Subjecting inoculated leaves of intact plants to a controlled atmospheric-environmental system with an atmospheric pressure of 233 millibars and 02 and CO2 parti pressures adjAsted to approximately that of normal ambient pressure during infection and disease development prevented most midvein chlorosis and complete chlorosis, but did not prevent necrotic lesion or chlorotic halo development. Under the hypobaric conditions, chlorophyll loss during disease development was reduced to 22% compared with controls at 96 hours. The observations suggest that ethylene may function late in pathogenesis of this host-pathogen interaction and is responsible for much of the chlorophyll loss after its maximum production at 48 hours.

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Several species of Streptomyces were evaluated for their ability to control Sclerotinia homoeocarpa (dollar spot) and Bipolaris sorokiniana (leaf spot) on the phylloplane of Poa pratensis (Kentucky bluegrass). Species evaluated included S. diastaticus (S32), S. galbus (S35), and S. hygroscopicus (isolates S13, S28). All evaluations were conducted on the upper epidermis of intact attached leaves of P. pratensis, and antagonism was measured as the ability of Streptomyces isolates to prevent chlorophyll loss from leaves inoculated with B. sorokiniana or S. homoeocarpa during pathogenesis. Only S. hygroscopicus (S13) effectively prevented infection and subsequent chlorophyll loss from leaves inoculated with B. sorokiniana or S. homoeocarpa. Isolate S28 of S. hygroscopicus showed erratic antagonism of both pathogens, depending upon how the isolate was prepared for use. Streptomyces diastaticus and S. galbus were antagonistic to S. homoeocarpa only in whole culture form.