Influence of Tall Fescue Cultivar and Endophyte Genotype on Rhizosphere Processes.

Tall fescue (Lolium arundinaceum (Schreb.) is a cool-season perennial grass  within which lives a fungal endophyte (Neotyphodium coenophialum) thought to provide tall fescue  with a greater competitive ability compared to its non-infected neighbors.  Because of the negative consequences of this associated with respect to animal health, lots of researches has been focused on elucidating the chemical components (i.e. alkaloids) produced by Neotyphodium coenophialum, with very little attention paid to the influence the relationship has on rhizosphere processes.  Our objective, therefore, is to study the influence of this relationship on root exudates.  Specifically, we grew two different tall fescue cultivars (PDF and 97TF1) under sterile conditions each without an endophyte (E-), with the common toxic endophyte (E+) and with the novel endophytes AR542 and AR584.  After 6 weeks of growth root and shoot biomass of the plants was determined and a portion of the exudates analyzed for total organic carbon, total organic nitrogen and total phenolic content.  Another portion of the exudates were used in a 96 well-plate microbial bioassay using Sinorhiizobium meliloti to test for bioactive components and another portion of the exudates was set aside for characterization using chromatographic and mass spectrometric techniques.  Preliminary results show that the root biomass, shoot biomass and total organic nitrogen content in novel endophyte infected tall fescue varieties are lower than in endophyte free tall fescue. Root exudates from common toxic endophyte infected tall fescue inhibited Sinorhizobium meliloti growth at the highest root exudate concentration. In contrast, novel endophyte infected tall fescue promote the growth of S. meliloti . These results suggested that endophyte genotype does have an influence on plant physiology which translates to changes in exudate chemistry and possibly soil microbial community structure as indicated by our bioassays.  Further research is underway to elucidate the exudate components responsible for these differences and to assess their influence on soil microbial community structure and function.