Abstract: The present invention relates to a method of predicting a plant seed trait, such as germination rate, vigour, aging and priming, by determining the presence of a target protein, i.e. diagnostic marker, in its active state in a protein sample derived from a plant seed or plant seed lot. Thereby, the quality of a plant seed or a plant seed lot can be predicted and/or diagnosed and seeds may be distinguished on basis of their characteristics and with respect to the traits described herein. Inter alia, seeds and seed lots having high germination quality may be distinguished from seeds and seed lots having low germination quality.