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Abstract
ABSTRACT The goosegrass (Eleusine indica (L.) Gaertn) is an annual plant that has a low-level resistance to glyphosate (LLRG), resulting in control failure in genetically modified soybean crops for resistance to this herbicide. Alleles related to resistance may cause changes in the plant biotype, such as inferior competitive ability. Thus, the objective of this work was to evaluated the competitive ability of soybean crops and susceptible and resistant (LLRG) goosegrass biotypes. Replacement series experiments were conducted with soybean crops and goosegrass biotypes. The ratios of soybean to susceptible or resistant (LLRG) goosegrass plants were 100:0, 75:25, 50:50, 25:75 and 0:100, with a total population of 481 plants m-2. The leaf area, plant height and shoot dry weight were evaluated at 40 days after emergence of the soybean crops and weeds. The soybean crop had superior competitive ability to the susceptible and resistant (LLRG) goosegrass biotypes. The soybean crop showed similar competitive ability in both competitions, either with the susceptible or resistant (LLRG) goosegrass biotypes. The intraspecific competition was more harmful to the soybean crop, while the interspecific competition caused greater damage to the goosegrass biotypes competing with the soybean crop.
Highlights
The Brazilian production of soybeans reached more than 95 million Mg in the 2015/16 crop season and an area of approximately 33 million hectares, representing an increase of 3.6% in the cultivated area compared with the previous crop season (BRASIL, 2016)
Since the significance is denoted by at least two variables with significant differences (BIANCHI et al, 2006b), the crop relative productivities (RP) differed only in shoot dry weight (SDW) compared with the goosegrass biotype with level resistance to glyphosate (LLRG) (Figure 2 and Table 1)
This results confirm those found by Agostinetto et al (2013) on soybean competing with Digitaria ciliaris, with the crop RP represented by convex lines, differentiating from the estimated lines for the variables leaf area (LA) and SDW
Summary
The Brazilian production of soybeans reached more than 95 million Mg in the 2015/16 crop season and an area of approximately 33 million hectares, representing an increase of 3.6% in the cultivated area compared with the previous crop season (BRASIL, 2016). Weed management is an essential measure to ensure high yields, especially the chemical control, which is the most practical and efficient method. The goosegrass [Eleusine indica (L.) Gaertn] is one of the most difficult species to control in Roundup Ready® (RR) crops, especially soybean (ULGUIM et al, 2013). Vargas et al (2013) identified goosegrass biotypes with low-level resistance to glyphosate (LLRG) using up to 1080 g of acid equivalent (a.e.) of glyphosate ha-1. Resistant weed biotypes may have inferior competitive ability, since the development of resistance cause changes in the plant metabolism, defense mechanisms, development or reproduction (VILA-AIUB; NEVE; POWLES, 2009). The resistance (LLRG) found in goosegrass biotypes may have caused physiological changes, with growth and development losses to this biotype, hindering its competitive ability with crops. The more adapted biotypes are the most competitive and able to increase their relative ratio in the niche over time
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