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Resistance in Seedlings of the Family Geraniaceae to Bacterial Blight Caused by Xanthomonas campestris pv. pelargonii. Kerry B. Dunbar, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Christine T. Stephens, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Plant Dis. 76:693-695. Accepted for publication 13 February 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0693.

Leaves on 5-wk-old seedlings of Geranium and Pelargonium species grown in culture tubes containing 15 ml of Hoagland’s solution solidified with 0.7% agar were swabbed with a 10⁷ cfu/ml cell suspension of Xanthomonas campestris pv. pelargonii. Eight weeks after inoculation all seedlings from susceptible P. × hortorum cultivars and from P. zonale, P. frutetorum, P. fulgidum, P. fruticosum, P. alchemilloides, P. inquinans, P. acraeum, and P. capitatum were severely blighted. These susceptible species had an average of more than 50% tissue blighted 3 wk after inoculation, and 50–100% of the inoculated plants were dead within 8 wk. However, P. cordifolium, G. nodosum, G. napalense, G. sylvaticum, G. richardsonii, and G. ibericum seedlings had significantly less blighted tissue than P. × hortorum. These resistant species had an average of less than 50% tissue blighted 3 wk after inoculation, and 0–18% of the inoculated plants died after 8 wk. P. cordifolium and G. ibericum seedlings had the lowest levels of blighted tissue 3 wk after inoculation.