Initialism hypothesis: can gibberellin synthesis inhibitor increase the oat crop competitive ability?

The initialism hypothesis proposes that gibberellin is involved in the cascade of events triggering the impact of weeds very early on the crop plant development. The objectives of this research were to demonstrate differences in competitive ability of two oat (Avena sativa) cultivars and to test the hypothesis that gibberellin inhibitors may increase the oat crop grain yield under limited Italian ryegrass (Lolium multiflorum) weed density. Two substitutive series experiments were conducted in a greenhouse to evaluate two oat cultivars (URS Brava (tall height) and URS Taura (short height)) in coexistence with Italian ryegrass. Additionally, two field additive-type experiments were conducted using a factorial arrangement of treatments with oat cultivar URS Brava and other URS Taura. The first factor consisted of gibberellin inhibitor (trinexapac-ethyl at 0 and 37.5 mL ha(-1)) and the second factor was the density of Italian ryegrass (ranging from 0 to 21 plants m(-2)). The substitutive series experiment evidenced that the competitive ability of oat plants is superior to Italian ryegrass plants. The gibberellin-treated 'Brava' oat crop grain yield increased at small ryegrass densities. This is the first experimental evidence that the gibberellin inhibitor can avoid crop grain yield losses caused by weeds.