*2.1. Plant Genotypes, Experimental Field Design and Conditions*

The sweet potato genotypes IPB-149, IPB-137, and IPB-052 used in the present study are from the Active Germplasm Bank of the Federal University of Sergipe (UFS). These genotypes were previously described by Marques, et al. [12,25]. In brief, the IPB-149 genotype, the most commercialized genotype in the northeast of Brazil, presents a white surface color in the tuberous roots, a high starch content, and a major resistance to insect attack. The IPB-052 genotype, commercially known as cultivar Brazlândia Rosada, shows similar characteristics to the IPB-149 genotype. In contrast, the IPB-137 genotype, from the breeding program of the Federal University of Lavras, Brazil and denoted as clone 2007HSF028-08, presents different characteristics, including a pink color on its tuberous root surface, a lower starch content, and a low resistance to insect attack. It has longer branches and a shorter length between nodes, and the use of its aerial part for animal feed purposes has been suggested. Other morpho-agronomic traits, including the dry mass of aboveground part and the total productivity of the roots, were presented in Alves, et al. [26].

In 2011, a field experiment with sweet potato plants was performed in the Research Farm "Campus Rural da UFS". The experimental farm is located in the 'São Cristóvão' municipality (10◦55'27" S/ 37◦12'01" W), Sergipe State, northeast of Brazil. The experimental farm soil characteristics were: pH (5.4), Ca2<sup>+</sup> (0.82 cmolc/dm3), Mg2<sup>+</sup> (0.43 cmolc/dm3), Al3<sup>+</sup> (0.65 cmolc/dm3), Na (3.5 mg/dm3), K (21.1 mg/dm3), P (7.0 mg/dm3), 73.82% sand, 20.72% silt, 5.46% clay, and 0.86% Corg [14–16]. The experimental field design was described in Marques, et al. [12,25]. The genotypes were planted in three replicate rows (randomized block design) in the experimental plot with spaces of 0.8 m between the rows and 0.35 m between plants. All of the cultural management processes used were those described in Alves, et al. [26]. After three (t1, \_3M) and six (t2, \_6M) months, sweet potato plants with similar plant growth developmental stages were randomly harvested from the research farm soil. A total of five plants/replicates of the three different sweet potato genotypes were collected in each sampling time. Their roots were shaken to remove the loosely attached soil, and the soil still adhering to the tuberous roots was aseptically brushed off from all tuberous roots of every plant. This soil was considered to be rhizosphere soil. The rhizosphere samples were kept at −20 ◦C before total community DNA (TC-DNA) extraction.
