Phosphorus Concentration and Application Interval Influence Growth and Mycorrhizal Infection of Tomato and Onion Transplants

Abstract

Abstract Transplants of ‘Healani’ tomato ( Lycopersicon esculentum Mill.) and ‘Yellow Granex’ onion ( Allium cepa L.) inoculated with the vesicular-arbuscular mycorrhizal fungus (VAMF) Glomus aggregatum (Schenck and Smith emend. Koske) were grown in peat-vermiculite fertilized with solutions containing 4, 16, 64, or 256 mg P/liter, applied daily or every 4 or 8 days. Increasing the total amount of P available to the transplants by either increasing the P concentration or by decreasing the interval between applications increased plant total fresh weights (TFW) and shoot P concentrations, but decreased root VAMF infection. Inoculation reduced tomato TFW when P availability was high. Inoculation increased onion shoot P concentrations and TFW only when P availability was very low. Frequent applications of solutions low in P produced larger transplants with higher levels of VAMF infection than did similar total amounts of P supplied less frequently but at higher concentrations. Different combinations of P concentration and application intervals were required for the production of vigorous mycorrhizal tomato and onion transplants.