Droplet size in spraying boosts plant defense and growth

Agriculture faces serious challenges due to ongoing climate changes, which destabilize rainfall patterns and raise temperatures. It is becoming necessary to seek alternative, more ecological solutions that will improve crop health without increasing the use of chemical pesticides.

A group of researchers from Huazhong Agricultural University in Wuhan, led by Man-Qun Wang, conducted experiments on tomato plants to study how mechanical stimulation in the form of water spraying affects their growth.

The researchers particularly focused on two droplet sizes: small, with a diameter of 0.008 inches, comparable to a pixel on a computer screen, and large, with a diameter of 0.04 inches, equivalent to the head of a pin.

To ensure full control over the study, the soil under the plants was covered with an impermeable layer, which eliminated the possibility of water reaching the roots affecting the results.

The results were surprising. Plants sprayed with larger water droplets were shorter and more compact compared to those that received smaller droplets or were not sprayed at all. Interestingly, the differences in the quality and quantity of fruit among these three groups were small. However, plants exposed to larger droplets showed increased resistance to pests and diseases, including the cotton bollworm (Helicoverpa armigera) and gray mold (Botrytis cinerea).

Metabolic analysis showed that plants sprayed with larger water droplets had elevated levels of hormones responsible for their defensive responses. Researchers also noted higher levels of chlorogenic acid in the leaves, which further enhanced plant resistance.

Moreover, there was a lower emission of volatile organic compounds, which usually attract insects that lay eggs on plant leaves. As a result, the number of eggs laid by insects decreased by 74 percent compared to unsprayed plants.

In light of these promising results, the study's authors suggest that the development of water spraying technology could improve agricultural practices, making them more environmentally friendly and efficient. Mechanically stimulating plants, for example, through appropriate spraying, could serve as an alternative to using pesticides while supporting the crops' natural defence mechanisms.

This study marks another step in the search for methods to help agriculture adapt to increasingly challenging environmental conditions while minimizing negative environmental impacts.