TITLE:
Incompatible Nodulation of Bradyrhizobium elkanii Strains BLY3-8 and BLY6-1 with Rj3 Gene-Harboring Soybean Cultivars
AUTHORS:
Aung Zaw Htwe, Takeo Yamakawa
KEYWORDS:
Bradyrhizobium elkanii, Nodulation, Incompatibility, Rj3, Soybean
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.8 No.2,
January
20,
2017
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 Rj3 soybean cultivars. Newly
isolated B. elkanii strains BLY3-8 and BLY6-1 from Myanmar and specific strain Bradyrhizobium elkanii USDA33, which
are incompatible with Rj3 soybean cultivars, and B. japonicum USDA110 were used as
inoculants to check compatibility or incompatibility with Rj3 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 Rj4-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 Rj3 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 Rj3 soybean cultivars potentially making them useful as specific strains to detect
the Rj3 gene in soybean cultivars.