Research: Fruit set and -retention and parthenocarpy (seedlessness) are agriculturally important traits. The manipulation of fruit set and retention can improve crop yield, while introduction of the quality trait of parthenocarpy into fruit and vegetable crops enhances edibility through seed elimination. Previous research has shown that the plant hormone auxin is an important primary signal in these processes. Sweet pepper is the most important greenhouse vegetable crop in the Netherlands. A major problem experienced by Dutch pepper growers is the strong week to week fluctuations in yield due to cyclic fluctuations in fruit set (flushing). This irregular yield is caused by the fact that the presence of developing fruits induces flower or fruit abortion on the next few nodes. Both flushing and occurrence of the physiological disorder blossom-end rot were found to be strongly reduced in plants with parthenocarpic fruit growth induced by exogenously applied auxin on the flower stigma. Apart from the involvement of the plant hormones auxin, gibberellins and cytokinin, little is known about the endogenous central regulators of fruit initiation and parthenocarpic fruit development, as only a few of these regulators have recently been identified through mutational studies. In this collaborative STW project we will develop new breeding strategies for parthenocarpy in sweet pepper that - in contrast to existing strategies - will be based on endogenous regulators of fruit set, thus allowing improved fruit set and/or parthenocarpy through a non-GMO approach. Our approach is in part based on physiological characterisation of the parthenocarpic response in sweet pepper (Heuvelink, Horticultural Production Chains Group, WUR), and in part on unravelling the molecular genetic control of parthenocarpy and fruit set retention in Arabidopsis and pepper (Offringa, Developmental Genetics, LU). We will employ genetic and genomics tools available in Arabidopsis, and develop new tools for sweet pepper, to identify endogenous regulators for fruit set and, with those, to develop new non-GMO breeding strategies for improved fruit set and fruit quality in vegetable crops.