Root staining was performed via the method of Phillips and Hayman
(1970) to observe the colonization of Romaine lettuce by AM fungi to
ensure plant swere colonized prior to inoculation with pathogens. Briefly,
roots were immersed in 10% [wt/v] potassium hydroxide (KOH) and
heated for 30 min at 90 °C. The KOH was poured off, roots were rinsed
with water twice, and then 1% hydrochloric acid (HCl) was added sufficient
to cover the roots. Tubes were then held with the solution inside
for five minutes, the HCl was poured off, and roots were stained with
the Diazo dye, Trypan blue (Phillips and Hayman (1970)). Tubes were
heated for fiveminutes at 90 °C, Trypan bluewas eluted and roots were washed once with water.