| Fourwing saltbush (Atriplex canescens) (Pursh) Nutt, is naturally colonized by a dark septate fungus identified as Aspergillus ustus. An in vitro culture system was developed to demonstrate a mutualistic association between A. ustus and fungus free-Ri T-DNA transformed Daucus carota roots. The individual response of the fungus and the roots and the combined response of dual cultured fungus and roots were evaluated without phosphorus 0P, with plant available P (KH2PO4) and plant unavailable P as either rock phosphate (RP) or tricalcium phosphate (TCP). Preliminary experiments showed that D. carota roots only responded to P as KH2PO4 and were not able to utilize either RP or TCP. A. ustus, however responded the best to TCP, which is greater than P, which was greater than RP and did not grow without P (0P).; A dual culture system was developed using divided petri dishes to separate carbon in a root chamber and phosphorus in the fungal and a chemical barrier to restrict the fungus to the fungal chamber. The dual culture system demonstrated that A. ustus solubilized and transported P from both RP and TCP, resulting in enhanced the number and length of branches in D. carota roots within the carbon supplemented root chamber. When plant available P was added to the fungus chamber, branching occurred mainly in the chamber with the available P.; In addition to enhanced root growth and branching, it was also demonstrated that the fungus accessed carbon from the root. The dual culture system effectively demonstrated a classical mutualistic association between A. ustus and D. carota roots. |
