Abstract

OSUNA-AVILA, Pedro  and  BARROW, Jerry. In vitro System to Determine the Role of Aspergillus ustus on Daucus carota Roots. Terra Latinoam [online]. 2009, vol.27, n.4, pp.363-372. ISSN 2395-8030.

Fourwing saltbush (Atriplex canescens) (Pursh) Nutt, is naturally colonized by a dark septate fungus indentified as Aspergillus ustus. An in vitro culture system was developed to demonstrate a mutualism 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 (WP), with plant available P (PAP) (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 best to TCP, which is greater than PAP, which was greater than RP and did not grow WP. A dual culture system was developed using divided Petri dishes to separate carbon in a root chamber and P in the fungal chamber 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, enhanced the number and length of branches in D. carota roots within the carbon supplemented root chamber. When PAP 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.

Keywords : fourwing saltbush; mutualistic association; phosphorus; carrot.