INDUCTION AND FORMATION OF COCHLIOBOLUS-SATIVUS APPRESSORIA

Germinating Cochliobolus sativus spores were induced to form appressor ia on a variety of artificial surfaces, including replicas of the barl ey leaf surface. Evidence was obtained for the involvement of chemical and topographic signals during induction of appressorium formation in C. sativus. Germ tube thigmotropism was also observed in vitro. Ultra structure relevant to appressorium formation was observed, including t he germ tube apex, apical swelling of the germ tube apex prior to appr essorium formation, the appressorium with associated septation and the penetration peg. Cytochemical probes applied to germlings at the elec tron microscope level failed to detect alpha-D-mannan, alpha-D-glucan, beta-D-galactan, D-glcNAc or D-galNAc polymers in the extracellular m ucilage associated with the fungal gernlings. The ultrastructure of hy phal apices from germlings grown under different nutritional condition s differed with respect to Spitzenkorper morphology, apex shape and in the quantity of associated extracellular mucilage. Experimental findi ngs are discussed relative to current understanding of appressorium in duction in more extensively studied systems.