The main objective of any cultivar evaluation trial is to determine which cultivar has the most value in terms of industrial product. This will certainly involve measurements of fruit quality including, brix, viscosity and colour, but a key factor must be yield. There is a risk in cultivar trials in which the cultivars have differences in days to maturity, that a single harvest may result in the results being badly biased. There is also the added difficulty of actually knowing when the optimum harvest date occurs for any one cultivar. We propose that for an accurate comparison between cultivars that a minimum of 5, and preferably 7 simulated machine harvests be taken. Our results have shown that the yield of factory grade fruit (red and red/orange) can be fitted to a normal distribution, and thus at the optimum harvest date can be estimated. This model might also be used to develop an estimate of the optimum harvest date to maximise factory yield. Our data suggests that an error of 7 days on either side of the optimum harvest date can result in a factory yield reduction of up to 20%, and therefore these findings have major commercial implications. It is suggested that a similar harvesting strategy is necessary for other agronomic studies with process tomatoes.
