Diffuse light and light spectrum in relation to pollination, fruit setting, and insects in tomatoes Literature study commissioned by Koppert Biological Systems Jan Janse Report WPR-702
Abstract We were commissioned by Koppert Biological Systems to conduct a desk study into the effects of diffuse greenhouse covers and greenhouse covering materials with different light spectrums on pollination and fruit setting in tomatoes. The relevant information found in literature proved to be limited. There is an increase in production under diffuse glass thanks to an increase in the size, and sometimes the quantity, of the fruit, although it is not known whether this is partially the result of better fruit setting. Red and pearl nets placed above the crop promote production, while yellow and pearl nets reduce virus infections by decreasing the activity of and repelling harmful insects respectively. A higher light absorption of UV light improves protection against harmful insects but can also reduce the search behaviour of predators and bumblebees. Report details Report WPR-702 Project number: 3742238300 DOI number: https://doi.org/10.18174/424934 Disclaimer 2017 Wageningen Plant Research (institute within the legal entity Wageningen Research Foundation), Postbus 20, 2665 MV Bleiswijk, Violierenweg 1, 2665 MV Bleiswijk, T 0317 48 56 06, F 010 522 51 93, E glastuinbouw@wur.nl, www.wur.nl/plant-research. Wageningen Plant Research. Wageningen University & Research, Greenhouse Horticulture Business Unit, cannot be held liable in any way whatsoever for any damage ensuing from the use of the results of this study or from the application of recommendations contained therein. Address Wageningen University & Research, Greenhouse Horticulture Business Unit
Table of contents Summary 5 1 Introduction 7 2 Diffuse light 9 2.1 Direct and diffuse light 9 2.2 Haze and F-scatter 10 2.3 Light transmission 10 2.4 Diffuse glass 10 2.5 Diffuse plastic films 11 2.6 Diffuse coatings 11 2.7 Diffuse screens 11 2.8 Whitewashing 11 3 Effects of diffuse light on crops 13 3.1 Light penetration in crops 13 3.2 Photosynthetic efficiency 13 3.3 Light distribution 14 3.4 Plant temperature 14 3.5 Photoinhibition 15 3.6 Production under a diffuse greenhouse cover 16 3.7 Diffuse coating, whitewashing, and screens 17 4 Influences of the light spectrum 19 4.1 Photoselective greenhouse covers 19 4.1.1 Photoselective nets and production 19 4.1.2 Photoselective nets and harmful insects 21 4.1.3 NIR reflection 21 4.1.3.1 High temperatures and pollination by bumblebees 22 4.1.4 UV radiation 22 4.1.4.1 UV and harmful insects 22 4.1.4.2 UV and predators 22 4.1.4.3 UV and bumblebees 23 4.1.4.4 UV and plant growth and production 23 References 25 WPR-702 3
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Summary More and more tomato growers both in the Netherlands and abroad are opting to use diffuse glass in new greenhouses. A literature review was carried out to examine the effect of a diffuse greenhouse cover or a greenhouse cover with a different light spectrum on pollination and fruit setting in tomatoes. Information was also collected on the influence of the light spectrum on insects and bumblebees. This desk study was carried out on the request of Koppert Biological Systems. Unfortunately, the amount of information found on the subject proved to be limited. Light scattering The extent of diffusivity or light scattering that occurs is expressed in terms of haze or F-scatter. The amount of diffuse light that occurs as a proportion of total radiation depends greatly on the area of cultivation and the time of year. In temperate climates, greenhouse covers that provide a high degree of light transmission are important for production. Direct light can be diffused by using diffuse glass, plastic films, moveable screens, or by applying a coating on the covering. Whitewash is particularly used on greenhouses in Mediterranean regions to keep out thermal radiation and to diffuse the light. Positive effects of diffuse light Diffuse light penetrates deeper into the crop canopy, allows for a greater horizontal spread of light, increases photosynthesis, and with high solar radiation lowers the plant head temperature and hence also the risk of photoinhibition. Diffuse glass can increase the production of tomatoes by around 10%, provided the light transmission of the greenhouse cover remains at the same level. Fruits become clearly larger, and sometimes increase in quantity, which could be the result of an increase in the number of fruit set due to improved flower quality. It is not known, however, whether there is an increase in the number of seeds per fruit under diffuse glass. Light spectrum The global radiation that penetrates the glass cover can be divided into ultraviolet radiation (UV), photosynthetic active radiation (PAR), and near-infrared radiation (NIR). UV radiation can, in turn, be divided into three bandwidths: UV-A (320-400 nm), UV-B (280-320 nm), and UV-C (100-280 nm). PAR radiation falls within the range of wavelengths between 400 nm and 700 nm and NIR radiation between 800 nm and 2500 nm. The light spectrum in the greenhouse can be altered by using plastic films, screens, and gauze or nets. The colour of the material influences spectral light penetration by absorbing its complementary colour. Photoselective greenhouse covering materials In an Israeli study into the use of different coloured nets, red and pearl nets resulted in a higher production of tomatoes than black and blue nets. The most probable reasons for this are improved flower quality and setting, better fruit growth, and lower temperatures with large amounts of sunlight when compared to the more commonly used black nets. Influence of photoselective materials on diseases and pests Yellow and pearl nets reduce virus infections by a factor of between 2 and 10 when compared to red and black nets. Pearl nets repel insects through light reflection and yellow nets cause insects to remain on the nets for longer which reduces the time they spend transmitting viruses to the plants. Insects use light signals to find their prey or host plant. There is a positive link between the extent of UV absorption in the greenhouse cover and the level of protection against insects, such as whiteflies, thrips, and aphids. However, limiting the amount of UV in the greenhouse can also have a negative effect on the search behaviour of useful insects, such as predators and bumblebees. The pollination activities of bumblebees are particularly reduced at temperatures above 30 C. o WPR-702 5
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Wageningen University & Research, Greenhouse Horticulture Business Unit Postbus 20 2665 ZG Bleiswijk Violierenweg 1 2665 MV Bleiswijk T +31 (0)317 48 56 06 F +31 (0) 10 522 51 93 www.wur.nl/glastuinbouw Greenhouse Horticulture Report WPR-702 Wageningen University & Research, Greenhouse Horticulture Business Unit initiates and encourages the development of innovations to promote sustainable greenhouse horticulture and quality of life. We pursue these goals by engaging in applied research in collaboration with partners from the horticulture sector, the supply chain, the plant breeding sector, other knowledge and research institutes, and government agencies. The mission of Wageningen University & Research is 'To explore the potential of nature to improve the quality of life'. At WUR, nine specialized research institutes from the DLO foundation and WUR bundle their strengths to develop solutions for major issues connected with healthy nutrition and the living environment. With approximately 30 locations, 6,000 members of staff, and 9,000 students, WUR ranks worldwide as a leading knowledge institute within its domain. Interdisciplinary cooperation and an integrated approach to issues lie at the heart of the unique Wageningen approach.