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Book: Proceedings of The Second International Turfgrass Research Conference
Published by: American Society of Agronomy, Crop Science Society of America



  1.  p. 328-334
    Proceedings of The Second International Turfgrass Research Conference

    Eliot C. Roberts (ed.)

    ISBN: 978-0-89118-573-4




Drought stress: an important factor stimulating the development of Helminthosporium sativum on Kentucky bluegrass1

  1. P.F. Colbaugh and
  2. R.M. Endo


Saprophytic and parasitic activities of Helminthosporium sativum, which causes leaf-spot and root rot of Kentucky bluegrass (Poa pratensis L.), were greatest following periods of temporary drought stress. Increases in the number and severity of infections and of conidial production on litter were observed in dry areas of turf following irrigation but not in areas receiving adequate water. Field measurements and laboratory studies on temperature, relative humidity, and aeration within the litter of moist and drought-stressed areas indicated that the dry litter did not support a physical environment that favored the growth of bluegrass isolates of H. sativum.

Moist bluegrass litter completely inhibited conidial germination and mycelial growth of H. sativum, but dry litter immediately after remoistening did not. The inhibitory property was restored to remoistened litter about 7 hours following remoistening. Laboratory studies on the nature of the inhibition indicated that a volatile inhibitor was present on moist litter but not on dry litter. The chemical identity of the inhibitor was not determined.

The release of protein and carbohydrate into water was shown to be 300% greater from remoistened litter than from continuously moist litter. The increased release of nutrients from dried litter after remoistening, the absence of an inhibitor on dry litter at the time of remoistening, and the reduction of microbial numbers and activities during desiccation of litter are believed to be important factors associated with the drying-wetting cycles which trigger the saprophytic and parasitic activities of the fungus. Additional index words: Helminthosporium sativum, Irrigation, Kentucky bluegrass, Soil moisture stress.

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Copyright © 1974. Copyright 1974 by the American Society of Agronomy, Inc. and the Crop Science Society of America, Inc., 5585 Guilford Rd., Madison, WI 53711 USA