Symbiotic efficiency and infectivity of an autochthonous arbuscular mycorrhizal Glomus sp from saline soils and Glomus deserticola under salinity

The purpose of this study was to compare the effect of salinity on the symb iotic efficiencies and mycelial infectivity of two arbuscular mycorrhizal f ungi (AMF), one isolated from saline soils (Glomus sp.) and the other (Glom us deserticola) from nonsaline soils (belonging to the Estacion Experimenta l del Zaidin collection). Lettuce plants inoculated with either of these tw o fungi or maintained as uninoculated controls were grown in soil with thre e salt concentrations (0.25, 0.50 or 0.75 g NaCl kg(-1) dry soil). Both AMF protected host plants against salinity. However, when the results of shoot dry weight and nutrient contents were expressed relative to the total leng th of mycorrhiza formed, it was found that both AMF differed in their symbi otic efficiencies. These differences were more evident at the two highest s alt levels. Glomus sp.-colonized plants grew less and accumulated less N an d P, whereas they formed a higher amount of mycorrhiza. The mechanism by wh ich Glomus sp. protected plants from the detrimental effects of salt was ba sed on the stimulation of root development, while the effects of G. deserti cola were based on improved plant nutrition. The increase in salinity of so il decreased the hyphal growth and/or viability of Glomus sp. to a higher e xtent than those of G. deserticola since the mycelial network generated by G. deserticola was more infective than that of Glomus sp.