Can Additional Inoculations Increase Soybean Nodulation and Grain Yield

By L. Moretti, E. Lazarini, J. W. Bossolani, T. Parente, Sheila Caioni, R. Araujo, M. Hungria. 2018

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715 Soybean is one of the most important commodities in the portfolio of Brazilian export products, accounting for approximately 13% of all the country’s exportations (CONAB, 2016; Embrapa Soja, 2016). The crop is highly demanding on N, requiring around 80 kg of N to produce 1000 kg of grains (Hungria and Mendes, 2015). The utilization of chemical N fertilizers would cost around US$15 billion every year, making soybean cultivation unattractive under Brazilian conditions (Hungria and Mendes, 2015). The supply of N for soybean in Brazil relies exclusively on the inoculation with elite strains of N2–fixing bradyrhizobia (Hungria et al., 2006; Hungria and Mendes, 2015). Soybean growth based on biological nitrogen fixation (BNF) is also a reality in Brazilian neighboring countries, such as Argentina, Paraguay, and Bolivia (Hungria et al., 2006; Hungria and Mendes, 2015). In addition to economic advantages, BNF with soybean in South America contributes to reduce the release, into the atmosphere, of millions of tonnes of CO2 resulting from the production of chemical fertilizers (Sá et al., 2017) Most of the nodules present on the roots of legumes are formed by the inoculant applied to the seed before sowing (Bhuvaneswari et al., 1981; Calvert et al., 1984). Previous studies (Kosslak and Bohlool, 1984; Reid et al., 2011; Tanabata and Ohyama, 2014; Wang et al., 2014) have demonstrated that the host exerts autoregulation of nodulation (AON), controlling the number of nodules and causing the majority of them to be formed near the root crown. In soybean, AON has been shown to be activated as early as 4 d after inoculation, suppressing further nodulation (Kosslak and Bohlool, 1984). Initial nodule formation is critical, and only a set of fully functional nodules can supply the adequate amount of N to the crop. However, symbiosis aging (Van de Velde et al., 2006), and environmental stresses (Matamoros et al., 1999; Puppo et al., 2005) may cause nodule senescence and cessation of BNF, generally coinciding with the stage of pod filling (Lawn and Brun, 1974; Bethlenfalvay and Phillips, 1977; Neves and Hungria, 1987; Barradas et al., 1989). Since AON has been mainly studied at early stages of plant growth, little is known if further boosts Can Additional Inoculations Increase Soybean Nodulation and Grain Yield?

Subfields: Plant Science

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