Symbiotic rhizobia acquisition was mainly in the endosphere of
apical root
The invasion process of chickpea symbiotic rhizobia (CSR) was the result
of genotype-niche interactions, as we didn’t detect any factors
interacting with soil type on CSR abundance (Table 1). The spatial
distribution of CSR showed more in the tissue of apical root than in the
basal root (Fig. 3c). In the nodulation process, rhizobia in the soil
may first colonise the root epidermis at the elongation zone following
root-microbe signal communications or may directly bind to the zone of
root hairs, while the exact sequence of this process is unknown (Poole
et al., 2018). Our root apical zone included the root elongation zone,
that was enriched in symbiotic rhizobia and likely facilitated the
nodulation observed in the basal root sections.
In addition, CSR enrichment among chickpea genotypes was not related to
the flowering phenological trait, as one LF genotype, rather than the EF
genotype, harboured a greater proportion of CSR bacteria in the root
apex, and the enrichment was stable across soil types. Our results
indicated the striking effect of host genotype in controlling nodulation
processes, e.g. , producing different host-specific flavonoids and
root receptors that recognize symbiotic rhizobia (Sachs et al., 2018).
CSR was not related to the phenological trait, e.g. , early
maturity, although they might contribute to the amount of N fixed by
chickpea (Sadras et al., 2016).