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The grassery caused by Bombyx mori nucleopolyhedrovirus (BmNPV) is the most severe disease in Thai sericultural practice. In this study, a resistance of Thai silkworm, Bombyx mori to grassery disease was determined. Fifteen Thai native strains, namely, Nang Lai, Nang Noi, Nang Tui, Sam Rong, Nang Seiw, Hua Fai, Nang Lueang, Kor Tung, Kaki, RE05, NK04, Pang Puay, SP2, PCh21, and NNK8, were investigated. The 3rd instar larvae of Nang Lai, and Sam Rong were used for the Lethal Concentration (LC50) test. The mulberry leaves were dipped in suspensions of BmNPV at 105,106, 107, 108, 109 OBs/ml. LC50 were analyzed by ToxRat Standard Program version 3.2.1. The result showed that the LC50 values of Nang Lai and Sam Rong were at 5.05x107 and 1.52x107 OBs/ml, respectively. The resistanceto grassery of all Thai silkworm strains mentioned above were determined at 107 OBs/ml of BmNPV (LC50). The mortality of grassery infected silkworm larvae was recorded and indicated. The results revealed that there were 4 levels of resistance and susceptibility based on mean mortalities; highly resistant, medium resistant, medium susceptible, and highly susceptible.The highly resistant strains were Sam Rong, NK04, Hua Fai, Nang Lai; (12.66±1.20, 13.00±2.08, 14.66±0.33, 18.33±0.33, respectively) and the medium resistant strains were Nang Seiw, Pang Puay, Kor Tung, Kaki, RE05, Nang Tui; (30.33±1.45, 31.33±1.20, 32.00±1.15, 33.33±1.20, 34.33±2.96, 35.33±0.3, respectively). On the other hand, the medium susceptible strains were SP2, Nang Noi, PCh21; (42.66±2.33, 43.33±0.88, 47.00±0.57, respectively) and the highly susceptible strains were NNK8 and Nang Lueang; (52.00±2.64 and 52.33±2.40, respectively). The results of this study will be useful for the farmers to improve the grassery resistant silkworm strains. |
