Impact of water potential on growth and germination of Fusarium solani soilborne pathogen of peanut

Bioassay-guided isolation of three new alkaloids from Suillus bovinus and preliminary mechanism against ginseng root rot

In order to control the occurrence of ginseng root rot caused by Fusarium solani (Mart.) Sacc., the antifungal compounds of the mushroom Suillus bovinus were investigated. And three new alkaloids (1-3), named bovinalkaloid A-C, along with one known analog (4), were isolated and identified by bioassay-guided isolation and spectroscopic analyses. Compound 1 strongly inhibited the mycelial growth and spore germination of F. solani with minimum inhibitory concentration of 2.08 mM. Increases in electrical conductivity, nucleic acid, and protein contents, and decreases in lipid content showed that the membrane permeability and integrity were damaged by compound 1. Compound 1 also increased the contents of malondialdehyde and hydrogen peroxide and the activities of antioxidant enzymes, indicating that lipid peroxidation had taken place in F. solani. Compound 1 may serve as a natural alternative to synthetic fungicides for the control of ginseng root rot.

Enhancement of soil aggregation and physical properties through fungal amendments under varying moisture conditions

Soil structure and aggregation are crucial for soil functionality, particularly under drought conditions. Saprobic soil fungi, known for their resilience in low moisture conditions, are recognized for their influence on soil aggregate dynamics. In this study, we explored the potential of fungal amendments to enhance soil aggregation and hydrological properties across different moisture regimes. We used a selection of 29 fungal isolates, recovered from soils treated under drought conditions and varying in colony density and growth rate, for single-strain inoculation into sterilized soil microcosms under either low or high moisture (≤-0.96 and -0.03 MPa, respectively). After 8 weeks, we assessed soil aggregate formation and stability, along with soil properties such as soil water content, water hydrophobicity, sorptivity, total fungal biomass and water potential. Our findings indicate that fungal inoculation altered soil hydrological properties and improved soil aggregation, with effects varying based on the fungal strains and soil moisture levels. We found a positive correlation between fungal biomass and enhanced soil aggregate formation and stabilization, achieved by connecting soil particles via hyphae and modifying soil aggregate sorptivity. The improvement in soil water potential was observed only when the initial moisture level was not critical for fungal activity. Overall, our results highlight the potential of using fungal inoculation to improve the structure of agricultural soil under drought conditions, thereby introducing new possibilities for soil management in the context of climate change.

Establishment and Application of a Multiplex PCR Assay for Detection of Sclerotium rolfsii, Lasiodiplodia theobromae, and Fusarium oxysporum in Peanut

Southern blight, stem rot, and root rot are serious soil-borne fungal diseases of peanut, which are caused by Sclerotium rolfsii, Lasiodiplodia theobromae, and Fusarium oxysporum, respectively. These diseases are difficult to be diagnosed in early stage of infection, causing the optimal treatment period was often missed. Therefore, establishing a rapid detection system is of great significance for early prevention of peanut soil-borne fungal diseases. Here, we have invented a multiplex PCR detection system to detect fungal pathogens of peanut southern blight, stem rot, and root rot at the same time. The quarantine fungal pathogen primer pairs were amplified to the specific number of base pairs in each of the following fungal pathogens: 1005-bp (F. oxysporum), 238-bp (L. theobromae), and 638-bp (S. rolfsii). The detection limit for the single and multiplex PCR primer sets was 1 ng of template DNA under in vitro conditions. Amplification of fungi of non-target species yielded no non-specific products. The validation showed that the multiplex PCR could effectively detect single and mixed infections in field samples. Overview, this study proved that this mPCR assay was a rapid, reliable, and simple tool for the simultaneous detection of three important peanut soil-borne diseases, which facilitated prompt treatment and prevention of peanut root diseases.

Environmental Effects of Temperature and Water Potential on Mycelial Growth of Neocosmospora solani and Fusarium spp. Causing Dry Root Rot of Citrus

This study aimed at evaluating the effect of environmental factors temperature and water potential (Ψw) on the growth of Neocosmospora (Fusarium) solani and three Fusarium species (F. oxysporum, F. equiseti and F. brachygibbosum) associated with citrus dry root rot and to determine the optimum and marginal rate for their growth. The effects of incubation temperature (5-40 °C), water potentials (Ψw) (- 15.54; - 0.67 MPa) (0.89-0.995 a_w) and their interaction (5-30 °C) was evaluated on the in vitro radial growth rates of Fusarium spp. and on their lag phase. Secondary models were used to model the combined effect of these factors on radial growth rate. The results underlined a highly significant effects (P < 0.001) of Ψw and temperature and their interactions on radial growth rates and lag phases (λ). The Four studied species were shown tolerant to a temperature of 35 °C with an optimum mycelial growth at 30 for N. solani and F. oxysporum and at 25 °C for F. equiseti and F. brachygibbosum. However, no growth was observed at both temperatures 5 and 40 °C and at Ψw of - 9.68 MPa (0.93 a_w). The optimum water potential for growth was ≥- 2.69 MPA (>0.98 a_w). The results from the polynomial model and response surface showing good agreement between observed and predicted values. The external validation on citrus fruit indicated slight differences between predicted and observed values of radial growth. The results of this study will be beneficial for understanding the ecological knowledge of these species and thereby limited preventively their occurrence.

Enhanced virulence of Fusarium species associated with spear rot of oil palm following recovery from osmotic stress

Fusarium spp., which are common inhabitants of oil palm leaves, are weak pathogens of common spear rot (CSR). We investigated the influence of osmotic stress on the growth, virulence, and activity of cell wall-degrading enzymes of CSR fungi, using potato dextrose agar (PDA) supplemented with KCl or sucrose (hyperosmotic medium). Hyperosmotic stress significantly inhibited mycelial growth, but growth rapidly recovered when mycelia were transferred to control medium. When inoculated into oil palm spear leaflets, Fusarium sp., and F. incarnatum precultured on 1.0 and 1.5 M KCl-hyperosmotic medium induced lesions that were two to four times larger than those in non-stressed cultures, suggesting enhanced virulence of the weak pathogens. Lesion size was not greatly affected in hyperosmotic cultures of moderately virulent F. sacchari. No activity of pectin lyase was detected in liquid cultures of the Fusarium isolates. All isolates except F. incarnatum BT48 secreted polygalacturonase (PG), which was active in both liquid cultures and inoculated leaves. Significantly increased PG activity (5-32-fold) was observed on leaves inoculated with hyperosmotic cultures of Fusarium sp. and F. sacchari. These findings suggest that Fusarium sp., F. incarnatum, and F. sacchari exhibit an adaptive physiological plasticity to hyperosmotic stress that results in enhanced virulence.