The influence of tuber position on periderm calcium content and its relationship to soft rot susceptibility

Summary Calcium levels in the periderm of tubers (cv. Sebago) growing in irrigated sands were influenced by the stem position at which the tuber grew, but the effect was not consistent over two seasons. Calcium levels were increased at all tuber positions by addition of calcium to soil; combined treatments of gypsum (1400 kg Ca²⁺/ha) pre-plant and calcium nitrate (37 kg Ca²⁺/ha) side dressings gave the greatest response. Percentage incidence of soft rot lesions caused byErwinia chrysanthemi pv.zeae was not influenced by periderm calcium content. The severity of infection (weight of tissue macerated within 48 h at 30°C) was significantly reduced only by the pre-plant gypsum treatment, but there was no correlation with calcium content of the periderm. Calcium levels in periderm tissue (60–208 mg Ca²⁺/100g) are within the range of published data for other cultivars and results support previous reports that the correlation between tuber susceptibility toErwinia spp. and periderm calcium content is inconsistent.