Graduate student. Current address: USDA-WRRC, ARS, 800 Buchanan St.; Albany, CA 94710.
Received for publication 19 Feb. 1988. Scientific Paper no. 7968, College of Agriculture and Home Economics Research Center, Washington State Univ. Pullman. This work was supported in part by the Washington State Tree Fruit Commission and the National Science Foundation Grant DCB-8801860 to B.W.P. 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.