Plant growth and genetic polymorphism in glyphosate-resistant sourgrass (Digitaria insularis L. Fedde)

Abstract

Weed herbicide resistance has been a challenge in agriculture. The objective of this study was to detect sourgrass (Digitaria insularis (L.) Fedde) glyphosate-resistant plants and to evaluate the growth and polymorphism rate between the resistant and susceptible biotypes, as a subsidy for the integrated management of species. An experiment was conducted primarily for the detection of weed resistance using increasing doses of glyphosate to generate a dose-response curve. Then, an experiment consisting of eight treatments (destructives analysis of growth) and five replications was conducted to characterize and compare the phenological stages of each biotype. In addition to visual assessments, the dry weight and leaf area, absolute and relative growth rates, net assimilation rate and leaf area ratio of plants were determined. Finally, polymorphism among biotypes was determined using inter simple sequence repeat molecular markers. A resistant factor of 3.12 was found among the biotypes. The resistant biotype grew faster and was more robust than the susceptible biotype, arriving first to flowering. The resistant biotype was better adapted to light interception. The 25 inter simple sequence repeat molecular markers analysis showed a polymorphism rate of 56.6% among the analyzed biotypes.

Growth and Development of Sourgrass Plants from Vegetative Parts of Clumps

“…Similar results were found by Martins et al (2016), who evaluated the growth of D. insularis and found faster development for resistant plants, which reached the flowering stage first than glyphosate-susceptible plants. In addition, seed-propagated sourgrass emits inflorescence between 63 and 70 days after sowing (Machado et al, 2006), which is much slower when compared to that from vegetative propagation-between 21 and 50 DAP (Table 3).…”

“…This resulted in the selection of glyphosate-resistant weeds (Koger and Reddy, 2005). There are several reports of glyphosate-resistant sourgrass in Brazil (Carvalho et al, 2012;Barroso et al, 2015;Galeano et al, 2016;Martins et al, 2016;Gazola, 2017). Sourgrass populations resistant to fenoxaprop-p-ethyl and haloxyfop-p-methyl herbicides have recently been reported in the State of Mato Grosso (Heap, 2018), which is a major concern to producers, as ACCase inhibitors are the main herbicides for controlling postemergent D. insularis.…”

“…The flowering of resistant sourgrass plants is faster than that of susceptible ones (Martins et al, 2016), which may affect the natural resistance selection process. Thus, plants with fast flowering may have more germinating seeds in the soil and, consequently, generate new individuals more quickly.…”

“…This result is partly explained by the great genetic variability of the species. Martins et al (2016) evaluated the use of random primers and found that sourgrass has a polymorphism rate of 56.6%, i.e., a sourgrass plant may be 56.6% genetically different from another plant of the species. This is important because genetic variability among weeds of the same species allows them to evolve and adapt to new locations, which has been occurring with D. insularis in Brazil (Lopez-Ovejero et al, 2017).…”

Monitoring of Resistance of Sourgrass to Glyphosate Herbicide in Urban Areas of the State of São Paulo, Brazil

“…Sourgrass plants have high variability. Martins et al (2016) evaluated random primers and found that the DNA of glyphosate-resistant and susceptible sourgrass plants presented a variation of 56.6%. This is a highly competitive plant with great infestation potential and fast and aggressive growth, which develops well in poor and acidic soils and has high seed germination percentages (above 90%) (Mondo et al, 2010).…”