THE DEPENDENCE OF INTERNAL BROWN SPOT DEVELOPMENT UPON CALCIUM FERTILITY IN POTATO-TUBERS

To determine calcium fertility and high temperature effects on interna l brown spot development in potato, cv. Russet Burbank plants were fer tilised with Hoagland's nutrient solution with or without calcium. Pre valence and severity of internal brown spot were greatest in tubers re ceiving no calcium fertilisation during growth. Internal brown spot wa s evident as early as tuber initiation. A high growth medium temperatu re (32 degrees C) at tuber maturity with a lack of calcium increased i nternal brown spot incidence and severity. No tubers subjected to the high temperature and fertilised with calcium developed internal brown spot. Peel calcium concentration of tubers receiving no calcium fertil isation was lower (0.5-0.8 g/kg) than tubers receiving calcium (1.2-1. 9 g/kg). Medullary tissue calcium concentration was similar under both calcium regimes. Calcium availability during early tuber growth was a n influential factor in internal brown spot development, however high temperature effects may not be discounted in exacerbating the disorder .