Mango Grafting Failure in a Lucknow Nursery
On 28 January, a nursery near Lucknow grafted 1,200 mango 'Dashehari' scions onto 10-month-old seedling rootstocks with collar diameters of 8–10 mm. The team used veneer grafting, tied the unions with 100-gauge polythene strips, but left the scion tips exposed. The polyhouse was held at 30–32°C and 35–40% relative humidity, and the 50% shade net was removed on day 5 to 'harden' the grafts. Rootstock sprouts were left untouched. At day 25, only 31% of grafts had sprouted. Most failed scions were shrivelled and the union tissue was blackened; some rootstocks had pushed vigorous new shoots. The nursery has another 2,000 rootstocks of the same age and must decide whether to re-graft immediately or wait. Budget allows only one more grafting round before the monsoon, and the buyer expects 1,500 saleable plants by October. Temperatures are rising but humidity is still below 45%.
1. Rank the likely causes of the 69% failure and explain which evidence supports each. Which single factor was most limiting?
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Ranking with evidence
- Scion desiccation - primary. Relative humidity of 35–40%, exposed scion tips and shade removal on day 5 all point to uncontrolled water loss. Shrivelled scions are the direct symptom. Mango veneer grafts need a humid microclimate until the union vascularises, typically 10–14 days.
- Poor cambial contact or union dehydration. Blackened union tissue can follow desiccation and failed callus formation. Rootstocks of only 8–10 mm are on the thin side for veneer grafting; poor matching of cambial layers reduces success even when the wrap is tight.
- Rootstock sprout competition. Unchecked sprouts divert assimilates and water away from the scion and can overgrow it. The presence of vigorous rootstock shoots supports this.
- Premature shade removal. Removing shade at day 5 exposed the grafts before the union was functional. This is a contributing factor rather than the sole cause because the scions were already exposed at the tip.
Most limiting factor: water loss from the scion. The low humidity and exposed tips explain why failures are dominated by shrivelled scions rather than by rotting or clear disease lesions. If blackening is wet and spreading rather than dry, send a sample for Colletotrichum testing, but do not assume disease before correcting humidity.
2. What should the nursery do with the 1,200 grafts now, and how should it allocate the remaining 2,000 rootstocks to meet the October target?
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Current grafts
- Grafts with shrivelled scions and blackened unions cannot be rescued. Cut those rootstocks back to 15–20 cm and retain one strong shoot for re-grafting when it reaches 8–10 mm, or hold them as rootstock for the next round.
- The 31% that survived (about 372 plants) should have rootstock sprouts removed every 7–10 days, remain under 50–75% shade, and be misted to keep humidity high without waterlogging the media.
- Do not apply heavy nitrogen to survivors; excess growth before the union is strong can cause later breakage.
Allocation of the 2,000 rootstocks
The target is 1,500 saleable plants. With 372 survivors, the gap is about 1,128. At a realistic 75% success rate, the nursery needs 1,128 ÷ 0.75 = 1,504 grafts. Graft 1,600–1,700 and keep 300–400 rootstocks as a reserve.
Because humidity is still below 45%, re-grafting immediately repeats the same risk. Either create a humid tunnel with fogging and 75% shade, or wait 2–3 weeks for pre-monsoon humidity. Waiting too long risks insufficient hardening by October, so stagger the work: graft 800 as soon as the tunnel is ready, then the remainder 10–14 days later. Record the actual success of each batch so the October supply estimate is based on data, not hope.
3. Set out the revised grafting protocol and the records needed to judge whether it worked.
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Revised protocol
- Use 12-month-old rootstocks, 10–12 mm collar diameter, healthy and well watered 24 hours before grafting.
- Collect scions from hardened current-season shoots with 3–4 plump buds. Cut in the early morning, wrap in moist cloth, and graft the same day.
- Graft at 15–20 cm height with a clean veneer cut; match cambial strips on at least one side and tie firmly without girdling.
- Cover the entire scion, including the tip, with a polythene tube or cap. This is the key change from the failed batch.
- Keep grafts at 25–30°C and 70–80% relative humidity under 75% shade for 10–14 days. Vent gradually, then reduce shade over 7–10 days.
- Remove rootstock sprouts weekly. Inspect at 10, 20 and 30 days; do not force shade removal by calendar alone.
Records
Record rootstock batch and caliper, scion source and date, grafter name, grafting method, number grafted, temperature and humidity, date of shade removal, number sprouted at 30 and 60 days, number with rootstock sprouts, and losses by cause. Calculate success per grafter and per batch. A batch success below 70% should trigger a review before the next round, not a repeat of the same procedure.