Evaluation of Piriformospora indica, a Mycorrhizal Fungi, on Adventitious Root Formation of Slow-to-Root Annuals and Perennials

Biological solutions to common production problems are welcomed by growers and consumers as our society continues to raise its expectations for sustainability and reduced chemical inputs. A relatively new mycorrhizal fungi, Piriformospora indica, has shown promise to improve overall plant growth and disease resistance of various plant species. One of the reported plant responses of high importance to the floriculture industry is increased adventitious root formation of slow-to-root annuals and perennials.  All such vegetatively-propagated species require an application of rooting hormone to produce a successful crop; however, auxin application increases labor time as well as chemical usage. The objectives of this study were to determine: 1) if P. indica can work successfully as a root hormone substitute and 2) if the presence of P. indicastimulates auxin production in the basal stem tissue of cuttings. Sterilized perlite was inoculated with P. indica and then incorporated into a peat-based propagation media at three rates (10, 20, or 30%, v/v) to determine the optimum chlamydospore count per volume of media.  Each treatment contained the same total volume of perlite with a varying percentage of inoculated perlite. Species used in this experiment were Crossandra, Dianthus (perennial), and Osteospermum.  Four weeks after sticking the cuttings, the plants were evaluated for the root colonization as well as root fresh weight. Crossandra and Dianthus cuttings propagated in media with 10% v/v of inoculated perlite produced significant higher root fresh weight (P < 0.01). No root weight response was observed for Osteospermum.  Colonization was not quantified due to previous research stating there being benefits of the fungi simply the presences in the media.   Colonization was simply noted but not quantified. Endogenous auxin (IAA and IPA) concentrations were determined on basal sections of cuttings through HPLC-based quantification.  Samples were taken from Dianthus cuttings grown with (10% v/v inoculated perlite) and without P. indica after five days in propagation.  Basal sections of cuttings grown with inoculum contained significantly higher amounts of auxin.