Differential Response of Rice Germplasm to Straighthead Induced by Arsenic

Abstract

The exact cause of straighthead is unknown, but independent studies have shown that straighthead is in-Straighthead disease is a physiological disorder of rice (Oryza sacreased by consistent flood (Wells and Gilmour, 1977; tiva L.) characterized by sterility of the florets leading to reduced Wilson et al., 2001), sandy to silt loam textured soils grain yield. Knowledge of the straighthead response of new cultivars (Collier, 1912;Adair et al., 1973), low soil pH and low is important for producer control of this disease, and identification of resistant germplasm is essential for breeding improved cultivars. free iron (Baba and Harada, 1954), rich organic matter The objectives of this study were to characterize U.S. cultivar reactions in soil (Jones et al., 1938, p. 28), and high arsenic (As) to straighthead and search for resistant germplasm. Twelve lines, inlevel in the soil (Wells and Gilmour, 1977; Horton et al., cluding 10 U.S. cultivars, a Chinese and Japanese cultivar, were tested 1983). Straighthead has been frequently observed when for straighthead reaction induced by monosodium methanearsonate rice is grown on land where As has accumulated from (MSMA) at 0, 6.7, and 9.0 kg ha Ϫ1 under nitrogen fertilizer of 0, 67, previous applications of herbicides with an As base such 134, and 269 kg N ha Ϫ1 in 1999 and 2000. Straighthead delayed heading as monosodium methanearsonate (MSMA) (Gilmour date, shortened plant height, and dramatically reduced grain yield. and Wells, 1980). Cocodrie, Mars, Kaybonnet, and Bengal were highly susceptible to MSMA is a popular herbicide in cotton (Gossypium straighthead with ratings from 7.2 to 8.0 and grain yield reductions spp.) production in the USA; therefore, rice fields with from 80 to 96%. Wells, LaGrue, Drew, Cypress, and Japan 92.09.31 were a cotton growing history usually have residual As (Gilsusceptible with ratings from 5.9 to 6.7 and yield reductions from 49 mour and Wells, 1980). Residual As chemicals in the soil to 73%. Priscilla and Jefferson were tolerant with ratings of 4.9 and have been shown to cause injuries in rice that are similar 5.3, and yield reductions of 24 and 36%, respectively. The Chinese indica cultivar Zhe 733 was essentially immune to straighthead, show-to straighthead (Baker et al., 1976; Schweizer, 1967; Wells ing neither symptoms nor detectable yield reduction. A total of 124 and Gilmour, 1977; Gilmour and Wells, 1980). Wells and Chinese cultivars including 109 indica and 15 japonica were evaluated Gilmour (1977) noted that cultivars showing tolerance for straighthead resistance in 2001. Nineteen cultivars, 18 indica and to MSMA also appeared to be resistant to straighthead. 1 japonica, were identified as straighthead resistant. Grain yields of On the basis of this observation, a straighthead testing the resistant cultivars were not significantly reduced by their straightarea based on the application of MSMA has been estabhead ratings of 1 to 3. Variation in yield, plant height, maturity, and lished at the University of Arkansas, Rice Research...

Arsenic Methylation in Soils and Its Relationship with Microbial arsM Abundance and Diversity, and As Speciation in Rice

“…11 Methylated As species are also implicated in the physiological disorder "straight-head" disease in rice, 1 causing spikelet sterility and yield losses. 12 Methylated As species have been found in soils, usually as minor species compared to the predominance of inorganic As. 13−17 Methylated As in soil may originate from anthropogenic sources (e.g., the widespread uses of mono-or disodium salts of MMA and DMA as herbicides and pesticides in the U.S.), atmospheric deposition and methylation mediated by soil microbes; 17 the latter is likely to be the main source where methyl arsenicals have not been used.…”

“…11 Methylated As species are also implicated in the physiological disorder "straight-head" disease in rice, 1 causing spikelet sterility and yield losses. 12 Methylated As species have been found in soils, usually as minor species compared to the predominance of inorganic …”

Market Basket Survey Shows Elevated Levels of As in South Central U.S. Processed Rice Compared to California: Consequences for Human Dietary Exposure

“…The As-rice situation in the South Central U.S. is quite unusual in that rice varieties were specifically selected to grow on arsenical-pesticide-treated soils (22), where rice yields were known to be affected by As, causing the physiological disorder "straighthead". Symptoms of straighthead range from an increase in blank florets to complete grain failure (23).…”

“…In field experiments by the University of Arkansas, MSMA was found to induce straighthead, with significant correlation coefficients for straighthead rating (r ) 0.50) and grain yield (r ) -0.55) (24). Constant flooding, soil texture, low soil pH, low free iron, and rich soil organic matter (22) all contribute to the diseases onset, although their precise importance is hard to determine as they all increase As bioavailability.…”

Uptake and translocation of inorganic and methylated arsenic species by plants

“…straight-head disease of rice, and on the other hand reduces the crop value if the arsenic concentration is over the permissible limits. [3,4] In Europe, permissible limits for As in fodder is generally between 2 and 4 mg of As per kg (moisture content 12%), for food plants a statutory limit of 1 mg As per kg of dry weight (d.w.) exists, e.g., in Spain. [5][6][7][8][9] The EU has not yet set maximum limits for arsenic in vegetables.…”