Morphophysiological and nitrogen metabolism responses of inoculated peanut cultivars with contrasting drought tolerance

Legumes grow in temperate and warm climates, being susceptible to unpredictable episodes of water deficit. This study aimed to evaluate (i) morphology and N-compound contents in roots and nodules, (ii) N and C contents in shoots and (iii) crop yield in two peanut cultivars with contrasting drought tolerance, inoculated with a reference N-fixing strain and challenged by water deficit conditions. For that, seeds of two peanut cultivars, Granoleico (sensitive, S) and EC-98 (tolerant, T) were inoculated with Bradyrhizobium sp. SEMIA6144 and 30 days after sowing, plants were separated into the experimental groups: control, drought stress and drought stress and subsequent rehydration. Although the results obtained on root anatomy and histology revealed differential responses between cultivars, they were not associated with tolerance traits in EC-98 (T). In contrast, nodules of EC-98 (T) showed invariable diameter and infection zone upon the exposition to drought stress and rehydration compared to nodules of Granoleico (S) plants exposed to the same treatments. EC-98 (T) showed invariable contents of C in shoots and of nitrates and ureides in roots and nodules of stressed and rehydrated plants, an increase in total amino acids only in nodules of stressed plants and a small reduction in N-content (compared with the sensitive cultivar). The status of these variables related to C- and N-metabolism could be associated with an efficient biological nitrogen fixation. Besides, EC-98 (T) yielded better both in a crop cycle with adequate water supply and in a dry year and the inoculation improved yield in both cultivars. Thus, the inoculation with N-fixing bacteria is recommended for EC-98 (T) in seasons with expected drought stress cycles in crops.