Hong-Sheng Wu

Cinnamic Acid Inhibits Growth but Stimulates Production of Pathogenesis Factors by in Vitro Cultures of Fusarium oxysporum f.sp. niveum

Long-term monoculture of watermelon leads to frequent occurrence of watermelon fusarium wilt caused by Fusarium oxysporum f.sp. niveum (FON). Some allelochemicals contained in watermelon root exudates and decaying residues are possibly responsible for promoting the wilt disease. The purpose of this study was to evaluate the allelopathic effect of artificially applied cinnamic acid on FON. Results demonstrated that hyphal growth of FON was strongly inhibited by cinnamic acid. At the highest concentration of cinnamic acid, the biomass in liquid culture was decreased by 63.3%, while colony diameter, conidial germination on plates, and conidial production in liquid culture were completely inhibited. However, mycotoxin production and activity of phytopathogenic enzymes were greatly stimulated. Mycotoxin yield, pectinase activity, proteinase activity, cellulase activity, and amylase activity were increased by 490, 590, 760, 2006, and 27.0%, respectively. It was concluded that cinnamic acid dramatically stimulated mycotoxin production and activities of hydrolytic enzymes by FON but inhibited growth and germination of FON. The findings presented here indicate that cinnamic acid is involved in promoting watermelon fusarium wilt.

Antibiotic effect of exogenously applied salicylic acid on in vitro soilborne pathogen, Fusarium oxysporum f.sp.niveum.

Salicylic acid, which is biosynthesized inside plant and is often found and accumulated in soil due to plant debris decaying, is considered as a signaling substance during plant-microbe interactions. It is involved in the cycling of biogeochemistry and related to plant resistance to biotic and abiotic stress. The antibiotic effect of salicylic acid on Fusarium oxysporum f.sp.niveum (FON) was studied to investigate the relationships between the salicylic acid and the fungus in the ecological interaction of plant-microbe. Results showed that the biomass, colony diameter, number of conidium germination and conidium production of FON were decreased by 52.0%, 25.7%, 100% and 100% at concentrations of 800 mg L(-1). However, mycotoxin yield was increased by 233%, pectinase activity raised by 168.0% and cellulase activity increased by 1325% compared to control at higher concentrations. It was concluded that salicylic acid as an allelochemical greatly inhibited FON growth and conidia formation and germination, though stimulated mycotoxin production and activities of hydrolytic enzymes by FON.

Evaluation of metal ions (Zn2+, Fe3+ and Mg2+) effect on the production of fusaricidin-type antifungal compounds by Paenibacillus polymyxa SQR-21

Effect of metal ions (Mg(2+), Zn(2+) and Fe(3+)) on the production of fusaricidin-type antifungal compounds by Paenibacillus polymyxa SQR-21 was studied in liquid culture. First, one-factor; three-level experiments were conducted to find out optimal concentrations of each metal ion for maximum production of fusaricidins. Later, three-factor; five-level experiments were performed and a quadratic predictive model was developed using response surface methodology (RSM). The results indicated that Fe(3+) and Mg(2+) positively affected the growth of P. polymyxa as determined by measuring the OD(600) of the liquid culture. The production of fusaricidin-type antifungal compounds was significantly inhibited by Zn(2+) (P=0.0114) and increased by Mg(2+) (P=0.0051) but the effect of Fe(3+) (P=0.2157) was non-significant. However, a synergistic positive effect of Mg(2+) and Fe(3+) on the production of antifungal compounds was observed. This study sheds lights on the pertinent effects of the individual and combined metal ions on the production of fusaricidins in P. polymyxa. It provides the key information for optimization of the metal ions in the fermentation media to achieve the maximum antibiotic production in this strain.

Effect of fusaric acid on biomass and photosynthesis of watermelon seedlings leaves

Abstract Wilt disease of watermelon caused by Fusarium oxysporum f. sp. niveum in long-term monoculture system has been much often found particularly in protected land cultivation system worldwide. Fusaric acid (FA), a fungal phytotoxin, was extracted from F. oxysporum f. sp. niveum isolated from diseased watermelon plant. The influence of FA on the biomass and leaves photosynthesis of watermelon seedlings was investigated in a laboratory study. Results obtained are listed as follows. Plant height, fresh weight, main root length and lateral roots of watermelon seedling exposed to FA (400 mg·L−1) for 12 hours and then grown in ordinary condition for nine days were decreased by 23.0%, 23.1%, 23.6% and 33.6% compared with control respectively. Cotyledons were wilted to death completely and necroses occurred on the first true leaf and the upper leaves had become crinkled and chlorosis, which was a typical symptom of wilting disease of watermelon. And thus physiological functions were inhibited and damaged strongly. Net photosynthesis rate, stomatal conductance, intercellular CO2 concentration, and chlorophyll (SPAD reading) of the seedlings decreased with the increasing of concentrations of FA and duration of exposure to FA. Compared with control, stomatal conductances of leaves treated with FA weredeclined by 87.4-98.4% and net photosynthesis rates of leaves were decreased by 51.8-92.1%. Intercellular CO2 concentration of the seedlings treated with FA was reduced by 66.6 -94.8%. Chlorophyll content in the leaves of the seedlings was decreased by 42.7-72.3%. Transpiration rate fell down to 86.8-96.3%. It was concluded that FA strongly reduced the chlorophyll content of watermelon seedlings leaves resulting to heavy suppression of leaf photosynthesis, which therefore affected seedlings growth finally leading to leaf wilting and necrosis.

Growth of in vitro Fusarium oxysporum f. sp. niveum in chemically defined media amended with gallic acid

Gallic acid was artificially added to the media to grow Fusarium oxysporum f.sp.niveum to investigate its effect on the pathogenic fungus. Results indicate that gallic acid inhibited the growth of F. oxysporum f.sp.niveum. The colony diameter, the conidia germinating rate and the conidia yield were reduced by 5.7-22.9%%, 35.8-55.6% and 38.9-62.2% respectively. However, the virulence factors by the fungus were stimulated. The activity of pectinase, proteinase and cellulase increased by 12.3-627.8%, 11.8-41.2% and 0.5-325.0% respectively, while the activity of amylase increased slightly. The results suggest that gallic acid repressed growth but facilitated the relative pathogenicity of invading pathogens.

In vitro physiological responses of Fusarium oxysporum f. sp. niveum to exogenously applied syringic acid.

ABSTRACT. Plant–microbe interactions are often accompanied by allelochemicals, such as syringic acid, released from the host plant. To explore the role of phenolic acids released from crop host plants in response to pathogen invasion, we examined the allelopathic effect of an artificially applied syringic acid on Fusarium oxysporum f. sp. niveum. We demonstrated that the growth and the conidial germination rate of F. oxysporum f. sp. niveum were stimulated at lower concentrations of syringic acid, though inhibited by higher dosage compared with control. The yield of fungus mycotoxin was increased from 60.9% to 561.5%. We conclude that syringic acid can be considered as a allelochemical inducer, stimulating the relative virulence factors of invading pathogens.

Responses of Fusarium oxysporum f. sp. niveum to exogenously added sinapic acid in vitro

To assess the influence of phenolic acids from plant root exudates on soil pathogens, we studied the effect of sinapic acid added to chemically defined media on the growth and virulence factors of Fusarium oxysporum f. sp. niveum. Sinapic acid inhibited the growth and conidial formation and germination of F. oxysporum f. sp. niveum by 6.7–8.8% and 11.2–37.3%, respectively. Mycotoxin production by F. oxysporum f. sp. niveum was stimulated by 81.6–230.7%. Pectinase, proteinase, cellulase, and amylase activities were stimulated at a lower concentration of sinapic acid, while they were inhibited at a higher concentration. It is concluded that sinapic acid inhibited the growth and conidial germination of F. oxysporum f. sp. niveum and decreased the pathogenic enzymes’ activity at higher doses.

Physiological and biochemical responses of in vitro Fusarium oxysporum f.sp. niveum to benzoic acid.

The allelopathic potential of an artificially applied allelochemical, benzoic acid, on in vitro Fusarium oxysporum f.sp. niveum (a soil-borne pathogen causing watermelon wilt) was evaluated. Benzoic acid strongly inhibited its growth, sporulation and conidia germination, whereas it stimulated virulence factors of this pathogen. The biomass was reduced by 83–96 % and the conidia germinating rate and conidia production rate were decreased by 100 % at a concentration of >200 mg/L. However, phytopathogenic enzyme activities and mycotoxin production were stimulated with an increase of 10.2–1250 % for enzyme activities and 610–2630 % for mycotoxin yield.