Internal browning

Internal browning, associated with boron deficiency, is a non-infectious physiological disorder that significantly impacts fruit quality and yield. The condition is not caused by fungi, bacteria, or viruses, but rather by the plant's inability to mobilize boron, which is essential for cell wall stability and sugar transport.

This disorder is commonly observed in apple trees and date palms. In apples, it manifests as brownish, corky patches deep within the flesh, which often extend outwards. For date palms, internal browning results in poor fruit development and necrotic internal tissues, rendering the crop unmarketable.

The characteristic symptoms include tissue discoloration that ranges from light brown to dark cork-like structures. Affected fruits often exhibit irregular surface shapes, premature dropping from the tree, and poor texture, making them susceptible to rotting during long-term cold storage.

Environmental factors are primary drivers of this condition. Alkaline soils with a high pH typically fix boron, making it unavailable to roots. Additionally, extreme fluctuations in soil moisture—either severe drought or waterlogging—disrupt the transpiration stream, preventing the necessary distribution of boron to the fruit sinks.

Integrated management is essential to mitigate the risk of this disorder. Growers should focus on a preventive approach rather than curative measures once the symptoms are visible. Recommended practices include:

• Regular soil testing to monitor boron and pH levels.
• Application of foliar boron sprays during pre-bloom and fruit set stages.
• Maintenance of adequate soil moisture through irrigation and mulch.
• Use of fertilizers that do not interfere with micronutrient uptake.