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Grow True To Type Citrus From Seed

Last fall about the same time I germinate lychee seeds, I had a kumquat seed from a fruit I ate. I sowed this seed and was surprised to see four small seedlings sprout about a month later. I did some research and learned that most citrus can be grow from seed and produce true to type fruit. The seedling will have the same characteristics as the mother plant.

Monoembryony, nucellar embryony and polyembryony in citrus seeds.
Monoembryonic– development of only one (usually zygotic) embryo in a seed.
Nucellar embryony- embryos form directly from the nucellar tissue of the seed without the genes of the father plant.

Polyembryony– occurrence of more than one (usually nucellar) embryo in a seed.
Zygotic – sexually produced, contains genes of both parents.

Monoembryonic Monoembryony is the usual case in many living creatures. A seed is formed that consists of one embryo that is sexually produced (zygotic) and inherits the genes of both parents. In other plants (not Citrus) the seeds being true to type is often caused by the incompatibility of the pollen of other species.

Three important citrus types produce monoembryonic and therefore zygotic seeds only.

‘Clementine mandarin
Pomelo, Citrus maxima
‘Temple’ tangelo

These three have been widely used in breeding because they are of high quality and all crosses of these as mother plants produce hybrid seeds and not cellars.

Nucellar embryony

Nucellar embryony is a form of seed reproduction that occurs in many citrus varieties. During the germination of seeds from plants that possess this genetic trait, the nucellar tissue which surrounds the embryo sac in the ovule can produce additional embryos (polyembryony) which are genetically identical to the parent plant. These nucellar seedlings are essentially clones of the parent. By contrast, zygotic seedlings are sexually produced and inherit genetic material from both parents. Nucellar embryos begin development as soon as pollination occurs while zygotic embryos take four weeks to develop; thus, nucellar embryos often crowd out the zygotic embryos. Pollination is usually needed to trigger nucellar development.

Nucellar embryony is important to the citrus industry. Most commercial rootstock varieties produce mainly nucellar seedlings which do not inherit any of the traits of the “father” plant. This allows for the production of uniform rootstock which yields consistent results in fruit production. However, this trait causes problems for cross-breeding. Hybridising two plants that produce mostly nucellar embryos can be very difficult.

Sweet oranges (mostly polyembryonic) cannot be successfully crossed. Practically all currently available sweet orange varieties are spontaneous mutations that first occurred either as seedlings or more often as limb sports or bud mutations.

Polyembryony

Polyembryony means the occurrence of several embryos in one seed. Most polyembryonic seeds are usually nucellar. The amount of polyembryony within a seed varies from type to type.

Which citrus fruits will come true to type from seed?

Tom McClendon writes in Hardy Citrus for the South East:
“Most common citrus such as oranges, grapefruit, lemons and most mandarins are polyembryonic and will come true to type. Because most citrus have this trait, hybridization can be very difficult to achieve. In the late 19th century, when the first attempts at controlled hybridization were attempted by the United States Department of Agriculture in Florida, Walter T. Swingle reported that more than 1,100 sweet orange seeds pollinated with trifoliate orange pollen were required to produce the first citranges, and seven of these came from a single fruit. The good news is that polyembryony helps stabilize varieties, which allows seeds to be passed around with little chance of spreading diseases such as viruses. This unique characteristic allows amateurs to grow citrus from seed, something you can’t do with, say, apples.”

Highly polyembryonic citrus types
Will mostly produce nucellar polyembryonic seeds that will grow true to type.

key lime
citranges
kumquats
rough lemon
Palestine lime (Indian sweet lime)
calamondin
grapefruit
sweet oranges (Blonde, navel and blood oranges)
‘Nasnaran’ mandarin
Shekwasha’ mandarin
Cleopatra’ mandarin
Trifoliate orange

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