**Joana Montezano Marques 1, Jackeline Rossetti Mateus 2, Thais Freitas da Silva 2, Camila Rattes de Almeida Couto 2, Arie Fitzgerald Blank <sup>3</sup> and Lucy Seldin 2,\***


Received: 23 October 2019; Accepted: 28 November 2019; Published: 3 December 2019

**Abstract:** We hypothesize that sweet potato genotypes can influence the bacterial communities related to phosphate mineralization and nitrogen fixation in the rhizosphere. Tuberous roots of field-grown sweet potato from genotypes IPB-149, IPB-052, and IPB-137 were sampled three and six months after planting. The total community DNA was extracted from the rhizosphere and analyzed by Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) and quantitative real-time PCR (qPCR), based on the alkaline phosphatase coding gene (*alp* gene) and on the nitrogenase coding gene (*nifH* gene). The cluster analysis based on DGGE showed that plant age slightly influenced the bacterial community related to phosphate mineralization in the rhizosphere of IPB-137, although it did not affect the bacterial community related to nitrogen fixation. The statistical analysis of DGGE fingerprints (Permutation test, *p* ≤ 0.05) showed that nitrogen-fixing bacterial community of IPB-052 statistically differed from genotypes IPB-149 and IPB-137 after six months of planting. The bacterial community of IPB-137 rhizosphere analyzed by *alp* gene also showed significant differences when compared to IPB-149 in both sampling times (*p* ≤ 0.05). In addition, *alp* gene copy numbers significantly increased in abundance in the rhizosphere of IPB-137 after six months of planting. Therefore, plant genotype should be considered in the biofertilization of sweet potato.

**Keywords:** sweet potato; bacterial communities; nitrogen fixation; phosphate mineralization; plant genotype
