPs). Seven different concentrations (0.1, 0.5, 1, 5, 10, 50 and 100 mg L^-1 ) of nanoparticles were applied. All AgNPs and SeNPs significantly inhibited the growth of the tested fungi. Among the tested NPs, PVP-AgNPs showed the best inhibitory effect on the tested plant pathogenic fungi, especially against S. sclerotiorum. The similar inhibition of the sclerotia formation was observed for S. sclerotiorum treated with PLL-SeNPs.

CONCLUSION

Obtained results provides new insights on fungicide effect of AgNPs and SeNPs stabilized with different coating agents on different plant pathogens. Further work should focus on detailed risk/benefit ratio assessment of using SeNPs or AgNPs in agriculture taking into account whole agroecosystem. © 2020 Society of Chemical Industry.

Correlation between lipophilicity of newly synthesized ionic liquids and selected Fusarium genus growth rate

In this work the correlation between lipophilicity descriptor and Fusarium growth rate for newly synthesized ionic liquids was established.

First Report of Septoria Leaf Spot of Lavandin Caused by Septoria lavandulae in Croatia

Lavandula × intermedia Emeric ex Loiseleur, commonly known as lavandin, is an aromatic and medicinal perennial shrub widely and traditionally grown in Croatia. The lavandin essential oil is primarily used in perfumery and cosmetic industries, but also possesses anti-inflammatory, sedative, and antibacterial properties. In June 2012, severe foliar and stem symptoms were observed on approximately 40% of plants growing in a commercial lavandin crop in the locality of Banovo Brdo, Republic of Croatia. Initial symptoms on lower leaves included numerous, small, oval to irregular, grayish brown lesions with a slightly darker brown margin of necrotic tissue. Further development of the disease resulted in yellowing and necrosis of the infected leaves followed by premature defoliation. Similar necrotic oval-shaped lesions were observed on stems as well. The lesions contained numerous, dark, sub-globose pycnidia that were immersed in the necrotic tissue or partly erumpent. Small pieces of infected internal tissues were superficially disinfected with 50% commercial bleach (4% NaOCl) and placed on potato dextrose agar (PDA). A total of 10 isolates from leaves and five from stems of lavandin formed a slow-growing, dark, circular colonies with raised center that produced pycnidia at 23°C, under 12 h of fluorescent light per day. All 15 recovered isolates formed uniform hyaline, elongate, straight or slightly curved conidia with 3 to 4 septa, with average dimensions of 17.5 to 35 × 1.5 to 2.5 μm. Based on the morphological characteristics, the pathogen was identified as Septoria lavandulae Desm., the causal agent of lavender leaf spot (1,2). Pathogenicity of one selected isolate (428-12) was tested by spraying 10 lavandin seedlings (8 weeks old) with a conidial suspension (10⁶ conidia/ml) harvested from a 4-week-old monoconidial culture on PDA. Five lavandin seedlings, sprayed with sterile distilled water, were used as negative control. After 5 to 7 days, leaf spot symptoms identical to those observed on the source plants developed on all inoculated seedlings and the pathogen was successfully re-isolated. No symptoms were observed on any of the control plants. Morphological identification was confirmed by amplification and sequencing of the internal transcribed spacer (ITS) region of rDNA (3). Total DNA was extracted directly from fungal mycelium with a DNeasy Plant Mini Kit (Qiagen, Hilden, Germany) and PCR amplification performed with primers ITS1F/ITS4. Sequence analysis of ITS region revealed at least 99% identity between the isolate 428-12 (GenBank Accession No. KF373078) and isolates of many Septoria species; however, no information was available for S. lavandulae. To our knowledge, this is the first report of Septoria leaf spot of lavandin caused by S. lavandulae in Croatia. Since the cultivation area of lavandin plants has been increasing in many continental parts of Croatia, especially in Slavonia and Baranja counties, the presence of a new and potentially harmful disease may represent a serious constraint for lavandin production and further monitoring is needed. References: (1) T. V. Andrianova and D. W. Minter. IMI Descriptions of Fungi and Bacteria, 142, Sheet 1416, 1999. (2) R. Bounaurio et al. Petria 6:183, 1996. (3) G. J. M. Verkley et al. Mycologia 96:558, 2004.

First Report of Alfalfa mosaic virus Infecting Lavandula × intermedia in Croatia

Lavandin (Lavandula × intermedia Emeric ex Loiseleur) is cultivated on a large scale in some South European countries for the extraction of essential oils or as an ornamental plant for gardens and landscapes. In May of 2012, virus-like symptoms including bright yellow calico mosaic, leaf distortion, and growth reduction were observed on 15% of lavandin plants in a commercial nursery in Banovo Brdo locality, Baranja County, Republic of Croatia. Leaves from 15 symptomatic lavandin plants were collected and examined by double-antibody sandwich (DAS)-ELISA using commercial antisera (Bioreba AG, Reinach, Switzerland) against two viruses known to infect Lavandula spp.: Alfalfa mosaic virus (AMV) and Cucumber mosaic virus (CMV) (2,3). Commercial positive and negative controls and extracts from healthy lavandin leaves were included in each ELISA. Only AMV was detected serologically in all 15 tested samples. Five plants each of Chenopodium quinoa, C. amaranticolor, and Nicotiana benthamiana were mechanically inoculated with sap from an ELISA-positive sample (70-12) using 0.01 M phosphate buffer (pH 7). Local chlorotic spots accompanied by systemic mosaic on both Chenopodium species and bright yellow mosaic on N. benthamiana were observed 6 and 12 days post-inoculation, respectively. Test plants were assayed by DAS-ELISA and all inoculated plants of each species tested positive for AMV. The presence of AMV in all symptomatic lavandin plants was further confirmed by reverse transcription (RT)-PCR assay. Total nucleic acid was extracted using RNeasy Plant Mini Kit (Qiagen, Hilden, Germany). RT-PCR was performed with the One-Step RT-PCR Kit (Qiagen) using AMV specific primer pair CP AMV1 (5'-TCCATCATGAGTTCTTCAC-3') and CP AMV2 (5'-AGGACTTCATACCTTGACC-3') (1). Total RNAs obtained from the Serbian AMV isolate from alfalfa (GenBank Accession No. FJ527748) and healthy L. × intermedia plant served as the positive and negative control, respectively. The 751-bp amplicons, covering the partial coat protein (CP) gene and 3'-UTR, were obtained from all 15 samples that were serologically positive to AMV as well as from positive control. No amplification product was observed when extract from healthy L. × intermedia plant was used as template in the RT-PCR assay. The RT-PCR product derived from isolate 70-12 was directly sequenced in both directions using the same primer pair as in RT-PCR and deposited in GenBank (JX996119). Multiple sequence alignment of the CP open reading frame was performed by MEGA5 software (4) and revealed that the isolate 70-12 showed the highest nucleotide identity of 99.4% (99.5% amino acid identity) with Serbian AMV isolate from tobacco (FJ527749). To our knowledge, this is the first report of AMV on L. × intermedia in Croatia. Because lavandin is an aromatic plant traditionally and widely grown in Croatia, the presence of AMV could be a limiting factor for its successful production. References: (1) M. M. Finetti-Sialer et al. J. Plant Pathol. 79:115, 1997. (2) T. Kobylko et al. Plant Dis. 92:978, 2008. (3) L. Martínez-Priego et al. Plant Dis. 88:908, 2004. (4) K. Tamura et al. Mol. Biol. Evol. 28:2731, 2011.

First Report of Foliar and Stem Blight on Sunflower Caused by Alternaria helianthiinficiens in Croatia

Sunflower (Helianthus annus L.) is the most important oilseed crop in Croatia. In August 2009, in six localities of eastern Croatia, severe foliar and stem blight symptoms were observed on several genotypes with disease incidence ranging from 10 to 50%. At the initial stage of the infection, irregular to oval, brown spots different in size, surrounded by a chlorotic halo, appeared on the leaves that gradually became enlarged and coalesced, and whole leaves turned yellow and necrotic, followed by defoliation. Lesions on the stems were light to dark brown, randomly distributed, rounded and tapered on the ends; later becoming large and elongated causing stem breakage. Tissue within the lesion was reddish on the cross section. To determine the causal agent, small pieces of symptomatic leaves and stem tissue of sunflower were surface disinfested and placed on potato dextrose agar. A total of 17 isolates from leaves as well as six from stems were obtained and all formed cottony, dark olivaceous to black colonies under 12 h of fluorescent light per day. All isolates formed uniform solitary, pale brown to brown, long ovoid conidia with five to eight transverse and one to two longitudinal septa. The conidia of all isolates were slightly constricted at the transverse septa, measuring 55 to 90 × 14 to 20 μm. Based on the morphological characteristics, the pathogen was identified as Alternaria helianthiinficiens E.G. Simmons, Walcz & R.G. Roberts (4). The pathogenicity was tested with one representative isolate (Alt5) by injection of a conidial suspension (106 conidia/ml) into stems of 20 healthy sunflower seedlings and by spraying 20 non-wounded detached leaves with a suspension of spores. Small necrotic spots on all inoculated seedlings and leaves formed 5 and 9 days after inoculation, respectively. The control sunflower seedlings and detached leaves, inoculated with sterile water, showed no reactions. The identity of isolate Alt5 was futher confirmed by amplification and sequencing of the internal transcribed spacer (ITS) region of rDNA. Because there are no available corresponding ITS sequences of A. helianthiinficiens in the GenBank, reference type strain CBS 208.86 (publicly purchased, CBS, Utrecht, Netherlands) was also sequenced in this study. Total DNA was extracted directly from fungal mycelium and PCR amplification and sequencing were performed with primers ITS1F/ITS4. Sequence analysis of ITS region revealed 100% nucleotide identity between isolate Alt5 (GenBank Accession No. JX101648) and isolate CBS 208.86 (GenBank Accession No. JX101649). The nucleotide identity of both isolates compared with A. helianthi (HM449991), another sunflower pathogenic fungus, was only 80%. A. helianthiinficiens has previously been reported on sunflower in Hungary and the USA (3), Serbia (1), and Korea (2). However, to our knowledge, this is the first report of A. helianthiinficiens occurrence in Croatia as a new and harmful parasite of sunflower, illustrating an expansion of its geographical range and underscoring the need for phytosanitary control because it is a seedborne fungus. References: (3) M. Aćimović and N. Lačok. Helia 14:129, 1991. (4) H. S. Cho and S. H. Yu. Plant Pathol. J. 16:331, 2000. (2) E. G. Simmons. Mycotaxon 25:203, 1986. (1) E. G. Simmons. Alternaria: An Identification Manual. CBS Fungal Biodiversity Centre, Utrecht, the Netherlands, 2007.

Resolving the Diaporthe species occurring on soybean in Croatia

Diaporthe (anamorph = Phomopsis) species are plant pathogens and endophytes on a wide range of hosts including economically important crops. At least four Diaporthe taxa occur on soybean and they are responsible for serious diseases and significant yield losses. Although several studies have extensively described the culture and morphological characters of these pathogens, their taxonomy has not been fully resolved. Diaporthe and Phomopsis isolates were obtained from soybean and other plant hosts throughout Croatia. Phylogenetic relationships were determined through analyses of partial translation elongation factor 1-alpha (EF1-α) gene and ITS nrDNA sequence data. By combining morphological and molecular data, four species could be distinguished on soybeans in Croatia. Diaporthe phaseolorum is described in this study and its synonyms are discussed. Diaporthe phaseolorum var. caulivora is raised to species status and the name Diaporthe caulivora is introduced to accommodate it. A species previously known as Phomopsis sp. 9 from earlier studies on sunflower, grapevine, rooibos and hydrangea is reported for the first time on soybean, and is formally described as Diaporthe novem. The well-known soybean pathogen Phomopsis longicolla was also collected in the present study and was transferred to Diaporthe longicolla comb. nov. The presence of these species on herbaceous hosts raises once more the relevance of weeds as reservoirs for pathogens of economically important plants.