Low graft success and poor air layering in a Ganjam nursery
A nursery near Berhampur, Ganjam, prepared 4,000 mango stone grafts and 2,000 guava air layers for the 2024 monsoon season. For mango, seeds of local seedling mango were sown in June; rootstocks were lifted at 24 days, when they were 15-20 cm tall and the stems had begun to harden. Scion sticks of cv. Amrapali were cut from an 8-year-old tree at 12 noon, leaves still attached, and carried loose in a jute bag. Grafting was done in an open shed with no mist or humidity chamber, and the grafts were watered twice daily with a rose-can directed over the scion. Only 32% survived. For guava, air layers were set on 3-year-old shoots of about 2 cm diameter; a 1.5 cm ring of bark was removed but the cambium was scraped away only partly; no IBA was used; moist field soil was used as the rooting medium; the polythene was tied with a single knot; and layers were separated after 30 days. Only 40% rooted. The owner blames the weather.
1. For the mango grafts, identify and rank the causes of the 32% survival, and state what you would look for in the nursery bed to confirm each one.
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Stone (epicotyl) grafting succeeds only when the rootstock is at the right stage, the scion is physiologically prepared, and the graft union stays in a saturated atmosphere until it heals. This batch fails on all three counts.
Rootstock too old (primary). Stone grafting in mango uses seedlings 8-12 days old, with soft, etiolated, unbranched stems 10-15 cm tall. At 24 days the stems have begun to harden and lignify, so the cambium does not align or heal readily. Confirm: cut a sample of failed rootstocks transversely a few mm below the union; a hardened, discoloured stem with no callus bridging the scion indicates this cause.
No humidity chamber (primary). The graft union loses water through the scion before union is established. Watering with a rose-can wets the scion and invites rot while failing to keep the air saturated. Grafts must be kept in a polyhouse or low tunnel at 85-90% RH, in shade, until the scion sprouts. Confirm: shrivelled scions that never sprouted, or blackened unions with fungal growth.
Scion quality and handling. Sticks cut at noon carry maximum transpiration load; leaves left attached continue losing water. Scions should be cut in the early morning from healthy terminal shoots that were defoliated 7-10 days earlier, kept wrapped in moist cloth, and used the same day.
Skill and speed of the operation. Only 32% success with a fixed date suggests uneven technique; a sharp graft, correct alignment of at least one cambium side, and a firm tie are decisive.
Weather is not the explanation: June-July is the correct season for stone grafting in Odisha.
2. For the guava air layers, what went wrong, and how would you demonstrate the diagnosis with a simple destructive check?
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Air layering in guava is reliable if the ring is complete, the medium is moist but not sodden, and the layer is left long enough. Four faults explain 40% rooting.
Incomplete cambium removal (primary). If cambium is left or only partly scraped, the cut surface reconnects and the shoot keeps being fed from the parent; no carbohydrate accumulates above the ring and roots do not initiate. Demonstrate: after separation, peel back the polythene on a random sample of failed layers. Smooth, healed bark bridging the ring is conclusive. A slight wounding of the exposed wood helps, but the cambium must be gone.
Wrong shoot age and thickness. Shoots of about 2 cm on 3-year-old wood are too old and woody; pencil-thick shoots of 1-1.5 cm, from the previous season's growth, root far better.
No IBA. Guava roots readily but still responds to auxin; 2,500 ppm IBA in lanolin applied to the upper cut surface improves rooting percentage and root quality.
Medium and moisture. Field soil dries and cracks. The standard medium is moist sphagnum moss or a 1:1 coco peat and soil mix, squeezed so that it holds together without free water, wrapped in 150-200 gauge polythene and tied at both ends so moisture is conserved.
Separation too early. At 22-28 degrees C guava layers need 45-60 days for roots to reach the 3-5 cm stage needed for survival after separation. Thirty days gives callus, not a root system.
Rooting percentage is a record-keeping issue too: the nursery should tag a sample of 50 layers per batch and record rooting, so it recognises a bad batch before potting 2,000 of them.
3. Write the corrected working protocol for both crops and estimate how the change would affect the number of saleable plants from the same 4,000 rootstocks and 2,000 layers.
Read the worked answer
Mango stone grafting - corrected protocol
- Sow seeds in June in polybags; use seedlings at 8-12 days, when the stem is soft and the first pair of leaves has just expanded.
- Defoliate selected scion shoots 7-10 days before grafting; cut 4-5 cm sticks with 3-4 buds early in the morning from the current flush of a known true-to-type Amrapali tree; wrap in moist cloth; use within the day.
- Lift the seedling, cut the epicotyl 4-5 cm above the stone, make a 3-4 cm wedge on the scion, insert, align one cambium side, and tie firmly with 150-gauge polythene or a grafting clip.
- Keep in a humidity chamber or low tunnel under 50-75% shade at 85-90% RH for 21-25 days; mist lightly, never water over the scion.
- Harden in partial shade for 10 days, then full sun. Remove the rootstock sprouts below the union and the tie after 30 days.
Guava air layering - corrected protocol
- Select pencil-thick shoots of 1-1.5 cm from the previous season's growth.
- Remove a 2-2.5 cm ring of bark and scrape the cambium clean.
- Apply 2,500 ppm IBA in lanolin to the upper cut surface; wrap with moist sphagnum or coco peat-soil mix; tie both ends.
- Separate at 45-60 days, when roots are 3-5 cm long; cut below the layer, retain the moss, pot in a polybag with a light mix, and keep under 50% shade for 3 weeks.
Effect on numbers At a realistic 65-75% success for stone grafting, 4,000 rootstocks give about 2,600-3,000 saleable grafts instead of 1,280. At 80-85% rooting for guava air layers, 2,000 layers give about 1,600-1,700 plants instead of 800. The extra roughly 2,300 plants, valued conservatively at 40 rupees each, add about 90,000 rupees of output from the same seed, scion material and labour. The added cost - a low tunnel, moss or coco peat, IBA, and shade net - is a few thousand rupees. It is the cheapest improvement the nursery can make.