Comparison of the effectiveness of different methods of screening for bacterial soft rot resistance of potato tubers

Tubers from eight potato cultivars (cvs) grown at two different locations in Wisconsin were tested for bacterial soft rot resistance using different inoculation techniques. The procedures included 1) point inoculations of tubers with different inoculum levels followed by incubation in ambient or low oxygen condtions, 2) inoculation of mechanically bruised tubers followed by incubation in a mist chamber, and 3) a standard slice inoculation method. The point titration test followed by incubation in dew chamber and the mist chamber-bruise test showed similar patterns of resistance for cultivars that were used in these experiments. These two methods are considered to be effective for screening potato tubers for bacterial soft rot resistance. Point titration methods are very useful if only limited numbers of tubers are available. The mist chamber-bruise test is simpler than the other procedures; however, to obtain reproducible results large numbers of tubers are required. Because of the great variability of the results obtained in inoculation of slices, the reliability of this approach can be questioned as a standardized method for evaluation of resistance. Tubers of somatic hybrids ofS. brevidens andS. tuberosum and their sexual progeny were significantly more resistant to bacterial soft rot than tubers of moderately resistant cultivars when evaluated by each of the assay procedures.