Abstract
Abstract: The objective of this work was to compare wild poinsettia (Euphorbia heterophylla) biotypes as to their morphological characteristics, as well as to determine their genetic similarity in the state of Rio Grande do Sul, Brazil, and to confront the light compensation point of susceptible biotypes and of biotypes with low-resistance level to glyphosate. Besides the morphology analysis, the study included the genetic characterization, by AFLP, of susceptible (GR50= 58.65 g ha-1 a.e.) biotypes and of biotypes with low resistance (GR50= 310.36 g ha-1 a.e.) to glyphosate. The competitive ability of the biotypes was inferred according to their light compensation point. The observed morphological characteristics do not allow to differentiate biotypes as to their geographical location, or their resistance level to glyphosate. The genetic analysis identified low genetic diversity among the 15 tested biotypes, with a large amount of subgroups. The biotypes with low resistance formed an isolated group. The susceptible biotypes showed the lowest values of light compensation point and, possibly, they have a greater competitive ability under low-luminosity conditions. The evaluated characteristics do not enable to differentiate genotypes with different levels of glyphosate resistance.
Highlights
Wild poinsettia (Euphorbia heterophylla L.) is a short-lived weed of Euphorbiaceae family with annual cycle, which can have more than one generation per year
The morphology analyses of biotypes were divided into two stages: exsiccatae preparation for species identification and for characterization of morphology differences between collected biotypes; and analyses of main morphological characteristics of two contrasting biotypes, one of low-resistance level to glyphosate, and another susceptible to glyphosate
Hairiness in stem was observed in 40% of cases, and contrasted with the presence of the trait in nodes and petioles. These results show that, even when collected in nearby areas, wild poinsettia biotypes can show a great morphological diversity
Summary
Wild poinsettia (Euphorbia heterophylla L.) is a short-lived weed of Euphorbiaceae family with annual cycle, which can have more than one generation per year. Poinsettia management in soybean crops have been improved with the Roundup Ready technology, since it generally shows low resistance to the glyphosate herbicide. Glyphosate is a nonselective, systemic herbicide that inhibits the enzyme 5-enolpyruvylshikimate-3phosphate synthase (EPSPs), from the shikimic acid route. This enzyme catalyzes the binding reaction of shikimate-3-phosphate and phosphoenolpyruvate (PEP) compounds. Glyphosate is believed to have a reduced potential to select resistant weed biotypes (Powles & Yu, 2010), but this concept was debunked due to the high number of resistance cases detected, 90% of which reported in the last 15 years (Heap, 2017)
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