Received for publication 25 Sept. 1985. Mention of trade names or commercial products does not constitute an endorsement or recommendations for use. 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.
Permanent address: Department of Horticulture, Institute of Agricultural Sciences, Banaras Hindu Univ., Varanasi-221 005, India. Recipient of a Visting Research Associateship sponsored by the Canadian International Development Agency and the Natural Sciences and Engineering Research Council of Canada.