Competitividade relativa entre cultivares de arroz irrigado e biótipo de capim-Arroz (Echinochloa spp.)

Abstract

RESUMO -As espécies pertencentes ao gênero Echinochloa se destacam como principais infestantes das lavouras de arroz irrigado do Rio Grande do Sul, causando dano econômico à cultura devido à elevada competitividade pelos recursos do ambiente. O trabalho teve por objetivo comparar as habilidades competitivas relativas entre dois cultivares de arroz e um biótipo de capim-arroz. Para isso, foram realizados experimentos em casa de vegetação na estação de crescimento 2006/07, em delineamento experimental inteiramente casualizado, com quatro repetições. Os tratamentos foram arranjados em série substitutiva, com cinco proporções de plantas de arroz e do competidor (100:0; 75:25; 50:50; 25:75; e 0:100), mantendo a população constante de 24 plantas vaso -1 das espécies associadas. O arroz foi representado pelos cultivares IRGA 417 ou BR-IRGA 410, e o competidor, pelo biótipo de capim-arroz. A análise da competitividade foi efetuada por meio de diagramas aplicados a experimentos substitutivos e através de índices de competitividade relativa. As variáveis estudadas foram área foliar e massa seca aérea das plantas. Os resultados mostram que houve competição entre os cultivares de arroz IRGA 417 ou BR-IRGA 410 com o capim-arroz, independentemente da proporção de plantas na associação, com redução na área foliar e massa seca da parte aérea dos competidores. O capim-arroz apresenta menor perda de produtividade relativa, reduz as variáveis morfológicas do arroz e demonstra possuir superioridade competitiva, comparativamente aos cultivares de arroz.Palavras-chave: Oryza sativa, interferência, competição, plantas daninhas, características morfofisiológicas.ABSTRACT -The Echinochloa species are among the most important weeds in flooded rice fields of Rio Grande do Sul, causing economic losses to the culture, due to its high competivity for environmental resources. The objective of this study was to compare the relative competitive abilities between two rice cultivars and an Echinochloa spp. biotype. Greenhouse experiments were conducted in 2006/07 growing season utilizing a completely randomized design with four replications. The treatments were arranged in a replacement series experiment by establishing five proportions of rice plants and competitor (100:0; 75:25; 50:50; 25:75 and 0:100), maintaining a constant population of 24 plants per pot. Rice cultivars were IRGA 417 or BR-IRGA 410, and the competitor was an Echinochloa spp. biotype. Competitive analysis was accomplished through diagrams usually applied to replacement series studies and indexes of relative competivity. The plant variables evaluated were: leaf area and shoot dry weight. There was competition between the IRGA 417or BR-IRGA 410 cultivars and the Echinochloa spp., independently of the proportion of the plants, with the competitors presenting reduced leaf area and shoot dry matter weight. Echinochloa spp. presents smaller relative productivity loss, reduces the morphological rice variables, and shows to be more competitive than the rice cultivars.

Competitive Ability of Canola Hybrids With Weeds

“…: if it is turnip, it is better to sow Hyola 433; if it is ryegrass, the possibilities of choice are increased with hybrids Hyola 61, Hyola 76, Hyola 433 and Hyola 571 CL. These results reinforce the findings by Bianchi et al (2006) and Agostinetto et al (2008), who reported the existence of competitive variability according to the intrinsic characteristics of each cultivar of soybean and rice assessed, respectively. Together with this (crop) tillage is the chemical tillage, where there are several options for the control of grasses (ryegrass) infesting canola and almost nonexistent options for turnip control, because of the botanical similarities that this crop and turnip present so that there are no selective herbicides.…”

“…It is noteworthy that, in substitutive experiments, there is little evidence of having qualitative changes due to population increase, i.e., the dominance of one species over another rarely changes with the change of the population (Cousens & O'Neill, 1993). The results observed in this study are corroborated by the ones verified by Agostinetto et al (2008), Fleck et al (2008), Agostinetto et al (2009) and Galon et al (2011Galon et al ( , 2015. However, conflicting results have been verified by Agostinetto et al (2013), who found different behavior when rice and soybeans competed with cockspur, and the crops, in this case, were more competitive than the weeds, therefore occurring differences between species in competition.…”

“…The results of this study are corroborated by the ones found by Bianchi et al (2006), when assessing soybeans versus turnip; Fleck et al (2008), studying rice versus red rice; Agostinetto et al (2008), when working with rice versus gulf cockspur grass; and Agostinetto et al (2013), when researching rice and soybeans versus cockspur. The competition quantitatively and qualitatively affects the production because it modifies the utilization efficiency of environmental resources such as water, light, CO 2 and nutrients (Bianchi et al, 2006), settling between the crop and plants of other species found on site.…”

“…With respect to the three indices assessed to define competitiveness, it was found that forage turnip was more competitive than soybean genotypes (Bianchi et al, 2006) and gulf cockspur grass stood out in relation to irrigated rice (Agostinetto et al, 2008). Nonetheless, Galon et al (2011) found differentiation regarding barley cultivars (BRS Greta, BRS Elis and BRS 225) when infested by ryegrass.…”

“…It also stands out that for the canola crop in competition with turnip and/or ryegrass no studies were found in the literature that have quantified the competitive ability of canola hybrids infested by these weeds. Many studies using the substitutive method show that there are differences in the competitive ability of other crops such as; rice versus red rice, gulf cockspur grass and Aeschynomene denticulata (common names vary regionally) (Fleck et al, 2008;Agostinetto et al, 2008;Galon et al, 2015), soybeans versus turnip, plantain signalgrass and cockspur (or cockspur grass), barnyard millet, Japanese millet, water grass, common barnyard grass, or simply "barnyard grass") (Bianchi et al, 2006;Agostinetto et al, 2009Agostinetto et al, , 2013, barley versus ryegrass (Galon et al, 2011), among others.…”