The effect of periods of high temperature and manipulating fruit load on the pattern of tomato yields

To assess whether cycles in the weekly pattern of tomato yields were due to the pattern of fruit load on plants, truss-removal and truss-pruning treatments were applied to individual rows within glasshouse compartments. When the pattern of fruit load was stabilized by pruning all trusses to five fruits, fruit size increased although the pattern of yield was similar to that from control rows. Furthermore, imbalances in fruit load caused by truss removal did not cause cyclical fruit production. The effect of temperature on the pattern of yield was investigated by raising air temperature within compartments by about 4.5 K for one week on two occasions. High yields were initially recorded following the start of the high temperature pulse but low yields were subsequently recorded. Overall, there was no significant effect of the treatment on. cumulative yields over the course of the experiment. The results show that changes in air temperature are important in determining the pattern of tomato yields. Fruit temperatures were recorded with thermal-imaging equipment and thermistor sensors inserted into fruits. Fruit temperatures in excess of 35degreesC were recorded, although fruit temperatures were only slightly above air temperatures when averaged over longer periods. Fruits at the south end of the rows were on average 1.9 K warmer than the air compared with 0.9 K warmer in the middle of the rows. For accurate predictions of the pattern of yield, fruit temperatures should be considered.