Well known microbial plant growth promoters provoke plant growth suppression and increase chili pepper wilt caused by the root pathogen Phytophthora capsici

Abstract

AbstractMicrobial plant growth promoters (MPGP) are known to improve crop nutrition and root health. Here we examined the effects of individual and combined inoculation of chili pepper (variety Camino Real) with the known plant growth promoters Rhizophagus irregularis (isolate BEG87) and a commercial product of Azospirillum brasilense on chili pepper growth and biocontrol against the oomycete root pathogen Phytophthora capsici (isolate CH11). In a greenhouse pot experiment, unfertilized ten-week-old chili pepper plants with individual and combined inoculation of R. irregularis and A. brasilense were confronted with P. capsici, and four weeks later plants were harvested and scored for plant growth and disease severity. Surprisingly, both MPGP not only decreased plant growth, but also promoted root rot caused by P. capsici. This increased disease severity with P. capsici root rot in mycorrhizal chili pepper was further corroborated in a second greenhouse pot experiment with inert growth substrate and mineral fertilization. In conclusion, individual and combined inoculation with R. irregularis and A. brasilense may not only cause plant growth suppression in chili pepper plants, but also increase root rot caused by P. capsici.