CAN THO – After a long falling streak, prices of purple-fleshed sweet potatoes in the Mekong Delta have suddenly picked up on the threshold of the Lunar New Year. Traders are now buying the first-grade purple sweet potatoes at VND1.1-1.2 million per 60-kilo bag, up VND500,000-600,000 against a month ago, said Son Van Luan, chairman of the sweet potato co-operative Tan Thanh in Binh Tan District,...