Introducing Walnut Hot Callusing Technology to Private Nursery Operator at Mongar

March 7th, 2025

With fund support from CARLEP, hot callusing technology (HCT) for enhanced walnut propagation has been introduced to a private nursery operator at Mongar on cost sharing mechanism. This marks the second promotion of HCT in farmers’ fields, following a successful implementation in Drepong last financial year, where a graft success rate of 76% was achieved.

The main objective of this technology is to significantly increase the graft success rate of walnut seedlings, thereby boosting income through the sale of high-value seedlings. Walnuts, recognized as a key commodity under the MFTP program, have high market value and demand, with grafted seedlings commanding prices between Nu 275 and Nu 305 per seedling. However, walnut seedlings typically exhibit lower graft success rates compared to other fruit species, primarily due to the specific temperature (27°C) and relative humidity (80-90%) required at the graft union for successful formation.
HCT effectively addresses this challenge by creating the precise environment needed for callus formation, which is critical to successful grafting. The system ensures that a constant temperature of 27°C and optimal humidity are maintained at the graft union. This is achieved by circulating hot water (heated to 50-55°C) from a reservoir tank through the graft unions, regulated by automated sensors. One sensor inside the callusing pipe ensures the internal temperature remains stable (27°C), while another sensor in the heating tank controls the water temperature (50-55°C).

The walnut seedlings were grafted on February 18th and will remain inside the callusing pipe for four weeks until the callus formation is complete. The process can be remotely monitored through the “eWeLink” app, allowing for precise control of both external and internal conditions. Moreover, the HCT system’s vertical stacking design maximizes space, making it ideal for nurseries in peri-urban areas. In a 5x11m net house, 1,440 seedlings can be accommodated efficiently. With an anticipated graft success rate of 70-80%, the projected income from the sale of these seedlings is estimated between Nu 277,200 and Nu 316,800. This technology will not only enhance local walnut seedling production but also reduce dependence on imports, contributing to increased income generation from this high-value crop.

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