Preinoculation of lettuce and onion with VA mycorrhizal fungi reduces deleterious effects of soil salinity

The hypothesis that inoculation of transplants with vesicular-arbuscular my corrhizal (VAM) fungi before planting into saline soils alleviates salt eff ects on growth and yield was tested on lettuce (Lactuca sativa L.) and onio n ( Allium cepa L.). A second hypothesis was that fungi isolated from salin e soil are more effective in counteracting salt effects than those from non saline soil. VAM fungi from high- and low-salt soils were trap-cultured, th eir propagules quantified and adjusted to a like number, and added to a pas teurized soil mix in which seedlings were grown for 3-4 weeks. Once the see dlings were colonized by VAM fungi, they were transplanted into salinized ( NaCl) soil. Preinoculated lettuce transplants grown for 11 weeks in the sal ine soils had greater shoot mass compared with nonVAM plants at all salt le vels [2 (control), 4, 8 and 12 dS m(-1)] tested. Leaves of VAM lettuce at t he highest salt level were significantly greener (more chlorophyll) than th ose of the nonVAM lettuce. NonVAM onions were stunted due to P deficiency i n the soil, but inoculation with VAM fungi alleviated P deficiency and sali nity effects; VAM onions were significantly larger at all salt levels than nonVAM onions. In a separate experiment, addition of P to salinized soil re duced the salt stress effect on nonVAM onions but to a lesser extent than b y VAM inoculation. VAM fungi from the saline soil were not more effective i n reducing growth inhibition by salt than those from the nonsaline site. Co lonization of roots and length of soil hyphae produced by the VAM fungi dec reased with increasing soil salt concentration. Results indicate that prein oculation of transplants with VAM fungi can help alleviate deleterious effe cts of saline soils on crop yield.