High nitrogen harms apples, Chinese researchers say

A Chinese research team has discovered that nitrogen inhibits the biosynthesis of apple epicuticular wax, a kind of significant external quality of apples, which decreases their glossiness and resistibility to damage.

A paper of the study, conducted by Professor Li Yuanyuan and her scientific research team from College of Horticultural Science and Engineering, Shandong Agricultural University, was published on Nature Plants on Jan 7. In the project, they utilized the fact that high nitrogen inhibits the accumulation of apple epicuticular wax as an entry point, revealing the regulatory mechanism of nitrogen to epicuticular wax.

The appearance of apple varies from species to species, while epicuticular wax serves as an important effect factor. Waxes are strong hydrophobic layers that cover the surface of apple organs, such as branches and trunks, leaves and fruits, as the first barrier for trees to defend against both biotic and abiotic menaces. They are also important elements determining the gloss quality of apple fruits.

However, the unilateral pursuit to high production and huge fruit forces the overuse of nitrogenous fertilizer in orchards. The high-nitrogen input production mode not only pollutes environment, but also decreases the quality and resistibility of apple. Therefore, the verification of influence and regulatory mechanism of nitrogen to apple epicuticular wax is vitally significant for the improvement of shine and resistibility of apples.

The study shows that in the apple groves where nitrogen fertilizer is overapplied, the wax content in apple fruits and leaves has significantly decreased. At the same time, analyses toward transgenic materials whose nitrogen responsive protein MdBT2 silencing show that their wax accumulation has significantly increased. All that proves that nitrogen inhibits the biosynthesis of apple epicuticular wax.

The first author of the paper, teacher Jiang Han from College of Horticultural Science and Engineering, Shandong Agricultural University, said the result not only scientifically explains why overuse of nitrogen leads to the decrease in apple quality and resistibility, analyzes the regulatory route of nitrogen to wax accumulation, but also provides a theoretical basis for resource screening and technology research and development to enhance fruit resistance to biotic and abiotic stresses, improve gloss quality and extend shelf life.

According to the team, they have obtained a series of functional genes related to apple resistibility and quality. Presently, pilot application is being carried out to uphold the high-quality and sustainable development of apple industry.