Truss
hooks
When some greenhouse
tomato cultivars are grown under relatively low light conditions, the
peduncles of the inflorescences (trusses) are too weak to support the
weight of fruit they bear and, are liable to bend [33]
or ‘kink’. Another reason sometimes given for kinking is too high a temperature
during the vegetative phase which causes the truss to become almost vertical
('stick trusses'). As fruit develop on these trusses, they may become
kinked.
Truss hooks suspended from the tomato stem prevent heavy trusses from tearing off the vine and keep the cluster from bending sharply under the weight of the fruit. Truss support devices, which also include peduncle clamps (Fig. 11), are thought to prevent a reduction in fruit size on kinked trusses. There is some evidence for this in the scientific literature, although results are not conclusive. Experimentally bending the peduncle either slightly or sharply reduced the total dry weight of fruit on that truss by 15.6-17%, depending on the season [34]. Reductions were greater in trusses developing on sharply bent peduncles. Distal fruit (those farther from the plant stem) were more adversely affected than the first, proximal fruit. If bending occurred when the fruit were 10 mm or less in diameter, the effect was less than when the fruit were larger, suggesting that inability to translocate assimilate was overcome. Compensation for kinked fruit also occurred in upper clusters, as assimilate that was not partitioned to the fruit of truss 1 was redistributed to the fruit of truss 2. The compensation was incomplete, however, as the total dry weight of all the fruit on trusses one and two of treated (bent) plant was still 5.6-6.7% less. These differences were not statistically different, however.
Topping
Six weeks before
the anticipated crop termination date, the growing point and small fruit
clusters at the top of the plant are removed. An individual fruit requires
7-8 weeks from anthesis to harvest so small fruit will not have enough
time to develop to maturity. Topping is thought to speed fruit development
and increase size of already-set fruit in the lower part of the plant.
However, it is often helpful to leave some suckers or leaves at the top
of the plant to shade the fruit and prevent sunscald. Leaving suckers
at the top (or not topping at all) is also thought by some growers to
provide shade to top fruit and increase transpiration, thereby reducing
fruit cracking, and russetting.