Modelling effects of photosynthetic adaptations on source sink relationships and yield patterns of recurrent flowering vegetable crops

Oliver Bain, John Billingham, John Fozard, Sunny Modhara, Adrian Pratt, John King, Arnd Korn & Jonathan Wattis

In commercial crops of pepper, cucumber and tomato, fruit production occurs continuously throughout the season. This results in the plant having to support flowers and fruit at different stages of development, and allocate its energy accordingly. If light and temperature were constant this would result in fairly consistent yield. In reality, growers are at the mercy of the climate and variable light and temperature results in fluctuating yield over the season. From experience, we know that variations in light and temperature cause peaks or ’flushes’ of yield followed by a lag period. This causes problems because when this happens across a region, it results in wide fluctuations in prices meaning that often when the grower has the most fruit, the prices are low, limiting their profitability. Even though glasshouse technology allows for considerable control over the growth environment, variable production is still a headache for many growers.
The difficulty of this issue from the standpoint of a plant breeder is that yield stability is impossible to assess without doing costly, long trials which may be useless if it happens to be a year with fairly consistent light and temperature. In addition to this, regulation of flowering and yield development is extremely complex leaving researchers with a myriad of variables that could be measured, but frequently there is little to guide a decision into which variables have the greatest influence and should be measured.
Growth models have been developed for many vegetable crops and include modules for light interception by the crop, photosynthesis (how much CO2 does the plant take up), source/sink partitioning (where the plant puts its carbon), dry matter production (net amount of carbon the plant keeps), fruit growth and several others. While we cannot address aspects of all of these modules during the study group, we would like to focus on photosynthesis and source-sink relations.
At the heart of this issue is the fact that vegetable crops with recurrent flowering have to allocate the carbon they take up from mature leaves (‘source’ tissues) between young leaves, new stem tissue, flowers, roots and developing fruit (collectively termed ‘sink’ tissues). This distribution of resource to sinks is obviously affected by how much carbon the leaves are able to take up, which in turn is affected by the climate. The current understanding is that the environment has a greater effect on photosynthesis, causing a range of adaptations. We have characterized photosynthetic behaviour in several tomato cultivars and have detailed growth and environmental data produced in commercial production conditions.

Proceedings of the 4th Mathematics in the Plant Sciences Study Group