SUBSTRATE SURFACE INFLUENCES UPON GERMINATION OF COLLETOTRICHUM-TRUNCATUM CONIDIA

Substrates influenced germination of conidia of the mycoherbicide, Col letotrichum truncatum. Very few (<10%) conidia germinated when incubat ed while suspended in water or when incubated on or in partially lique fied agar. Many (>70%) were induced to germinate when incubated on fir m agar. The percentage of germinated conidia increased as agar firmnes s increased. Not all solid substrates equally influenced germination. Over 50% of the conidia germinated on chromatography paper, cellulose acetate filter, or on hard (plastic cover slip) substrates. In contras t, germination was relatively poor on cellulose nitrate filter and gla ss cover slips. Some natural substrates of dissimilar texture (wood, l ive plant leaf) produced good germination. Lower O-2 levels or limited gas exchange for submerged conidia did not prevent germination becaus e many conidia germinated while submerged on or between firm substrate s. Subjecting conidia to motion during incubation between glass cover slips favored germ tube production rather than appressoria formation. Evidence suggests a positive germination response of C. truncatum coni dia to solid substrates that occurs prior to the well-documented thigm otropic response of germ tubes of germinated conidia.