Incompatible Nodulation of <i>Bradyrhizobium elkanii</i> Strains BLY3-8 and BLY6-1 with <i>Rj</i>3 Gene-Harboring Soybean Cultivars

Abstract

Bradyrhizobia are known symbiotic partners of soybean. However, some soybean cultivars restrict nodulation by some Bradyrhizobium bacterial strains. These restrictions are related to compatibility between the Rj genes of soybean cultivars and nodulation types of inoculated bacteria. The objective of this study was to determine nodulation incompatibility of Type B strains with Rj 3 soybean cultivars. Newly isolated B. elkanii strains BLY3-8 and BLY6-1 from Myanmar and specific strain Bradyrhizobium elkanii USDA33, which are incompatible with Rj 3 soybean cultivars, and B. japonicum USDA110 were used as inoculants to check compatibility or incompatibility with Rj 3 soybean cultivars. Nitrogen fixation activity was measured by the acetylene reduction method. Ethylene concentration (reduction of acetylene) was determined by flame ionization gas chromatography. According to the inoculation test results, USDA110 was compatible with all soybean cultivars because it formed effective nodules ( Figure S1 in Appendix) and possessed nitrogenase activity.Similarly, B. elkanii strains BLY3-8, BLY6-1, and USDA33 were highly compatible with non-Rj and Rj 4 -gene harboring soybean cultivars because they had the ability to form functional nodules and possessed nitrogenase activity.Inversely, BLY3-8, BLY6-1, and USDA33 were incompatible with Rj 3 soybean cultivars because they produced ineffective nodules. Consequently, the ratio of ineffective nodule number to total nodule number was >0.5. Therefore, nodule formation by the newly isolated B. elkanii strains BLY3-8 and BLY6-1 was restricted by the Rj 3 soybean cultivars potentially making them useful as specific strains to detect the Rj 3 gene in soybean cultivars.

Mutants Disrupted in the Type III Secretion System of <i>Bradyrhizobium elkanii</i> BLY3-8 Overcame Nodulation Restriction by <i>Rj</i>₃-genotype Soybean

“…2b), but a few ineffective nodules ( Fig. 2a), which is consistent with our previous findings (Htwe and Yamakawa, 2017). In contrast, the mutants MttsI and MrhcJ both overcame this nodulation restriction (Fig.…”

“…This is cultivar-specific nodulation restriction because the nodulation of B. elkanii BLY3-8 was not restricted by non-Rj 3 genotype soybean cultivars (e.g. Yezin-3, Yezin-6, Bragg, and Fukuyutaka) (Htwe and Yamakawa, 2017). A Rj 3 gene has not yet been identified in soybean (Hayashi et al, 2012).…”

“…We previously reported that B. elkanii BLY3-8 nodulation was restricted by Rj 3 -genotype soybean (cultivar D-51) (Htwe and Yamakawa, 2017). This is cultivar-specific nodulation restriction because the nodulation of B. elkanii BLY3-8 was not restricted by non-Rj 3 genotype soybean cultivars (e.g.…”

Identification of a gene encoding a sugar transporter as a potential target of a novel LysR‐type transcriptional regulator rluD from rhizobium required for symbiotic nodulation in soybean (Glycine max Merr.)

“…In early defence responses to nodulation, the signal transduction factors DMI1 , DMI2 and DMI3 were mined via QTLs in Medicago truncatula (Ané et al., ). The QTLs associated with nodulation have been described in soybean, which were identified as Rfg1 , Rj1 , Rj2 , Rj3 , Rj4 , Rj5 , Rj6 , Rj7 and Rj8 (Caldwell, ; Harper & Nickell, ; Htwe & Yamakawa, ; Vest, ; Vuong, Nickell, & Harper, ). To date, Rfg1 , Rj2 and Rj4 have been cloned and have been shown to control restricted nodulation in specific strains of soybeans (Tang, Yang, Liu, & Zhu, ; Tsurumaru et al., ; Yang et al., ).…”