Grafting and microbial inoculation are promising strategies for enhancing organic pepper production, mainly to manage soil-borne diseases and optimize nutrient utilization. This study conducted in a high tunnel environment evaluated the performance of two Phytophthora-resistant rootstocks, CM-334 and YC-207, grafted with a common scion (Mama Mia Giallo), and the application of a mycorrhizal and bacterial mix consortium under two organic fertilization rates (100:40:60 kg NPK ha-1 as optimal rate and reduced to half as low rate). Our hypothesis explored whether the synergy of microbial inoculation and grafting could compensate for the reduced growth of the low rate by improving nutrient use efficiency. Chlorophyll content was higher (~10 %) in inoculated plants compared to non-inoculated plants under low fertilization. At the peak bloom stage, leaf net photosynthesis was similar at both fertilization rates, while inoculated plants had an increase in plant water use efficiency (~12 %). Microbial inoculation and low fertilization induced early flowering compared to non-inoculated plants grown at optimal fertilization rate. Under low fertilization, inoculated YC-grafted plants exhibited higher electron transport rate, stomatal conductance, and transpiration rate than other inoculated plants. CM-grafted plants responded negatively to inoculation at optimal fertilization, as shown by the lower net photosynthesis (~16 %) and stomatal conductance (~44 %) compared to non-inoculated plants. The correlation of these physiological traits with fruit yield, quality, and soil health will provide further understanding applicable to rootstock selection and microbial inoculation to optimize pepper production, particularly in resource-limited conditions.
