ADHESION OF COLLETOTRICHUM-GRAMINICOLA CONIDIA TO CORN LEAVES - A REQUIREMENT FOR DISEASE DEVELOPMENT

Ungerminated conidia of Colletotrichum graminicola, the causal agent of anthracnose leaf blight of corn, adhered to corn leaves within minutes of contact. Adhesion approached 30 % of the conidial population by 30 min on the fourth and fifth leaves of 5-week-old plants. In contrast, adhesion of conidia on the eighth or ninth leaf of 8-week-old plants reached a maximum of only 20 % by 2 h suggesting that the adhesion of ungerminated conidia to the leaf is influenced by leaf age. Germination of conidia began 6 h after inoculation. Within 3 h after germination was first observed, the percentage adhesion increased and reached a new maximum level, indicating that a second phase of adhesion occurred as a result of germination. These results show that adhesion of ungerminated conidia as well as conidial germlings is essential to the infection process and the successful development of disease by C. graminicola. Scanning electron microscopy and micromanipulation of adhered conidia revealed both the alteration of the leaf surface to which the conidia had been adhered and the presence of a possible adhesive material on the contact surface of the ungerminated conidia and the contact surface of the conidial germ tube.