Viability and Colonization of Vesicular Arbuscular Mycorrhiza on Tomato and Cowpea Roots

Symbiotic relationship between vesicular arbuscular mycorrhiza (VAM) and plant roots is beneficial to plant growth due to increased nutrient uptake, protection of host roots from pathogens, and increased tolerance to drought. This study was conducted to evaluate the viability and efficacy of the VAM inoculum used in plant-microbe interaction studies at the University of Maryland Eastern Shore Agricultural Experiment Station.  The viability of the VAM was determined via culturing. VAM were grown on potato dextrose agar at 26^oC and examined after three days. Fungal colonies of different sizes and colors were produced indicating the viability of VAM.  VAM was then evaluated on organic tomato roots that were grown in a certified organic research field with three treatments (poultry compost, VAM, and poultry compost plus VAM) and a control. Roots were separated from the plants, washed, and cleared with 10% KOH and 5.6% HCl. They were then stained with 0.05% tryphan blue lactoglycerine to visualize the mycelium of the fungi in the roots. Two variations of this technique were attempted yielding inconclusive results at both times. An alternate method of determining the presence of VAM in the roots was then employed. Roots were surface sterilized and placed on potato dextrose agar plates and incubated at 26^oC. All samples yielded colonies similar to those that were observed in the VAM cultured for viability, indicating that VAM was present in the roots of the tomato plants, including those in the control group.  However, the presence of the VAM within the roots of the control and poultry compost only groups suggests that VAM was either present in the soil before inoculation or spread during the experiment to contaminate other plots.  Additional evaluation of the university inoculum was conducted by inoculating cowpeas in a sterile environment to examine its ability to colonize the roots.  Cowpea seeds were surface sterilized, germinated on nutrient agar, and incubated at 26^oC. Mycelium plugs from cultures of the university inoculum were introduced to the cowpea seedlings and incubated at 26^oC. The roots were cleared and stained using the same method as for the tomato roots.  Endophytic growth was observed indicating that the inoculum was viable and effectively colonized the tomato and cowpea roots.