Potato Protoplast‐derived Callus Tissue Challenged with Erwinia carotovora subsp. carotovora: Survival, Growth and Identification of Resistant Callus Lines*

Abstract

Abstract Potato (cv. Crystal) protoplast‐derived callus tissue was evaluated for survival and growth when exposed to Erwinia carotovora subsp. carotovora (strain Ecc71). Calli were either directly exposed to the pathogen by inoculation or to metabolites produced by the pathogen via a bilayer medium. Individual calli were inoculated with 0.5 μl of bacterial suspensions at 104, 105, 106, 107, 108 and 109 cfu/ml. The bilayer consistedof 10 ml of callus proliferation medium supplemented with pectin (2 g/l) and contained bacteria at 102, 103, 104, 105 and 106 cfu/ml. This medium was overlaid with 10 ml of bacteria free callus induction medium. Mean callus diameter of the inoculated treatments increased for 24 h, then declined. Over 90% of the inoculated calli were killed within 5 days but some survived as long as 14 days. Calli grown on the bilayer medium containing 106, 105 and 104 cfu/ml also decreased in size. Most were killed within 9 days but some survived 20 days. Calli exposed to 103 and 102 cfu/ml experienced limited growth with 20% and 7%, respectively, surviving after 27 days. Reactions to the pathogen varied considerably within the callus populations and individual calli with extended survival were identified in both experiments.