Salicylic Acid Spray Keeps Daisy Mandarins From Splitting on the Tree

Few things are as disheartening for a citrus grower as walking through an orchard in the weeks before harvest and finding perfectly formed mandarins lying cracked open on the ground. Fruit splitting, a physiological disorder that strikes late in fruit development, can claim a substantial share of a Daisy mandarin crop and drag down the quality of what remains. Now, a two-year field study from Punjab Agricultural University in India suggests that a simple, precisely timed foliar spray of salicylic acid can dramatically reduce the problem by strengthening the fruit’s peel at the biochemical level.

The research, published in BMC Plant Biology, was conducted across the 2021 and 2022 growing seasons by a team led by Komalpreet Kaur, with colleagues from the Department of Fruit Science at Punjab Agricultural University in Ludhiana and the Fruit Regional Station at Jallowal-Lesriwal in Jalandhar. The team set out to test whether plant growth regulators could mitigate splitting in Daisy mandarin, a hybrid mandarin cultivar valued for its flavor but hampered by its tendency to split pre-harvest. Because the disorder has proved stubbornly resistant to conventional management, the researchers looked beneath the surface, asking what actually happens inside the peel as a fruit begins to fail.

Fruit splitting in citrus is generally understood as a failure of the peel, or rind, to keep pace with the expansion of the internal pulp. As juice sacs swell and internal pressure builds, a rind that has lost structural integrity can no longer contain the contents, and the fruit ruptures, often along the weakest point of the peel. The peel is not merely a passive wrapper; it is a living tissue whose strength depends on the architecture of its cell walls and on the balance of sugars, proteins and other solutes it carries. When cell wall degrading enzymes become active in the rind, those walls weaken, and the peel becomes vulnerable to the mechanical stresses of rapid fruit growth.

The Punjab team designed their experiment around this biology. Daisy mandarin trees budded on two different rootstocks, Rough lemon and Carrizo citrange, were sprayed with a range of plant growth regulators at critical stages of fruit development. The treatments included salicylic acid, naphthaleneacetic acid and gibberellic acid, applied as foliar sprays at concentrations measured in parts per million. The researchers then tracked splitting incidence alongside a battery of biochemical and enzymatic measurements in the peel, pooling the data across both seasons to ensure that the conclusions reflected consistent effects rather than the quirks of a single year.

The standout result was clear from the pooled analysis: salicylic acid at 100 parts per million was the most effective treatment for reducing fruit splitting. Salicylic acid is best known to the public as the compound behind aspirin’s precursor, but in plants it is a powerful signaling molecule that orchestrates defenses against pathogens and stress. The study shows that in Daisy mandarin peel, it also acts as a kind of structural guardian, intervening in the enzymatic processes that would otherwise dismantle the cell walls holding the rind together.

At the enzymatic level, the salicylic acid treatment significantly reduced the activities of a suite of cell wall degrading enzymes: polygalacturonase, cellulase, peroxidase and beta-galactosidase. Each of these enzymes attacks a component of the peel’s structural framework. Polygalacturonase and cellulase break down pectins and cellulose respectively, the load-bearing polymers of the primary cell wall, while beta-galactosidase trims sugar residues that help anchor wall components together. Peroxidase, though it can contribute to wall stiffening in some contexts, was also suppressed in this system. By quieting these enzymes, the salicylic acid spray preserved the integrity of the cell wall network, keeping the peel firm and resistant to the internal pressures of a swelling fruit.

The treatment also reshaped the peel’s biochemistry in ways that reinforced its structural stability. Salicylic acid application reduced the concentrations of total soluble sugars, proteins and amino acids in the rind. This matters because these solutes draw water into the peel tissue and can alter its osmotic balance; a peel loaded with readily mobilized nutrients may become softer and more prone to expansion beyond its mechanical limits. Lower solute concentrations, combined with the preserved cell wall architecture, translated into a rind that held its shape under stress. The researchers found that the treated fruits maintained thicker peels, higher chlorophyll content, greater proline accumulation and enhanced antioxidant activity, a combination that collectively improved peel firmness and resistance to splitting.

Some of these effects point to a broader stress-buffering role for salicylic acid. Proline is a well-known compatible osmolyte that plants accumulate under stress, helping cells maintain function under difficult conditions. Enhanced antioxidant activity in the peel suggests that the treatment helped the tissue manage reactive oxygen species, the volatile signaling and damaging molecules that surge when plant tissues are under duress. Catalase and superoxide dismutase, the classic enzymatic antioxidants of plant cells, form the front line of that defense. By bolstering these systems while simultaneously restraining the wall-degrading enzymes, salicylic acid appears to have acted on both the mechanical and the physiological fronts of the splitting problem at once.

The study also carried a rootstock dimension, with trees on Rough lemon and Carrizo citrange both included in the trial. Rootstocks shape water uptake, vigor and nutrient partitioning in citrus, all factors that influence how quickly fruit expands and how much stress the peel endures. While the headline finding centered on the salicylic acid treatment itself, the inclusion of two rootstocks grounds the work in real orchard practice, where growers select rootstock and canopy management together. The authors note that despite extensive research on citrus fruit physiology generally, limited information has been available on the biochemical and physiological pathways that plant growth regulators influence specifically in Daisy mandarin, making this study a novel contribution to understanding how salicylic acid regulates peel characteristics and maintains fruit integrity.

For growers, the practical message is appealingly simple: a foliar spray of salicylic acid at 100 parts per million, timed to critical stages of fruit development, offers a strategy for managing fruit splitting while improving overall fruit quality. Because salicylic acid is inexpensive, widely available and already familiar in agricultural contexts, adoption could be straightforward, and the treatment’s added benefits for peel thickness and antioxidant status may carry over into better handling and storage performance. As mandarin production expands in many parts of the world and consumers demand blemish-free fruit, protecting the crop from a disorder that strikes at the last moment before harvest could make the difference between a profitable season and a devastating one. This study suggests that sometimes the answer lies not in new machinery or new varieties, but in helping a fruit’s own peel hold itself together.

Subject of Research: Mitigation of pre-harvest fruit splitting in Daisy mandarin through salicylic acid modulation of peel enzymatic activity and biochemistry

Article Title: Mitigation of fruit splitting in Daisy mandarin through modulation of peel enzymatic activity and biochemical traits by growth regulators

Article References: Kaur, K., Gupta, M., Rattanpal, H. S., Chahal, T. S., Gill, P. P. S., Singh, G., & Raina, D. (2026). Mitigation of fruit splitting in Daisy mandarin through modulation of peel enzymatic activity and biochemical traits by growth regulators. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09995-5

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09995-5

Keywords: Daisy mandarin, fruit splitting, salicylic acid, plant growth regulators, peel thickness, cell wall metabolism, polygalacturonase, cellulase, antioxidant activity, rootstocks, citrus physiology, pre-harvest disorder