Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2016
Publication Date: 2/22/2017
Citation: Scagel, C.F., Bryla, D.R., Lee, J. 2017. Salt exclusion and mycorrhizal symbiosis increase tolerance to NaCl and CaCl2 salinity in ‘Siam Queen’ basil. HortScience. 52(2):278-287. doi: 10.21273/HORTSCI11256-16.
Interpretive Summary: A study was conducted to evaluate the effects of salinity on growth and nutrient uptake in basil ('Siam Queen'). Plants were fertilized with a complete nutrient solution and exposed to no, low, or moderate levels of salinity from NaCl or CaCl2. Plants in the control and moderate salinity treatments were also inoculated or not with the arbuscular mycorrhizal fungus (AMF), to determine whether AMF mitigate the effects of salinity stress. Results indicate that basil may be more sensitive to salinity from NaCl than CaCl2. Physiological responses to salinity were detectable before changes in plant biomass. Both salts reduced uptake of specific nutrients and salinity decreased efficiency of nutrient use. Plants also became deficient in these nutrients as duration of exposure to salinity increased. Inoculation with AMF improved nutrient uptake during early exposure to salt, but by the end of the experiment differences in nutrient content between non-inoculated and inoculated plants were primarily a result of differences in plant size. Our results indicate that tolerance of basil to salinity varies with duration of exposure, salinity level in the root environment, and salt type. While short-term exposure to salinity with an electrical conductivity of 4 to 8 dS/m may not alter dw of basil, the effects of salinity on plant physiology may influence crop quality even when productivity is not significantly impacted. Differences in basil tolerance to NaCl and CaCl2 indicate plants may have different mechanisms for dealing with salinity and sensitivity are not solely a function of EC. This highlights the importance of understanding the source of salinity in irrigation waters and soil for predicting damage.
Technical Abstract: A study was conducted to evaluate the effects of salinity on growth and nutrient uptake in basil (Ocimum basilicum L.). Plants were fertilized with a complete nutrient solution and exposed to no, low, or moderate levels of salinity from NaCl or CaCl2. Plants in the control and moderate salinity treatments were also inoculated or not with the arbuscular mycorrhizal fungus (AMF), Glomus intraradices (syn. Rhizophagus intraradices), to determine whether AMF mitigate the effects of salinity stress. Electrical conductivity of leachate in salinity treatments reached levels = 8 dS/m but had no effect on plant growth (dry weight; DW) within the first 41 d of treatment. By 75 d, exposure to low and moderate levels of salts decreased DW by 20% to 38%. Reductions in DW were similar between plants exposed to the same concentration of each salt and was salinity had a greater effect on root DW than shoot DW. Both NaCl and CaCl2 reduced stomatal conductance within 25 d, but hastened flowering by 2–3 d, and nearly doubled the DW of flowers at 75 d. NaCl increased uptake of Na and reduced uptake of Ca, whereas CaCl2 increased uptake of Ca and reduced uptake of Mg and Mn. Both salts also increased relative uptake of N, Cu, and Zn, and reduced relative uptake of S and Fe. In general, Na was concentrated in the roots and excluded from the shoots whether or not the plants were treated with NaCl, while Cl was concentrated primarily in the leaves when plants were treated with NaCl or CaCl2. Both salts reduced root colonization by AMF. However, in the presence of the salts, AMF increased stomatal conductance by 10% with NaCl and 22% with CaCl2, and increased total shoot DW by 22% and 43%, respectively. Other than Ca and Cl, AMF did not enhance nutrient uptake under NaCl or CaCl2 salinity. Overall, ‘Siam Queen’ basil was moderately tolerant to salinity, due at least in part to exclusion of Na from the shoots, and inoculation with AMF increased tolerance to both NaCl and CaCl2 salinity.