Host cell wall synthesis and its role in resistance to a mycoparasite

Label from the radioactive chitin precursor, [ 3 H]- N -acetyl-glucosamine, accumulated at the hyphal apices and infection sites of Choanephora cucurbitarum and Phascolomyces artictulosus , a susceptible and resistant host, respectively, to a mycoparasite, Pipocephalis virginiana . The degree of incorporation varied as a function of host-parasite compatibility and duration of the incubation period. Autoradiographs of Phascolomyces articulosus prepared 18, 24 and 36 h after inoculation revealed silver grains over the infection zone. Labelling was extensive at 24 and 36 h. This pattern of label accumulation coincides with formation of a papilla (18 to 20 h) and early development of a well differentiated sheath (20 to 22 h) previously reported. In contrast, negligible levels of label accumulated at infection sites 18 h after inoculation in susceptible host, C. cucurbitarum . Although incorporation increased significantly by 24 h, levels of grain density comparable to those observed in the resistant host, Phascolomyces articulosus , were not apparent until 36 h following inoculation, coinciding with time when sheath appears in C. cucurbitarum . Significance of chitin synthesis stimulation in infection zone as a response to parasitism is discussed.