The Preservation of Plant Pathogenic Bacteria

Some 160 cultures were preserved by freeze drying, under mineral oil and in soil. After storage for 5 years all freeze dried cultures were viable; most cultures of xanthomonads were viable under oil and in soil; pseudomonads survived well in soil but only moderately well under oil; soft‐rotting Erwinia spp. survived poorly but storage under oil was better than in soil; other Erwinia spp. and most Corynebacterium spp. survived well in soil and under oil. The mean half lives in years ( h ) calculated for freeze dried cultures of groups of closely related bacteria were: Erwinia ‘chrysanthemi group’, 0·40; Erwinia ‘carotovora group’, 0·51; Pseudomonas ‘syringae group’, 0·50; Xanthomonas spp., 0·84 years. Estimated half lives for Corynebacterium spp. ranged from 1·8 to 6·5 years. There was no evidence that bacteria which had been in culture for more than 3 years before being freeze dried had a longer storage life than those freeze dried within 3 years of isolation. Cultures of the Pseudomonas ‘syringae group’had a longer storage life when freeze dried by Greaves’method ( h = 0·73) than when freeze dried by Annear's method ( h =0·50). There appeared to be no general correlation between half life in storage and either the proportion of cells surviving the freeze drying process or the viable cell count immediately after freeze drying. Most of the variation in the results could be attributed to variation in viable cell count between different ampoules of the same batch of a culture.