In this investigation levels of calcium were measured on the flag leaves of the suscepti-ble spring wheat cultivar Thatcher and its near-isogenic line that has Yr-۱۸ gene-mediated durable adult-plant resistance (APR ). The results showed that crystals of vari-ous shapes were frequently present on the infected leaf areas in the spring wheat that has the APR to stripe rust. Crystals were characterized with an energy-dispersive X-ray mi-croanalayser in conjunction with scanning electron microscopy (SEM). More calcium was mobilized into infected areas of the resistance line than into the susceptible genotype. The level of calcium in the non-infected areas of both resistant and susceptible hosts and on the infected areas of the susceptible genotype were nearly the same. The results indicated that calcium mobilization in the resistant near isogenic line upon infection with P. stri-iformis correlated with the elicitation of a defense response conditioned by the Yr-۱۸ gene. This is the first report on the mobilization of calcium in a cereal-rust pathosystem as part of a resistance response.

Wheat, Resistance, Calcium, Mobilization, Rust stripe