Oryza sativa (weedy red rice), the same species as cultivated rice, is a serious problem in rice production worldwide. Seed dormancy contributes to its persistence. We determined the effect of germination temperature and after-ripening period on germination capacity (GC) of red rice seeds from Arkansas rice fields in three production zones. We also determined the gene diversity (GD) of dormancy-linked loci among selected populations. The germination behaviour was evaluated at three temperatures (1°C, 15°C and 35°C) and four after-ripening periods (0, 30, 60 and 90 days) in two independent experiments. Germination response to temperature and after-ripening time differed among and within populations in each production zone. Overall, populations from the Delta and Grand Prairie were more dormant than those from White River. Regardless of ecotype or production zone, incubation at 35°C (mean GC = 84-100%) favoured the germination of seeds after-ripened for 60 days. Germination of these seeds was most variable at suboptimal temperature (15°C), with mean GC ranging from 44 to 97%; at 1°C, none of the seeds germinated. Primary dormancy was released in the majority of populations after 90 days of after-ripening. Blackhull populations generally had lower mean GC than strawhull populations, regardless of temperature, and required longer after-ripening time to release dormancy. They also showed a higher inter-and intrapopulation variation in germination and after-ripening than strawhulls and had the highest gene diversity (GD = 0.55-0.58) among test populations. Nondormant strawhulls were most distant (D = 0.63) from dormant blackhulls. Ecotype influenced genotypic clustering more than the dormancy trait.

We conducted a greenhouse study to evaluate the differential response of Palmer amaranth to glyphosate and mesotrione and to quantify the level of tolerance to mesotrione in recalcitrant (difficult-to-control) accessions and their offspring. Seeds were collected from 174 crop fields (corn, cotton, and soybean) across Arkansas between 2008 and 2016. Palmer amaranth seedlings (7 to 10 cm tall) were treated with glyphosate at 840 g ae ha–1or mesotrione at 105 g ha–1. Overall, 47% of the accessions (172) were resistant to glyphosate with 68% survivors. Almost 35% of accessions were highly resistant, with 90% survivors. The majority of survivors from glyphosate application incurred between 31% and 60% injury. Mesotrione killed 66% of the accessions (174); the remaining accessions had survivors with injury ranging from 61% to 90%. Accessions with the least response to mesotrione were selected to determine tolerance level. Dose–response assays were conducted with four recalcitrant populations and their F1progeny. The average effective doses (ED50) for the parent accessions and F1progeny of survivors were 21.5 g ha–1and 27.5 g ha–1, respectively. The recalcitrant parent populations were three- to five-fold more tolerant to mesotrione than the known susceptible population, as were the F1progeny.

This study sought to assess the effect of paclobutrazol on the performance of lowland rice when grown in acidic and alkaline soils. Determine the soil type that can produce maximum productivity, and evaluate the profitability of growing lowland rice to the paclobutrazol application under acidic and alkaline soils. The experiment was set out in a split plot organized in RCBD with soil types (ideal, acidic, and alkaline) as the main plot while the time of paclobutrazol is the subplot. The time of paclobutrazol application is indicated as follows: S1control, S2at the vegetative stage, S3at the heading stage, and S4in both vegetative at heading stages. Statistical analysis revealed that regardless of the time of paclobutrazol application in lowland rice ideal soil showed a significant influence in most agronomic and yield and yield component parameters, and achieve the highest gross income (PHP 143,820.00) and gross margin of PHP 100,368.72. The application of paclobutrazol at heading (S3) shows a significant outcome on the number of nodal roots plant -1 (411.11) and obtained the highest gross income comparing other subplot treatments. A remarkable effect on leaf area index (2.27), fresh straw yield (8.37 t ha -1 ), and root length (41.53 cm) were obtained in S3 plants and had a higher grain yield of 3.77 t ha -1 . Paclobutrazol is advisable in lowland rice regardless of the time of application under ideal soil to effect higher productivity. This can promote the development of panicles when applied under acidic soil.

Fimbristylis miliacea, a weed in rice, has evolved resistance to acetolactate synthase (ALS) inhibitors. This study aimed to investigate the competitive abilities of ALS-resistant (R) and ALS-susceptible (S) F. miliacea with rice. A replacement series experiment was conducted in the glasshouse at the Federal University of Pelotas, Brazil. The proportions of rice to F. miliacea were 100:0, 75:25, 50:50, 25:75 and 0:100, with 1060 plants m À2 . The experimental units were arranged in a completely randomised design with four replications. A follow-up study was conducted at the University of Arkansas, Fayetteville, USA, in a split-plot design with four replications. The main plot was species mixture (rice 9 R, rice 9 S, R 9 S). The subplot was competition partitioning (below-and above-ground, below-ground only, above-ground only and no interspecific competition). Leaf area, plant height and shoot dry mass were recorded. Rice was more competitive than the R or S F. miliacea. In equal proportions of rice and F. miliacea, regardless of ecotype, the relative leaf area, height and dry mass of rice were greater than that of F. miliacea. The ALS-resistant ecotype was less competitive with rice than the S ecotype. Intraspecific competition among rice plants was stronger than rice competition with F. miliacea. Competition for below-ground resources was the most critical aspect of interference among rice and F. miliacea. In production fields, high infestation levels of F. miliacea results in significant yield losses; thus, resistance to ALS inhibitors needs to be curtailed.

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