Mango seeds are either mono-embryonic (single embryo) or poly-embryonic (multiple embryos) depending on the variety. Only poly-embryonic seeds produce true-to-type (clones) of the parent.
Most cultivars of mango do not produce seedlings true-to-type. Therefore, grafting is often necessary to overcome this problem. Grafting also means that trees produce uniform yield, fruit size and quality.
Propagation by seed
Propagation by seed is only recommended for poly-embryonic mango varieties such as Kensington Pride. Poly-embryonic seeds produce a number of shoots, one of which originates from fertilisation. The fertilised seedling is often weak and stunted and should be discarded. The other seedlings are clones of the mother tree.
However, any seed can be used to grow seedlings for grafting. The seedling will become the rootstock. Collect seconds fruit and use to propagate rootstock.
Preparing seed for planting
Mango seeds lose viability very rapidly. It is essential to clean the seed as soon as possible after its removal from the fruit. It then needs to dry in the shade for a day or two.
The outer husk must be removed before planting. The easiest way to extract the embryo is to cut the husk at the stalk end of the fruit to create a small slit. Then pry open the husk with a seed opening tool. A tool can be made by welding the heads of two flat screw drivers to a pair of circlip pliers.
You can tell if the seed is mono- or poly-embryonic by the number of segments.
Use a seedling bed
If you are propagating large numbers of seeds consider using a seedling bed. This method saves space, potting medium and time.
Have a large tray filled with potting medium. Good potting medium contains slow release fertiliser, 50% coarse river sand, 25% vermiculite and 25% sphagnum peat moss, and as a minimum should meet the Australian Standard for a standard potting media. Premium media is also available. This is indicated by Standards Australia certification stamped on the bag.
Plant seeds next to each other, about a centimetre apart. The seeds are kidney-shaped. Plant the seed on its edge with the concave edge facing downwards.
Leave part of the top of the seed uncovered. If in a few days the seed is green it is healthy and should grow well. If the seed is brown or black it is probably rotting and can be removed and replaced with anothe seed.
As the seeds germinate they can be carefully removed from the seedling bed and planted into individual pots.
Germination takes between 10 and 14 days. Within eight months they will have reached a stem diameter of 8-10mm and be 10-15cm high.
Propagation by grafting
Grafting is the process by which part of the parent tree to be reproduced (scion) is joined with a rooted plant (rootstock).
Selection of rootstock
It is important to have rootstocks of similar characteristics to ensure a uniform plantation.
Grafting is best performed when weather conditions are milder, for example autumn or spring. If the seedlings are not yet big enough, delay grafting by two to six months.
Preparation of scion material
The best scion material is obtained from the tips of mature shoots with prominent buds (tip wood) immediately before flushing.
Tip wood can be prepared on the parent tree 7-10 days before they are cut for grafting. Prepare the tip wood by cutting off the leaves but leaving the petioles (leaf stems) attached. The petioles will fall off easily when the scion is ready.
The scion is cut from the mother tree when required and needs to be 6-8cm long and as close as possible in diameter to that of the rootstock.
Scions can be stored for up to seven days wrapped in a moist towelette or newspaper in a zip lock plastic bag in a cool, dark place. If propagating large numbers, drop batches of scion wood into a bucket of water to stop them drying out.
Alternatively, the budwood can be selected on the day and prepared by remove leaves, but leaving the petioles. The scion is ready for immediate use.
The wedge graft is the easiest graft to perform with a 90-100% success rate.
The keys to success are:
- Choose vigorous rootstock and scion material.
- Use a razor sharp knife or scalpel.
Materials required include grafting/budding tape (12mm wide) and zip lock plastic bags.
Select a scion that is the same width or slightly narrower than the width of the rootstock.
The scion needs to be semi-hard, so that when slight pressure is applied it bends slightly. If the tip is too soft it will not cut easily and will dry out quickly.
Cut the end of the scion into a wedge. Use as few cuts as possible, only one or two on each side of the scion.
Cut off the top off the rootstock and then cut a 2cm slit down the middle.
Push the scion wedge into the slit on top of the rootstock. Try and line up the cambium on at least one side. The join on at least one side should feel smooth where the edge of the scion and rootstock meet. It does not matter if there is a slight indentation on the opposite side.
The cambium layer can be seen as a dark green ring just inside the bark. The ring can be seen when looking at the cut end of the scion and the rootstock once the top has been removed ready for grafting.
Place a zip lock bag over the graft with two leaves inside the bag and seal on each side.
About two weeks after grafting the terminal bud will start swelling. As leaves appear the bag can be removed.
The grafting tape can be removed after 8-10 weeks once the graft union has healed, or longer if necessary.
Graft tape should be removed immediately after any restriction of plant stem is seen. Suckers from the rootstock, below the graft, must be removed as they appear.
This graft is used when the rootstock is much larger than the scion material. This is an effective graft, but requires more experience.
First, cut a long sloping cut (25-30mm) on the side of the rootstock at about 10-20cm above soil level. Do not sever the rootstock. The top portion is temporarily retained.
Cut the scion into a wedge with one side slightly longer on one side. The length of the wedge needs to match the length of the cut in the rootstock.
Exert slight pressure on the rootstock above the incision. Insert the scion lining up the cambium layers. Cut off the top of the rootstock just above the union. Bind the graft with grafting tape. Cover the graft with a zip lock bag and seal on each side.
Care of grafts
Newly-grafted plants need 50% shade. Do not overwater, remember that the reduced leaf area means that the plants require less water.
Remove any shoots that may develop below the graft.
Depending on the growth and vigour of the plants, the trees should be able to be planted out six months after grafting.
Do not plant out if the trees are flushing. The new growth will get sunburnt and lead to poor establishment.
Varieties of mature trees can be changed by “reworking”. The tree needs to be in good health for this process to be effective.
First, the old trunk is cut leaving one nurse branch. The nurse branch will provide some shade and help produce energy to grow new shoots. Paint the trunk with diluted white acrylic paint to protect it from sunburn.
Shoots will develop around the trunk. When these are 7-10mm long, three or four can be grafted as described previously. Cover the grafts with paper bags to protect them from sunburn.
The reworked tree should produce fruit within two years.
The only disadvantage of this technique is the possibility of weak unions. Some branches may break off when heavy production starts or during severe storms.