INFLUENCE OF WATER POTENTIAL ON GROWTH, ANTIBIOTIC PRODUCTION, AND SURVIVAL OF CEPHALOSPORIUM GRAMINEUM

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Abstract
Cephalosporium gramineum grew on agar media at osmotic water potentials from − 1.3 bars to between − 98 and − 112 bars. The growth of antibiotic-producing (+) and nonproducing (−) isolates was affected equally by water potential. Antibiotic production was detected by bioassay over the entire range of significant growth (to about − 83 to − 98 bars). Production of antibiotic relative to the growth rate of C. gramineum was least when the fungus grew fastest and most when the fungus was under moderate water stress (between − 27 and − 55 bars). When straws infested with C. gramineum were incubated on soil at 15 C at various water potentials, + isolates had the least advantage over − isolates on water-saturated soil (near 0 bar) and at the driest condition tested (−258 bars). In contrast, antibiotic-producing isolates had the greatest survival advantage between − 10 and − 67 bars, which corresponds to the range of water potentials within which antibiotic production was greatest relative to mycelial growth. The vigor of C. gramineum in straw on water-saturated soil indicates coexistence with bacteria; its performance between about − 10 and − 137 bars indicates that relatively xerophytic soil fungi are its most severe antagonists in nature.

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