Cajanus cajan L. Millsp. (pigeonpea, guandul) is a pulse used in human feeding in several countries of Africa, Asia and South America (Odeny, 2007, Saxena et al., 2010, Beekham et al., 2010, Araujo et al., 2015) and it provides dietary proteins to humans at relevant rates in developing regions located at tropical and subtropical areas (Khoury et al., 2015). Moreover the ability of C. cajan to fix atmospheric nitrogen in symbiosis with rhizobia and its resistence to dought makes this legume resilient to the climatic change assuring the survival of farmers in arid and semiarid regions of developing countries (Jorrin et al., 2021).

C. cajan establishes symbiosis with rhizobia in its primary and secondary distribution centers of Asia and Africa, from where this legume probably arrived at American countries (van der Maesen, 1990, Odeny, 2007, Kassa et al., 2012). The studies about this symbiosis showed that C. cajan is nodulated by fast and/or slow growing rhizobia in Asian countries such as India (Dubey et al., 2010, Arora et al., 2018, Jain et al., 2020, Jorrin et al., 2021), in African countries such as Ethiopia (Degefu et al., 2018), Côte d’Ivoire (Fossou et al., 2016 and Fossou et al., 2020) and South Africa (Bopape et al., 2023) and in American countries such as Brazil (Costa et al., 2014), the Caribbean Island Trinidad Tobago (Ramsubhag et al., 2002) and Dominican Republic (Araujo et al., 2015; Araujo et al., 2017 and Araujo et al., 2020). The slow growing rhizobia nodulating C. cajan are closely related to different Bradyrhizobium species such as B. yuanmingense (Araujo et al., 2015, Jorrin et al., 2021) and Bradyrhizobium pachyrhizi (Araujo et al., 2020) and some of them constituted new species named Bradyrhizobium cajani and Bradyrhizobium ivorense being isolated in Dominican Republic and Côte d’Ivoire, respectively (Araujo et al., 2017, Fossou et al., 2020).

Although in the most recent studies the identification of Bradyrhizobium strains nodulating C. cajan has been already based on the housekeeping gene analysis, in the oldest ones it was only based on the analysis of the 16S rRNA gene analysis, which is not enough to differentiate among several Bradyrhizobium species, being necessary the use of other methodologies for the identification at species level. Within them, MALDI-TOF MS has been proposed as a reliable tool for Bradyrhizobium species differentiation and it has been used to analyse C. cajan isolates in Africa (Fossou et al., 2016). Nevertheless, the analyses of protein-coding genes and complete genomes are necessary to place the isolates within several Bradyrhizobium species and particularly to differentiate subspecies (Bromfield et al., 2022).

The definition of symbiovars within the genus Bradyrhizobium is performed through the analysis of the nodC gene and it has been proposed that the Dominican strains of B. cajani belong to the symbiovar cajani together several type strains nodulating different legumes worldwide (Klepa et al., 2022). Nevertheless, the identification at symbiovar level lacks in most of studies carried out to date on the Bradyrhizobium microsymbionts of C. cajan although it has been recently shown that they belong to nodC gene groups which correspond to unnamed symbiovars (Jorrin et al., 2021).

Therefore, the aims of this study were to identify at species and symbiovar levels several Bradyrhizobium strains isolated in this and in previous studies from C. cajan nodules in several Dominican Republic locations using MALDI-TOF MS, phylogenetic analyses and genomic comparisons, which allowed the definition of two new symbiovars within the genus Bradyrhizobium and a novel symbiovar within the species B. pachyrhizi.