Fruits
Senior 2 · Agriculture
Fruits
Lesson 2 of 5
20 min
Let's begin
Habimana plants the seed of a delicious avocado he bought in Kigali. Seven years later the tree finally fruits, and the avocados are small, stringy and ripen at the wrong time of year. His neighbour bought a grafted seedling of a known variety from a certified nursery; it fruited in its third year, and every fruit looks like the parent.
The difference is the propagation method. Propagation means producing new plants from a parent plant, either from seed (sexual propagation) or from a vegetative part such as a stem, bud or sucker (asexual or vegetative propagation).
A seed forms after pollen from one flower fertilises an ovule. The seedling inherits a new mix of characteristics from both parents, so it is not "true to type": it may be better or, more often, worse than the tree the seed came from.
| Advantages | Disadvantages |
|---|---|
| Cheap and simple; many plants from little material | Offspring vary; fruit quality is unpredictable |
| Seedlings have strong, deep tap roots and live long | Long juvenile period: many fruit trees take 5–9 years to bear |
| Seeds are easy to store and transport | Trees are often tall and hard to harvest |
| Source of new varieties and of rootstocks for grafting | Some fruits have few or no viable seeds (banana, pineapple) |
Seed is used for papaya and often for passion fruit, and above all to raise rootstocks for grafting avocado, citrus and mango.
A new plant grows from part of one parent, so it is a clone: genetically identical to the parent and true to type.
| Advantages of vegetative propagation | Disadvantages |
|---|---|
| True to type: fruit quality is known | Needs skill, tools and time (grafting, tissue culture) |
| Early bearing, often in 2–4 years | More expensive planting material |
| Grafting combines a good fruiting variety with a tough rootstock (disease, drought or soil tolerance) | Diseases (especially viruses) pass from parent to all its clones and spread on dirty knives |
| Works for seedless or low-seed crops | All plants are identical, so one new pest or disease can hit them all |
Question: For each case choose the best propagation method and give one reason. (a) Establishing an export avocado orchard of the Hass variety. (b) Expanding a pineapple field. (c) Raising citrus rootstocks. (d) Planting bananas in a district where banana diseases are common.
(a) Grafting Hass scions onto seedling rootstocks: every tree gives true-to-type Hass fruit, bears early, and the rootstock provides a strong root system.
(b) Suckers, slips or crowns: pineapple sets few viable seeds, and these shoots grow quickly into plants identical to the parent.
(c) Seed: rootstocks do not need to be true to type for fruit, and seedlings have vigorous tap roots; citrus seeds are also often nucellar (they produce seedlings identical to the mother tree), which keeps rootstocks uniform.
(d) Tissue-culture plantlets: they start free of pests and diseases, unlike suckers dug from an infected field.
Tip
Memory hook: "Seed surprises, clones copy." Seed gives variable offspring; vegetative methods copy the parent exactly (good fruit and bad viruses alike).
Exam technique: in advantages and disadvantages questions, write matched pairs and use comparative words ("earlier bearing than seedlings") so the examiner sees you are comparing the two methods.
Define vegetative propagation.
Solution: Producing new plants from a vegetative part (stem, bud, root, sucker or tissue) of one parent, without seed, so the new plants are identical to the parent.
Give two reasons why farmers rarely plant avocado seeds to establish a commercial orchard.
Solution: Seedlings are not true to type, so fruit quality is unpredictable; they take many years (often 5–9) to bear, and grow into very tall trees.
State three planting materials used to propagate pineapple.
Solution: Suckers, slips and crowns.
What is air layering?
Solution: Making a stem form roots while it is still on the parent: a ring of bark is removed, the wound is wrapped in moist soil or moss and covered with plastic, and the rooted stem is later cut off and planted.
Explain how vegetative propagation can spread passion fruit woodiness virus.
Solution: Every plant propagated from an infected parent carries the virus, and sap on cutting tools transfers it to healthy plants. Clean, certified planting material and disinfected tools prevent this.
Summary
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
