Tomatoes require relatively high light and high temperatures for rapid growth and good production. In cropping environments, however, productivity in terms of yield is most likely to be limited by the fruitfulness of the plant and the abitlity of the grower to protect the fruit from damage. As Joness (1980) comments: 'The key to yield success is to obtain a good fruit set on each cluster and to ripen the fruit as quickly as possible ... The loss of one or two fruit per cluster or a missing cluster will significantly reduce yield.' Thus, genetic traits, environmental conditions and cultural practices predisposing plants to unfruitfulness, physiological disorders and fruit defects are also significant limitations to productivity. Comparing production of tomatoes from varying environments is highly subjective. Many people who have worked with tomatoes in many environments feel that given reasonable cultural conditions, tomatoes will produce at about the same rate. For example ' ... per plant fruit yields do not vary much for best fruit yields obtained under these wide ranges of growing conditions. Per plant yields will be from 8-12 pounds of fruit during the normal growing season ... These yields can be increased only by keeping the plant alive and productive during a longer period of time. One can only conclude that the genetic potential of the tomato plant is being achieved and that any dramatic yield increase per plant must come from some factor or groups of factors which will break the genetic yield potential' (Jones, 1980). Not surprisingly, highest yields are recorded in situations where the crop stays in production for long periods of time. For example yields from greenhouses in the UK are recorded at 190 tons acre (-1) (Aikman, 1988). These yields represent the long-season with the harvest beginning in April and continuing through the end of October. For the field crop, highest yields are seen in arid climates with good soils and ample, properly managed and good quality irrigation water (Stevens, 1986). In the San Joaquin Valley of California and in Israel, yields of 155 tons ha (-1) have been recorded using drip irrigation (Stevens, 1986). These yields are particularly impressive given the short harvest period of the field crop, and are comparable to those recorded even by good greenhouse tomato growers for the long-season crop (Ailman, 1988).[AS]