Introduction

From the araruta, three cultivars of great importance in Brazil are: Common, Creoula and the Banana, the first two being predominant, the first being the most widespread commercially. The plants of the common cultivar are those that produce starch of better quality, are of low size (more or less 0.60 m in height), have clear rhizomes that are conical-elongated or spindle-shaped, are covered by scales and reach up to 0.30 m in length depending on the quality of the soil, although the normal size varies from 0.10 to 0.25 m. It is also characterized by little to no flowering in tropical conditions. At Creoula, which originates in the Antilles (Barbados and Saint Vincent Islands), the plant is tall (over 1.0 m); produces clumped rhizomes on the surface of the soil, which need to be washed several times to remove the surface layer, otherwise they produce black starch of poor quality. It presents abundant flowering in tropical conditions, without however, having fruit and seed formation (LEONEL & CEREDA, 2002; MONTEIRO and PERESSIN, 2002).

The industrial ararut (Maranta arundinacea L.) is an herbaceous plant, with an articulated stem of 1.20 m in height, fusiform rhizome, shiny bark that is scaly and produced in tufts adherent to the rhizomes. Harvesting of the rhizomes can be done from 9 to 12 months after planting, when the leaves are wilted, showing brown coloration, which later becomes straw-yellow and whitish (MONTEIRO and PERESSIN, 2002). The fresh rhizome contains, according to plant age, more than 20% starch (PEREIRA et al., 1999).

Zárate and Vieira (2005) concluded that, for the planting of the common arrowroot, they recommend the use of propagules formed by pieces of the middle part or the tips of the rhizomes, with six buds.

The planting is done in grooves or shallow pits (0.10 m depth) spaced in a line of 0,70 to 0,80 m and 0,30 to 0,40 m between plants. For commercial propagation and planting, both the whole rhizomes, with a mean mass of 60 g and the basal part (fine part) of large rhizomes, between 50 and 100 g, may be used. The amount of seed rhizomes required for planting is around 2.0 to 3.0 t/ha (LAURA et al., 2000; MONTEIRO and PERESSIN, 2002).

According to MONTEIRO & PERESSIN (2002), ideal climatic conditions for araruta cultivation are found in climate type Cfa, humid mesothermic climate, without drought. The soil must have a porous surface layer, loose soils, where the best yields are obtained, because this crop prefers the sandy alluvial rich in organic matter and also the soils of the taxonomic units, Podzólico Red-Amarelo orto and Podzolisado with Gravel.

Agricultural production takes place in a successive decision-making process by the producer, who needs to choose when and how to carry out the recommended procedures for the research or technicians including the choice whether or not to use herbicide.

Roundup® is a product whose active ingredient is glyphosate and it may be the most important herbicide ever developed (Jiraungkoorskul et al., 2002).

Glyphosate is absorbed primarily by the chlorophylls of plants (green leaves and tissues) and is preferentially translocated by phloem to meristematic tissues. Because it is a derivative of glycine (an essential amino acid present in plants), the glyphosate molecule is not perceived as a potential offender.

In the plant, it acts as an inhibitor of the enzyme activity of the enzyme 5-enolpyruvylshiquimate-3-phosphate synthase (EPSPS), which catalyzes one of the synthesis reactions in the biosynthesis of phenylalanine, tyrosine and tryptophan, which are precursors of other products such as lignin, alkaloids , flavonoids and benzoic acids (Amarante Jr. et al., 2002, Galli and Montezuma, 2005).

Glyphosate is an herbicide belonging to the chemical group of substituted glycines, of post-emergent action, and is classified as non-selective and systemic. It presents a broad spectrum of action, which allows for the control of annual and perennial weeds (Galli and Montezuma, 2005).

The starch-producing industries annually move billions of dollars in starch, which is used in a wide range of products. The main world sources of commercial starch are maize, wheat, cassava, potatoes and rice. In Brazil only maize (70%) and cassava (30%) are processed for this purpose (DA SILVA, ASSUMPTION & VEGRO, 2000).

In the Brazilian corn and cassava starch extraction industries, the minimum installed capacity allows for the grinding and processing of 400 tons of starch a day and many of the cassava starch processing plants already have a daily crushing capacity of 800 tons of raw material, per day.

Arrowroot could be considered a potential raw material for the extraction of starch in Brazil, since in China there is already commercial extraction of this starchy.

It is one of the tropical amylaceae that deserve prominence, besides the manioc whose Brazil is the second producing country. Although potato starch (Arracacia xanthorrhiza) and sweet potato (Ipomoea potates) have their starches seen as for regular consumption, mainly for use in baking and confection of "baby foods" (BERMUDEZ, 1997; KIBUUKA and MAZZARI, 1981; LEONEL , Zéin (1985), and Zéin (1998).

In order for arrowroot to be considered a raw material for starch production, there is a need for adjustments in its production form. Earlier, arrowroot was planted among the maize lines, which was also a poorly grown crop. With the improvement of the corn production system, arrowroot cultivation was abandoned and has only survived as a relic by small farmers as an heirloom culture.

Therefore, the objective of this work is to rescue the cultivation of arrowroot and increase its production. As such, this investigations sought to verify the effects caused by the use of herbicide in large-scale araruta planting.

Material and methods

The earlover rhizomes, "Common" variety, were obtained from an existing planting in the locality of Fazenda Escola - UCDB, São Vicente Institute, Campo Grande-MS, the size of the area for planting was determined according to its availability of rhizomes, with an area of 1000 m².

Two soil analyzes were performed, the first one performed before planting millet served to verify the physical and chemical qualities of the soil, while the second analysis was performed after the incorporation of millet into the total area.

In order to prepare the soil, a subsoiler was used to break the compacted layers of the soil, a light harvesting was carried out of 1,5 kg of millet of the variety Pennisetum glaucum for the area of 1000 m², thus providing a better structuring of the soil. For the demarcation of the planting lines, the cultivator was adapted with four stems to obtain a line spacing of 0.90 m x 0.50 m x 0.90 m x 0.50 m, thus making the planting and semi-mechanized harvesting. The rhizomes were sectioned (cut) containing approximately 6 buds and distributed in rows with 0.25 m spacing, with a total area of 1000 m² (20 m x 50 m).

To control for weeds, a chemical control was applied with the glyphosate herbicide in the middle of the area with 110 DAP of the arrowroot. Manual de-weeding was performed in the other part of the area.

The survival index (plant number count and percentage loss) was calculated for the treated area with and without glyphosate at 121 DAP.

With 233 DAP, growth analysis, namely chlorophyll test and the number of leaves, was performed. Twenty plants were chosen at random, ten being treated with glyphosate and the other ten from the weeding area. For the measurements, a ruler was used to measure from the ground level to the height of the inflection of the highest leaf. The chlorophyll content was obtained by measuring with a chlorophyll meter (SPAD model 102).

The Ikeda implement was used to harvest the soil in a homogeneous manner and to facilitate the ripening of the rhizomes.

The production was evaluated by counting, length and diameter measurements and weighing of the rhizomes collected from the two treatments.

Results

Comparing the soil analysis before and after planting of millet, a considerable improvement was observed not only in the physical part of the soil (structuring), but also in the chemical part (see table 1 and 2).

After the application of glyphosate herbicide, plants showed a height development delay when compared to the weeding with manual weeding (see Figure 1).

Plants treated with glyphosate herbicide presented a lower total chlorophyll content when compared to plants with manual weeding, signifying that the herbicide is not harmful with respect to the average content of chlorophyll in arrowroot plants (see Figure 2).

The number of rhizomes harvested from glyphosate-treated (2,513 units) araruta plants was half the number produced by the control plants (4,953 units).

Importantly, the use of glyphosate did not affect the size of the rhizomes, but rather their weight: rhizomes of the safflower plant treated with glyphosate had a mean diameter of 0.2943 m, a mean length of 0.1201 m and an average weight of 27.78 grams. These values are  ??slightly higher than those found for rhizomes of control plants (respectively 0.2415 m, 0.1140 m and 33.13 grams).

Plants that received treatment with the glyphosate herbicide presented a significant decrease in the number of leaves in relation to the plot of manual weeding (Figure 3).

 Figure 1. Average height of arrowroot plants after glyphosate application and de-weeding.

Figure 2. Average total chlorophyll content (mg/g FW of leaf) of arrowroot plants after application of glyphosate herbicide and no herbicide.

Figure 3. Average number of leaves per plant treated with glyphosate and no glyphosate.

Table 1. Chemical analysis of soil for evaluation of soil characteristics. (P (phosphorus) and K (potassium): Mehlich; pH 12.5; MO: Colorimetric; Ca (calcium), Mg (magnesium) and Al (aluminum): KCL 1N; H (hydrogen) + Al (aluminum): Calcium Acetate pH 7.0.)

Table 2. Chemical analysis of soil for evaluation of residual capacity of millet corn. (P (phosphorus) and K (potassium): Mehlich; pH 12.5; MO: Colorimetric; Ca (calcium), Mg (magnesium) and Al (aluminum): KCL 1N; H (hydrogen) + Al (aluminum): Calcium Acetate pH 7.0.)

Discussion

There are potential consequences to the use of post-emergence glyphosate in RR soybean, such as direct changes in soybean mineral nutrition in the case of Mn and other nutrients such as N, Ca, Mg, Fe and Cu may have their levels changed under the application of glyphosate. Plants with nutritional problems may present lower accumulation of biomass and, consequently, lower productivity (Albrecht et al., 2010). Glyphosate formulations for post-emergence, both in a single application and in sequential applications found no effect on soybean grain yield in the MSoy 8888-RR variety (Albrecht et al., 2010).

Initially, the effect of glyphosate was verified in the shoot development of arrowroot, while its later effect was observed in the production of rhizomes. This is due to the inhibitory effect of glyphosate on the synthesis of tryptophan, the amino acid linked to the production of auxin, a plant growth hormone.

Under certain concentrations and formulations of the glyphosate, salt-tolerant soybeans may suffer injury. Roundup Ready, whose formulation corresponds to 648 g of glyphosate isopropylamine salt or 480g of glyphosate acid equivalent, is the only herbicide registered for application in genetically modified soybeans in Brazil using single or sequential applications at the registered dose of 1.2 to 2.5 L/ha of Roundup Ready commercial product, in the period from 20 to 45 days after emergence of the crop (Correia et al., 2007; Gazziero et al., 2007).

The potential for deleterious action by glyphosate may be due to changes in the nutritional balance of the farmed crop, the generation of phytotoxic effects, affecting water use efficiency, photosynthesis, rhizosphere, biomass accumulation, amino acid synthesis and secondary compounds (Kremer et al. 2005).

Conclusion

From the obtained results, arrowroot seems to have tolerance to the herbicide glyphosate. However, the use of this herbicide initially affected stem development and, late on, the amount of arrowroot rhizome produced. It is therefore recommended that glyphosate be not used in weed control in arrowroot plantation because it directly affects the production of the rhizome and consequently the production of starch.

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