Abstract
Soybean plants establish symbiotic relationships with soil rhizobia which form nodules on the plant roots. Nodule formation starts when the plant roots exudate isoflavonoids that induce nod gene expression of a specific Bradyrhizobium. We examined the specific indigenous rhizobia that form nodules with the soybean cultivars Peking and Tamahomare in different soils. PCR-RFLP analysis targeted to the 16S-23S rRNA gene internal transcribed spacer (ITS) region of the bacterial type of each root nodule showed that Bradyrhizobium japonicum (USDA110-type) and Bradyrhizobium elkanii (USDA94-type) had high compatibility with the Tamahomare and Peking cultivars, respectively. We grew 93 recombinant inbred lines (RIL) of soybean seeds derived from the cross between Peking and Tamahomare in three different field soils and identified the indigenous rhizobia nodulating each line using the same PCR-RFLP analysis. QTL analysis identified one QTL region in chromosome-18 with a highly significant additive effect that controls compatibility with both B. japonicum USDA110 and B. elkanii USDA94. We also measured the amount of daidzein and genistein secretion from roots of the 93 RILs by HPLC analysis. QTL analysis showed one QTL region in chromosome-18 controlling genistein secretion from roots and coinciding with that regulating compatibility of specific indigenous rhizobia with soybean. The amount of genistein may be a major regulatory factor in soybean-rhizobium compatibility.
Highlights
Soybean (Glycine max) is one of the most important crops in the world
Peking was highly compatible with USDA94-type while Tamahomare was highly compatible with USDA110-type (Table 1)
Of the 24 QTLs that we identified, eight QTLs coincided at the same position on Chr.18 near Sat_064 in all three experimental conditions
Summary
Soybean (Glycine max) is one of the most important crops in the world. It is highly suitable for human and animal diets and is the source of 30% of the world’s oil derived from processed crops. From 2010 to 2014, its planted area increased from 111 to 124 million ha and its production quantity increased from 280 to 320 million tons. The current largest producers are the USA (34%), Brazil (27%) and Argentina (17%) (FAO, 2017). The use of legumes in biofuel production will further increase the economic impact of soybean[1,2]. Its rising economic importance has led to increased efforts over the past several years to improve soybean productivity. Enhancing the efficiency of biological nitrogen fixation by improving legume-rhizobium
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