Polymer and photo-selective covers on plant and fruit development : a review

Growers have increasingly adopted protected cropping in tunnels or greenhouses to ensure sustainability and continuous crop productivity against a backdrop of climate change. The predominant types of covers used in controlled-environment agriculture are polymer-based shade nets or structures covered with polymer sheets. These have three main functions: (1) physical protection from birds, hail, and excessive radiation; (2) modification of the environment by controlling humidity, shade, and temperature; and (3) increasing the proportion of diffuse light. In order to address concerns regarding the amounts of useful light potentially blocked by these covers, researchers and growers have suggested several innovative solutions that involve altering the light received by plants. This includes supplementation of artificial illumination, filtering solar radiation with colored films, or altering the incident spectrum with spectral-shifting covers containing light-emitting fluorescent compounds embedded within a polymer matrix. In principle, any of these methods have the potential to selectively modify the spectrum of incident light and subsequently induce plant physiological responses, resulting in increased crop yield, improved fruit quality, and reduced susceptibility to pests and diseases. This review focuses on the benefits offered by passive covers in terms of their variable shading and light transmittance properties and their effects on vegetative growth and fruit development in various crops. It is anticipated that through a better understanding of photo-selective covers in protected cropping, primary producers will be better equipped to make informed decisions regarding their deployment and thereby achieve better yields and more nutritious produce from their crops.