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A Device for Precise and Nondisruptive Stomatal Inoculation of Leaf Tissue with Bacterial Pathogens. Tim R. Gottwald, Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Orlando, FL 32803; James H. Graham, Professor, Citrus Research and Education Center, IFAS, University of Florida, Lake Alfred 33850. Phytopathology 82:930-935. Accepted for publication 9 June 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/Phyto-82-930.

A stomatal inoculation apparatus (SIA) was developed to produce water congestion of leaf tissues and provide a reproducible noninjurious means of introducing two Xanthomonas campestris pathovars of citrus into leaf tissues without wounding. The SIA consisted of a small inoculation chamber attached to an intact leaf. Water and inoculum were metered into an airstream and focused to impact on a 1-mm-diameter area of the leaf surface. Leaf tissues on the abaxial surface of Duncan grapefruit leaves expanded 50–75% were more susceptible to infection than were other growth stages. Inoculum concentrations of 10⁶ cfu/ml consistently induced infection and resulted in discrete individual lesions. Airstream impact pressures of 6.28–8.04 kPa against the leaf surface consistently produced tissue congestion and infection without wounding. These same pressures were the minimum threshold for increasing water volume in the leaf. From calculations of volume versus concentration of inoculum that enters a leaf via SIA, it was determined that as few as 2 cfu were required to cause a single lesion.