Present address: Dept. of Horticultural Science, Massey Univ., Palmerston North, New Zealand.
Received for publication 13 July 1987. We thank the Broodbank Fund, the Wolfson Foundation, and the Univ. of Georgia for the financial support of this work; Ann Webb for technical assistance; and Eurof Walters and David Brown for advice on statistical procedures. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty by either university and does not imply its approval to the exclusion of other products or vendors that may also be suitable. 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.