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A Vacuum Injection Method for Quantitative Leaf Inoculation of Poa pratensis with Helminthosporium sorokinianum. Clinton F. Hodges, Associate Professor of Horticulture and Agronomy, Departments of Horticulture and Agronomy, Iowa State University, Ames 50010; Phytopathology 63:1265-1269. Accepted for publication 3 April 1973. DOI: 10.1094/Phyto-63-1265.

A vacuum injection inoculation method was devised for inoculating Poa pratensis L. with Helminthosporium sorokinianum for leaf lesion development. Individual tillers were inoculated by inserting a hypodermic needle into the sheath fold; then, under vacuum, a suspension of conidia was siphoned into the sheath fold. Evaluation of lesion development was made on the youngest visible leaf of inoculated tillers 4 to 5 days after inoculation. On the basis of numbers of conidia introduced per lesion developed, inoculation was most efficient at low concentrations of conidia. As conidia concentrations were increased, mean number of lesions and disease severity increased; however, direct lesion-to-conidia efficiency decreased. The method provides a quantitatively repeatable means of leaf inoculation and eliminates potential saprophytic development of H. sorokinianum on senescing leaves.