Synergistic Action of Commercially Available Fungicides for Protecting Wheat from Common Root Rot Caused by Bipolaris sorokiniana in China

Identification and Fungicide Control of Bipolaris sorokiniana Causing Leaf Spot and Blight on Common Hop (Humulus lupulus) in Korea

Hop (Humulus lupulus) is a perennial herbaceous vine belonging to the family Cannabaceae. This crop is commercially grown for the brewing industry for its bitter and aromatic flavor, as well as its antiseptic properties. In June 2021, leaf spot and blight was observed on common hop plants in Buan-gun, Jeollabuk-do, South Korea. The typical symptoms were small to large, dark-brown, necrotic lesions with yellow halos on the leaves. This study aimed to clarify the causal agent of this disease. Two fungal species, Alternaria alternata and Bipolaris sorokiniana, were isolated from the diseased leaf samples and identified by combining morphological observations and phylogenetic analysis using sequence datasets of internal transcribed spacer (ITS), Alt a1, rpb2, endoPG, and OPA10-2; and ITS, gpd, and tef1, respectively. Pathogenicity of the fungal isolates on detached leaves and living plants revealed that B. sorokiniana is the causal pathogen of this disease, while A. alternata is potentially a saprophyte. Fungicide sensitivity of the pathogen B. sorokiniana was further estimated in vitro using three classes of fungicides represented by fluxapyroxad, pyraclostrobin, and hexaconazole. The effective concentrations that inhibited 50% of spore germination (EC50) were 0.72, 1.90, and 0.68 μg ml-1, respectively. Moreover, all of these fungicides were able to control B. sorokiniana on detached common hop leaves at their recommended concentrations. In conclusion, this study reports leaf spot and blight of common hop caused by B. sorokiniana for the first time and proposes potential fungicides for this disease.

Improving suppressive activity of compost on phytopathogenic microbes by inoculation of antagonistic microorganisms for secondary fermentation

Antimicrobial activity contributes to plant disease control property of composts but its source is still not clear. From composting cow manure during secondary fermentation, 50 microbial strains with antifungal activity were isolated and identified. Two bacterial strains Bacillus mojavensis B282 and Pseudomonas aeruginosa F288, antagonistic against both phytopathogenic fungi and bacteria, were respectively used as the inoculum of compost for secondary fermentation. Inoculation of B282 or F288 significantly shifted microbial community structure of compost and genera functionally linked to antagonistic activity and plant growth promotion were enriched. Notably, culturable cells of B282 increased by about 40 times during secondary fermentation. The inoculation of each strain significantly increased antifungal activity of compost extracts and enhanced disease suppressive effects of compost on wheat root rot. This study demonstrates that inoculation of compost-indigenous microorganisms could improve antimicrobial activity of compost and provides a low-cost strategy for producing bio-organic fertilizers with biocontrol function.

Graphene Oxide Exhibits Antifungal Activity against Bipolaris sorokiniana In Vitro and In Vivo

The antimicrobial properties of graphene in vitro have been widely reported. However, compared to research performed on graphene’s antibacterial properties, there have been relatively few studies assessing graphene’s antifungal properties. In particular, evaluating graphene’s pathogenic effects on host plants in vivo, which is critical to using graphene in disease control, has rarely been performed. In this study, the fungal pathogen of wheat, barley, and other plants, Bipolaris sorokiniana (B. sorokiniana) and graphene oxide (GO) were selected for materials. A combination of physiological, cytological, and biochemical approaches was used to explore how GO affects the growth and pathogenicity of B. sorokiniana. The mycelial growth and spore germination of B. sorokiniana were both inhibited in a dose-dependent manner by GO treatment. The addition of GO significantly alleviated the infection of pathogenic fungi in host plants. The results of scanning electron microscopy demonstrated that the inhibitory effect of GO on B. sorokiniana was primarily related to the destruction of the cell membrane. Our study confirmed the antifungal effect of graphene in vitro and in vivo, providing an experimental basis for applying graphene in disease resistance, which is of great significance for agricultural and forestry production.

Root rot a silent alfalfa killer in China: Distribution, fungal, and oomycete pathogens, impact of climatic factors and its management

Alfalfa plays a significant role in the pasture ecosystems of China's north, northeast, and northwest regions. It is an excellent forage for livestock, improves soil structure, prevents soil erosion, and has ecological benefits. Presently root rot is a significant threat to the alfalfa productivity because of the survival of the pathogens as soil-borne and because of lack of microbial competition in the impoverished nutrient-deficient soils and resistant cultivars. Furthermore, these regions' extreme ecological and environmental conditions predispose alfalfa to root rot. Moisture and temperature, in particular, have a considerable impact on the severity of root rot. Pathogens such as Fusarium spp. and Rhizoctonia solani are predominant, frequently isolated, and of major concern. These pathogens work together as disease complexes, so finding a host genotype resistant to disease complexes is challenging. Approaches to root rot control in these regions include mostly fungicides treatments and cultural practices and very few reports on the usage of biological control agents. As seed treatment, fungicides such as carbendazim are frequently used to combat root rot; however, resistance to fungicides has arisen. However, breeding and transgenic approaches could be more efficient and sustainable long-term control strategies, especially if resistance to disease complexes may be identified. Yet, research in China is mainly limited to field investigation of root rot and disease resistance evaluation. In this review, we describe climatic conditions of pastoral regions and the role of alfalfa therein and challenges of root rot, the distribution of root rot in the world and China, and the impact of root rot pathogens on alfalfa in particular R. solani and Fusarium spp., effects of environmental factors on root rot and summarize to date disease management approach.

Identification and Pathogenicity of Fungi Associated with Leaf Spot of Muskmelon in Eastern Shandong Province, China

Leaf spot is a serious disease in the growth and development of muskmelon, which can affect its quality and yield. Over the past years, Malianzhuang Muskmelon Base, the main muskmelon producing area in Shandong Province, China, has been seriously affected by leaf spot. Since 2018, symptomatic leaves were collected from 11 production areas of this base to determine the pathogens of muskmelon foliar diseases. Two-hundred fungal strains were isolated and 10 genera and 17 species were identified based on morphological characteristics and multilocus phylogenetic analysis (ITS, GADPH, RPB2, HIS3, EF-1α, and LSU). The most frequently isolated species from each sampling area was Alternaria tenuissima with 77 strains, followed by A. alternata. Pathogenicity experiments showed that A. alternata, A. tenuissima, Fusarium neocosmosporiellum (formerly Neocosmospora vasinfecta), F. acuminatum, Exserohilum rostratum, Bipolaris sorokiniana, and Stagonosporopsis cucurbitacearum (formerly Didymella bryoniae) could cause symptoms highly similar to those of infected leaves observed under natural conditions in the field. Therefore, these fungal isolates are considered to be the primary pathogens causing muskmelon leaf spot, and A. tenuissima and A. alternata were the most common and virulent pathogens in this study. In addition, this is the first study of F. neocosmosporiellum, F. acuminatum, E. rostratum, and B. sorokiniana as pathogens associated to muskmelon leaf spot in China as well as the world.

Bipolaris sorokiniana-Induced Black Point, Common Root Rot, and Spot Blotch Diseases of Wheat: A Review

Wheat is among the ten top and most widely grown crops in the world. Several diseases cause losses in wheat production in different parts of the world. Bipolaris sorokiniana (teleomorph, Cochliobolus sativus) is one of the wheat pathogens that can attack all wheat parts, including seeds, roots, shoots, and leaves. Black point, root rot, crown rot and spot blotch are the main diseases caused by B. sorokiniana in wheat. Seed infection by B. sorokiniana can result in black point disease, reducing seed quality and seed germination and is considered a main source of inoculum for diseases such as common root rot and spot blotch. Root rot and crown rot diseases, which result from soil-borne or seed-borne inoculum, can result in yield losses in wheat. Spot blotch disease affects wheat in different parts of the world and cause significant losses in grain yield. This review paper summarizes the latest findings on B. sorokiniana, with a specific emphasis on management using genetic, chemical, cultural, and biological control measures.