Differential response of rice germplasm to straighthead induced by arsenic

Straighthead disease is a physiological disorder of rice (Oryza saliva L.) characterized by sterility of the florets leading to reduced grain yield. Knowledge of the straighthead response of new cultivars is important for producer control of this disease, and identification of resistant germplasm is essential for breeding improved cultivars. The objectives of this study were to characterize U.S. cultivar reactions to straighthead and search for resistant germplasm. Twelve lines, including 10 U.S. cultivars, a Chinese and Japanese cultivar, were tested for straighthead reaction induced by monosodium methanearsonate (MSMA) at 0, 6.7, and 9.0 kg ha(-1) under nitrogen fertilizer of 0, 67, 134, and 269 kg N ha(-1) in 1999 and 2000. Straighthead delayed heading date, shortened plant height, and dramatically reduced grain yield. Cocodrie, Mars, Kaybonnet, and Bengal were highly susceptible to straighthead with ratings from 7.2 to 8.0 and grain yield reductions from 80 to 96%. Wells, LaGrue, Drew, Cypress, and Japan 92.09.31 were susceptible with ratings from 5.9 to 6.7 and yield reductions from 49 to 73%. Priscilla and Jefferson were tolerant with ratings of 4.9 and 5.3, and yield reductions of 24 and 36%, respectively. The Chinese indica cultivar Zhe 733 was essentially immune to straighthead, showing neither symptoms nor detectable yield reduction. A total of 124 Chinese cultivars including 109 indica and 15 japonica were evaluated for straighthead resistance in 2001. Nineteen cultivars, 18 indica and 1 japonica, were identified as straighthead resistant. Grain yields of the resistant cultivars were not significantly reduced by their straighthead ratings of 1 to 3. Variation in yield, plant height, maturity, and endosperm type within the resistant germplasm was also observed.