Morphoanatomical Characterization, Chromosome Count and Pollen Viability of Glyphosate-Susceptible and Glyphosate-Resistant Italian Ryegrass

ABSTRACT

Ryegrass is an annual weed found in all winter crops, orchards and vineyards of southern Brazil. The species is typically controlled by glyphosate. However, continued use of this product has selected resistant biotypes. Differences in herbicide susceptibility of ryegrass have been attributed to differences in morphology, anatomy and genetics of the plants. The objectives of this study was to conduct a morphological and anatomic characterization, adapt the methodology for cytological analysis of chromosomes and select dyes for pollen viability tests with glyphosatesusceptible and resistant ryegrass biotypes. The seeds of ryegrass biotypes with suspected resistance came from the town of São Valentim, RS (SVA 1 and SVA 4) and Passo Fundo, RS (PFU 5) and seeds of the susceptible biotype (SVA 2) were from São Valentim. The ryegrass biotypes with resistance to glyphosate cannot be distinguished from the susceptible biotype by morphological aspects and there are no anatomical differences in leaf and root that allow differential absorption of glyphosate among ryegrass biotypes. The methodology for the cytological analysis of ryegrass biotypes should be adapted for better clarity of chromosomes, allowing an increase in hydrolysis time and exposure to the antimitotic agent used in this study; moreover, other dyes can be tested. All dyes showed good performance in determining pollen viability against the assessed biotypes except for trypan blue, which had poorer results.

anatomy; chromosomes; Lolium multiflorum; morphology; Poaceae