Flowering, pollination, and fruit setting in tomatoes Literature study commissioned by Koppert Biological Systems. Jan Janse Wageningen UR Greenhouse Horticulture Wageningen, February 2017 Report GTB-5142
Report details Report GTB-5142 Project number: 3742238300 Disclaimer 2016 (institute within the legal person 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 Research Foundation accepts no liability for any damages resulting from the use of the results of this study or the application of the recommendations. Address Postbus 20, 2665 ZG Bleiswijk Violierenweg 1, 2665 MV Bleiswijk T +31 (0)317 48 56 06 F +31 (0)10 522 51 93
Contents Summary 5 1 Introduction 6 2 Flower development and flowering 7 2.1 Flower 7 2.2 Flower cluster 7 2.3 Reproductive organs 8 3 Pollen formation 10 3.1 Assimilates deficit 10 3.2 High-temperature effects 11 3.3 Varieties and high temperatures 12 3.4 Low-temperature effects 13 4 Ovule production 14 5 Pollination 15 5.1 Pollination by bumblebees 15 5.2 Release of pollen and pollination 15 6 Pollen germination 17 7 Pollen tube growth 18 8 Fertilization 19 8.1 High and low temperatures 19 9 Fruit growth 22 9.1 Number of seeds and fruit size 22 9.2 Number of seeds and fruit quality 22 10 Flower abnormalities 23 10.1 Undeveloped flowers 23 10.2 Flower abortion 24 10.2.1 Undeveloped flowers 24 10.2.2 High temperature 25 10.2.3 Water supply and salt stress 25 10.2.4 Ethylene 25 10.2.5 Growth stagnation 25 10.2.6 Virus infection 25 10.2.7 Predatory bugs 25 10.2.8 Continuous lighting 25 10.3 Excessively long style and other abnormalities 25 10.4 Fruit abnormalities 27 11 Literature 28
Summary The whole process of fruit setting in tomatoes may be divided into various subsidiary processes, namely pollen formation, ovule production, pollination, pollen germination, pollen tube growth, fertilization, and fruit growth. Based on a literature study, the author has examined which factors affect the various subsidiary processes and deformations in flowers. The tomato is a self-pollinator and has hermaphrodite flowers. In order to achieve good production and quality, good pollination and fruit formation are very important. Unfortunately, for all kinds of reasons, these processes do not always proceed optimally. In many cases, a shortage of assimilates is the cause. This can particularly occur in low light conditions and/or at high temperatures and a low CO2 level. The formation of pollen grains is a more sensitive process in this regard than the development of the ovules. In particular, reduction division (meiosis), which takes place about nine days before flowering, and the period up to five days before flowering, are sensitive periods. High temperatures, for example several hours at 40 o C or temperatures above 25 o C for 24 hours, can greatly disrupt the development process of pollen grains. Effects of high temperatures include: formation of a low number of pollen grains, poor vitality of the pollen formed, the loculi remaining closed so that pollen grains are not released, long styles, and poor germination. In susceptible varieties, at prolonged high temperatures there may even be distortion to the stamens, resulting in zero fruit set. Varieties clearly differ in their sensitivity to heat stress. 24-hour temperatures below 10 o C to 13 o C also cause poor pollen quality. Report GTB- 5 The ovules are especially sensitive to high temperatures seven to five days before flowering, as well as one to three days after fertilization. They can still die at that point. As a result of vibration, for example caused by bumblebees, the pollen is released from the stamens and, ideally, ends up on the sticky stigma. A long style caused by low light or high temperatures is negative for pollination. At a higher temperature, germination, i.e. the emergence of the pollen tube from the pollen grains, takes place more quickly: at 10 o C and 35 o C, it was 5 and 0.7 hours, respectively. The number of germinating pollen grains depends on their vitality. The time required for fertilization also depends on the temperature: at 10 o C and 35 o C, it was 34 and 7.5 hours, respectively. Fruit setting proceeds optimally at a 24-hour temperature of approximately 21-25 o C. The cause of flower abortion may be a shortage of assimilates (incorrect light/temperature ratio). This occurs with undeveloped flowers, for example. It can also be caused by growth stagnation, salt stress, ethylene, viruses, and an excessive number of predatory bugs.
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