Relative competitive ability of rice with strawhull and
Transcrição
Relative competitive ability of rice with strawhull and
Jaboticabal ISSN: 1984-5529 v.44, n.2, p.176–184, 2016 http://dx.doi.org/10.15361/1984-5529.2016v44n2p176-184 Relative competitive ability of rice with strawhull and blackhull red rice biotypes Habilidade competitiva relativa de arroz com biótipos de arroz-vermelho strawhull e blackhull Marcos André NOHATTO1; Dirceu AGOSTINETTO2; David Robert GEALY3; Luis Antonio de AVILA4; Bruno Moncks da SILVA5; Nixon da Rosa WESTENDORFF6 “Autor para correspondência” Eng. Agr. Doutor em Fitossanidade, Universidade Federal de Pelotas, Departamento de Fitossanidade – Campus Universitário Capão do Leão. Caixa Postal 354 -96010-900 – Pelotas-RS, [email protected] 2 Eng. Agr. Doutor em Fitotecnia. Universidade Federal de Pelotas. [email protected] 3 Dr. Plant Physiologist. USDA-Agricultural Research Service - Dale Bumpers National Rice Research Center. [email protected] 4 Eng. Agr. Ph.D. em Agronomia. Universidade Federal de Pelotas. [email protected] 5 Eng. Agr. Mestrando em Fitossanidade. Universidade Federal de Pelotas. [email protected] 6 Eng. Agr. Doutorando em Fitossanidade. Universidade Federal de Pelotas. [email protected] 1 Recebido em: 20-08-2015; Aceito em: 27-10-2015 Abstract The weed interference varies on several factors, especially the composition of the weed community and the ability to compete with the culture. Thus, this study aimed at evaluating the competitive ability of rice and different populations of red rice (strawhull or blackhull). The experiments were conducted in greenhouse from January to August 2013, at United States Department of Agriculture, Dale Bumpers National Rice Research Center (USDA/DBNRRC) in the city of Stuttgart, Arkansas. The experimental design was completely randomized with four replications. Treatments consisted of rice or red rice plant ratios (100:0, 75:25, 50:50, 25:75 and 0:100%). Variables evaluated included: shoot dry weight, leaf area and plant height. Results show that strawhull or blackhull red rice biotypes have superior competitive ability than rice, CL 142 AR. Overall, the blackhull red rice biotype has superior competitive ability compared to strawhull one. For rice, the interspecific competition dominates, while for red rice biotypes the intraspecific competition was more harmful. Additional keywords: interference; Oryza sativa; replacement series. Resumo A interferência de plantas daninhas varia em função de vários fatores, destacando-se a composição da comunidade infestante e a capacidade dessa de competir com a cultura. Diante disso, o objetivo do trabalho foi avaliar a habilidade competitiva entre arroz e diferentes populações de arroz-vermelho (strawhull ou blackhull). Os experimentos foram conduzidos em casa de vegetação, no período de janeiro a agosto de 2013, no Departamento de Agricultura dos Estados Unidos, Dale Bumpers National Rice Research Center (USDA/DBNRRC), na cidade de Stuttgart, Arkansas. O delineamento experimental utilizado foi o completamente casualizado, com quatro repetições. Os tratamentos consistiram nas proporções de plantas de arroz ou arrozvermelho (100:0; 75:25; 50:50; 25:75 e 0:100%). As variáveis avaliadas foram: massa da matéria seca da parte aérea, área foliar e estatura de planta. Os resultados obtidos evidenciam que os biótipos de arroz-vermelho strawhull ou blackhull apresentam habilidade competitiva superior ao arroz, cultivar CL 142 AR, enquanto, o biótipo de arroz-vermelho blackhull, em geral, apresenta superioridade competitiva comparada ao strawhull. Para o arroz, a competição interespecífica predomina, enquanto para os biótipos de arroz-vermelho a competição intraespecífica foi mais prejudicial. Palavras-chave adicionais: interferência; Oryza sativa; série de substituição. Introduction Rice cultivation plays important role in the world economy and is considered protein and calorie source for more than half the world's population (FAO, 2015). In Brazil and the United States are produced annually 11.7 and 8.6 million tons with average productivity of 5.1 and 8.6 tons per hectare, respectively. Despite the significant values in productivity in the United States, it is known that culture did not reach the productive potential observed in experimental areas and crops that adopt high technological level. Among the main limiting factors for increased productivity in the culture, there is the competition with red rice, as this weed has the same demand for the niche. Botanically, red rice belongs to the same genus of the cultivated rice, there being different populations 176 Científica, Jaboticabal, v.44, n.2, p.176-184, 2016 in the United States that can be mainly classified as strawhull or blackhull. It is believed that strawhull red rice came through the crossing between the varieties of cultivated rice O. sativa L. spp. indica and O. rufipogon Griff., while blackhull comes from O. sativa indica var. Aus and O. rufipogon (Londo & Schaal, 2007). The degree of interference depends on factors related to the environment (soil, climate and crop management), culture (cultivar, spacing and seeding rate), the weed community (species composition, population and distribution) and the timing and extent of period in which culture and weed community live in the same environment (Carvalho, 2011). Therefore, the study of the competitive dynamics between different populations of rice and red rice is needed to understand the losses caused by weeds and development of management strategies appropriate for each biotype. Thus, this study aimed at evaluating the competitive ability of rice and different populations of red rice (strawhull or blackhull). Material and methods The experiments were conducted from January to August 2013 in greenhouse at the United States Department of Agriculture, Dale Bumpers National Rice Research Center (USDA / DBNRRC) in the city of Stuttgart, Arkansas. A completely randomized design with four replications was used. Each experimental unit consisted of plastic pot with four liters capacity filled with soil from rice ISSN: 1984-5529 cultivation area classified as Neosoil of silty and clayey texture. It used seeds of CL 142 AR (PI 659515) rice cultivar, while the red rice biotypes (strawhull or blackhull) (PI 653422) were from paddy crop of Stuttgart-AR, stored in the germplasm bank of the research center. In the first experiment was carried out preliminary assessment to rice cultivar and red rice biotypes in monoculture in order to get the population to the replacement series experiment, using populations of 4, 8, 16, 32 and 64 plants per pot (equivalent to 143, 286, 571, 1,143 and 2,286 plants m-2). Constant final production of shoot dry weight (SDW) was obtained with a population of 16 plants per pot, equivalent to 571 plants m-2 (data not shown). The other experiments were conducted to replace series by varying the ratios of rice plants to strawhull or blackhull red rice per pot of 100: 0, 75:25, 50:50, 25:75 and 0:100 (16:0, 12:4, 8:8, 4:12 and 0:16), maintaining the total plant population (Experiments II and III). The study also evaluated the relative competitiveness between the red rice biotypes (strawhull and blackhull) to determine which one has more competitive ability (Experiment IV). The levels of light and temperature were measured at the top of plants, daily throughout the experiment, with the aid of ceptometer AccuPAR Model LP-80 PAR/LAI and local thermometer, respectively (Figure 1). At 45 days after emergence (DAE) were evaluated the variables: SDW, leaf area (LA) and plant height (H). Light Temperature 31 1400 30 o 1200 Temperature ( C) 2 -1 Light intensity (mol m s ) 1600 1000 29 800 28 600 400 27 200 0 26 0 5 10 15 20 25 30 35 40 45 Days after emergence Figure 1 - Characterization of light intensity and temperature during the relative competitive experiments between irrigated rice (CL 142 AR) and red rice (strawhull or blackhull) and, among the weed biotypes. SDW was quantified by weighing the shoots after being dried at 60 °C for 96 hours. Quantitation of LA was performed with the aid of a leaf area meter (model LI 3000), whereas H was obtained by measuring the distance from the base to the end of the last leaf. For analysis of growth variables, it used the method of the relative productivity graphical analysis (Cousens, 1991). This procedure, also known as a conventional method of substitution experiments, consists of a diagram based on the relative yield (RY) and total (RYT) variation. When the result of RY tends to straight, it means that the skills of the species are equivalent. If the RY results a concave line, it indicates 177 Científica, Jaboticabal, v.44, n.2, p.176-184, 2016 loss in growth of one or both species. On the contrary, if the RY shows a convex line, there is the advantage in growth of one or both species. When RYT is equal to the unity (1) (straight line), there is competition for the same resources and if it is greater than 1 (convex line), competition is avoided. If the RYT is less than 1 (concave line) occurs mutual growth impairment (Cousens, 1991; Radosevich et al., 2007). The relative competitiveness index (RC), clustering coefficient (K) and competitiveness coefficient (C) were calculated. RC represents the comparative growth of cultivated rice (r) in relation to red rice (rr); K indicates the relative dominance of one species over another (Kr = rice and Krr = red rice); and C indicates which of the species is more competitive. Thus, the RC, K, and C indices indicate which species is more competitive and their combined interpretation indicates a safer competitive species (Cousens, 1991). Rice is more competitive than red rice when RC>1, Kr>Krr and C>0. On the other hand, red rice is more competitive than rice when RC<1, Kr<Krr and C<0 (Hoffman & Buhler, 2002). To calculate these rates proportions of 50:50 of species were used as well as the following equations: CR = RYr / RYrr; Kr = RYr / (1RYr); Krr = RYrr / (1-RYrr); C = RYr - RYrr. The statistical analysis for productivity or relative variation includes the calculation of the differences in the RY values (DRY) obtained in the proportions 25, 50 and 75% of the values belonging to the hypothetical straight in the respective proportions (Bianchi et al., 2006). The "t" test was used to assess differences in the indices DRY, RYT, RC, K and C (Hoffman & Buhler, 2002). The criterion to consider the RY and RYT curves different from the hypothetical lines and the existence of differences in competitiveness for RC, K and C indexes, was the occurrence of differences by the "t" test at least in two proportions (Bianchi et al., 2006). Results obtained for variables, expressed as average values per plant, were analyzed for normality by the Shapiro-Wilk test and then were subjected to analysis of variance (p≤0.05). Afterwards, the proportions effects in relation to the monoculture (control) were evaluated by the Dunnett test (p≤0.05) and between the proportions in the mixture, using the Tukey test (p≤0.05), separately for each competitor. Results and discussions In RY graphical analysis, the combination of the rice cultivar with strawhull or blackhull red rice, it was found that the culture was less competitive than the red rice, with rice RY represented by concave line and weed RY by convex line (Figure 2). RY deviations were significant for all variables, except for blackhull red rice RY for SDW and RY for both weed biotypes for H (Table 1). This showed an overall benefit for weed and damage to the crop. ISSN: 1984-5529 Regarding the RYT, there was no difference between the expected and estimated values for the variables studied, except for RYT from the combination of rice and strawhull in H (Table 1). This demonstrates that plants interact by the same resources available in the environment, but the red rice uses resources more efficiently than rice. More weed competitiveness has also been reported in studies on other species such as the wild radish with soybean (Bianchi et al., 2006) or wheat (Rigoli et al., 2008), hairy fleabane with soybean (Silva et al., 2014), besides the red rice competing with rice (Fleck et al., 2008; Dai et al., 2014). There was reduction of SDW, LA and H on rice in competition with strawhull or blackhull red rice compared to the monoculture, except for 75:25 ratio competing with blackhull for SDW and H variables (Table 2). When analyzing the differences between proportions in the presence of strawhull red rice, it was observed that a smaller culture proportion (25:75) showed the lowest SDW, LA and H compared to 75:25; while in competition with blackhull, none of the plant proportions with the competitive presence differed from each other except in SDW, when similar behavior to rice competing with strawhull. Despite the different crop responses to competition with red rice biotypes, cultivated rice remains in disadvantage in the competitive process. Study on six red rice biotypes and cultivated rice from China also reported the superiority of the weed in relation to crop, showing that as it increases the presence of red rice in the proportion, it decreases the values of height, tillering, shoot dry weight and productivity in the crop (Dai et al., 2014). Still, it was noted for rice cultivation, the interspecific competition was more damaging than the intraspecific one; it is rather live with the crop than with the weed. Studies have shown that although rice belonging to the same genus of red rice, the culture has distinct morphological and physiological characteristics that diminish its competitive ability in relation to red rice, with less ability to tillering (Balbinot Junior et al., 2003), lower efficiency of CO 2 use (Ziska & McClung, 2008) and nitrogen (Chauhan & Johnson, 2011). Furthermore, the study demonstrated that rice plants have fewer roots than red rice (Eberhardt et al., 1999). For strawhull or blackhull red rice living with the culture, there were differences in the proportions 50:50 and 75:25 compared to the control for the SDW and LA variables (Table 2). It was also observed that the proportion 25:75 showed lower value of SDW and LA compared to 75:25 for strawhull. For blackhull, none of the plant ratios differed for SDW and LA in the rice presence. In the H analysis for strawhull or blackhull red rice competing with rice, there was no differences in plant proportions compared to the control or to each other. 178 Científica, Jaboticabal, v.44, n.2, p.176-184, 2016 Rice Blackhull RYT 1.4 1.2 1.2 1.0 1.0 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0.0 16-0 12-4 8-8 4-12 0.0 0-16 1.2 1.0 1.0 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0.0 16-0 8-8 4-12 0.0 0-16 Rice Strawhull RYT 1.4 1.4 1.2 1.2 1.2 1.2 1.0 1.0 1.0 1.0 0.8 0.8 0.8 0.8 0.6 0.6 0.6 0.6 0.4 0.4 0.4 0.4 0.2 0.2 0.2 0.2 0.0 16-0 12-4 8-8 4-12 0.0 0-16 0.0 16-0 Rice and blackhull proportions Rice Blackhull RYT 12-4 8-8 1.4 4-12 0.0 0-16 Rice and strawhull proportions Rice Strawhull RYT 1.4 1.4 1.2 1.2 1.2 1.2 1.0 1.0 1.0 1.0 0.8 0.8 0.8 0.8 0.6 0.6 0.6 0.6 0.4 0.4 0.4 0.4 0.2 0.2 0.2 0.2 0.0 16-0 12-4 8-8 4-12 Relative plant height 1.4 Relative plant height 12-4 Rice and strawhull proportions Relative leaf area Relative leaf area 1.4 1.4 1.2 Rice and blackhull proportions Rice Blackhull RYT Rice Strawhull RYT 1.4 Relative shoot dry weight Relative shoot dry weight 1.4 ISSN: 1984-5529 0.0 0-16 0.0 16-0 Rice and blackhull proportions 12-4 8-8 1.4 4-12 0.0 0-16 Rice and strawhull proportions Figure 2 - Relative yield (RY) and total (RYT) for shoot dry weight, leaf area and plant height to rice (CL 142 AR) and red rice biotypes (strawhull or blackhull). (●) RY of rice, (○) RY of red rice and (▼) RYT. Dashed lines refer to the hypothetical relative yields, when there is no interference from one species over another. Overall, growth variables in red rice were increased when in competition with the cultivated rice, except for the H variable, i.e., unlike what occurred for the culture, intraspecific competition proved to be more damaging to weed plant. No differences occurred for RY in the evaluated variables for the combination of strawhull with blackhull red rice, except for LA of strawhull and H for blackhull (Table 1). As for RYT, there were differences between the values of expected and observed deviations only for H (Figure 3 and Table 1). Thus, overall competitors have equal competitive ability, or compete for the same resources. 179 Científica, Jaboticabal, v.44, n.2, p.176-184, 2016 ISSN: 1984-5529 Table 1 - Differences on relative yield (DRY) and total relative yield (RYT) in the rice (CL 142 AR) to red rice biotypes (strawhull or blackhull) proportions of 75:25, 50:50 and 25:75. Plant proportion Variable 75:25 50:50 25:75 SDW DRYr (rice) -0.15(±0.03)* -0.19(±0.03)* DRYrr (strawhull) 0.19(±0.02)* 0.22(±0.03)* 0.05(±0.03)ns RYT 1.04(±0.04)ns 1.03(±0.06)ns 0.93(±0.03)ns -0.11(±0.06)ns -0.15(±0.01)* DRYrr (blackhull) 0.10(±0.04)ns 0.20(±0.03)* 0.07(±0.02)ns RYT 0.99(±0.10)ns 1.05(±0.03)ns 0.96(±0.03)ns DRYrrs (strawhull) -0.00(±0.04)ns -0.07(±0.01)* -0.02(±0.01)ns DRYrrb (blackhull) -0.08(±0.01)* 0.03(±0.01)ns 0.03(±0.03)ns 0.92(±0.04)ns 0.97(±0.02)ns 1.01(±0.03)ns DRYr (rice) RYT -0.13(±0.00)* -0.11(±0.01)* LA DRYr (rice) -0.26(±0.03)* -0.23(±0.01)* -0.14(±0.01)* DRYrr (strawhull) 0.16(±0.03)* 0.18(±0.05)ns 0.11(±0.02)* RYT 0.90(±0.04)ns 0.95(±0.06)ns 0.97(±0.02)ns DRYr (rice) -0.27(±0.04)* -0.23(±0.01)* -0.13(±0.01)* DRYrr (blackhull) 0.11(±0.03)ns 0.20(±0.03)* 0.14(±0.02)* RYT 0.84(±0.06)ns 0.97(±0.02)ns 1.01(±0.02)ns DRYrrs (strawhull) -0.03(±0.05)ns DRYrrb (blackhull) -0.04(±0.02)ns 0.08(±0.03)ns 0.04(±0.07)ns 0.94(±0.07)ns 0.99(±0.03)ns 1.00(±0.07)ns RYT -0.09(±0.01)* -0.05(±0.01)* H DRYr (rice) -0.11(±0.01)* -0.09(±0.02)* -0.07(±0.00)* DRYrr (strawhull) 0.00(±0.00)ns -0.00(±0.02)ns 0.03(±0.00)* RYT 0.89(±0.00)* 0.91(±0.04)ns 0.96(±0.00)* -0.07(±0.02)ns -0.08(±0.01)* -0.04(±0.01)* DRYrr (blackhull) 0.01(±0.01)ns -0.01(±0.00)ns 0.04(±0.02)ns RYT 0.94(±0.03)ns 0.91(±0.01)* 0.92(±0.02)ns DRYrrs (strawhull) -0.00(±0.03)ns -0.02(±0.01)ns -0.01(±0.01)ns DRYrrb (blackhull) 0.01(±0.00)* -0.04(±0.01)* 0.07(±0.01)* RYT 0.99(±0.03)ns 0.95(±0.01)* 0.92(±0.02)* DRYr (rice) * Significant difference by t test (p≤0.05). Values in brackets represent the mean's standard error. 180 Científica, Jaboticabal, v.44, n.2, p.176-184, 2016 In the evaluation among competitors, for the strawhull there were no differences in the proportions of plants among each other and in relation to the control, except for SDW when there was a reduction of the variable of equal and smaller proportion of strawhull compared to the control (Table 2). As for blackhull, there was no difference between the monoculture of weeds and proportions, except for ISSN: 1984-5529 75:25 in SDW variable and for all proportions in H. Overall, there was the less influence of competition among red rice biotypes on variables analysis, i.e. both have lower phenotypic plasticity when in competition among weeds. The exception was the plant height, which was reduced in the red blackhull red rice compared to monoculture when there was the presence of strawhull red rice. Table 2 - Responses of shoot dry weight (SDW), leaf area (LA) and plant height (H) of rice cultivar (CL 142 AR) and red rice biotypes (strawhull or blackhull) in competition. Experiment II 75:25 50:50 25:75 0:100 (T) 25:75 50:50 75:25 Proportion 100:0 (T) 75:25 50:50 25:75 0:100 (T) 25:75 50:50 75:25 Proportion 100:0 (T) 75:25 50:50 25:75 0:100 (T) 25:75 50:50 75:25 Experiment IV SDW (g plant-1) Proportion 100:0 (T) Experiment III Rice Rice Strawhull 1.26 a 1.02* b 0.78* b 0.62* 1.25 a 1.07ns ab 0.87* b 0.72* 1.51 a 1.45ns a 1.30* a 1.28* Strawhull Blackhull Blackhull 1.51 c 1.62 ns b 2.17* a 2.66* 1.70 a 1.86ns a 2.35* a 2.36* 1.76 a 1.83ns a 1.88ns b 1.21* LA (cm2 plant-1) Rice Rice Strawhull 149.29 a 95.15* a 81.26* a 72.69* 171.56 a 165.69ns a 141.48ns a 139.13ns Strawhull Blackhull Blackhull 175.17 b 201.21ns ab 237.49* a 285.23* 189.57 a 225.71ns a 264.98* a 272.09* 145.03 a 94.94* ab 78.35* b 63.12* 183.17 a 193.68ns a 211.30ns a 154.90ns H (cm plant-1) Rice Rice 70.86 a 60.5* ab 58.3* b 51.8* 68.8 a 62.6ns a 57.2* a 56.6* Strawhull Blackhull 91.6 a 95.0ns a 91.5ns a 91.9ns 86.0 a 81.9ns a 84.3ns a 90.6ns Strawhull 93.1 a 93.4ns a 90.3ns a 90.1ns Blackhull 87.8 a 79.1* a 81.5* a 82.8* * ou mean differs or not from the control (T) in the column by the Dunnett test (p≤0,05). 1 Means preceded by letters in the same column, in the presence of competitors, do not differ by Tukey test (p≤0.05). ns 181 Científica, Jaboticabal, v.44, n.2, p.176-184, 2016 Strawhull Blackhull RYT Strawhull Blackhull RYT 1.4 1.4 1.2 1.2 1.2 1.2 1.0 1.0 1.0 1.0 0.8 0.8 0.8 0.8 0.6 0.6 0.6 0.6 0.4 0.4 0.4 0.4 0.2 0.2 0.2 0.2 0.0 16-0 12-4 8-8 Relative leaf area Relative shoot dry weight 1.4 ISSN: 1984-5529 0.0 0-16 4-12 0.0 16-0 Strawhull and blackhull proportions Strawhull Blackhull RYT 4-12 0.0 0-16 1.4 1.2 1.2 1.0 1.0 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0.0 16-0 8-8 Strawhull and blackhull proportions 1.4 Relative plant height 12-4 1.4 12-4 8-8 4-12 0.0 0-16 Strawhull and blackhull proportions Figure 3 - Relative yield (RY) and total relative yield (RYT) of shoot dry weight, leaf area and plant height of strawhull and blackhull red rice biotypes. (●) RY of red rice strawhull, (○) RY of blackhull red rice and (▼) RYT. Dashed lines refer to the hypothetical relative yields, when there is no interference from one species over another. Study aimed at characterizing phenotypically the different types of red rice in the State of Arkansas found that the blackhull showed higher H compared to strawhull (Shivrain et al., 2010). However, it is noteworthy that the blackhull has higher genetic diversity compared to strawhull due to the greater proximity with wild rice, which has less selection pressure imposed by man and therefore less reduction in genetic diversity (Londo & Schaal, 2007), which could partly explain the lowest H observed for blackhull plants in the experiment. Assuming that the rice is more competitive than red rice when RC>1, Kr>Krr and C>0 (Hoffman & Buhler, 2002) and the occurrence of differences in at least two of these indices (Bianchi et al., 2006) it was observed for all variables that both weed biotypes have more competitiveness than the crop (Table 3). Overall, strawhull or blackhull red rice, when competing with the rice cultivar, showed higher growth than the later in all variables, as indicated by RC index (Table 3). There was dominance of competitors on rice cultivar, as indicated by the index K. Furthermore, it has been found through the index C that the red rice was more competitive than the culture. Based on the combined analysis of the three competitiveness indices, blackhull was more competitive than strawhull for SDW and LA variables, while there was no difference among biotypes for H (Table 3). These results are possibly related to greater tiller emission capacity of blackhull as described by Shivrain et al. (2010). Study showed that tillering ability is the best predictor of plant competitiveness, including being used for selection of rice cultivars with greater competitive ability (Ni et al., 2000), which helps explain the results. 182 Científica, Jaboticabal, v.44, n.2, p.176-184, 2016 ISSN: 1984-5529 Table 3 - Competitiveness indices among red rice biotypes, competing with rice (CL 142 AR) and among weed biotypes, expressed by relative competitiveness (RC), relative clustering coefficient (K) and competitiveness coefficient (C). Proportion RC Kr Krr C 2.64(±0.37) 2.43(±0.40) 1.15(±0.05) -0.41(±0.00)* -0.35(±0.04)* -0.10(±0.01)* 2.23(±0.45) 2.38(±0.32) 1.39(±0.18) -0.41(±0.04)* -0.43(±0.04)* -0.16(±0.03)* 1.00(±0.08) 0.95(±0.01) 0.86(±0.02) -0.09(±0.00)* -0.07(±0.01)* 0.02(±0.01)ns SDW Rice:Straw Rice:Black Straw:Black 0.43(±0.03)* 0.50(±0.04)* 0.81(±0.01)* 0.45(±0.06)* 0.53(±0.03)* 0.76(±0.03)* Rice:Straw Rice:Black Straw:Black 0.40(±0.01)* 0.39(±0.03)* 0.72(±0.04)* 0.37(±0.02)* 0.37(±0.01)* 0.70(±0.01)ns Rice:Straw Rice:Black Straw:Black 0.82(±0.01)* 0.85(±0.02)* 1.05(±0.02)ns 0.70(±0.04)* 0.71(±0.01)* 0.94(±0.03)ns LA H Not significant and * significant by t test (p≤0.05). Values in brackets represent the mean’s standard error. Kr and Krr are relative clustering coefficients for rice and red rice, respectively. ns Conclusions The intraspecific competition is more harmful to red rice biotypes, while the interspecific competition is more pronounced for culture. The rice cultivar CL 142 AR has lower competitive ability in relation to the red rice biotypes from the United States (strawhull or blackhull), while the blackhull red rice biotype generally has competitive advantage compared to the strawhull. Acknowledgements The authors thank the financial support of DECIT / SCTIE-MS through CNPq and FAPERGS. References Balbinot Junior AA, Fleck NG, Menezes VG, Agostinetto D (2003) Competitividade de cultivares de arroz irrigado com cultivar simuladora de arrozvermelho. Pesquisa Agropecuária Brasileira 38(1):5359. http://dx.doi.org/10.1590/S0100204X2003000100007. Bianchi MA, Fleck NG, Lamego FP (2006) Proporção entre plantas de soja e plantas competidoras e as relações de interferência mútua. Ciência Rural 36(5):1380-1387. http://dx.doi.org/10.1590/S010384782006000500006. Carvalho, LB de (2011) Estudos ecológicos de plantas daninhas em agroecossistemas, Jaboticabal. 58p. 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