The bumps that appear along the stems of your tomato leaves are root buds or nodes. These root buds normally form when a vine falls to the ground and stays moist. It recognizes the right conditions to grow roots.
When you get consecutive days of rain and 80% or higher humidity for several days... your tomato gets tricked into thinking it is contacting the moist ground. It forms these bumps up and down the stem anticipating the need to grow roots. It is not a disease and not a reason to worry. It just look bizarre and freaky.
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