Received for publication 26 Dec. 1984. The authors gratefully acknowledge technical and material assistance given by G. Suttle and Microplant Nurseries, Inc., Gervais, Ore. Contribution from the Missouri Agr. Expt. Sta. J. Ser. No. 9776. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.