Germinative metabolism and seedling growth of cowpea (Vigna unguiculata) under salt and osmotic stress

Abstract

Cowpea (Vigna unguiculata) plays a strategic role in arid and semi-arid regions being used in both human food and animal supplementation. Although it is described as moderately tolerant plant to soil salinity, little is known about the salinity tolerance amongst different cultivars and phenological phases. In this study, we investigated the response of seed germination and seedling establishment of V. unguiculata cv. BRS Imponente under conditions of both salt (NaCl) and osmotic stress (Polyethylene glycol 6000; PEG). Although such conditions lead to an accumulation of hydrogen peroxide (H2O2), oxidative damage was observed only in seeds exposed to PEG. The maintenance of H2O2 concentrations in seeds exposed to NaCl, as well as the increase in respiratory activity, were the main mechanisms of tolerance identified in seeds exposed to NaCl. However, although germination was not affected, NaCl concentrations ≥75 mM were phytotoxic, reducing seedling growth. The osmotic component of salinity (PEG) reduced germination (Ѱo < -0.123 MPa) and seedling establishment (all osmotic potentials) showing the cultivar sensitive to osmotic stress in the early stages of development. After germination, the BRS Imponente cultivar presented reduced tolerance to salt stress, which limits its performance in soils with high salinity (≥ 75 mM of NaCl).