Allelopathic impact of artificially applied coumarin on Fusarium oxysporum f.sp. niveum

Abstract

Watermelon production is threatened by fusarium wilt caused by Fusarium oxysporum f.sp. niveum (FON) in continuous cultivation system. Some elements, mainly allelochemicals, released from living roots or decayed plants might be associated with the disease. The purpose of this work was to evaluate the possible impact of coumarin, one kind of watermelon allelochemical, on FON. Furthermore, possible new mechanisms might be investigated during the ecological interactions of plant-microbe. Results showed that coumarin strongly inhibited growth of FON leading to a decrease in its biomass, dry weight of mycelia of FON in a liquid culture. The dry weight was decreased by 62.9% compared with control. The hyphal growth of FON on plates was stopped at high ([400 mg l -1 ) concentrations of coumarin. At 320 mg l -1 , sporulation and enzyme activities of FON were also severely suppressed by coumarin. The yield of conidia, and the activities of proteinase, cellulase, and amylase were reduced by 98.9%, 79.7%, 29.8% and 15.9% respectively. However, conidial germination and mycotoxin (MT) production of FON were greatly stimulated, being increased by 55.7% and 14.9 fold at 320 mg l -1 respectively. We conclude that coumarin acted as an allelochemical substance to inhibit growth and pathogenic enzyme activities of FON but to stimulate mycotoxin production and conidial germination. It was suggested that coumarin acted as a signal transduction element bridging plant and pathogen in the process of plant-microbe interactions.

Pathogen profile update: Fusarium oxysporum

“…Wu et al . (2008a,b,c) showed that cinnamic acid, coumaric acid or vanillic acid, when applied to F. oxysporum f. sp. niveum cultures, increased mycotoxin production (probably predominantly fusaric acid) and the activity of hydrolytic enzymes, such as pectinase, cellulose and amylase (only in the presence of cinnamic and vanillic acids).…”

Paenibacillus polymyxa SQR-21 systemically affects root exudates of watermelon to decrease the conidial germination of Fusarium oxysporum f.sp. niveum

“…The conidial suspension of FON was diluted to no more than 1000 conidia per milliliter with sterile distilled water. The diluted suspension (0.1 ml) was spread on Petri-plates containing 2% water agar and incubated at 28°C for 3 d. The number of colonies was counted after 3 d of incubation (Wu et al 2008b). …”

Antifungal activity of rice straw extract on some phytopathogenic fungi

“…In this respect, Muhsin et al (2001) reported high reductions in the activities of amylase, cellulase and protease for A. flavus, A. alternate and other 16 fungal species subjected to garlic extract in the growth medium. Furthermore, Wu et al (2008) demonstrated that the artificially applied coumarin inhibited the activity of protease, amylase and cellulase of F. oxysporum. In addition, Fawzi et al (2009) reported that cinnamon, halfa barr, laurel, avocado and ginger extracts inhibited the production of glucosidase, pectin lyase and protease by A. alternata and F. oxysporum.…”

“…Total amylase activity was assayed according to DNS method (Wu et al, 2008). The mixture contained 100 µl of the above prepared filtrate, 2 ml of 0.15 M citrate-phosphate buffer (pH 5.0) and 3 ml of 4% (w/v) soluble starch previously maintained at 40°C for 15 min.…”