Climate change and global warming are increasing the frequency of drought incidents, which negatively impact crop production. Onion is one of the major vegetable crops produced in Texas, which requires a long growth period and prone to drought stress as it has shallow roots and needs frequent irrigation. Plant biostimulants may offer a potential solution to mitigate drought stress in onion production. This study investigated the effect of different biostimulants (no application as control, Kelpak, Spectrum DS, MycoApply, and Tribus Continuum) on onion seedling growth under well-watered and drought stressed (50-60% field capacity) conditions. Results showed that there was no significant interaction between biostimulants and drought stress on most of the parameters we collected. All biostimulants significantly increased shoot weight, leaf area, plant height, and root weight compared to the control. Notably, Spectrum DS, MycoApply, and Kelpak specifically enhanced root morphology by increasing root length, root area, and root volume compared to the control. But the application of biostimulants didn’t significantly affect average root diameter or the number of root tips. Drought stress significantly reduced the growth of onion seedlings across all measured parameters, except for the number of root tips, compared to the well-watered group. While drought stress caused a 36.9% decrease in shoot fresh weight, application of Kelpak, Spectrum DS, MycoApply, and Tribus Continuum increased shoot fresh weight by 29.8 to 34.9%, partly offsetting the growth reduction and alleviating the stress experienced by the seedlings. In conclusion, the application of the investigated biostimulants shows promise for enhancing drought tolerance in onion seedlings.
