Advances in Host Plant and Rhizobium Genomics to Enhance Symbiotic Nitrogen Fixation in Grain Legumes

Abstract

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Response of determinate and indeterminate soybean cultivars to basal and topdressing N fertilization compared to sole inoculation with Bradyrhizobium

“…In the USA, for example, heavy applications of N fertilizer may have limited nitrogen fixation capacity of soybean (Chang et al, 2015). As yield potential is a result of several genes, neglecting N 2 -fixation-related genes may result in cultivars that are less responsive to rhizobial inoculation, and more dependent on N fertilizers (Graham and Vance, 2000;Dwivedi et al, 2015). Indeed, Kiers et al (2007), by performing experiments with old and new soybean cultivars, have found that soybean breeding in the USA has contributed to loosen efficient rhizobial symbioses in the field.…”

“…van Kessel and Hartley (2000), when analyzing sets of experiments before and after increased use of N fertilizer in soybean reached similar conclusion. In Africa, where suitable rhizobial inoculants are scarce for socio-economic reasons, soybean breeding has promoted the release of promiscuous soybean cultivars, meaning that they are less responsive to inoculation with soybean elite specific strains, but able to nodulate with indigenous bradyrhizobia (Graham and Vance, 2000;Dwivedi et al, 2015). In the places mentioned above and perhaps in other places (e.g.…”

“…Santa Rosa producing about 1200 kg ha −1 in 1960 to Conquista producing about 4000 kg ha −1 in 2010; , and also that the selection of Bradyrhizobium inoculant strains might not catch up soybean breeding (e.g. Dwivedi et al, 2015). However, as N 2 fixation and photosynthetic rates are reciprocally up-regulated (Kaschuk et al, 2010a(Kaschuk et al, , 2012Dwivedi et al, 2015), it remains unsolved whether this expected photosynthetic compensation in plants relying solely on N 2 fixation would play a different role in cultivars of distinct seed filling periods or growth types (Fujita et al, 1988;Argaw, 2014).…”

“…Dwivedi et al, 2015). However, as N 2 fixation and photosynthetic rates are reciprocally up-regulated (Kaschuk et al, 2010a(Kaschuk et al, , 2012Dwivedi et al, 2015), it remains unsolved whether this expected photosynthetic compensation in plants relying solely on N 2 fixation would play a different role in cultivars of distinct seed filling periods or growth types (Fujita et al, 1988;Argaw, 2014). For soybean, it has been demonstrated that cultivars with longer seed filling periods have higher yield potential than cultivars with shorter periods, particularly in years of stressing environmental conditions (e.g.…”

“…Earlier observations suggested that indeterminate cultivars are potentially more resilient to environmental stresses after the onset of reproductive stage than determinate cultivars, as indeterminate cultivars are able to recover from occasional growth restrictions if environmental conditions allow (Fehr et al, 1977). Indeterminate cultivars would also be more benefited from symbiotic N 2 fixation because N 2 fixation and photosynthesis are synchronized (Kaschuk et al, 2010a;Kaschuk et al, 2012;Dwivedi et al, 2015). Indeed, late maturing cultivars can benefit from rhizobial inoculation, even in the presence of soil nitrate (Argaw, 2014).…”