Lesson-2A (Complementary Video-note) Seed Germination and Dormancy 18OCT2026
Lesson-2A (Complementary Video-note) Seed Germination and Dormancy 18OCT2026
Every crop we grow begins as a seed, and every seed carries a problem: it must survive, sometimes for years, until the moment is right to grow. In Lesson 2A of AGR3301 Crop Physiology, we look at how seeds are built, how they survive storage, and why a perfectly healthy seed may refuse to germinate. The full lecture video is embedded below, with edited subtitles and chapter markers so you can jump to any topic.
How a seed is made
Most seeds arise through sexual reproduction. Flowering plants use double fertilisation: one sperm fuses with the egg to form the zygote (2n), which becomes the embryo, and a second sperm fuses with the two polar nuclei to form the triploid (3n) endosperm, the seed’s food store. The ovule becomes the seed and the ovary becomes the fruit. A fun consequence: when you drink coconut water or enjoy roasted coffee, you are consuming triploid endosperm.
Seeds bring new gene combinations, which breeders depend on. Vegetative propagation, by contrast, gives genetically identical clones. That uniformity is convenient for a plantation, but risky: one disease can sweep through a whole field of identical bananas.
From dust to 25 kilograms
Orchid seeds are so small they look like dust. They carry no endosperm and need a specific fungus to germinate in the wild, which is why commercial orchids are grown by tissue culture. At the other extreme, the coco de mer produces a seed of up to 25 kg that can float across oceans. Between these extremes, seeds use hard seed coats, dormancy, size strategies, the soil seed bank and dispersal by wind, animals, water or explosive pods to survive. The soil seed bank explains why weedy rice (padi angin) is so hard to eradicate from Malaysian rice fields.
Inside the seed
We look at the parts of the dicot and monocot seed, and at endospermic seeds such as rice and maize versus non-endospermic seeds such as beans. In cereals, the aleurone layer, the living outer layer of the endosperm, is packed with nutrients and enzymes. Polishing brown rice into white rice removes this layer along with the bran (dedak), which is why the most nutritious part of the grain often ends up as animal feed.
Drying, storage and survival
As many seeds mature, they dry out, their metabolism slows almost to a stop, and their cytoplasm turns glassy. This maturation drying lets them survive storage, but it is not the same as dormancy. Seeds also differ in how much drying they can take:
Orthodox seeds, such as rice, can be dried and stored cold for years.
Recalcitrant seeds, such as rambutan, durian and cocoa, are damaged by drying and cannot be frozen.
Intermediate seeds, such as coffee and papaya, fall in between.
Proper drying also protects food safety. Damp, poorly dried grain can be colonised by Aspergillus moulds that produce aflatoxin, a toxin dangerous to humans.
Dormant, quiescent or dead?
A seed that fails to germinate is not necessarily dormant. A quiescent seed simply lacks water; a dormant seed refuses to germinate even when conditions are right; a dead seed never will. In class, students worked through three seed lots, using germination tests and the tetrazolium viability test to tell them apart.
We then covered the five dormancy classes used in seed science: physical, physiological, morphological, morphophysiological and combinational. Each is broken by a different treatment, from scarification and stratification to controlled dry heat for oil palm. A class quiz on 20-year-old rice seeds found in a grandmother’s bedroom showed how Occam’s razor helps us reason our way to the answer.
What’s next
Lesson 2B continues with germination itself: what a seed needs, the three phases of water uptake, how hormones and enzymes mobilise the food store in barley, how light controls lettuce germination through phytochrome, and how a seedling establishes itself in the field. Complementary Note:
Video Transcript:
Comments