Arbuscular mycorrhizal colonization and growth of wild and cultivated lettuce in response to nitrogen and phosphorus

Abstract

Lettuce (Lactuca sativa) is a crop with high water and nutrient demand. Its nearest wild relative, Lactuca serriola, is tolerant of low moisture and nutrient-poor conditions. Due to selection in different types of environments, the two taxa may differ in response to mycorrhizal colonization. Pot experiments were used to determine if mycorrhizal colonization, growth, root allocation, and P and N tissue concentrations differed between the two Lactuca taxa when inoculated with Glomus intraradices. In Experiment 1, two levels of P [0 (P0) or 0.25 (P1) mmol P kg−1] were added to a sand/soil medium with and without G. intraradices at low N supply (0.89 mmol N kg−1) for 4 weeks. In Experiment 2, two levels of N [1.7 (N1) or 5.0 (N2) mmol N kg−1] were supplied to the same soils containing 0.25 (P1) mmol P kg−1, and plants were grown for 6 weeks. In Experiment 1, the two taxa had similar mycorrhizal colonization, and shoot and root dry weight. In Experiment 2, cultivated lettuce had slightly higher colonization and growth than wild lettuce. Mycorrhizal plants at N1 were small with high root allocation and colonization. Colonization decreased and growth increased at N2. In these experiments, no major difference in mycorrhizal response occurred between L. sativa and L. serriola. Use of wild lettuce for breeding improved cultivars of lettuce, will at least maintain any ability, to benefit from mycorrhizas, especially in farming systems with low P inputs.