Fungicide Treatments to Control Seed-borne Fungi of Sunflower Seeds

Fusarium bilaiae, a new cryptic species in the Fusarium fujikuroi complex associated with sunflower

A Fusarium species associated with sunflower based on multilocus genealogy, morphological, physiological, ecological, mating type, and mycotoxin production data is formally described as the newly discovered species Fusarium bilaiae. The F. bilaiae strains formed a genealogically exclusive lineage within the African clade of the F. fujikuroi species complex. Comparison of morphological characteristics of F. bilaiae strains with those of the closely related F. phyllophilum strain NRRL 13617 revealed similarities in the main micromorphology of both species: production of numerous one-celled microconidia in false heads and short chains on monophialides and polyphialides and the absence of macroconidia and sporodochia. There was a slight but significant distinction between the two species when the strains were grown on different agar media, as well as in the shape and width of microconidia. Fusarium bilaiae strains isolated from symptomatic sunflower were not pathogenic to members of the Asteraceae tested; apparently, they live as saprophytes or endophytes in sunflower tissues. A difference between the strains of the two species in the production of mycotoxins was demonstrated with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis. On autoclaved rice, F. bilaiae did not produce fumonisins and beauvericin but produced moniliformin, whereas F. phyllophilum produced all these mycotoxins. A polymerase chain reaction (PCR) assay specific for mating type alleles identified F. bilaiae as a putative heterothallic species with MAT1-1 and MAT1-2 idiomorphs, but laboratory crosses were unsuccessful. Determining the area and host range of the new endophytic species F. bilaiae is a priority for future research.

Diversity of Fungal Endophytes in American Ginseng Seeds

Seeds play a critical role in the production of American ginseng. Seeds are also one of the most important media for the long-distant dissemination and the crucial way for pathogen survival. Figuring out the pathogens carried by seeds is the basis for effective management of seedborne diseases. In this paper, we tested the fungi carried by the seeds of American ginseng from the main production areas of China using incubation and highly throughput sequencing methods. The seed-carried rates of fungi in Liuba, Fusong, Rongcheng, and Wendeng were 100, 93.8, 75.2, and 45.7%, respectively. Sixty-seven fungal species, which belonged to 28 genera, were isolated from the seeds. Eleven pathogens were identified from the seed samples. Among the pathogens, Fusarium spp. were found in all of the seed samples. The relative abundance of Fusarium spp. in the kernel was higher than that in the shell. Alpha index showed that the fungal diversity between seed shell and kernel differed significantly. Nonmetric multidimensional scaling analysis revealed that the samples from different provinces and between seed shell and kernel were distinctly separated. The inhibition rates of four fungicides to seed-carried fungi of American ginseng were 71.83% for Tebuconazole SC, 46.67% for Azoxystrobin SC, 46.08% for Fludioxonil WP, and 11.11% for Phenamacril SC. Fludioxonil, a conventional seed treatment agent, showed a low inhibitory effect on seed-carried fungi of American ginseng.

In Vitro Evaluation of Azoxystrobin, Boscalid, Fentin-Hydroxide, Propiconazole, Pyraclostrobin Fungicides against Alternaria alternata Pathogen Isolated from Carya illinoinensis in South Africa

Black spot disease or Alternaria black spot (ABS) of pecan (Carya illinoinensis) in South Africa is caused by Alternaria alternata. This fungal pathogen impedes the development of pecan trees and leads to low yield in pecan nut production. The present study investigated the in vitro effect of six fungicides against the mycelial growth of A. alternata isolates from ABS symptoms. Fungicides tested include Tilt (propiconazole), Ortiva (azoxystrobin), AgTin (fentin hydroxide), and Bellis (boscalid + pyraclostrobin). All fungicides were applied in 3 concentrations (0.2, 1, and 5 μg mL^-1). Tilt and Bumper 250 EC containing propiconazole active ingredient (demethylation Inhibitors) were the most effective and inhibited all mycelial growth from up to 6 days post-incubation. The other active ingredients (succinate dehydrogenase inhibitors, organotin compounds, and quinone outside inhibitors) showed 75-85% mycelial growth inhibition. The effective concentration to inhibit mycelial growth by 50% (EC₅₀) was estimated for each isolate and fungicide. The overall mean EC₅₀ values for each fungicide on the six isolates were 1.90 μg mL^-1 (Tilt), 1.86 μg mL^-1 (Ortiva), 1.53 μg mL^-1 (AgTin), and 1.57 μg mL^-1 for (Bellis). This initial screening suggested that propiconazole fungicide was the most effective for future field trials test and how these fungicides could be used in controlling ABS disease.

Identification and comparison of biological characteristics and pathogenicity of different mating types of V. dahliae isolated from potato and sunflower

Potato is one of the most important staple crops in the world. China is one of the leading producers of potatoes, but the industry faces soilborne diseases such as Verticillium wilt. Most potato planting areas in China rotate the crop with sunflower which is also highly susceptible to Verticillium wilt. The comparison of the biological characteristics and pathogenicity of different mating types of Verticillium dahliae isolated from potato and sunflower in the major planting regions in China is of great importance. This is to help unravel the diversity in V. dahliae population and the sudden increase in infected fields. The diseased samples collected were cultured on PDA and the growing colony of pathogen isolated. Molecular techniques using specific primers were used to identify the V. dahliae pathogens and their mating type of the isolates obtained from the diseased sunflower and potato plants as well as their planting materials. The data obtained revealed that the dominant mating type population in sunflower was MAT1-1, whiles that of potato was MAT1-2, but Race 2 was the only race type identified for all the samples. There was a significant presence of MAT1-1 isolates present in potatoes, which is a new trend. Conventional crop rotation farming using sunflower is causing an increasing prevalence of MAT1-1 and mating type shift of isolates in potato in these regions.

Control of Seed-Borne Fungi by Selected Essential Oils

Seed-borne pathogens reduce the quality and cause infections at various growth stages of horticultural crops. Some of the best-known are fungi of genus Alternaria, that cause destructive vegetable and other crop diseases, resulting in significant yield losses. Over several years, much attention has been paid to environmentally-friendly solutions for horticultural disease management regarding the environmental damage caused by chemicals. For example, plant extracts and essential oils could be alternative sources for biopesticides and help to control vegetable seed-borne pathogens. This study aimed to evaluate essential oils’ influence on the growth of seed-borne fungi Alternaria spp. The microbiological contamination of vegetable seeds (carrot, tomato, onion) was determined by the agar-plate method. The essential oils’ impact on the growth of fungi was evaluated by mixing them with PDA medium at different amounts. The hydrodistillation was used for extraction of thyme and hyssop essential oils, and common juniper essential oil was purchased. The investigation revealed that the highest contamination of carrot and tomato seeds was by Alternaria spp. fungi. Furthermore, the highest antifungal effect on Alternaria spp. growth was achieved using 200–1000 μL L−1 of thyme essential oil. Meanwhile, the antifungal effect of other investigated essential oils differed from low to moderate. Overall, essential oils expressed a high potential for fungal pathogens biocontrol and application in biopesticides formulations.

Draft Genome Sequence of Alternaria longipes Causing Tobacco Brown Spot

Alternaria is a cosmopolitan fungal genus associated with diverse hosts. Tobacco brown spot caused by Alternaria longipes is one of the most destructive diseases of tobacco. A. longipes can also infect many other plants, some animals and even humans. Here, we report a genome assembly of A. longipes CBS 540.94 using Oxford Nanopore Technologies. A total of 15 contigs were assembled, and the genome size was 37.5 Mb with contig N50 of 4.33 Mb. This genome resource will provide information for further research on comparative genomics of the genus Alternaria and be a valuable resource in investigations of the molecular interactions of pathogen and hosts.

First Report of Fruit Rot of Grapes (Vitis vinifera) Caused by Cladosporium cladosporioides in Xinjiang, China

Xinjiang Province accounts for nearly 20% of the total grape (Vitis Vinifera L.), proles orientalis) (wine, table and raisin combined) production, being the largest production area in China. Fruit rot is the most common disease that impacts grape quality and yield. A new disease where the ripe grape berry surfaces were coated with brownish mildew was observed, and the disease mainly occurred on whole clusters or most of the berries in the cluster. In September 2019 and 2020, 125 diseased grape clusters were collected from 10 locations in northern Xinjiang where the disease incidence was 15.3% - 27.4% ((diseased clusters/ total clusters)*100). To identify the pathogen, symptomatic grape berries were disinfected with 1% NaClO for 2 min, followed by 70% ethanol for 30 s, and rinsed thrice in sterile distilled water. Three pieces of ~0.5 cm2 diseased grape skin with partial exocarp were placed on potato dextrose agar (PDA) amended with streptomycin sulfate and kanamycin (50 µg/mL each). The PDA plates were then incubated at 25℃ under light condition with the luminous intensity 3500 Lux for 7 days. Fungal colonies emerging from the plated tissue were subcultured and single-spored three times to obtain pure cultures. From 20 strains with similar colony phenotype and grey olive hue, flocculent, felt-like surface, six (Cc-Vivi-3, 7, 9, 11, 13 and 19) isolates were chosen for further characterization after 7 days of incubation. Conidia were either single or grew in chains, with around 4 conidia per chain. Conidia were ovoid, nearly spindle or globose with slightly smooth or irregular reticulate surface. Conidiophores were solitary, smooth, septate, erect or geniculate. These characteristics were consistent with the descriptions for Cladosporium cladosporioides. To confirm this identification, PCR was performed on the genomic DNA of the selected strains using primers for internal transcribed spacer (ITS) region ITS1/ITS4, actin (ACT) and translation elongation factor (TEF) (Schubert et al., 2007; Braun et al., 2003). Amplified ITS sequences provided a 100% match to C. cladosporioides (AY213641) in NCBI. Homology of ACT sequences to C. cladosporioides (HM148527 and MH047330) was 99.57% and 100%, respectively; and the homology of TEF sequences with C. cladosporioides (HM148258, HM148289, HM148260 and HM148266) was 97.56% ~ 100%. To further confirm the evolutionary relationship of strains from grapes with Cladosporium spp., phylogenetic analyses based on ITS, ACT and TEF conjoint sequences from the six experimental isolates, five C. cladosporioides strains, eight proximal Cladosporium species were analyzed. The phylogenetic tree showed that the six isolates from grapes clustered with C. cladosporioides strains, but not other proximal Cladosporium species. This confirmed that all six isolates evaluated were C. cladosporioides. Pathogenicity tests with one C. cladosporioides isolate (Cc-Vivi-3; accession No. ITS: MW556429, ACT: MW567144, TEF: MW567143) were carried out as follows: ripe and healthy grape clusters from cultivars Xinyu and Munag when total soluble solids were 20-21°Bx and 19-20 °Bx, respectively, were detached from the vines. Five berries of three clusters of each cultivar were punctured with a sterile syringe, then inoculated with a 20 μL conidial suspension (107 conidia/mL). And uninoculated, punctured berries in clusters treated with sterilized water served as controls. The experiment was repeated three times. Symptoms were recorded 15 days after incubation at 80% relative humidity and 25℃ with a 14 h light/10 h dark cycle. The olive green or blackish green mildew layer was produced on all inoculated berries. No symptoms were observed on the uninoculated berries. Koch's postulates were fulfilled by reisolating C. cladosporioides from all symptomatic tissues and identifying them by PCR targeting the ACT gene. This is the first description of C. cladosporioides causing grape fruit rot in Xinjiang, China. In recent years, worldwide reports of Cladosporium spp. damaging crops are increasing (Briceño et al., 2008; Walker et al., 2016; Meneses et al., 2018; Robles-Yerena et al., 2019; Ding et al., 2019; Yang et al., 2021). However, relatively few methods of management including some fungicides and biocontrol agents are available in different crops (Wang et al., 2018; Addrah et al., 2019). In view of the important role of Xinjiang in China agricultural production, that should arouse strong attention.

Screening of Marine Bioactive Antimicrobial Compounds for Plant Pathogens

Plant diseases have been threatening food production. Controlling plant pathogens has become an important strategy to ensure food security. Although chemical control is an effective disease control strategy, its application is limited by many problems, such as environmental impact and pathogen resistance. In order to overcome these problems, it is necessary to develop more chemical reagents with new functional mechanisms. Due to their special living environment, marine organisms have produced a variety of bioactive compounds with novel structures, which have the potential to develop new fungicides. In the past two decades, screening marine bioactive compounds to inhibit plant pathogens has been a hot topic. In this review, we summarize the screening methods of marine active substances from plant pathogens, the identification of marine active substances from different sources, and the structure and antibacterial mechanism of marine active natural products. Finally, the application prospect of marine bioactive substances in plant disease control was prospected.