Ethylene and Chitosan Affected the Seed Yield Components of Onion Depending More on the Dose than Timing of Application

(1) Background: the production of onion seeds is limited by competition between and vegetative organs scape lodging. However, information on effects plant growth regulation seed scarce. Aim present study was to evaluate yield components germination ability as affected timing dose an ethylene application, a regulator able modulate shoot–flower competition; chitosan, elicitor defense mechanisms increase its tolerance various stresses. (2) Methods: Onion treated with at recommended (100% RD) commercial product, 150% RD in two contrasting phenological phases or untreated (control), ‘with’ ‘without’ trend were measured. (3) Results: 100% early phase did not influence increased thousand weight (TSW) 3.2%. The application decreased 33.5%, this occurred irrespective application. Such decreases due reduction number per flower. chitosan affect crop slightly increased, but significantly, TSW under RD. Germination fresh 92%, 17 months aging reduced it 14%, no treatments pattern. (4) Conclusions: mostly yield, whereas high doses yields result may have been delay flowering onset that relatively dry month. Chitosan sustained when potential RD, such likely physical protection from transpiration since synthetic fungicides applied allow pathogens infections. These results implications for establishing regulators elicitors onions sustain quality.