|Kaiser Jr, Walter|
Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/1996
Publication Date: N/A
Interpretive Summary: We studied the effect of moisture on some fungi that grow inside certain grasses (fescue, barley, sleepy grass). These fungi (endophytes) also produce some toxic chemicals inside the host plant that may lead to serious disease symptoms (fescue foot, sleeping disease) in cows or horses that eat these plants. We wanted to know how the availability of moisture inside these grasses (it varies widely during the plants' growth, reaching a very low level as the plants mature) affects the growth, reproduction, and antibiotic production of the fungi. We found that moisture availability affected different isolates of these fungi very differently, some were even able to reproduce (produce spores) over the whole range of moisture tested. Antibiotic production stopped, though, when moisture levels dropped to very low levels. Antibiotic production may drop off as the grasses mature.
Technical Abstract: Acremonium coenophialum, A. starrii, and A. typhinum were grown on potato dextrose agar (PDA) amended with potassium chloride (PDA + KC1) or sucrose (PDA + S) to attain a wide range of osmotic water potentials. Radial growth was greatest between -0.3 MPa (PDA without amendment) and -3.0 to -4.0 MPa, below which growth diminished to near zero at -8 MPa. Acremonium isolates grew well on corn meal agar (CMA + KC1), but antibiotic and halo-production were not detected on these media. Haloes consisting of an unknown opaque deposit formed within the media around colonies of some isolates in PDA and in certain PDA + KC1 combinations. Inhibition zones were not detected on media adjusted to an osmotic water potential below about -3.5 to -4.2 MPa. Aerial hyphae were sparse on CMA A + KC1 at -5.47 MPa or lower, facilitating visual observation of sporulation. Sporulation by some isolates occurred over the entire range of water potentials. Isolates varied in radial growth, production of inhibition zones, sporulation, and in production of haloes within the media and these responses appear to be characteristic of the isolate rather than the species. Growth of an unknown Acremonium species from Stipa robusta was restricted at -2.33 MPa on PDA amended with sucrose.