Abstract
ABSTRACT: Glyphosate is easily exuded by the roots of plants. However, there is still some lack of information in the scientific literature as to whether Urochloa brizantha is capable of exuding glyphosate to influence the growth of crops such as sugarcane and citrus. Thus, the objective of this research was to evaluate the translocation and root exudation of 14C-glyphosate by U. brizantha and its transport in sugarcane and citrus. Sugarcane seedlings, varieties SP80-1842, and citrus ‘Limão Rosa’ (Citrus limonia L. Osbeck) were cultivated with U. brizantha around the seedlings. Using a microsphere, 14C-glyphosate was applied on the leaves of U. brizantha. The plants were cultured for 12 days after treatment (DAT). The radioactivity of the herbicide was evaluated by liquid scintillation spectrometer, after oxidizing the soil and parts of the plants (leaves, culms and roots) of U. brizantha, sugarcane and citrus. The highest amount of glyphosate was detected in the U. brizantha leaves, where the applications were carried out, regardless of the culture studied. Only traces of glyphosate (0.001%) were detected in soil cultivated with sugarcane. On the other hand, in citrus, U. brizantha exuded 9.46% of the glyphosate by the root system in the soil. The total amount of herbicide found in sugarcane and citrus seedlings was only 0.006 and 0.095%, respectively, in all parts of the plant. These concentrations are lower than those required to cause intoxication in those crops. Considering the results, it is possible to state that the translocation of glyphosate in young plants of U. brizantha associated with citrus was higher in relation to sugarcane, and it was not exuded by the root system of the weed with sugarcane, but presented root exudation with citrus, however, the amount did not reach what is necessary to affect the dry mass of the agricultural crops.
Highlights
Glyphosate [N-(phosphonomethyl)glycine] is a water-soluble herbicide, and it penetrates the cuticles of the leaves of the plant, where it is simplistically translocated through the phloem to the apical meristems and, through the apoplast (Shaner, 2009)
When glyphosate gets in touch with the soil during spraying or when it is exudated by weeds, it may be strongly adsorbed to the soil particles (Al-Rajab et al, 2008; Gómez Ortiz et al, 2017), degraded by the microorganisms on the soil (Rueppel et al, 1977; Yu et al, 2015) or absorbed by the roots of adjacent plants, mainly those very close to the root of weeds treated with the herbicide (Tuffi Santos et al, 2005, 2008)
The mass balance of 14C-glyphosate applied in Association with sugarcane and citrus seedlings was, on average, 85.08 and 80.86%, respectively, which is the ratio of the sum of the radioactivity of the herbicide found by biological oxidation and the total radioactivity applied to the individual plant
Summary
Glyphosate [N-(phosphonomethyl)glycine] is a water-soluble herbicide, and it penetrates the cuticles of the leaves of the plant, where it is simplistically translocated through the phloem to the apical meristems and, through the apoplast (Shaner, 2009). When glyphosate gets in touch with the soil during spraying or when it is exudated by weeds, it may be strongly adsorbed to the soil particles (Al-Rajab et al, 2008; Gómez Ortiz et al, 2017), degraded by the microorganisms on the soil (Rueppel et al, 1977; Yu et al, 2015) or absorbed by the roots of adjacent plants, mainly those very close to the root of weeds treated with the herbicide (Tuffi Santos et al, 2005, 2008) Considering this scenario, sugarcane and citrus crops are currently still frequently infested by brachiaria (Urochloa brizantha), and such infestation was already common in the past, as reported by Carmona (1995), in which Urochloa spp. Among the herbicides used on sugarcane and citrus cultures, glyphosate stands out due to its effective control on a large number of weed species, since it is a non-selective herbicide
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