Abstract
ABSTRACT: Ryegrass is an important weed in wheat cultivations due to the evolution of resistance to different mechanisms of action. This study aimed to compare the phenological development, fitness cost, and competitive ability between ryegrass biotypes susceptible and with multiple resistance to 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) and acetolactate synthase (ALS) inhibiting herbicides. Fitness cost and phenological development were evaluated from biotypes grown in pots, and morphological growth variables were determined up to 140 days after emergence. Phenological development was evaluated with a fitness cost. Competitive ability was determined in a replacement-series experiment with proportions of resistant and susceptible ryegrass. The tested proportions were 100:0 (pure resistant ryegrass stand), 75:25, 50:50, 25:75, and 0:100% (pure susceptible ryegrass stand), where the number of tillers, height, leaf area, and shoot dry matter were evaluated at 50 days after emergence. The longer tillering period of resistant ryegrass was the main factor involved in the difference in phenological development between biotypes. The resistant biotype was superior to the susceptible regarding height, shoot dry matter, and absolute growth rate, while the susceptible biotype had a higher number of tillers and leaf area ratio. Thus, the resistant biotype had no fitness cost. For competitive ability, no difference was observed between biotypes in the different tested proportions when they occupied the same ecological niche.
Highlights
Ryegrass (Lolium multiflorum L.) is an allogamous, annual monocotyledonous species adapted to different soil types and highly productive in fertile soils, where it supports intense grazing and presents resprout with a large tillers number (Carámbula, 2007)
The natural reseeding of ryegrass allows its permanence in the soil seed bank and heterogeneous emergence flows, making the management of this species onerous when present in fields cultivated with winter cereals (Tironi et al, 2014)
The results showed differences in the length of phenological stages of ryegrass susceptible (Susc) and with multiple resistance (110) for periods between emergence and physiological maturity (Figure 1)
Summary
Ryegrass (Lolium multiflorum L.) is an allogamous, annual monocotyledonous species adapted to different soil types and highly productive in fertile soils, where it supports intense grazing and presents resprout with a large tillers number (Carámbula, 2007). These characteristics make ryegrass an important winter forage for temperate regions of southern Brazil. The reduction in the negative impact of ryegrass on yield and quality of harvested grains is indispensable, and the chemical control with 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) and acetolactate synthase (ALS) inhibiting herbicides are considered the main management tool. Herbicide-resistant of weed biotypes have evolved in response to the intensive use of the same active principle or mechanism of action, which makes control more costly and difficult, especially in wheat crop in which the herbicide options are limited (Vargas et al, 2006)
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