Allelopathy of Aspergillus japonicus on Crops

Steffens and Robeson, 1987). The compound inhibited the onion seedling elongation by 4, 32, 40, 68, and 94% The seeds of some dicotyledons fail to germinate and grow well at concentrations of 1029, 1028, 1027, 1026, and 1025 M, when contaminated by Aspergillus japonicus Saito. One strain of A. japonicus isolated from the seeds of contaminated rape (Brassica respectively. Penicillium oxalicum, which caused a storcampestris L.) inhibited the seedling growth of rape and radish (Raage rot of cucumber (Cucumis sativus L.) and tomato phanus sativus L.) when the fungus was directly inoculated on the seed [Lycopersicon lycopersicum (L.) Karsten] fruit, also surface. Metabolites released from the fungus inhibited the seedling produced SAD and oxalic acid (Jarvis et al., 1990). germination and seedling growth of rape and radish. The culture The genus Aspergillus is a saprophyte that occurs in filtrate and mycelium acetone (C3H6O) extract inhibited the seedling and on a variety of substrates, including grains, decaying growth of rape. The major allelochemical of A. japonicus was identivegetation in the field, and cattle dung (Raper and Fenfied by spectroscopic methods as secalonic acid F (SAF). Bioassays nell, 1965; Tzean et al., 1990, p. 43). It is particularly showed that SAF at concentration 0.038 mM significantly inhibited abundant in soils in the tropics and subtropics. During the seedling growth of several crops. routine laboratory work, we found that some dicotyledons that failed to germinate or grew poorly were infected by Aspergillus sp. In this paper, we report on the T term Allelopathy was coined by Molisch allelopathic effects of the fungus on several crops. We (1937) to refer to the biochemical interactions behave demonstrated that SAF is the major chemical retween all types of plants, including microorganisms sponsible for these effects. (Rice, 1974, 1995). Rice (1974) pointed out that only a small amount of research had been done on the chemical MATERIALS AND METHODS inhibition of higher plants by microorganisms, except for the specialized field of plant pathology. Metabolites Isolation and Culture of A. japonicus of many fungi may have adverse or stimulatory effects The strain of the fungus was isolated from the surface of on plants (Heisey et al., 1985; Rice, 1995) such as supinfected radish seeds that failed to germinate and then purified pression of seed germination, malformation, and retarby successive transfers of mycelia tips. Stock cultures were dation of seedling growth (Lynch and Clark, 1984). maintained on PDA slants at 288C for 7 d and then kept Many crop seeds are infected by fungi before harvest at 4 to 58C thereafter. The fermentative media consisted of: or during storage (Neergaard, 1979). If conditions are D-glucose, 20; potassium monophosphate (K2HPO4), 0.5; magnot favorable, then the situation is more serious (Kozanesium sulfate (MgSO4), 0.25; corn flour steep liquor, 20; and potato (Solanum tuberosum L.) liquor, 200 g L2. Each 500kiewicz et al., 1996). Some fungi on the surface of seeds mL Erlenmeyer flask contained 100 mL of media. The flasks may produce mycotoxins that affect food quality (Bewere incubated at 268C in the dark for 4 d on a gyratory tina, 1984), and some may produce phytotoxins that shaker at 180 rotations min2. affect seed germination and seedling growth (Neergaard, 1979). Plant Materials Secalonic acids, which represent a series of ergochrome pigments, are a group of fungal metabolites Seeds of radish, rape, cucumber, corn, and sorghum (Sorghum vulgare Pers.) were obtained from a local market in (Kurobane et al., 1979). They are the stereoisomers and Guangzhou, China. Seeds of hairy beggarticks (Bidens pilosa differ only in the placement of substituting groups. The L.) and barnyardgrass [Echinochloa crus-galli (L.) Beauv.] producing strains often produce one or more secalonic were collected at the campus of South China Agricultural Uniacids when they grow on rice (Oryza sativa L.), corn versity. (Zea mays L.), and rye (Secale cereale L.). Secalonic acid D (SAD) is the major mycotoxin of this group of Inoculation of A. japonicus on Seedling ergochromes (Betina, 1984). Secalonic acid A (SAA) was the first compound that was reported to have a Seeds of radish and rape were surface-sterilized with 1 g L2 mercury chloride (HgCl2) for 10 min, then with 750 g L highly potent phytotoxicity. It was isolated from Pyrenoethanol (C2H5OH) for 10 s. After sterilization, the seeds were chaeta terrestris, the pathogen of pink root disease of thoroughly rinsed with sterile water. Fifty seeds and one piece onion (Allium cepa L.) and other species of Allium of filter paper were each placed in 9-cm petri dishes. Seven mL 20% (V/V) PD was added. The spores of A. japonicus were R.S. Zeng, S.M. Luo, M.B. Shi, and Y.H. Shi, Inst. of Tropical and inoculated on the surface of the seeds before incubation. The Subtropical Ecology, S. China Agric. Univ., Wushan, Guangzhou, controls consisted of noninoculated seeds. The dishes were incu510642, P.R. China; Q. Zeng and H.F. Tan, Elemento Organic Chem. bated at 258C in a greenhouse with 10 h of artificial light (250 Lab. Nankai Univ., Tianjin 300071, P.R. China. This paper was presented orally at the Second World Congress on Allelopathy (Symposium: Allelopathy in Natural and Managed Ecosystems) held during Abbreviations: DMF, dimethyl formamide; EIMS, electron impact 9–13 Aug. 1999 at Lakehead Univ., Canada. Received 29 Nov. 1999. ionization mass spectrometry; EtOAc, ethyl acetate; NMR, nuclear *Corresponding author ([email protected]). magnetic resonance; SAA, secalonic acid A; SAD, secalonic acid D; SAF, secalonic acid F. Published in Agron. J. 93:60–64 (2001).