Abstract

The purpose of this experiment was to evaluate five cassava commercial varieties for cassava mosaic disease tolerance : Rayong 1, Rayong 72, Kasetsart 50, HuaiBong 60 and CMR-89, The experimental unit size was 14 m² with spaeings of 1 x 0.8 m. unsing Randomized Complete Block Desigh (RCBD). The experimental was established at SoengSang District, Nakhon Ratchasima province. The severity of the disease was assessed , in every months since planting after one month until at 7 months. The severity was classified into 5 levels: level 1 without showing symptoms of the disease (highly resistant), level 2 showing slight alkalinity on the leaves (moderately resistant), level 3 showing alkalinity. The leaves are full on the leaf blades and the leaves begin to curl (tolerant). Level 4 shows spotted symptoms throughout the leaves. The leaves are twisted, curled, and begin to lose shape (susceptible). Level 5 shows signs of twisting and curling. The leave shape was severely reduced (highly susceptible). The data were used to determine the disease index by using formula using data from the degree of disease severity. After harvesting, fresh root weight and starch content of each variety were measured for comparison. The disease index experiment showed that Huay Bong 60 variety was more other commercial varieties of cassava that were planted in experiments together. Fresh root yield and starch content of Huay Bong 60 variety yield was 5,116.67 kg. and 1,228 kg.