**6. Most probable Brazilian weed groups to evolve resistance to herbicides**

**Table 2** shows the main weed species in the Brazilian agriculture [2]. Surely, a great number of significant Brazilian weed species are out of the list, but the most cited ones in the specialized literature in soybean, corn, cotton, wheat, sugarcane, *Eucalyptus*, citrus, and cassava are included in **Table 2**. Orders and families with gray background are those identified in the reference countries as the most probable ones to contain weed species with superior ability to evolve resistance to herbicides. Genera and species with gray background are those that already present at least one resistant biotype in Brazil.

To date (November 2016), 20 weed species have been reported in Brazil as presenting at least one resistant biotype (**Table 2**). Three plant orders (Gentianales, Lamiales, and Solanales) are considered to contain weed species with superior ability to evolve resistance to herbicides, being these orders complemented by those that already present weed species with resistant biotypes (Asterales, Brassicales, Caryophyllales, Malpighiales, Alismatales, and Poales).

Eight botanical families are considered as presenting superior risk to evolve resistance to herbicides in Brazil (Asteraceae, Brassicaceae, Caryophyllaceae, Polygonaceae, Rubiaceae, Convolvulaceae, Solanaceae, and Poaceae), and five of them (Caryophyllaceae, Polygonaceae, Rubiaceae, Convolvulaceae, and Solanaceae) still do not present any weed species in Brazil with confirmed resistance to herbicides (**Table 2**).

Researchers should be aware, however, not to consider only the data summarized in **Table 2** to collect evidences about future cases of weed resistance in Brazil, as that table included

**Figure 17.** Occurrence of weed resistance as a function of the **probable** geographical region of origin of the genus.

from the real tendency which will be corrected by nature in the future. One should consider the probable loss of superiority from C4 plants over C3 as a consequence of the heavy

The **probable** geographical center of origin of the families with resistant biotypes is summarized by the studied country in **Figure 17**. The region of origin for each botanical family is

anthropogenic effect in arable fields, as hypothesized by Ghannoum [24].

150 Herbicide Resistance in Weeds and Crops

**5. Geographical region of origin of families with resistant biotypes**

Source: adapted from Heap [8].



**Class Order Family Genus / species Common** 

Dicot Asterales Asteraceae *Bidens pilosa* Hairy

Dicot Asterales Asteraceae *Bidens subalternans* Greater

Dicot Asterales Asteraceae *Acanthospermum* 

Dicot Asterales Asteraceae *Ageratum* 

152 Herbicide Resistance in Weeds and Crops

Dicot Asterales Asteraceae *Galinsoga* 

Dicot Asterales Asteraceae *Parthenium* 

Dicot Asterales Asteraceae *Synedrellopsis* 

Dicot Caryophyllales Amaranthaceae *Alternanthera* 

Dicot Caryophyllales Caryophyllaceae *Stellaria media* Common

Dicot Apiales Apiaceae *Bowlesia incana* Hoary bowlesia Erva-salsa Wheat

*hispidum*

*conyzoides*

Dicot Asterales Asteraceae *Conyza spp*. Hairy Fleabane Buva Cotton,

Dicot Asterales Asteraceae *Emilia sonchifolia* lilac tasselflower Falsa-serralha Citrus,

*parviflora*

*hysterophorus*

Dicot Asterales Asteraceae *Sonchus oleraceus* Sow thistle Serralha Citrus,

*grisebachii*

*tenella*

Dicot Caryophyllales Polygonaceae *Rumex* spp Língua-de-

Dicot Asterales Asteraceae *Tridax procumbens* Coatbuttons Erva-de-touro Citrus,

Dicot Brassicales Brassicaceae *Raphanus* spp. Cassava,

Dicot Caryophyllales Amaranthaceae *Amaranthus spp* Caruru Cotton,

**name**

Tropical whiteweed

Beggarticks

Beggarticks

Ragweed parthenium

chickweed

**Common name (PT)**

de-carneiro

Gallant soldier Picão-branco Citrus,

Straggler daisy Agriãozinho Citrus,

Parrotleaf Apaga-fogo Cotton

Erva-depassarinho

vaca

Losna-branca

Mentrasto Cotton,

Picão-preto Cotton,

Picão-preto Cotton,

Bristly starbur Carrapicho-

**Main crops**

Cotton, Citrus

Citrus

Citrus, Cassava, Soybean, Wheat, Maize

Wheat

Eucaliptus, Cassava, Citrus, Soybean, Wheat

Cassava

Wheat

Wheat

Eucaliptus

Eucaliptus

Wheat, Maize

Sugarcane, Citrus, Maize, Cassava

Wheat

Wheat



NOTE: Botanical orders and families marked with gray background present superior potential risk of including weed species with resistant biotypes in the future based on the history of the reference countries (Australia, Canada, France and United States). Genus/Species with gray background already include weed species with resistant biotypes in Brazil as of November, 2016.

**Table 2.** Botanical classification highlighting orders, families and Genus/species of weeds with superior ability to evolve resistance in Brazil.

only a few weed species from the total Brazilian pool of weed species listed by some authors [3, 26–28]. The additional data supplied in the present chapter (herbicide mechanism of action, carbon metabolism, geographical region of origin, etc.) should be also considered together with the list of herbicides available for each crop grown in Brazil, as well as the frequency of application of each herbicide in each crop.
