Why do trees have to be certain age to produce fruit?

A similar question is "How does a fruit producing tree differ in anatomy and physiology from a juvenile tree that has not yet fruited? Why doesn’t a tree start producing fruit soon after its seed has germinated?

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The tree would be killed by th fruit before it was sizable enough to take care of itself

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Genetics. I couldn’t reproduce soon after being born. Fruit is part of the tree reproduction. It takes energy to grow. It takes energy to reproduce. Trees growing allows a better chance of getting sun and supporting fruit. First growth then fruit it makes sense for natural selection or design.

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I have some apple rootstocks I grafted mature scions onto last year. They are ~16” tall and already developing fruit buds. I doubt anything develops from those buds but it is interesting how fruiting does not seem to be entirely connected to the size of the tree but rather to the genetics and having the nutrients needed to reproduce. I guess that is how bonsais are capable of fruiting.

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Typically it’s the age of the wood that determines when a blossom bud develops that can produce fruit. Its common for new grafts to set fruit the first year. This is important to know before you begin pruning any variety because you want to preserve your fruit buds:
Nectarines (Prunus persica nectarina) – fruit mainly on 1-year old wood. Self-fertile, only varieties with ‘Hale’ in their parentage will require another variety for pollination. Nectarines are really just smooth peaches without the ‘peach fuzz’.

Peaches (Prunus persica) – fruit mainly on 1-year old wood. Self-fertile, only varieties with ‘Hale’ in their parentage will require another variety for pollination.

Plums, European (Prunus domestica) – fruit on long-lived spurs on 2-year old wood and older. Most varieties require a suitable pollinator, but some varieties, such as Green Gage, and Damsons are self-fertile.

Plums, Japanese (Prunus salicina) – fruit on 1-year old wood, and on short-lived spurs on older wood. Most varieties require a suitable pollinator, but some varieties, such as Santa Rosa are self-fertile, while varieties such as Mariposa are partially self-fertile…

Quinces (Cydonia oblonga ) – fruit on current season’s new growth. Self-fertile.

Cherries, Sweet (Prunus avium) – fruit on 1-year old wood and older on branches and on long-lived spurs. Some varieties are self-fertile, while others require a pollinator. Popular red cherry is the Stella variety, and dark cherry is the Lapin variety, both are self-fertile.

Cherries, Sour (Prunus cerasum) – fruit on 2-year old wood. Self-fertile. The popular dark-red sour cherry is the Morello variety.

Figs (Ficus carica) – fruit at the base of current season’s new growth, but some varieties crop twice a year and also produce an early breba crop on the tips of 1-year old wood. Self-fertile.

Apples (Malus spp .) – most apples fruit on spurs on 2-4-year-old wood, some fruit on tips of short side branches. Most varieties require a suitable pollinator, but some varieties, such as Golden Delicious, Red Fuji, and Red Jonathon are all partially self-fertile. Apples are wind pollinated.
Dennis
Kent, wa

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Your profile says you teach Biology.

Just thought the question a little queer.

Unless this is a practice exam.

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The age of the wood makes sense, but my rootstocks are older than the scion wood yet no fruit buds on any of the backup branches, understandably, because the rootstocks are not mature enough. So in addition to the age of the wood there must also be some genetic programming involved.

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@BlueBerry By “college biology courses” that I teach, I meant biochemistry, human genetics, microbiology and human anatomy and physiology as well as introductory biology.

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Humans become capable of reproduction at a certain age because a part of the brain keeps track of time and at the appropriate time, certain hormones are released that result in physical maturation and ability to reproduce.
What about trees? Where is their time keeper and what happens when the time keeper says it is time to become mature? Are certain hormones released? (Probably not because an immature scion grafted to a mature rootstock does not bear fruit sooner.)

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A one year apple tree seeling may take 7 or 8 years to bear fruit.

So, you’re saying if I snip that seedling and graft to a mature tree, I’ll still not get apples for 6 or 7 years?

I don’t believe so.

For citrus trees Maturity is triggered by leaf node counts from the roots. A tree with out enough resources will drop its fruit or fail to flower.

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Perhaps there are genes that just need to be “activated” to begin to produce fruit buds, but I am sure there are more dependencies than just that.

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Staying away from the idea that plants can sense when they are ready, here is a paper that discusses microRNA changes that influence change from juvenile to adult phase in three selected tropical fruit species (Avocado, mango, macademia). I think it’s pretty complicated biochemically. I can’t speak to whether domestication has changed that molecular biology process. Quoting that article, “In plants, juvenile to adult phase transition is regulated by the sequential activity of two microRNAs: miR156 and miR172. A decline in miR156 and increase in miR172 abundance is associated with phase transition.” I imagine that in some undomesticated plants, delaying fruiting might allow greater plant height before fruiting, which might improve chances for successful reproduction.

Some people graft seedlings onto precocious rootstocks or already-fruiting branches to induce early transition from juvenile through to productive phases. I don’t know how successful they are. I had a NorthPole apple that I grafted onto Bud-9 rootstock make apples when two feet tall, which I didn’t want it to do out of concern for stunting growth.

Again, quoting that article, "Various endogenous factors interact with environmental cues to facilitate vegetative to reproductive phase transition in annual as well as perennial plants. However, limited information regarding the molecular regulators of phase transition is available in commercially significant horticultural tree crops, mainly due to their complex life cycle and limited genomic resources. "(stopping to take a breath now)

Looking at it a completely different way, these folks found that apple seedlings didn’t flower until they reached 77 internodes and didn’t fruit until 122 internodes. They surmised that horticultural practices that speed getting to that size would speed the transition from juvenile to adult, and adult to fruiting phases. I think that once a tree branch has transitioned from juvenile to productive phase, it usually stays that way even if you cut it off and graft it onto different stock. Not always but I think it happens a lot.

I think it would be fun if apples could be grown like tomatoes, planting seeds in spring and harvesting big fruits throughout the summer. Obviously it works differently for tomatoes. I have two seedling apple trees, grown last year from cross of Redlove™ Calypso™ x Golden Sentinel™, which look a lot to me like they have flowering spurs at about 50 internodes. I did start them indoors so they had a long growing season. Who knows, those might not be flowers at all.

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I haven’t read the paper in the link yet, but this internode relation is interesting. I guess you could provide a ton of nitrogen to promote green growth but prune in a way that it produces multiple branches from each cut and keep going like that to rack up the internode count. You would end up with a dense mess of branches but they would be “eligible” to fruit by year 3 from seed.

I have Jonagold and Arkansas Black trees on M111 I got in winter 2020 from Stark Bros. I grafted a G11 rootstock to the base as a goofy experiment and last spring the deer ate the bajeezus out of the leaves and stunted their growth, but now they have several fruit buds each. They are certainly not at the 100+ internode count, seeing as they are both only 4ft tall, but maybe the secondary G11 dwarf rootstock is affecting that somehow.

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@BlueBerry That is not what I said.

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What would happen if a 2-year old human got pregnant? The fetus would steal needed nutrients from the mother, so the mother would grow poorly. The mother would find it impossible to supply adequate nutrients to the fetus, so the fetus would grow poorly. And if the fetus did manage to grow, its size and weight would break the mother. Basically the same answer for fruit trees, right?

@jrd51 In plants, as in humans, there is a selective advantage in delaying reproduction until the organisms is capable of successfully carrying progeny. But that is not what my question is about.

@Bear_with_me Thank you very much for the article. I skimmed it and it seems very interesting. I will read it carefully later. According to the paper, no one knows what triggers the transition from juvenile to adult to reproductive phases. I am not surprised that a change in gene expression accompanies each transition but what is (are) the trigger(s)?

@jeremybyington I recommend you read the second article. It’s accessible and not too long. The first is there if anyone wants it but wont change gardening practice and is too scientific at least for me to understand more than minimally.

According to the second article, pruning to make a tree bushy wont bring about maturity. Rather, they state it must be internodes on the same stem. They prune off all side branches in their seedlings.

I think the situation is different for grafts taken from already-mature varieties. They already made the biochemical transition to maturity and maybe don’t go back to juvenile but rather just have to grow big enough and make spurs or something.

@Vlad I think that’s the $64,000 question. I don’t have access to academic journals so google scholar is as far as I go. It looks to me like the specific biochemical signals isn’t known, but it’s probably not just biomass.

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@Vlad anthropomorphizing plants is not ideal but analogies work well at a simplistic level. Teaching introductory biochem certainly gives a basic understanding of light and dark reactions but beyond that undergrad biochem does not extend.

To make a point I may anthropomorphize. If we allow a fruit tree to crop too heavily it suffers in large fruit production as they are primed evolutionarily to reproduce unless they are given ideal conditions, in which case they selfishly grow and fruit minimally. This is again an evolutionary mechanism as these plants want to produce but if they have perfect conditions they will be all about growth when not considering survival as this is for lack of a better term more likely to bear fruit. Likewise young plants consider survival over reproduction since that takes up all the energy and focus and they’d rather survive. They are epigenetically focused on doing so as evolution has given us the plants we have now based on their preference to delay fruiting and instead promote growth in the interim.

Unlike human/mammalian biology there is limited funding. I agree that seasonal changes in gene expression is no shock however nailing down the trigger to flower/fruit is likely more complicated than 1 or 2 variables. For example most patients with cancer find the same mutations in healthy cells derived from the same tissue type. This indicates that despite knowing this that additional unknown variables lurk which is a similar sentiment across sciences

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