Morphophysiological Responses of Wheat Cultivars in Competition With Diploid and Tetraploid Ryegrass

Wheat crop growth and development can be affected by weed infestation, especially ryegrass. Thus, the objective of this study was to evaluate the competitive ability of wheat cultivars with the diploid and tetraploid ryegrass biotypes. Greenhouse experiments were conducted in a completely randomized design with four replications. BRS Parrudo and TBIO Sinuelo wheat cultivars and the competitors ryegrass diploid and tetraploid were used. The population of each species was defined and then the replacement series experiments were carried out, containing the following proportions of wheat and ryegrass plants- 100-0, 75-25, 50-50, 25-75; and 0-100%, equivalent to 32-0; 24-8; 16-16; 8-24; and 0-32 plants per pot. Fifty days after species emergence, physiological traits, such as photosynthetic activity (A), stomatal conductance (gS), transpiration rate (E), internal concentration of mesophyll CO2 (Ci), water use efficiency (WUE), and carboxylation efficiency (CE), were evaluated, along with the morphological traits of leaf area (LA), stem diameter (SD), number of tillers (NT), and shoot dry mass (DM). Competitiveness analysis was performed by means of diagrams applied to substitutive experiments using relative competitiveness indices. The ryegrass, both diploid and tetraploid, had a negative effect on the variables related to A, WUE and also those associated with plant growth. The ryegrass negatively changed the LA, DM, SD, and NT of the cultivars BRS Parrudo and TBIO Sinuelo, which demonstrates competition between the cultivars of wheat and the weed ryegrass with mutual damage to the species involved in the community. Interspecific competition caused greater damage to species development when compared to intraspecific competition. Therefore, ryegrass control, even at low density, is recommended for wheat cultivation.