Kolkata, Aug 21 (PTI) Retail sugar prices have shot up to Rs 70 per kg in Kolkata markets ahead of the festive season, traders said on Friday. Prices have surged by Rs 20 a kg in the past month alone, while the last four to five days have seen a sudden 10 per cent jump, they said. Sugar-associated products such as jaggery, batasa (sugar drop), and nakuldana…