The interaction between foliar GA3 application and arbuscular mycorrhizal fungi inoculation improves growth in salinized tomato (Solanum lycopersicum L.) plants by modifying the hormonal balance

The agriculture industry is frequently affected by various abiotic stresses limiting plant productivity. To decrease the negative effect of salinity and improve growth performance, some strategies have been used, such as exogenous application of plant growth regulators (i.e. gibberellic acid, GA3), or arbuscular mycorrhizal fungi (AMF) inoculation. To gain insights about the cross-talk effect of exogenous GA3 application and AMF inoculation on growth under salinity conditions, tomato plants (Solanum lycopersicum, cv. TT-115) were inoculated or not with the AMF Rhizophagus irregularis and exposed to different treatments during two weeks: 0 M GA3 + 0 mM NaCl, 10−6 M GA3 + 0 mM NaCl, 0 M GA3 + 100 mM NaCl and 10−6 M GA3 + 100 mM NaCl. Results have revealed that AMF inoculation or GA3 application alone, but especially their interaction, resulted in growth improvement under salinity conditions. The growth improvement observed in AMF-inoculated tomato plants under salinity conditions was mainly associated to ionic factors (higher K concentration and K/Na ratio) while the alleviating effect of GA3 application and its interaction with AMF appear to be due to changes in the hormonal balance. Foliar GA3 application was found to increase the active gibberellins (GAs), resulting in a positive correlation between GA3 and the growth-related parameters. Furthermore, cytokinins, indoleacetic acid and abscisic acid concentrations increased in AMF inoculated or GA3 treated plants but, notably, in AMF plants treated with GA3, which showed improved growth under salinity conditions. This suggests that there is an interactive positive effect between GAs and AMF which alleviates growth impairment under salinity conditions by modifying the hormonal balance of the plant.