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Citrus And Avocado From Seed

71227Is it possible to grow citrus from seed? The quick and simple answer to that question is, “Yes.” After all, many cultivars of citrus were originally bred from other cultivars, and then grown from seed. But of course, this an overly simplified answer to an unrealistically simple question about a surprisingly complicated process. Perhaps a better question is “Should citrus be grown from seed?”.

Almost all citrus are grafted for a variety of reasons. Those that are not grafted are grown from cuttings only because they do not need whatever advantages understock (or rootstock) provides for their counterparts. Either way, they are all cloned by some form of vegetative propagation. This ensures that they are all genetically identical to their parents, without potential for genetic variation.

Citrus have been bred and developed so extensively that most types are very genetically variable. Those that are the most variable tend to produce fewer seeds, and might even be classified as seedless. Those with more seeds are probably more genetically stable. Nonetheless, it is impossible to predict if seed grown citrus will resemble their parents, or be something totally different.

Furthermore, citrus are cloned from ‘adult’ growth that is ready to bloom and develop fruit. Those grown from seed start out with vegetative ‘juvenile’ growth that will not bloom. Juvenile growth is typically more vigorous and thornier than adult growth, and possibly wickedly thorny! Some types of citrus outgrow their juvenile phase quite readily, while others may take several years to do so.

Avocado trees grown from seed exhibit some of the same difficulties. Although they lack thorns, they do grow very vigorously and very tall for quite a few years before they bloom. By the time they develop fruit, the fruit could be too high to reach, and quite different from the original.

Just because citrus and avocados can be grown from seed does not mean that they should be. However, different is not necessarily bad. Many seed grown avocado trees get pruned into

Posted on by tonytomeo · 14 Comments

Oasis

P80630KWhat are they doing out there, in those two pots in the island of such a vast parking lot? It is hard to say from this distance. They are so isolated. They might be happy and healthy summer blooming annuals. They might just be weeds. They could be plotting World domination. Plants can do some weird things in isolation.

Mexican fan palm is the most familiar palm in Los Angeles. Some know them as skydusters because they are so tall and lanky, and do not seem to have anything better to do than lazily brush against the undersides of clouds as they float by. In Los Angeles, there are not many clouds to keep them busy, and there is not even much smog anymore. Mexican fan palms certainly do not make much shade, and because they are so tall, their little shadows land in neighbors’ yards. They are so tall that you might be able to see them from wherever you are merely by looking towards Los Angeles. Instead of getting Frisbees and kites stuck in their canopies, they collect satellites. When they drop one of their big leaves, it burns up in the atmosphere.

In their natural environment, Mexican fan palm lives in a large and mostly contiguous native range (areas) in which individual colonies are not isolated for too long. Pollen gets shared rather thoroughly. Trees are consequently very similar throughout the range. Slight genetic variation is only perceptible in regions such as Los Angeles, where various groups of trees are grown from seed collected from various regions of the native range.P80630K+

Sometime in the ancient history of the specie, a few individuals decided to leave the rest of the herd and go live in isolation out in the adjacent deserts. They could only survive where there was a bit of water, so they inhabited any oasis they could find. This might have happened as some trees migrated up canyons that had perennial creeks flowing through them only to have the lower portion of the canyon go dry as outflow from above decreased. Seismic activity within the region has a way of altering the outflow of springs. Anyway, these more reclusive palms eventually became a separate species, or subspecies, or variety, depending on the botanist providing the information. This separate species (or subspecies or variety) is now known as the California fan palm, or the desert fan palm. It thrives on the hot and arid desert air, but is not very happy in milder and more humid coastal climates. (I am sorry that I do not have a good picture at the moment.)

Unlike Mexican fan palm that lives in a big contiguous range, California fan palms lives in small isolated colonies where they can not share their pollen freely with other colonies. Over thousands of years, each colony adapts to its specific environmental conditions. Genetic variation within colonies is not perceptible, but is quite obvious in landscape situations where trees grown from seed from different colonies can be compared.

California fan palm is much shorter and stouter than Mexican fan palm. It does not need to compete with too many other specie out in the desert. The trunks are straighter, and the canopies are fluffier. Unlike the very informal and relaxed Mexican fan palm, it is an excellent palm for formal landscapes. It is the specie that flanks the famous Palm Driveway at the Winchester House in San Jose. The only stipulation for these formal installations is that all the palms must be grown from the same batch of seeds procured from the same colony.

Posted on by tonytomeo · 12 Comments

Cultivars Are The Real Cloned Mutants

80516thumbIt is not science fiction. It involves neither ninjas nor turtles. Cultivars really are mutant plants that can only be propagated by cloning. The word ‘cultivar’ is a portmanteau (two words combined into a single word) of ‘cultivated’ and ‘variety’. Unlike other varieties of plants that can be perpetuated by seed, cultivars must be cultivated by unnatural techniques to maintain their genetic distinction.

For example, ‘Alamo Fire’ is a variety of Texas bluebonnets with maroon flowers. The original seed were collected from a few naturally occurring variants with maroon flowers, and grown into more plants with maroon flowers, which provided more seed. No seed was collected from those that bloomed blue. By repeating this process of selection a few times, the variety was developed.

The variety ‘Alamo Fire’ is now sufficiently genetically stable to perpetuate itself, which means that subsequent generations will also bloom with maroon flowers. However, a few blue flowers might bloom in any generation; and unless they are weeded out before producing seed, they will eventually dominate until the entire colony reverts from maroon back to the more genetically stable blue.

‘Meyer’ lemon is an example of a cultivar. It must be propagated vegetatively by cuttings, or perhaps grafted onto understock. In other words, it must be cloned. It is a genetically unstable hybrid of a lemon and an orange, so plants grown from their seed would be very different from the parent. Many hybrids are so genetically unstable that they are sterile, and unable to produce viable seed.

Many variegated or dwarf cultivars of all sorts of plants are not hybrids, but are mutants. It is common for some arborvitaes to produce ‘sports’, which are simply mutant growth that is somehow different from the original growth. If a sport has a desirable characteristic, such as densely compact growth, variegation, or golden foliage, it can be cloned as a cultivar. Just like ‘Meyer’ lemon, a dwarf golden arborvitae is very unlikely to produce genetically similar seedlings.