One of the most well-known and widely accepted physiological functions of boron in plants relates to the role of plants in generative growth and development. Boron plays an important role in pollen viability, pollen germination and pollen tube formation. It is stated that Boron is an essential element for the synthesis and development of the pollen tube, which plays a critical role in pollination, possibly due to its effects on cell wall formation and function.
Decreased flowering and shedding of flowers is a common problem in plants under boron deficiency. For this reason, although vegetative growth (green parts growth) is affected very little or not at all in boron deficiency, seed or fruit production is adversely affected by boron deficiency. As a matter of fact, the critical deficiency of Boron concentration of the generative organs is much higher than the critical deficiency of Boron concentration determined for the leaves. For example, the recommended critical deficiency concentration for the male reproductive organ stamen (anther) of flowers is 16 ppm in wheat and 38 ppm in rapeseed, while this value is reported to be 1 and 17 ppm in leaves, respectively (Dell and Huang, 1997, Plant Soil, 193:103–120).
The effect of boron application on the vegetative and generative growth of red clover (Sherell, 1983)
As seen in the table below, vegetative growth of plants is not affected much due to increased Boron nutrition, while very strong increases in seed formation occur.
The results indicate that foliar boron fertilization may be important in the generative period in plants. However, foliar boron fertilization may need to be repeated very often due to the problem of boron not being transported within the plant. In this case, perhaps the most correct agronomic approach would be to consider slowly soluble Boron fertilization, such as colemanite, which is slow in solubility and releases little Boron into the plant roots.