Paul A. Counce

Effects of Nighttime Temperature During Kernel Development on Rice Physicochemical Properties

ABSTRACT Rice quality can vary inexplicably from one lot to another and from year to year. One cause could be the variable temperatures experienced during the nighttime hours of rice kernel development. During the fall of 2004, a controlled temperature study was conducted using large growth chambers, testing nighttime temperatures of 18, 22, 26, and 30°C from 12 a.m. until 5 a.m. throughout kernel development, using rice cultivars Cypress, LaGrue, XP710, XL8, M204, and Bengal. As nighttime temperature increased, head rice yields (HRY) significantly decreased for all cultivars except Cypress and Bengal, for which HRY did not vary among nighttime temperature treatments. Kernel mass did not vary among temperature treatments for any cultivar. Grain dimensions generally decreased as nighttime temperature increased. The number of chalky kernels increased with an increase in nighttime temperature for all cultivars but Cypress. The amylose content of Cypress and LaGrue was significantly lower at the nighttime tem...

Correlation of Head Rice Yield with Individual Kernel Moisture Content Distribution at Harvest

Time of harvest experiments were conducted in Arkansas in 1989 and 1990 to measure head rice yield and individual kernel moisture content distributions for ‘Newbonnet’, ‘Lemont’, and ‘Tebonnet’ long-grain varieties. Individual kernel moisture content frequency distributions for the three rice varieties showed two or three modes on the early harvest dates. As time progressed, the high moisture content modes gradually diminished, and only one mode was shown in the kernel moisture content frequency distributions for the late harvest dates. Head rice yields of the three varieties did not change significantly when the average rice moisture content ranged from 15% to 22%. Head rice yield reductions occurred as a result of rapid rewetting by rain when the moisture content decreased to 15% or lower before rain. The head rice yields obtained from the harvest dates after rain were most significantly correlated with the percentage of kernels with moisture contents above 10.5% for ‘Newbonnet’, 13.5% for ‘Lemont’, and 12.5% for ‘Tebonnet’ as measured on the harvest dates before the rain.

Optimal Harvest Moisture Contents for Maximizing Milling Quality of Long- and Medium-Grain Rice Cultivars

The objective of this study was to determine the harvest moisture contents (HMCs) at which rice milling quality peaked for various rice lots. Multiple samples per field of cultivars Bengal, Cypress, and Drew were harvested at northeast and southeast Arkansas locations in 1999 and 2000. Additional field sample sets of multiple cultivars were collected in 2004, 2005, and 2006 at various locations in Arkansas, Mississippi, and Missouri. Head rice yields (HRYs) were described by a quadratic equation with HMC as the independent variable. Peak HRYs varied from 63.8% to 70.6%. Optimal HMCs, determined as the MC at which HRY peaked, varied from 18.7% to 23.5% for long-grain cultivars and 21.5% to 24.0% for medium-grain Bengal. The general range of optimal HMCs was 19% to 22% for long-grains and 22% to 24% for medium-grain Bengal. For rice lots with HMCs less than the optimal HMC, the amount of HRY reduction from peak values was strongly correlated to the percentage of fissured kernels at harvest; fissured kernel percentage accounted for 77% of the variation in HRY reduction from peak HRYs.

Mediation of Partial Resistance to Rice Blast Through Anaerobic Induction of Ethylene

ABSTRACT The correlation between anaerobic soil conditions and increased resistance to rice blast disease has long been observed without benefit of an adequate explanation. We researched flood depth, dissolved oxygen (DO), and ethylene relative to expression of partial blast resistance in cvs. M-201, Newbonnet, LaGrue, Mars, and Cypress. Cultivar blast index (BI) and flood DO decreased with increasing flood depth. BIs were positively correlated with DO. Total leaf blast lesions were 3.4 and 3.2 times greater in cvs. M-201 and LaGrue growing in a 5.0-mul liter(-1) DO nutrient solution than when growing in a 0.1-mul liter(-1) DO solution. Treatment with 0.25 mM ethephon, which releases ethylene, lowered BIs of Newbonnet, LaGrue, and Cypress growing upland when applied drench, foliar, or foliar-drench. If flooded, BIs of ethephon-treated cultivars were decreased by drench and foliar-drench applications only. BIs of upland plants were unchanged, whereas BIs of analogous flooded plants increased following treatment with 0.31 mM aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor. We hypothesize that varying anaerobic conditions mediate production of phytohormones, particularly ethylene, which modify expression of inherent partial blast resistance in these rice cultivars.

Explaining Rice Milling Quality Variation Using Historical Weather Data Analysis

ABSTRACT Rice quality, specifically head rice yield (HRY), can vary inexplicably from one lot to another, and from year to year. In an effort to correlate air temperatures during various growth stages to HRY, growth staging data expressed in degree day units was used to predict the occurrence of sequential growth stages within a set of 17-year historical data, which included HRY and 50% heading dates for two long-grain rice cultivars, (Oryza sativa L) Newbonnet and Lemont, and area weather data. HRY was most strongly affected by the average daily low temperature (or nighttime temperature) during the R8 developmental stage. Lower HRY were associated with high nighttime air temperatures during this stage for both Newbonnet and Lemont. When used as a single variable in a regression model, the nighttime temperature during the R8 developmental stage explained over 25% of the variation in HRY.

PANICLE EMERGENCE OF TILLER TYPES AND GRAIN YIELD OF TILLER ORDER FOR DIRECT-SEEDED RICE CULTIVARS

Grain yield of rice (Oryza sativa, L.) tillers is critical to rice crop yield and quality but relatively little is known about variations that occur among panicles and grains for tiller types and emergence orders of direct-seeded rice cultivars. The objective of research was to examine how tillering may affect yield and quality at low plant population densities with profuse tillering. Single rice plants were grown in pots in a greenhouse in 1990 and in 1992 and in the field in 1991. The aim was to maximize tillering and thus better see effects of tiller emergence order and type on yield and panicle emergence. Culm and panicle emergence dates were successively later for primary, secondary, and tertiary tillers but with a smaller delay among panicle emergence dates than was observed for tiller emergence. Grain yield of tillers was related more to emergence order than to tiller type. Secondary and tertiary tillers in sufficient numbers could cause delays in crop grain maturity. Specifically, the beginning of grain-filling (closely following top anthesis) was 1 to 5 d later for primary tillers and 3 to 9 d later for secondary tillers, compared to main stems. These data indicate direct-seeded rice cultivars have partial but not complete synchrony of panicle emergence. Consequently, production strategies that increase preflood N to increase tillering in thin (sparsely populated) rice stands, could potentially delay maturity of the crop as well as increase yields.

Effects of Nighttime Air Temperature During Kernel Development of Field-Grown Rice on Physicochemical and Functional Properties

ABSTRACT Elevated nighttime air temperatures (NTATs) occurring during critical grain-filling stages affected rice physicochemical properties, which impacted functional quality. Six cultivars were grown at multiple field locations from northern to southern Arkansas during 2007 to 2010. Nighttime temperatures were recorded throughout production at each of the locations, and 95th percentiles of NTATs were calculated for each cultivars reproductive (R) stages. Amylose content and crude protein content decreased linearly, whereas total lipid content increased linearly, with increasing NTATs occurring during the grain-filling stages (R6–R8). Effects of NTAT on proximate composition influenced functional properties. Peak viscosities increased linearly as NTAT increased, whereas setback viscosities decreased. Setback viscosities were linearly correlated to NTATs for medium-grain cultivars, but correlations were quadratic for the long-grain cultivars. Gelatinization temperatures increased linearly with increasing...

Estimating the Economic Value of Rice (Oryza Sativa L.) as a Function of Harvest Moisture Content

The net value (NV) of rice, as affected by drying costs and milling quality changes associated with harvesting rice at various moisture contents (MCs), was studied using a five-year data set comprising eight cultivars harvested over a range of MCs from 11 southern U.S. locations. A quadratic relationship was used to characterize the change in NV across harvest MC (HMC); this relationship was due to the progressively-increasing fee structure for commercial drying costs and the quadratic nature of head rice yield (HRY) changes with HMC. A sensitivity analysis revealed that as the price of brokens increased, there was a slight decrease in the HMC at which NV was maximized. Relative to the price of brokens, the optimum HMC was not influenced by fluctuations in head rice price. At a given HMC, the NV of a rice bulk increased with the price of brokens, and the extent of the increase was heavily influenced by the HRY versus HMC relationship. In all instances, the optimal HMC to maximize HRY (HMCopt-HRY) was greater than the HMC corresponding to the maximum NV (HMCopt-NV). When HMC, NV and HRY were plotted regardless of cultivar, location, or harvest year, the MC at which HRY was maximized was 21.7% whereas the MC at which NV was maximized was 18.5%, representing a 3.2 percentage point difference between HMCopt-HRY and HMCopt-NV.

Impact of Elevated Nighttime Air Temperatures During Kernel Development on Starch Properties of Field-Grown Rice

ABSTRACT The structural features of starch were examined to better understand the causes of variability in rice quality resulting from nighttime air temperature (NTAT) incidence during kernel development. Starch samples were isolated from head rice of four cultivars (Bengal, Cypress, LaGrue, and XL723) field-grown in four Arkansas locations (Keiser, Pine Tree, Rohwer, and Stuttgart) in 2009 and 2010. Average NTATs recorded during the grain-filling stages of rice reproductive growth in the four locations were 3.0–8.4°C greater in 2010 than 2009. Elevated NTATs altered the deposition of starch in the rice endosperm. Means pooled across cultivars and locations showed that amylose content was 3.1% (percentage points) less for the 2010 sample set. The elevated NTATs in 2010 resulted in a decrease in the percentage of amylopectin short chains (DP ≤ 18) and a corresponding increase in the percentage of long chains (DP ≥ 19) by an average of 1.3% (percentage points). The greater NTATs in 2010 also produced greate...

Rice Kernel Dimensional Variability Trends

Rice kernel dimensions affect the performance of various post-harvest processes. This study assessed variability trends in kernel dimensional distributions of Bengal (medium-grain), Cypress, and Drew (long-grains) rice varieties. Rice was harvested at various stages of maturity from Stuttgart and Keiser, Arkansas during the autumns of 1998, 1999, and 2000. Brown rice kernel dimensions decreased with harvest moisture content [HMC (Moisture contents are expressed on a wet basis)] below 24% HMC. Kernel dimensional distributions were usually single-modal and near normal. Brown rice dimensional variability, expressed by kernel dimensional standard deviation (SD), was significantly affected by HMC and location. Kernel dimensional SD generally was linearly and directly related to HMC. Among kernel dimensions, thickness had the greatest shrinkage with decreasing HMC, followed by length and then width. Among varieties, Bengal had the greatest kernel shrinkage, followed by Drew, and then Cypress.