In vitro responses of Fusarium oxysporum f.sp.niveum to phenolic acids in decaying watermelon tissues

To establish the relationships among wilt disease and pathogens and the chemical environment during the allelochemical interactions of plant–microbe–soil, extracts from decaying watermelon tissues were added to media to investigate the effect of allelochemical decaying watermelon tissues on Fusarium oxysporum f.sp.niveum (FON) in vitro. Twelve types of phenolic acids from various decaying watermelon cultivars (Zaojia 82-24 and Jingxing 3) with different levels of resistance to FON were analysed using HPLC. The results demonstrated that there were fewer types and quantities of chemical components released from decaying susceptible watermelon tissues (Zaojia 84-24) than there were from decaying resistant watermelon tissues (Jingxing 3). More antifungal phenolic acids in decaying resistant watermelon tissues (with a ratio of 29.2:1 of antifungal phenolic acids to fungus-stimulation phenolic acids) were observed than in decaying susceptible tissues (with a ratio of 8.4:1 of antifungal phenolic acids to fungus-stimulation phenolic acids). Decaying resistant watermelon tissue extracts inhibited the growth and conidia germination and formation of FON, while decaying susceptible extracts stimulated growth and conidia germination and formation.Extracts from decaying resistant watermelon tissues stimulated virulence factors considerably less than did those from decaying susceptible tissues. We conclude that the decaying plant extracts from susceptible watermelon cultivars stimulated FON because of their higher content of fungus-stimulation phenolic acids, while the decaying resistant watermelon plants inhibited FON because of their higher content of antifungal phenolic acids. These results imply that phenolic acids containing decaying plant residues in soil would induce or inhibit pathogens in plant–microbe interactions.