acterial soft rots, commonly caused by Erwinia carotovora subsp. carotovora or Erwinia chrysanthemi, and slippery skin,
caused by Burkholderia gladioli subsp. allicola as well as sour skin, caused by Burkholderia cepacia of onion bulbs are among the most serious storage diseases of onion (Allium cepa L.) that lead to great loss in bulbs. In this study some biostimulants; chitosan, seaweed extract and humic acid were in vivo tested on onion plants, to determine their controlling potential against bacterial rot diseases. Application of biostimulants proved to be effective in reducing the bacterial rot in stored onion bulbs. All tested biostimulants increased photosynthetic pigments content in onion leaves and total phenols
content in onion bulbs, meanwhile they declined lipid peroxidation and the electrolyte leakage percentage in onion bulbs. As a summary, chitosan, seaweed extract and humic acid could be applied to improve plant growth and stimulate plant defense against diseases in concern.These materials are cheap, available, easy to apply, hazardless and
environmentally safe.