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ABSTRACT
Background: Megathyrsus maximus (Jacq.) is a perennial weed that
affects many crops. In Argentina, sugarcane is the most affected.
Objective: Study effective techniques to break dormancy and the effect
of environmental factors on the germination of this weed.
Methods: Experiments were carried out in cabinet incubators twice, with
five replicates per treatment. The experimental unit was made up for
50 seeds.
Results: Seed dormancy was strongly associated with the presence of
glumes. Manual extractions of glumes and immersion in sulphuric acid
were the most effective techniques for breaking dormancy. Megathyrsus
maximus did not depend on light to germinate, and it did so both under a
12 h-light-dark photoperiod and in complete darkness, with maximum
mean germination percentages of 73 and 76%, respectively. Mean
germination percentage (G) and coefficient of germination (CG: number
of germinated seeds per day) showed that this weed responded to a wide
range of temperatures, the optimal varied between 25 and 35 °C. Both
mean germination percentages and CG decreased as osmotic potential
became increasingly negative (0 MPa to -0.6 MPa), and as sodium
chloride solution concentrations increased (10 to 130 mmol L-1). No
germination was observed at -0.8 MPa and with a 150 mmol L-1 sodium
chloride solution.
Conclusions: The optimal germination conditions for M. maximus can be
found in central sugarcane areas in Argentina, since soils are in ideal
conditions and are kept under irrigation. In marginal areas, M. maximus
germination would depend on rainfall and certain sodium chloride
concentrations in the soil.

Keywords:
Megathyrsus maximus
guinea grass
scarification
salt stress
temperature
osmotic stress
dormancy