| Straighthead causes yield losses in rice (Oryza sativa L.). Monosodium methanearsonate (MSMA), an arsenic-based herbicide widely used on cotton, can induce sterility in rice. The symptoms are similar to those of straighthead.;Six rice genotypes and four arsenic (applied as MSMA) rates were evaluated in a pot test to determine the effects of arsenic on straighthead and agronomic traits of rice. Rexmont and CI 9546 were more resistant to straighthead than the other genotypes. Plant height, panicle length, the number of primary branches, yield, floret number per panicle, the number of filled grains per panicle, seed set percentage, and 1000-seed weight were reduced by arsenic.;A factorial experiment was conducted in the field. For most genotypes, straighthead increased as arsenic rate increased. Straighthead appeared to be more serious in the row plot than in the two hill plots for most genotypes. Row plots should be used in screening for resistance to straighthead in rice. In the row plot, CI 9308, CI 9326, CI 9546, CI 9973, PI 162320, PI 160826, PI 502796, Lemont, Rexmont did not show straighthead symptoms when arsenic was applied at the lowest rate (1.42 kg/ha).;Fifty rice genotypes were grown in single plant hills within rows of purple-leaf rice at different arsenic rates. There were no significant differences in straighthead rating among the three positions within a row of purple rice plants. Differences in straighthead rating among rice genotypes and among arsenic rates were significant (P = 0.01). This technique should be used in tests in which a single plant estimation of straighthead is necessary.;Two resistant parents, CI 4322 and PI 502796, and two susceptible parents, PI 160394 and PI 160593, were selected to conduct the genetic analysis of resistance to straighthead in rice. The results demonstrated that the resistance in CI 4322 and PI 502796 to straighthead is controlled by a single recessive gene. |
