Emulsifiers, alternative thinning agents for sustainable apple production

One of the key measures in apple fruit growing is fruit thinning. Fruit set in the spring must be reduced to provide commercially acceptable fruit size at harvest and to prevent biennial bearing of apple trees. Widely accepted chemical fruit thinning is a ‘must’ measure in commercial apple fruit production, because it successfully reduces hand thinning, improves fruit growth and additionally enhances flower bud formation for the next season. Chemically thinning is performed at the time of flowering or in the first weeks thereafter. After the abscission of flowers and/or small fruits is finished, hand thinning is performed to set exact crop load on fruit trees. Up to now only seven thinning chemicals have been introduced to fruit production, but each of them has its own shortcomings, such as inconsistent thinning results, temperature or humidity dependency or are excessively phytotoxic. Researchers are trying to find chemicals and application patterns which would satisfy growers’ needs as well to match environmental sustainability. Therefore the recently discovered physiological activity of polysorbates 40, 60 and 80 may be a welcomed solution for the problem in fruit thinning. Their main qualities are: -         have relatively reliable thinning activity on apples, -         can be applied very late (10-20 mm of apple fruitlets diameter) and thereby on more convenient and safe application time comparing to existing thinners (late application ensure better fruit set estimation after first fruitlet drop and can overcome possible spring frost), -         are substances used in food industry as additives (E-substances) and thereby recognised as non-toxic, -         may be easily registered -         are readily available as they are broadly used in food industry around the globe, -         are cheaper than other thinning agents especially from recently registered hormon-based thinners. Our team made several experiments which proved polysorbates as effective and relatively reliable apple fruit thinning agents. With the project we want explore further the physiological base of polysorbates activity through detailed observation of physiological parameters like photosynthesis and biochemical fruit and leaf analyses after their applications. The aim is to get a clear picture about polysorbates action from application to fruitlet abscission. Additionally, the effect of polysorbate use on final fruit quality and quantity will also be evaluated. In addition to polysorbates, we will test whether some other selected emulsifiers have a similar thinning effect. Honey bees are one of the most important pollinators of fruit plants. As part of the project, we will check whether polysorbates have a toxic effect on bees, both larvae and adults. At the same time, we would like to check whether the use of polysorbates has an effect on the marbled stink bug and spotted wing drosophila. Understanding physiological base of fruit thinning and plant response to polysorbate treatment can lead to discovery of other new environmental friendly fruit thinners. Future introduction of polysorbates to commercial fruit production will improve the economic status of growers while the consumers can dine fruits with less questionable chemical residues.