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Reduced Severity of Erwinia Soft Rot in Potato Tubers with Increased Calcium Content. Raymond G. McGuire, Graduate research assistant, Department of Plant Pathology, University of Wisconsin, 1630 Linden Drive, Madison 53706; Arthur Kelman, professor, Department of Plant Pathology, University of Wisconsin, 1630 Linden Drive, Madison 53706. Phytopathology 74:1250-1256. Accepted for publication 14 April 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1250.

The severity of bacterial soft rot caused in potato tubers by Erwinia carotovora pv. atroseptica, was linearly and inversely related to the concentration of tuber calcium in laboratory and field experiments. Vacuum infiltration of Ca(NO3)2 solutions into potato tubers increased the calcium content of peel and medulla. When tubers inoculated with E. carotovora pv. atroseptica during infiltration were incubated in a mist chamber at 20 C for 60 hr, bacterial soft rot was significantly lower in calcium-infiltrated tubers than in untreated ones. Infiltration with solutions containing Mg++ and Sr++ also reduced the subsequent severity of tuber decay, but not as effectively as Ca++; however, these divalent cations proved more effective than Na+ and K+. A field trial was designed with different sources of nitrogen and calcium to establish a group of 18 subplots representing a range in concentrations of soil calcium. The tubers obtained from these plots in 1981 and 1982 had calcium contents ranging from 0.06 to 0.28% (dry weight basis) in the peel and from 0.01 to 0.06% (dry weight basis) in the medulla as determined by inductively coupled plasma - optical emission spectrometry. As the tuber calcium was increased, the percent surface area of the tubers decayed by E. carotovora pv. atroseptica under mist chamber conditions was reduced significantly each year. The results indicate that in certain soils with a low cation exchange capacity, tubers may be low in calcium and that increasing it may reduce the potential for bacterial soft rot in storage and transit.

Additional keywords: blackleg, Solanum tuberosum.