Extracts of killed Penicillium chrysogenum induce resistance against Fusarium wilt of melon

Dry fungal biomass of Penicillium chrysogenum (dry mycelium), a waste product of the pharmaceutical industry, was extracted with water and applied to the roots of melon plants before or after inoculation with Fusarium oxysporum Esp. melonis (Fom). Seedlings (4-6 days after emergence) treated with either acidic dry mycelium extract (DME) or neutralized dry mycelium extract (NDME) were protected against challenge infection with Fom. A single drench with 2-5% DME applied 12-72 h before inoculation provided significant control of the disease compared with water-drenched, challenged seedlings. No protection was seen in plants treated 0-6 h before inoculation or 0-48 h after inoculation. Neither DME nor NDME (0.5-5%) had any effect on fungal growth in vitro, which implied that disease control in vivo was mediated by induced resistance. The resistance induced by DME protected melon plants not only against race 1,2, but also against the three other races of the pathogen, indicating a race-non-specific resistance against Fom. Both DME and NDME significantly increased peroxidase activity and free L-proline content in seedlings 12 h and 48 h after soil drench, respectively. Resistance to Fusarium wilt was significantly associated with elevated levels of peroxidase activity but not with free L-proline content. Thus, peroxidase might be involved in the defense mechanisms activated by DME or NDME.