Autecology of Fusarium oxysporum f. sp. raphani in soils suppressive and conducive to Fusarium-wilt of radish

Effects of organic amendments and alterations of environmental conditions on the inoculum potential of Fusariumoxysporum f. sp. raphani PEG-4 (PEG-4), estimated from its population dynamics and spore germinability, were investigated using soils suppressive (S-soil) and conducive (C-soil) to Fusarium-wilt of radish. The results on the population dynamics of PEG-4 in S- and C-soils showed that the germination-lysis mechanism, proposed by Chinn and Ledingham (Can. J. Bot. (1962) 39, 739–748), seemed to be applicable to S-soil, while not application to C-soil. Germination of PEG-4 microconidia in soils supplemented with glucose and asparagine (1 mg g−1 of soil) was higher in C-soil than in S-soil, showing that S-soil possessed a greater degree of fungistasis than C-soil. Organic amendments, especially rice straw and fresh radish residue (FRR), brought about suppressive effects on the germination of PEG-4 in both soils along with their decomposition. These results suggest that the autecology of PEG-4 in S- and C-soils was quite different depending on incubation conditions, and presence or absence of organic amendments.