Biocontrol potential index of pseudomonads, instead of their direct-growth promotion traits, is a predictor of seed inoculation effect on crop productivity under field conditions

Abstract

Agricultural bioproducts became interesting alternatives for sustainable agricultural practices, because they aim to reduce the use of agrochemicals without losing crop yields. As Pseudomonas genus has been largely studied for the high number of plant probiotic species it contains, in this work we evaluated the field performance of 10 genetically diverse native Pseudomonas that have been isolated from productive plots of the Argentine Pampas. Previously, they have been characterized in vitro, and we have developed several indexes to organize the isolates’ collection based on their potential to perform biocontrol of fungal pathogens (BPI), to promote plant growth by direct mechanisms (DGPI), or by integrated direct plus indirect mechanisms (PGPI). At three geographical sites, we tested the effect of single- and co-inoculations with a commercial bio-input based on the fungus Trichoderma harzianum Th2, in wheat and maize crops during 3 consecutive seasons. Most of single inoculations improved wheat and maize grain yields. For wheat, improvement seemed to be related with a higher plant emergence by the positive correlation between yield and plant number; whereas for maize increased yields would be rather associated with a better plant structure by the positive correlation between yield and the vegetation index NDVI. The co-inoculation of Th2 with different P. chlororaphis isolates also increased the grain yield of both grain crops, despite P. chlororaphis strains displayed fungal inhibition in dual culture in vitro tests. We found a positive and significant correlation between BPI and the yield percentage improvement of both crops, but a negative correlation with DGPI. Thus, this work shows the usefulness of the in vitro characterization of biocontrol-related traits and the estimation of a biocontrol potential index as a proxy for crop yield performance, but not of direct plant growth-promoting features.