Differential expression of induced resistance by an aqueous extract of killed Penicillium chrysogenum against Verticillium wilt of cotton

Dry mycelium of Penicillium chrysogenum (PEN), a waste product of the pharmaceutical industry, was extracted with water and applied to the roots of two Gossypium hirsutum cultivars (H552 and Vered) and two G. barbadense cultivars (PF15 and P906) to examine its efficacy in controlling Verticillium dahliae Kleb. Soil application of 5% PEN provided significant protection against Verticillium wilt in all the tested cultivars, although PF15 and P906 were genetically more resistant to the wilt disease than H552 and Vered. As PEN did not inhibit mycelial growth of V dahliae in vitro, it is inferred that the disease controlling effects of PEN are attributed to induced resistance. Percentage protection induced by PEN in H552 and Vered was significantly higher than that of PF15 and P906, and the older seedlings of H552 showed a relatively higher percentage of protection than younger seedlings of the same cultivar, suggesting that the expression of induced resistance was somewhat cultivar-dependent and seedling age-dependent. Treatment with 5% PEN increased peroxidase (POX) activity and lignin deposition in hypocotyls at 16-48 and 24-48 h after PEN treatment, respectively. We assume that POX might result in lignification and thus be associated with the defense against Verticillium wilt. It is concluded that dry mycelium of PEN may be used to induce resistance against V. dahliae in cotton. (C) 2002 Elsevier Science Ltd. All rights reserved.