In our last post, we discussed how commercial avocado growers overcome the juvenile phase using seed as a rootstock to grow their trees. However, the seeds may have been cross-pollinated and therefore not be a true clone of the cultivar from which it was taken.
Thankfully, there is a second method, known as clonal rootstock propagation, that solves this problem.
Clonal propagation is commonly done according to the Frolich method. A seed is used the starter material, just like the seedling rootstocks. The seedling is grown and then grafted with a bud belonging to a mature plant of a rootstock cultivar, like ‘Duke 7’ or ‘Dusa’.
Afterwards, the plants are placed in a dark room, causing the shoots from the buds to etiolate and grow new shoots. Paper bags can be used to mimic the effects of a dark room. Once these shoots are about 20cm long, the plant is removed from the dark.
Rooting hormone is applied just below the graft. The seedling is covered with soil, leaving only the upper third of the etiolated shoot emerging from the soil. The plants are then left in a greenhouse to harden off and recover.
Following this, a second graft will take place using buds be taken from a matured scion cultivar. These buds will grow the desired fruit of choice, like ‘Hass’ or ‘Fuerte’. As the tree grows, the root system from the first graft will overtake the roots that were grown from the starter seed.
The clonal method is more time consuming and requires specialized materials, which is why smaller growers propagate trees using seed as the rootstock. However, the main benefit of clonal propagation is that the grower will know the exact characteristics of the rootstock because the first graft was made using cloned material from the rootstock cultivar.
We may be able to tell you why!