S08 - Session O1 - Regulation of fruit set by light quality: A case study on pepper

Authors: Sijia Chen *, Ep Heuvelink, Leo Marcelis

Fruit set is a crucial plant developmental process, determining yield in many crops. Pepper ( Capsicum annuum L.) is a crop with poor fruit set as typically about two-third of all flowers abort, even in protected cultivation. Weeks with good fruit set are alternated with weeks with poor fruit set in their indeterminate growth, resulting in a flushing pattern in fruit set and yield. Abortion of flowers and fruit in peppers is an active process involving the formation of an abscission layer. So far, the effect of light spectrum on this process has hardly been investigated. Opportunities for detailed investigations of light quality effects on fruit set have strongly increased because of the development of narrow band LED lighting. LEDs are increasingly used as sole lighting sources in indoor farming, thus the interest in regulating plant growth by manipulating light spectrum is currently expanding. Our research aims to investigate how fruit set can be manipulated by light spectrum, by studying the physiological and molecular mechanisms. Red: far-red ratio of the light is a crucial environmental signal to plants. We have observed improved fruit set in pepper at high red: far-red ratio. The research presented here aims at explaining this effect. A high red: far-red ratio has been suggested to improve fruit set by reducing the dominance effect through decreasing auxin level in the main stem, and/or by reducing abscisic acid and ethylene levels in flowers and young fruit. Currently this is further investigated in a series of climate room experiments. The outcomes will be meaningful for lighting optimization in the cultivation of fruit bearing crops in the vertical farms.