Present address: Campo Agricola Experimental del Norte de Guanajuato, Apdo. Postal 25, San Jose Iturbide, Gto., Mexico.
Received for publication 14 July 1986. This research was supported by funds from AES/USDA Regional Research Project W-168 and grants from the California Tomato Research Institute, Inc. The technical assistance of Z. Stan Ski-binski and Stacy Lee in some of these experiments is gratefully acknowledged. 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.