Pollination & Fruit Development in Tomatoes
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Pollination and Fruit Set
Development of high-quality tomatoes requires pollination. Pollen produced in the anthers is transferred during pollination to the stigma of the flowers (Figure 1). The pollen then germinates and the pollen tube grows through the style reaching the ovules. The ovary protecting the ovules enlarges and develops into the tomato fruit.
Several factors influence the success of the pollination process. Sufficient amounts of viable pollen must be produced in the anthers and transferred to the stigma. At the time of pollen transfer, the stigma must be receptive to allow rapid pollen germination and growth through the style. The pollen tube must reach the ovules for the ovary to increase in size
Failure in any of these processes prevents normal fruit development. The symptoms of unsuccessful pollination are 鈥渄ry set鈥 or rough fruit. Adverse environmental conditions such as temperature, light and humidity or poor nutrition can also result in inadequate pollination.
Environmental Conditions
Temperature
Greenhouse temperatures during the pollination period should not fall below 60掳F at night or exceed 85掳F during the day. At higher or lower temperatures, pollen germination and pollen tube growth are greatly reduced. Night temperatures are particularly important.
Light
Dark, cloudy weather retards pollen development and germination to reduce the fruit set in many tomato varieties. Since tomatoes are self-pollinated, the length of the pistil affects the ease with which pollen is transferred from the anthers to the stigma. If the pistil and style are short, the stigma is surrounded by the pollen sacs of the anthers to ease pollen transfer (Figure 2). In some tomato varieties, the style and stigma extend beyond the anthers, making adequate pollen transfer difficult. Higher solar irradiance tends to increase yields of tomatoes while the styles of the flowers grow shorter. A combination of low carbohydrate and high nitrogen content in the plant tissue, on the other hand, often results in long style lengths. These conditions are common under prolonged low light with high soil fertility.
Humidity
Relative humidity of 70 percent is optimal for pollination, fruit set and development.
Very high humidity keeps the pollen too damp and sticky, reducing the chance of sufficient
pollen transfer from anthers to stigma.