How do mother plants protect their seedlings?

In mammals, a mother’s transfer of passive immunity is pivotal for fitness and survival of newborns. Plants on the other hand have less developed immune system, but recent evidence showed that a portion of microbiome is transferred from mother plants to seed and seedlings. We hypothesize that, as in mammals, this is a form of passive immunity the mother plants use to safeguard their seedlings from deadly pathogens when their immunity remains underdeveloped.