Growth promotion and protection against root rot of sugar beet (Beta vulgaris L.) by two rock phosphate and potassium solubilizing Streptomyces spp. under greenhouse conditions

Purpose Phosphorus (P) and potassium (K) shortages inhibit crop production, and soil borne plant diseases such as root rot by Fusarium spp. can cause extensive damage to crops. Streptomyces bellus (SB) and S. saprophyticus (SS) solubilize P and K and inhibit sugar beet ( Beta vulgaris L.) associated Fusarium strains in laboratory conditions. Methods To address their performance in vivo, their effects on sugar beet growth and root rot development was tested. Results The tested strains showed a significant beneficial effect on growth and yield parameters of sugar beet when mixed in the soil with insoluble natural rock phosphate (RP) and/or K mineral orthoclase (OT). Compared to the non-inoculated treatment, the highest shoot and root dry biomass were recorded with RP+OT+SB. Highest P and K levels in leaves were with OT+SB and RP+SB, and the treatment RP+OT+SB increased both soil P and K. Interestingly, these SS and SB strains exhibited high protection effects of 100% and 75%, respectively, when the soil was infested by F. equiseti and F. fujikuroi , causal agents of root rot disease of sugar beet in Beni Mellal region. Conclusions These results can be exploited to mitigate the detrimental impacts of nutrient limitation for and disease susceptibility of sugar beet.