Ascospore Discharge in Hypoxylon

SUMMARY

Portions of wood, bearing stromata of three species of Hypoxylon, collected in the field and then maintained in a mist chamber in the greenhouse, were studied under controlled conditions in ISCO Environmental Chambers. Kramer-Collins spore samplers were used to study effects of various environmental factors on ascospore discharge. H. investiens (Schw.) Curt, displayed a light-positive response; spore discharge began within 20–30 min after exposure to light and under constant light was continuous. Under constant dark, spore discharge did not occur. In H. truncatum (Schw. ex Fr.) Miller, spore discharge was inhibited by light of 1,500 ft-c; however, with light less than 500 ft-c, the periodic pattern (with maxima occurring during the dark periods previously established under alternating 8 hr of higher intensity light and 16 hr of dark) was maintained in an endogenous rhythm. When H. rubiginosum Pers. ex Fr. was subjected to alternating 8 hr light and 16 hr dark, spore discharge began to increase while still in the light period and peaked approximately midway through the dark period. After conditioning in alternating light/dark, spore discharge ceased after several days in continuous light; however, under continous dark, it remained relatively constant, showing no indication of a gradual decrease.