Priming of plant defences by PGPR against fungal and bacterial plant foliar pathogens

Root inoculation with PGPR has been reported to reduce the severity of foliar diseases by priming the plant's innate immune system and indirectly, by promoting plant growth. There may also be unaccounted-for effects on yield by suppression of deleterious soil microorganisms and pests. Here, current knowledge of the effects of PGPR inoculants on the innate immune system is discussed. The commercial exploitation of plant priming by PGPR is considered with regard to the interaction between PGPR soil inoculants, the eroded genome of domesticated crop varieties, modes of microbial pathogenesis and environmental factors including soil antagonism. The conclusion is that PGPR priming, as with other applications of inoculants, may not have the commercial potential of broad-spectrum disease control across a range of crops, soil types and environments but may have potential in niche applications, especially with weakly domesticated crop in growth substrates lacking antagonists.