Information

Can we graft a tree with cells from the seed directly?


Are there any limitation to the grafting so we could only graft a branch to another tree? Could we just use cell from the seed, or just a sprout, to graft onto the tree of the same species?


Tree grafting involves a rootstalk and a scion (part to be grafted onto the rootstalk). Here is a reference on the basics of grafting. Usually, this is done to combine the advantage of a strong or mature root system (from the rootstalk) with desired fruits or buds (produced by the scion). In this case, the roots of the scion plant might be sensitive, disease-prone, or just take a long time to develop (read more here). It is also possible to graft a scion onto the same variety of cultivar. Grafting refers to the joining of vascular cambium of a scion and a rootstock in such a way that they can share resources and continue to grow together (see previous links). As such, adding cells from a seed to a larger plant would not be grafting, because there wouldn't be that pre-established vascular tissue to connect with the vascular cambium of the rootstock. Additionally, a single sprout would not have a good chance of binding well to the vascular system of the rootstock (see link 2).

If you are interested in reading more about different forms of (non-seed) propagation, this resource describes the why/when/and how of grafting and layering (another technique that might help you, if you're trying to propagate only one tree variety as indicated in your question), and there are many great resources on youtube about the basics.


Scion control of miRNA abundance and tree maturity in grafted avocado

Grafting is the common propagation method for avocado and primarily benefits orchard production by reducing the time to tree productivity. It also allows use of scions and rootstocks specifically selected for improved productivity and commercial acceptance. Rootstocks in avocado may be propagated from mature tree cuttings (‘mature’), or from seed (‘juvenile’). While the use of mature scion material hastens early bearing/maturity and economic return, the molecular factors involved in the role of the scion and/or rootstock in early bearing/reduced juvenility of the grafted tree are still unknown.

Results

Here, we utilized juvenility and flowering associated miRNAs miR156 and miR172 and their putative target genes to screen pre-graft and post-graft material in different combinations from avocado. The abundance of mature miR156, miR172 and the miR156 target gene SPL4, showed a strong correlation to the maturity of the scion and rootstock material in avocado. Graft transmissibility of miR156 and miR172 has been explored in annual plants. Here, we show that the scion may be responsible for grafted tree maturity involving these factors, while the rootstock maturity does not significantly influence miRNA abundance in the scion. We also demonstrate that the presence of leaves on cutting rootstocks supports graft success and contributes towards intergraft signalling involving the carbohydrate-marker TPS1.

Conclusion

Here, we suggest that the scion largely controls the molecular ‘maturity’ of grafted avocado trees, however, leaves on the rootstock not only promote graft success, but can influence miRNA and mRNA abundance in the scion. This constitutes the first study on scion and rootstock contribution towards grafted tree maturity using the miR156-SPL4-miR172 regulatory module as a marker for juvenility and reproductive competence.


Reasons for Grafting and Budding

Budding and grafting may increase the productivity of certain horticultural crops because they make it possible to do the following things:

  • Change varieties or cultivars. An older established orchard of fruiting trees may become obsolete as newer varieties or cultivars are developed. The newer varieties may offer improved insect or disease resistance, better drought tolerance, or higher yields. As long as the scion is compatible with the rootstock, the older orchard may be top worked using the improved variety or cultivar.
  • Optimize cross-pollination and pollination. Certain fruit trees are not self-pollinating they require pollination by a second fruit tree, usually of another variety. This process is known as cross-pollination. Portions of a tree or entire trees may be pollinated with the second variety to ensure fruit set. For example, some hollies are dioecious, meaning that a given plant has either male or female flowers but not both. To ensure good fruit set on the female (pistillate) plant, a male (staminate) plant must be growing nearby. Where this is not possible, the chances that cross-pollination will occur can be increased by grafting a scion from a male plant onto the female plant.
  • Take advantage of particular rootstocks. Compared to the selected scion, certain rootstocks have superior growth habits, disease and insect resistance, and drought tolerance. For example, when used as rootstock for commercial apple varieties, the French crabapple (Malus sylvestris, Mill.) can increase resistance to crown gall and hairy root. Malling VIII and Malling IX are used as dwarfing rootstocks for apple trees when full-sized trees are not desired, such as in the home garden.
  • Benefit from interstocks. An interstock can be particularly valuable when the scion and rootstock are incompatible. In such cases, an interstock that is compatible with both rootstock and scion is used. An interstock could increase the disease resistance or cold hardiness of the scion. Plants also may be double worked to impart dwarfness or influence flowering and fruiting of a scion.
  • Perpetuate clones. Clones of numerous species of conifers cannot be economically reproduced from vegetative cuttings because the percentage of cuttings that root successfully is low. Many can be grafted, however, onto seedling rootstocks. Colorado blue spruce (Picea pungens, Engelm), Koster blue spruce (Picea pungens var. Kosteriana, Henry), and Moerheim spruce (Picea pungens var. Moerheimii, Rujis) are commonly grafted onto Norway spruce (Picea abies, Karst.) or Sitka spruce (Picea sitchensis, Carr.) rootstock to perpetuate desirable clones. Numerous clones of Japanese maple (Acer palmatum, Thunb.) that either root poorly or lack an extensive root system are grafted onto seedling Acer palmatum rootstock.
  • Produce certain plant forms. Numerous horticultural plants owe their beauty to the fact that they are grafted or budded onto a standard, especially those that have a weeping or cascading form. Examples include weeping hemlock (Tsuga canadensi.3, Carr. var. pendula, Beissn.), which is grafted onto seedling hemlock rootstock (Tsuga canadensis, Carr.) weeping flowering cherry (Prunus subhietella var. pendula, Tanaka), which is grafted onto Mazzard cherry rootstock (Prunus avium, L.) and weeping dogwood (Cornus florida, L. var. pendula, Dipp.), which is grafted onto flowering dogwood rootstock (Cornus florida, L.). In most cases, multiple scions are grafted or budded 3 feet or higher on the main stem of the rootstock. When used this way, the rootstock is referred to as a standard. It may require staking for several years until the standard is large enough to support the cascading or weeping top.
  • Repair damaged plants. Large trees or specimen plants can be damaged easily at or slightly above the soil line. The damage may be caused by maintenance equipment (such as lawn mowers, trenchers, or construction equipment), or by disease, rodents, or winter storms. The damage can often be repaired by planting several seedlings of the same species around the injured tree and grafting them above the injury. This procedure is referred to as inarching, approach grafting, or bridge grafting.
  • Increase the growth rate of seedlings. The seedling progeny of many fruit and nut breeding programs, if left to develop naturally, may require 8 to 12 years to become fruitful. However, if these progeny are grafted onto established plants, the time required for them to flower and fruit is reduced dramatically. Another way to increase the growth rate of seedlings is to graft more than one seedling onto a mature plant. Using this procedure as a breeding tool saves time, space, and money.
  • Index viruses. Many plants carry viruses, although the symptoms may not always be obvious or even visible. The presence or absence of the virus in the suspect plant can be confirmed by grafting scions from the plant onto another plant that is highly susceptible and will display prominent symptoms.

The world's smallest fruit picker controlled by artificial intelligence

The goal of Kaare Hartvig Jensen, Associate Professor at DTU Physics, was to reduce the need for harvesting, transporting, and processing crops for the production of biofuels, pharmaceuticals, and other products. The new method of extracting the necessary substances, which are called plant metabolites, also eliminates the need for chemical and mechanical processes.

Plant metabolites consist of a wide range of extremely important chemicals. Many, such as the malaria drug artemisinin, have remarkable therapeutic properties, while others, like natural rubber or biofuel from tree sap, have mechanical properties.

Harvesting cell by cell

Because most plant metabolites are isolated in individual cells, the method of extracting the metabolites is also important, since the procedure affects both product purity and yield.

Usually the extraction involves grinding, centrifugation, and chemical treatment using solvents. This results in considerable pollution, which contributes to the high financial and environmental processing costs.

"All the substances are produced and stored inside individual cells in the plant. That's where you have to go in if you want the pure material. When you harvest the whole plant or separate the fruit from the branches, you also harvest a whole lot of tissue that doesn't contain the substance you're interested in," explains Kaare Hartvig Jensen.

"So there are two perspectives to it. If you want to extract the pure substances, you need to do it cell by cell. And when you can do that, as we've shown, you don't have to harvest the plant. Then you can put the little robot on and it can work without damaging the plant," says Kaare.

The team is currently working with plants and leaves, but in the future this type of harvester may be used on a slightly larger scale.

The hope is that this unique approach can create a new source of biomass and spark research into a new area of sustainable energy production.

One thing the technology might be used for in the future is tapping energy from trees, which contain a lot of biofuel.

"In the forests of northern Canada and Russia, there are spruce forests with around 740 billion trees that are completely untouched. That's about 25% of the total number of trees on the planet. By developing this technology, we can tap trees for sugar and make biofuel without chopping down or damaging the trees," explains Kaare.

Artificial intelligence at a microscopic level

The cells in the fruit and leaves that the harvester looks for are 100 microns in diameter, and the tip of the needle is around 10 microns in diameter. The harvest is therefore happening on the scale of the width of a hair.

Magnus Valdemar Paludan, the PhD student at DTU Physics who created the system of image analysis, image recognition, and robot control, explains.

"It's all done with a microscope camera. To begin with, I manually marked pixels on the microscopy images showing the cells that the robot will harvest. That information can be used to train a computer to find similar cells in new images."

Machine learning and a pre-existing neural network, GoogLeNet, are the building blocks of the technology. The network can already recognize macroscopic structures and can sift through an image and tell you if, for example, there's an elephant or a red pepper hiding in the photo.

"We used a technique called transfer learning, where you use the existing neural network's ability to recognize different objects in an image. By showing the computer a number of new images with the manually marked cells, we succeeded in adjusting the network's parameters so it recognizes the microscopic metabolite-rich cells," says Magnus.

"The harvester can then go in and take a picture of the leaf with the microscope camera, run it through the software, and recognize the cells it needs to harvest. Next, it can extract the chemicals automatically using a microrobot, while the rest of the plant remains undisturbed," explains Magnus.


Methods

Study site

The study site is located on the central coast of the Gulf of Mexico (GoM) at the La Mancha lagoon (Fig. 1a) at 19°33′−19°36′ N 96°22′−96°24′ W 44 . The surface of the lagoon’s waterbody covers 135 ha and is surrounded by 300 ha of mangrove forest 45 . Annual precipitation in the area ranges between 1200 and 1500 mm, and the annual mean temperature is 25 °C 46 . Freshwater and marine water inputs into the lagoon come from extreme opposite directions: the connection to the GoM is located in the northern extreme, while a main riverine input is located in the southern extreme. This creates a year-round salinity gradient that increases northward, regardless of seasonality 15,47,48 . This is also reflected in the zonation of the mangrove species, where the northern and most saline environments are mainly represented by A. germinans with minor Rhizophora mangle, which gradually pass into mixed stands co-dominated by R. mangle and A. germinans or A. germinans and Laguncularia racemosa towards the southern end of the lagoon 47,49 .

Within this mangrove forest, 30 × 30 m permanent plots established in 2010 are arranged along the salinity gradient. They are all oriented to true north and located equidistant from the main waterbody. The seven plots selected for this study are located at increasing distances from the lagoon’s inlet to the GoM (between 500 and 3000 m) to capture the salinity gradient along the lagoon. A new plot within the highest salinity range was established in 2017 to include a site with a stand density similar to other sites but with contrasting salinity. For the pre-established plots, existing tree parameters were recovered from a publicly available database 15,50 , including a unique ID, species, x- and y-axis positions in the plot, stem diameter at 130 cm from the soil surface (D130) and height (H). For the newly established plot, the same tree parameters were measured using a laser rangefinder (Laser Rangefinder Forestry Pro 550 Nikon Vision Co., Ltd, Tokyo, Japan), and tree positions were determined using a compass and the rangefinder following standard forestry procedures 51 . A total of 482 trees were recorded for all plots.

For each plot, during April and September 2017, two pseudo-replicate porewater samples were collected from each corner and the middle of the plots from 20 cm below the ground surface using a custom-made porewater extractor 52 and immediately analysed for pH, salinity, temperature and redox potential (Ultrameter II Myron L Company) 53 .

Root graft data collection

A non-destructive method was used to detect the potential location of root grafts using a portable Doppler ultrasound probe (DU SonoTrax Basic Edan Instruments GmbH, Hessen, Germany) and a set of steel rods. The mangrove roots were gently located with steel rods with the DU probe placed on the tree stem. Following an adapted method originally developed to measure the woody root extensions of A. germinans 30 , the probe was then gradually moved from the stem to the consecutive rods in contact with the target root. Each tree was examined following the consecutive order of the tree tag numbers within the plots by assessing their grafting to all immediate neighbours.

Placing the DU on a tree stem collar ring, a steel rod was used to probe the soil to shallow depths, and an amplitude monitor indicated when a root belonging to the stem was touched. Leaving this first steel rod in contact with the root, a second rod was used to further probe close to the first rod in the assumed direction of the course of the root until another positive signal was obtained. The interchangeable waterproof probe of the DU was then attached to the second steel rod, having been proofed to be in contact with the initial root, and the process repeated until either the root was too deep or too thin to be followed or led to another tree. In the latter case, the probe was held on the second tree stem and the last verified steel rod was used to again probe until another positive signal was returned by the DU from the second stem. The DU-located root graft was then verified by localised excavation of each target tree’s neighbour. Although we were unable to verify false negatives, we calculated a 6% probability of finding false-positive connections (i.e. 12 false positives out of 200 connections detected), all identified false positives were treated as non-grafted trees. We did not have any means to evaluate false-negative rates.

Using this method, all A. germinans tree’s (376) root systems were followed during April and May 2017. These were mapped and used to determine the grafted network topology: node degree (number of direct connections for each tree), number of groups of grafted trees and mean group size (number of individuals within a group).

To estimate the pressure each tree receives from its neighbours, an index of neighbourhood asymmetry was calculated as a function of the size and distance of all neighbouring trees (treesj) within a 5 m radius of the target tree (treei see Supplementary Methods for computation details) regardless of their species. A large index of neighbourhood asymmetry implies that the neighbours are large and in close proximity, potentially exerting higher competition pressure on a target tree than a small neighbourhood asymmetry would. The 5 m radius was chosen because it had been previously identified as the optimal radius for detecting the responses of trees to its neighbours at the same study site 15 . Neighbourhood asymmetry was only calculated for trees where their complete neighbourhood was within the limits of the sampling plots (183 trees) to avoid biased neighbourhood asymmetry sizes related to incomplete information for neighbouring trees located outside a plot.

Statistics and reproducibility

Both the density of the target species A. germinans and the total stand density (including A. germinans, R. mangle and L. racemosa) were calculated as the number of trees per hectare. The replicate porewater salinity values for each sampling point were averaged, and the resulting five salinity values were used to estimate a mean plot salinity, including the standard error. The proportion of grafted trees at each plot was calculated as the number of A. germinans grafted trees divided by the total number of grafted A. germinans trees in the stand. The top-height trees at each stand (the 20% biggest) were selected as per stem diameter because it was measured in the field and is considered more accurate than tree height, which is estimated through stem diameter measurements 51 .

Logistic regression was implemented using a generalised mixed effects model to assess the probability of grafting as a function of stem diameter, total stand density and salinity. The model included site identity as a random effect and stem diameter, site salinity and total stand density as fixed effects after assessing the autocorrelation between response variables (Supplementary Fig. 6) and all intra- and cross-level interactions between stand density and salinity. All the variables were z-transformed using the mean and standard deviation of each variable across all sites. To additionally estimate confidence intervals of the odd ratios based on stem diameter, for smaller trees (assumed to be 1 SD below the mean) we added 1 SD from the z-transformed value of stem diameter 54 , and accordingly, we subtracted 1 SD from the z-transformed value of stem diameter for higher stem dimeter trees 54 .

To explore the effect of root grafting and neighbourhood pressure on tree allometry, in the generalised additive mixed effects model (GAMM), salinity and condition were included as fixed effects (cyclic cubic regression spline), neighbourhood asymmetry and stem diameters were included as smooth terms with smooth functions (Duchon spline) and the sampling plot was included as a random effect. The best model explaining tree height was selected using a minimal Akaike information criterion value following a stepwise removal of non-significant response variables (N = 141 single-stem A. germinans trees with a computed neighbourhood asymmetry).

In the existing database of tree parameters 50 , multiple-stem trees are recorded following the traditional convention of summing the diameters of each stem but by measuring only the height of the tallest stem 26 , leading to inaccurate diameter -height allometry. To avoid biased results when relating stem diameter to stem height and the probability of root grafting, multiple-stemmed trees (52 trees) were neither included in the logistic regression, nor GAMM, (for which we also excluded trees that did not have their full neighbourhoods inside de plots), resulting in a final number of trees of 324 and 141 included in the logistic regression and GAMM, respectively.

To further assess the effects of root grafting on tree slenderness ratio (an allometric trait that modulates mechanical stability), a linear model was used to evaluate the variations in the slenderness coefficient on the 141 single-stem A. germinans trees for which neighbourhood asymmetry was computed. To normalize the data, we performed a square root transformation of both the slenderness index and stem diameter. The model included slenderness as response, and an interaction term between grafting condition stem diameter and neighbourhood asymmetry. The final model was plotted back transforming the x- and y-axis to the original values of stem diameter and slenderness for simplicity of figure presentation (Fig. 2c).

Network parameters (node degree, number of groups per hectare and group size) were used to assess random network formation by comparing the probability of networks having a scale-free power-law distribution with random process distributions (i.e. log-normal, exponential, and Poisson). Scale-free networks do not occur randomly because a relative change in one node results in a proportional, relative change in another node. Scale-free power-law distributions indicate the continuous expansion of networks and preferential attachment, where new nodes are constantly added and previously well-connected nodes are more likely to acquire new connections 39,55 . We then related network node degree, group size and frequency (number of trees grafted within groups and frequency of groups per hectare, respectively) to stand density and site salinity using simple linear regressions. All 376 A. germinans trees, including multi-stemmed trees, were included in this analysis, as these tests did not use any tree allometric attributes, such as tree height or stem diameter. For the linear regression assessing the relationship between average node degree and forest stand density however, we removed plot 3 from the analysis, as it has an atypical high stand density and low graft frequency that can be explained by the overall high density of small trees (51% of all A. germinans trees had stem diameters <15 cm).

All the statistical analyses were conducted using R programming language 56 . Specifically, we used the lme4 57 , DHARMa 58 , and gamm4 59 packages for the logistic regression and the GAMM construction and diagnosis. For the network analyses, we used igraph 60 to estimate the node degrees and PoweRlaw 61 to explore the distribution. All figures presented were developed using ggplot2 62 .

Reporting summary

Further information on research design is available in the Nature Research Reporting Summary linked to this article.


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How to get all the seeds you need

The first thing you could do to get the seeds is to gather them from their natural environment…

This is the easiest way. For example, in my area I found few naturalised varieties from which I took seeds.

Although their fruit is not that tasty, these will be a good rootstock as they already display the characteristics I need, i.e. the ability to survive in my climate, grow well in my soil, and are pest and disease resistant…

When you’re taking seeds, choose a plant that displays the characteristics you’re looking for. It is important to check for health and vigour, taking seeds from weak plant results in weak offspring.

Collect your seeds after they’ve matured, generally in autumn, and then clean and dry them. Nuts and pods area easy to clean but many seeds in fleshy fruit need little more cleaning. In case you’re wondering ‘how to’ here is a great video to explain it.

Now you can simply use newspaper and kitchen towels to dry your seeds…

Voila! You have your seeds …

Alternatively, you can just buy them…

Luckily, seeds are easy to ship and can be delivered from anywhere in the world. Of course, there are certain restrictions and conditions that have to be met when importing seeds, so you might want to check first.

Buying seeds can be tricky because you’ll need a reputable source. In my example, I ordered my seeds from Balkep, a nearby permaculture project in a similar climate. If the opportunity is available, you can do the same and find someone in your area/region/state from which to order.

I also ordered my Antonovka apple seeds on eBay and received them surprisingly quickly. In a virtual world where everybody can leave feedback on a product, you can easily know who can be trusted on these sites.

If you’re after a specific seed and you can’t find it online, look at The Seed Search Book, this is an excellent resource that offers a list of places where you can find any kind of seed imaginable.

Once you got your seeds, store them in sealed containers in a cool and dry area until you’re ready to sow them. Just remember that annually, seed potency is reduced by 10-20%, so you’ll want to use them as soon as possible.


Introduction

Plant grafting is a vegetative propagation technique that connects two severed plant segments together. The chimera, consisting of the scion and rootstock, survives as a new individual after wound healing. Natural grafting, which occurs when stems or roots of plants attach and fuse (Mudge et al., 2009 ), has facilitated the invention of classic grafting techniques (Fig. 1). In recent years, micrografting protocols have been used increasingly as a tool to evaluate signaling and transport (Turnbull et al., 2002 Turnbull, 2010 ).

The success of the graft depends on the compatibility between the rootstock and scion. Studies have indicated that grafts in different genera of the same family are rarely compatible, but grafts of different species within the same genus can survive by forming an effective graft union (Goldschmidt, 2014 ). The majority of homografts are compatible, with the exception of monocots. Since the wound required for grafting disrupts the plant vascular system (Asahina & Satoh, 2015 ), reconnection of the vasculature is necessary to maintain normal water and nutrient transportation. Most monocots do not have vascular cambia, which may be a reason why grafting fails (Sachs, 1981 Melnyk & Meyerowitz, 2015 ). This further suggests that vascular differentiation during wound healing is a prerequisite for successful grafting.

After cell walls fuse in the graft union, plasmodesmata stretch in small groups over the spaces of the inner cell wall, interconnecting the protoplasts of contiguous cells (Kollmann & Glockmann, 1985 ). Heterogeneous cells then interdigitate through the plasmodesmata (Melnyk & Meyerowitz, 2015 ). The plasmodesmata provide tunnels for small molecules and even selectively permit the movement of macromolecules, such as proteins and nucleic acids. Additionally, vascular reconstruction at the graft union enables macromolecules to be transported (Harada, 2010 ). In recent years, increasing effort has been made to determine how macromolecules are transferred between scions and rootstocks in grafting plants to reveal the mechanisms that control graft-induced changes in plant traits (Paultre et al., 2016 ).

In this review, we first describe several different types of graft-induced phenotypic changes. We highlight existing evidence for the molecular and physiological mechanisms underlying grafting and then propose a framework to interpret how the transportation of genetic materials between the scion and rootstock is related to vascular reconnection and regeneration.


Apple Tree Reproduction

As a child I remember learning about Johnny Appleseed (John Chapman) in school. After eating a Jonathan apple at home I carefully removed the seeds from the core and wrapped them safely in a napkin. My plan was to plant them in the spring and eventually have a tree that would produce all of the Jonathan apples my heart could desire. At the time, I did not know anything about the reproductive life of plants, let alone animals.

The apple tree is an angiosperm or flowering plant. Angiosperms make their first unmistakable appearance in the fossil record during the Cretaceous period (Kenrick & Davis 2004, p. 195). New reproductive strategies helped angiosperms become a great success and diversify into the forms we know today. Male and female structures develop within flowers. Many organisms such as birds, bats, and insects have coevolved to help pollinate angiosperms. Animals have also coevolved to help disperse the seeds of angiosperms.

A variety of insects are attracted to the scent, color and shape of the apple blossom. The honeybee Apis mellifera is the major pollinator of apple trees. Some solitary bees like the orchard mason bee Osmia lignaria are much more efficient at pollinating apple blossoms and are used by many orchards. However, it is the ability to produce honey (which humans desire) that has made Apis mellifera the primary pollinator.

The honeybee eats the nectar and collects pollen (a good protein source) to feed their larvae. As the bee visits different flowers it becomes coated with pollen, which gets transferred to other flowers on other trees. Although the apple blossom has both male and female parts (the apple tree is a hermaphrodite), it is self-incompatible. Apple trees require cross-pollination (Browning 1998, p. 19). So, when the pollen of one apple cultivar or crab apple comes into contact with a flower on a different apple cultivar, specifically the stigma on that flower, the growth of a pollen tube is activated. Click on flower image to enlarge.

Each pollen grain carries two sperm. In the domestic apple Malus pumila each sperm and egg contains 17 chromosomes. One sperm fertilizes the egg in the ovule the other sperm unites with two haploid cells in the same ovule. This process is known as double fertilization and is an important adaptation found in angiosperms. The fertilized egg with 34 chromosomes will undergo cell division to become a zygote and then an embryo. The second fertilization results not in offspring, but rather the development of endosperm, which acts as a nutrient for the embryo. Note the cells in the endosperm have three sets of chromosomes or 51 in this case. The endosperm not only serves as an important food source for the embryos of flowering plants it also is important to other animals. Humans depend upon the endosperm of rice, wheat, and corn. Recent research indicates the endosperm may also act as a fertilization sensor helping to abort embryos of incompatible crosses (Juniper & Mabberley 2006, p.27).

A seed is formed when the endosperm and the embryo become enveloped in a part of the ovule that hardens into the seed coat. The ovary or other parts of the flower in angiosperms develop into a fleshy fruit surrounding the seeds. The apple is a type of fruit called a pome. The calyx forms a tube and the hypanthium becomes a fleshy pome surrounding the true fruit made of five carples each encasing 2 to 3 seeds. Click on seed image to enlarge.

The fleshy fruits of angiosperms are an adaptation for seed dispersal. Many animals use the fruit as a food source, which results in the dispersal of seeds encapsulated within a natural fertilizer! Each seed in every apple represents a unique combination of genes brought together through sexual reproduction. The fact that each seed is unique helps to ensure that the apple tree can adapt to many different environments. The seeds I wanted to plant, as a child, would have each produced a unique tree with unique apples.

How do we get an entire orchard of apple trees all producing identical fruit? The answer is cloning. If you find a particular apple tree that produces excellent apples, budding or grafting can be used to clone the tree. A twig with buds, called a scion, can be taken from the desired tree. The scion and an apple grown from seed are given compatible cuts that will fit like puzzle pieces. The tissue between the bark of both stems must be carefully lined up, so that the cambium layers match. The cambium is tissue between the bark and wood, it produces water-conducting tissue called xylem (which helps make up the wood) towards the center of the plant and food conducting tissue called phloem towards the inner bark layer. Without a healthy cambium layer trees cannot survive. The graft is sealed with wax and bound together with cord or tape. Budding is a type of grafting in which a single bud of the desired tree is used. Click on graft image to enlarge.

Sometimes you can get good apples by crossing two different apple trees. The Pink Lady apple is a hybrid between Golden Delicious and Lady Williams (Juniper & Mabberley 2006, p.176). However, to get an orchard of trees that produce Pink Lady apples you will need to do a lot of grafting because each seed in a Pink Lady is a unique genetic combination! Remember, once you have your orchard of clones you will need the pollen provided by another compatible apple cultivar and some busy bees to produce your crop! Browing (1998) reminds us that the work does not end here just as the American colonists, French, Celts, Romans, and Persians discovered before us, this human-made monoculture will require intense pruning and pest management to be successful (pp. 33-34).

You can explore fascinating connections between the evolution of American apple orchards and the development of apple parers by reading Appeal to American Apple Parers: Historical Perspectives on Orchards and Yankee Ingenuity published in the Autumn 2016 issue of The Midwest Quarterly.


Life Cycle of a Conifer

Pine trees are conifers (cone bearing) and carry both male and female sporophylls on the same mature sporophyte. Therefore, they are monoecious plants. Like all gymnosperms, pines are heterosporous, generating two different types of spores: male microspores and female megaspores. In the male cones (staminate cones), the microsporocytes give rise to pollen grains by meiosis. In the spring, large amounts of yellow pollen are released and carried by the wind. Some gametophytes will land on a female cone. Pollination is defined as the initiation of pollen tube growth. The pollen tube develops slowly as the generative cell in the pollen grain divides into two haploid sperm cells by mitosis. At fertilization, one of the sperm cells will finally unite its haploid nucleus with the haploid nucleus of an egg cell.

Female cones (ovulate cones) contain two ovules per scale. One megaspore mother cell (megasporocyte) undergoes meiosis in each ovule. Three of the four cells break down leaving only a single surviving cell which will develop into a female multicellular gametophyte. It encloses archegonia (an archegonium is a reproductive organ that contains a single large egg). Upon fertilization, the diploid egg will give rise to the embryo, which is enclosed in a seed coat of tissue from the parent plant. Fertilization and seed development is a long process in pine trees: it may take up to two years after pollination. The seed that is formed contains three generations of tissues: the seed coat that originates from the sporophyte tissue, the gametophyte that will provide nutrients, and the embryo itself.

In the life cycle of a conifer, the sporophyte (2n) phase is the longest phase. The gametophytes (1n), microspores and megaspores, are reduced in size. This phase may take more than one year between pollination and fertilization while the pollen tube grows towards the megasporocyte (2n), which undergoes meiosis into megaspores. The megaspores will mature into eggs (1n).

Figure (PageIndex<1>): Life cycle of a conifer: This image shows the life cycle of a conifer. Pollen from male


Watch the video: Fruit Tree Grafting for Beginners (November 2021).