KEN MUDGE: Now let's take a look at some examples of natural adventitious root formation. Here, for example, is a plant called dischidia. And you can notice at each one of the nodes, there are small roots forming. These are adventitious roots occurring on the stem of an intact plant. And so this is basically an example of the natural layering. Let's take a look at another plant up the way.
Here is Philodendron [? stillosum. ?] And you can see all these roots here. Now, you might think that those are just branches of the root system, but no. This is actually the stem. Those are leaf scars. This is stem tissue. And these are adventitious roots occurring on the stem system of this philodendron plant. So this, once again, is an example of natural layering. These larger roots have actually growing down and anchored themselves into the soil, and they can provide water and nutrients for the entire plant.
This monstera is an example of a chimeral plant where we have two distinctly different types of tissues of different genetic composition within the same plant. And when you're propagating this from cuttings or different asexual propagation techniques, it's important how you propagate the plant if you want to maintain this chimera, this variegation pattern.
If you propagation from a portion of the stem where the tissue is entirely green, you'll get a green plant. If you propagate from a section that's entirely white, you'll get a white plant. Only by choosing selected buds that have both white and green tissues will you get a plant that maintains this mixture of colors, this variegation. Notice too the adventitious roots on the stem of this plant.
Here's an interesting plant called Kalanchoe or Bryophyllum. You'll notice that these are just normal looking leaves, but when one of these leaves falls off-- or we could actually detach one and stab it on the end of this leaf of an aloe-- and leave it there for a few weeks, and it would form foliar embryos. There are some examples of those over here as a matter of fact.
A couple of leaves have fallen to the ground. I'll pull one up, and you can see at the margin of that leaf, we have a foliar embryo that has initiated. Its root system has grown out to anchor it into the soil down there, and it's growing its own shoot system. So this is an example of foliar embryogenesis that is induced by wounding or by the leaf falling off. Other plants, it occurs spontaneously while the leaf is still attached to the parent plant. I don't see any good examples there.
Here's another example of basically leaf cutting propagation. This is a jade plant, or crassula argentia. It's possible to remove these leaves, just pinch them off. There's no bud there. This is strictly leaf tissue, and it will form an adventitious bud which turns into an adventitious shoot. There's one that's happened to fall off here, and that's an adventitious bud. Now, unlike the foliar embryos that I've shown you earlier, this is actually not foliar embryogenesis, but in fact adventitious bud formation first. And then subsequently, adventitious roots will form at the base of that bud or developing shoot. Very similar, but slightly different developmentally.
Here are some cacti that have been broken off from the main plant. And you notice they're just laid down on a fairly dry media, and they form adventitious roots even in this very dry environment. So this is basically a natural cutting propagation.
Now, this is one of several citrus we have growing in the greenhouse here. It is a Meyer lemon, citrus lemon. And these are typical of citrus fruits. They produce seeds. You've all seen them. And that seed is basically an example of apomixus. A given seed will have several embryos in it. And if you plant that seed, instead of seeing a single seedling, you'll see two or three. One of those two or three will be a normal sexual, or zygotic, embryo, but the other one or two will be apomictic embryos. That is, they are genetic copies, clonal copies, of the parent plant.
That's a mango, but nothing in particular. It's also a plant that forms apomictic seed.
These begonias happen to be a group of plant that can be propagated by leaf cuttings. Actually, if you look at it from the standpoint of which plants will and will not propagate from leaf cuttings, most of them won't. But certain plants like begonias, various different kinds here, or Sansevierias will easily propagate from loose cuttings. And a case like this, you would just detach a leaf, take out your handy pocket knife that no horticulturist is without, and make some incisions in the leaf veins without cutting your fingers, and then simply lay this leaf down on a suitable media like sand, perlite, or even soil. Often necessary to pin it down. You can do that by placing a couple of small pebbles on it.
And at each of the damaged or wounded veins, you'll get, first of all, adventitious root formation. And then some weeks later, you'll get adventitious buds forming. So again, that is not a matter of foliar embryogenesis, but instead sequential adventitious organ formation, adventitious roots followed later on by adventitious shoots.
I talked about how one of the earliest domesticated plants that was propagated asexually was fig. In fact, this is a member of the genus Ficus. And figs typically are very easy to root from cuttings. And so we could chop off one of these larger branches, strip off all the leaves, sharpen the end to a point, and jam it in the ground, and it would within a matter of a few weeks, form adventitious roots and the shoot system would continue to grow.
African violet is another example of the relatively few species that can be easily propagated from leaf cuttings. In fact, most plants in the Gesneriaceae family are readily propagated from leaf cuttings. In a case like this, you would just take a portion of the leaf, place it in the suitable growing media, and it would form adventitious shoots and adventitious roots.
Now, this plant is also propagated by micropropagation in which case you would have to sterilize this leaf, cut it up into pieces, place it in a culture vessel on a suitable nutrient media in the presence of the hormone cytokinin. And the cytokinin hormone would stimulate adventitious bud formation followed by adventitious rooting.
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In this Room I share with you my fascination with plant reproductive biology and its application to horticulture and related disciplines.
I begin by dispelling the widely held oversimplification that "plants grow from seeds" - indeed many of them do, but quite a few have evolved the capacity for asexual (clonal) reproduction. Even before the origins of agriculture, about 12,000 years ago, mankind has been observing wild plants performing feats of asexual reproduction.
From this increasingly sophisticated understanding of the natural history of cloning, early agriculturists domesticated a number of fruit, nut and other food crops and eventually a host of ornamentals as well. The Room includes hands-on demonstrations of clonal propagation by layering, cuttings, grafting and micropropagation.
This video is part 7 of 7 in the Natural and Human History of Plant Cloning series.