Abstract
Changes in the structure of the rhizosphere microbiome are influenced by many factors. In the current investigation, the microbial community composition in the rhizosphere of four potato cultivars was monitored using the soil dilution plating technique on specific media. Tested cultivars were grown for two consecutive cropping seasons. Initial soil samples were collected before planting to assess the initial microbial soil species pool. During the growing period, rhizosphere samples were collected at three timing points. For both cropping seasons, the pH and EC of the rhizosphere varied upon sampling periods but not between cultivars. Bacterial and fungal populations at both cropping seasons and that of actinomycetes at the late-season crop were significantly increased by 35-55%, 14-18% and 17-42%, respectively, in the rhizosphere of all grown potato cultivars as compared to the initial soil stage. The relative abundance of Pseudomonas spp., actinomycetes, Aspergillus spp., and Fusarium spp. populations for all potato cultivars combined were 17.4, 26-64, 51-59 and 10-14% higher at the late-season than at the extra-early cropping season, respectively. For both cropping seasons and all sampled soils combined, the highest abundancies of fungal and actinomycetes communities were recorded at plant senescence and 15 days post-harvest. The total culturable bacteria were more relevant at plant emergence and 15 days post-harvest for the late-season crop and at plant senescence for the extra-early crop. The total culturable bacteria were more abundant in the rhizosphere of cvs. Spunta, Elata and El-Mundo at the late-season crop and that of cvs. Spunta and El-Mundo for the extra-early trial. The highest Pseudomonas spp. populations were associated to cvs. Cerata, Elata, and El-Mundo for the late-season crop and to Spunta, Elata and El-Mundo for the extra-early crop. The highest fungi counts were noted in the rhizosphere of cv. El-Mundo at the late-season crop and in Spunta for the extra-early trial.