Experiments with some endophytic and endozoic Acrochaetium species

Abstract

In vitro unialgal cultures of two endophytes, Acrochaetium endophyticum and A. asparagopsis, and of the endozoic species A. infestans have been established. In studies on the liberation of spores the monospores showed amoeboid changes of shape immediately after release and for periods up to 60 min. Early developmental stages of sporelings have also been studied. Monospores of A. endophyticum are able to withstand protracted periods of storage in the dark or at very low light intensity, and begin development on return to ‘normal’ light conditions. Filaments survive up to 4 months dark storage, and after 2 months release viable spores soon after return to ‘normal’ light conditions. Monospore release was obtained in a light intensity range of 19–420 lumens/sq.ft but spores quickly bleached and died at 480–500 lumens/sq.ft. ‘Healthy’ sporeling and filament growth were obtained at intensities up to 300 lumens/sq.ft, and slow growth at 19 lumens/sq.ft. Repeated monosporangium formation was found under a long day/summer temperature regime; sporangia were not obtained under a short day/low temperature regime. Growth and sporulation were obtained in a salinity range 0.5–1.4 times that of normal sea water, and significant differences in cell size were found in media of high and low salinity. Filaments survive protracted periods of exposure to low temperature and subsequently released spores. The upper thermal death point lies between 27–30°C. Filament growth and spore liberation were obtained in media of pH range 6–9. Spore settlements were obtained on endophyte-free plants of Heterosiphonia and ‘infection’ stages have been studied. In experiments with other animals and plants, endozoic growths of A. endophyticum have been induced in a hydroid organism. A. asparagoposis and A. infestans form distinctive epiphytic growths on substrata other than their normal ‘host’ material. A. endophyticum formed Erythrocladia-like growths on the rhizoids of Heterosiphonia. A. endophyticum penetrates into calcareous substrata and the filaments show shellboring properties, but this property was not observed with A. asparagopsis and A. infestans.