Effects of elicitor from Colletotrichum graminicola on the response of sorghum to Periconia circinata and its pathotoxin

The effects of an elicitor (CG-elicitor) from Colletotrichum graminicola and the host-specific pathotoxin (PC-toxin) produced by Periconia circinata were studied to determine the interactions of responses associated with resistance and susceptibility, respectively. Roots of sorghum ( Sorghum bicolor) accumulated 3-deoxyanthocyanidin phytoalexins in response to CG-elicitor but not in response to PC-toxin over a range of concentrations. Elicitation of the phytoalexins prior to treatment with PC-toxin had no effect on the genotype-specific induction of electrolyte leakage or on the toxin-enhanced synthesis of a specific group of 16 kDa proteins. Similarly, prior treatment with the elicitor did not prevent infection and development of milo disease symptoms in susceptible seedlings inoculated with conidia of P. circinata. However, treatment of roots with the CG-elicitor enhanced the synthesis of the 16 kDa proteins in both resistant and susceptible genotypes without expression of disease symptoms. Thus, the activities of PC-toxin and CG-elicitor are separable and independent. PC-toxin apparently does not produce disease symptoms by inducing phytoalexins, and induction of phytoalexins does not prevent pathogenesis by P. circinata or the detrimental effects of PC-toxin.