Mycorrhiza In Citrus: What Causes Uneven Growth Of Citrus Fruit

Mycorrhiza In Citrus: What Causes Uneven Growth Of Citrus Fruit

By: Liz Baessler

Usually, “fungus” is a bad word when it comes to gardening. There are, however, some fungi that help plants and should be encouraged. One such fungus is called mycorrhiza. Mycorrhizal fungi have a special symbiotic relationship with citrus plants that is more or less essential for citrus growth.

Because of the positive mycorrhizal fungi effects on citrus, a lack or uneven spread of fungus can lead to unhealthy or lackluster trees and fruit. Keep reading to learn more about mycorrhiza in citrus and mycorrhizal fungi fertilizer.

Uneven Growth of Citrus Fruit

Mycorrhizal fungi grow in the soil and attach themselves to tree roots, where they thrive and spread. Citrus trees have especially short roots and root hairs, meaning they have less surface area for taking in water and nutrients. Mycorrhiza in citrus roots helps to bring in extra water and nutrients that the roots can’t manage on their own, making for a healthier tree.

Unfortunately, a single mycorrhiza spore on your tree’s roots is not enough to make a difference. The fungus has to be directly attached to a root in order for its benefits to take place. Because of this, fungus growing on just one section of roots may result in uneven growth of citrus fruit, with the fruit on some branches bigger, healthier, and brighter (differing color) than on other branches of the same tree.

Mycorrhizal Fungi Effects on Citrus

If you notice an uneven growth of citrus fruit, it may be caused by an uneven spread of mycorrhizal fungi on the roots. If this is the case, or if your citrus tree just seems to be failing, you should apply mycorrhizal fungi fertilizer to the soil.

This fertilizer is an inoculum, a small collection of spores that attach to the roots and grow into the beneficial fungus. Apply a lot of inoculum to many sites – they will grow and spread, but slowly. If you get good coverage to begin with, your plant should perk up more quickly.

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Get Associated With Mycorrhizae

Say the word “Fungus” and most people think of the familiar white or brightly colored toadstools, puffballs, or bracket fungi on rotting logs. Many picture slimy growths of putrescence, moldy bread, spots on the leaves of their favorite rose and other nuisances. But apart from the subtle white thread-like mycelium and occasional spore producing mushroom, the extremely beneficial mycorrhizal fungi remain largely invisible to most humans.

A mycorrhiza (plural mycorrhizae or mycorrhizas) is a mutualistic symbiosis between a fungus and a vascular plant. The word is derived from greek: mykós (fungus) and riza (root) and was first coined in 1885. Yet it was not until over 100 years later that the relationship became known to agriculture and eventually home gardening. Now we know that over 90% of all land plants and probably more, form mycorrhizae, and that they influence plant nutrition, community structure and nutrient cycling. In fact, nearly 500 million years ago, these fungi allowed plants to leave the ocean, and begin to colonize the earth.

Mycorrhizas were first classified as two types: ectotrophic and endotrophic, but there are now seven distinct symbioses. In each, the fungus receives sugars from the plant and in exchange the plant receives certain nutrients, water and protection against pathogens.

Endomycorrhizas, in which most of the fungal structure is contained within the root, are the most common type. They were first to evolve, and associate with a diverse array of plants including most crop plants, grasses, forbs (flowering plants) and many trees. Most do not form typical mushrooms.

In Ectomycorrhizas, the association is more advanced. The fungus grows close to the root surface, forming a sheath around the root system, and a network in between root cells. From this layer, it extends outward into the surrounding soil to forage for moisture and nutrition. Many form edible or otherwise noteworthy mushrooms, and typically associate with woody shrubs or trees such. Examples of common mycorrhizal mushrooms are Amanitas, Boletes, Chanterelles, and the prized Truffles.

Mycorrhizal fungi can extend a plant’s root system up to 1000x, increasing moisture and nutrient uptake capacity. A significant role is finding and retrieving hard-to-capture nutrients such as organic nitrogen, phosphorus, and iron. Fungal enzymes also free Copper, Calcium, Magnesium, and Zinc making them available for plant use.

Not only can ectomycorrhizal fungi connect entire communities of plants enabling them to exchange information, but they can access many nutrient sources not directly available to plants (e.g. rocks, nematodes, pollen, and insects.) Without mycorrhizae, many plants are unable to obtain adequate nutrition to perform the best. A perfect example of this followed the catastrophic eruption of Mt. St. Helens in May of 1980. After the eruption, patters of succession revealed that seedlings which germinated from soils where mycorrhizae were present were much more successful. Research also indicates that certain mycorrhizal fungi can confer protection to plants from metals or acidic contaminated soils, which shows promise for their use in restoration projects.

Although ecologically influential, soil fungi are actually quite fragile – the use of fungicides, pesticides, inorganic fertilizer and many physical factors can reduce or eliminate mycorrhizae. Rototilling and double digging break up the delicate tubes known as hyphae, while soil compaction from heavy machinery and other vehicles can crush and destroy these critical networks. Practicing no-till and other permaculture techniques coupled with the use of Mycorrhizal inoculants can help restore and promote healthy populations of these beneficial fungi and other soil organisms in your garden and yard.

For more information on the role of Mycorrhizae in the garden, we offer a fantastic book entitled Teaming with Microbes: The Organic Gardener’s Guide to the Soil Food Web.

If you are interested in promoting and restoring populations of these beneficial fungi, it is easy to re-introduce mycorrhizal fungi to the soil in an effective, safe and 100% natural way. Fungi Perfecti’s MycoGrow products are designed for everyone from the home gardener/landscaper to the professional forestry manager, promoting faster growth, speeding transplant recovery and reducing the need for fertilizers and other additives. A number of different formulations are available, for all methods of plant cultivation.

Using Mycorrhizal Fungi To Bring Nutrients To Your Plants

Mycorrhizal fungi are incredible helpers when it comes to soil and plant health.

They provide nutrients and water to plants in exchange for food in return. It really is a partnership.

In fact, they’re among the most important microbes that partner with plants.

You can buy the fungal spores as a powder. Some of my clients swear by this stuff.

I’ve had landscapers install new lawns with my powder and contact me afterwards in total shock at how much faster and fuller the lawn came up.

I use mycorrhizal fungi in my organic garden, too, almost every time I seed or plant, especially in a new garden or a garden where I feel the fungi might not already be established.

They should already be abundant in our soil, but often aren’t anymore because of compaction, tilling, overwatering, chemical use and other reasons.

So it makes sense to spend a few pennies here and there to reintroduce them.

There are two main categories:

  1. Endomycorrhizal fungi (aka arbuscular mycorrhizal fungi) associate with over 90% of plant species, including vegetables, grasses and many ornamentals.
  2. Ectomycorrhizal fungi associate with only 5 or so percent of plants, but are especially important for some deciduous trees and especially conifers.

You can buy a mix of both and then you don’t have to think about it. It’s best to apply them at planting/seeding/sodding in order to promote contact between the plant roots and fungi. That’s where the partnership occurs.

  • When planting, rub the fungi on the root ball or throw a pinch into the planting hole.
  • When seeding, mix it with the seed before sowing.
  • When sodding, mix with water and spray it on the soil before laying the sod, or second best would be to spray it on after and water it in.
  • If your plants are already planted, you can mix a powder form with water and spray it onto the soil. This works best on more porous soils, or after aerating a lawn if possible.

You can definitely mix the product with biostimulants before you apply it.

And if you treat your soil well, you don’t have to apply it more than once to a plant (whereas something like compost tea or effective microorganisms is best applied once in awhile).

I sell mycorrhizal fungi on this site. That link has even more detail about how it all works.

Effect of inoculation with npk fertilizer and arbuscular mycorrhizal fungi on growth and yield of cassava



*Sridevi, S. and

Ramakrishnan, K.

Research and Development Centre, Bharathiar University, Coimbatore-641046

Department of Botany, Annamalai University, Annamalainagar – 608 002

The present investigation was undertaken to study the effect of inoculation with NPK fertilizer and Arbuscular mycorrhizal fungi on growth and yield of cassava (Manihot esculenta Crantz). The growth attributes like shoot length, total number of leaves, number of roots per plant and root length and yield attributes, like number of tubers, tuber yield and starch content were noticed maximum under increased 100 per cent NPK with AM fungi inoculated plants. The application of 50 per cent of recommended dose of NPK fertilizer with AM fungi inoculation will results in improved growth and yield of cassava.

Copyright © 2013 Sridevi, S. and 2Ramakrishnan, K. This is an open access article distributed under the Creative Commons Attribution License, which permits

unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Cassava (Manihot esculenta Crantz) is one of the major tuber crop. It is grown in more than 80 countries of the humid tropics of the world and forms the most subsistence crops for farmers. Cassava possesses a high potential for yielding large amounts of food per unit area and also it is an efficient producer of calorie (135 calorie/100 g fresh tuber) compared with other cereal crops. In India, cassava ranks first in area (2.35 lakh ha) and production (5.4 million tonnes of fresh tubers) followed by sweet potato. Its average productivity is 23 tonnes/ha, the highest in the world (Department of Economics and Statistics, Season and Crop Report, 2005). A special type of root, resulting from a mutuality association between a plant and a fungus, is called mycorrhizae. The term mycorrhizae were first coined by Frank (1885) to describe plant root fungus association. It can be classified broadly into ectomycorrhizae and endomycorrhizae. A diverse group of soil fungi spanning the Zygomycetes, Asycomycetes and Basidiomycetes from mycorrhizae (Harley and Smith, 1983).

Arbuscular mycorrhizae are formed by non-septate

phycomycetous fungi belonging to the genera Glomus, Gigaspora, Acaulospora and Sclerocystics in the family

*Corresponding author: Sridevi, S.

Lecturer in Botany, KNC, Cuddalore – 607 001

Endogonaceae of the order Mucorales. These fungi are none specialized in host range. Yet are apparently obligate symbionts (Gerdemann, 1968). They depend on their host plants for deriving energy source viz., carbohydrate. They can be recognized by the irregular coenocytic hyphae which ramify within the cells of the root cortex. The latter are finally branched to help in the absorption of nutrients. The fungal hyphae produce spores. It is well documented that the increase in plant growth resulting from arbuscular mycorrhizal symbiosis is usually associated with increased nutrient uptake by the hyphae from the soil (Rhodes and Gerdemann, 1980). The increased ability of plants to absorb phosphates (Mosse, 1973) and possibly other elements such as nitrogen, potassium, calcium, zinc, iron and manganese (Gray and Gerdemann, 1973) are the instances to cite. The other beneficial effects are their role in reducing the disease incidence (Schenck and Kellam, 1978), enhancing biological nitrogen fixation (Sivaprasad and Rai, 1987), protecting plants from stress condition (Aldon, 1975), as well as increasing phytochrome production and photosynthetic rates (Allen et al., 1981). Cassava crop responds to mycorrhiza and increase in growth can be obtained by mycorrhizal inoculation in low nutrient soils. This mycorrhizal infection can lead to increase the nutrient content of cassava plants and as well as shoot and root dry weights (Howeler, 1982). The present investigations was therefore undertaken with study the


International Journal of Development Research

Vol. 3, Issue, 9, pp.046-050, September,2013

What is it About Phosphorus That Makes it Challenging for Plants?

Phosphorus is an extremely reactive element never found free in nature. The phosphorus ions used in fertilizers are negatively charged. The first thing phosphorus does when it hits the soil is draw positively charged ions to it. These turn into new insoluble compounds, and these compounds do not move in the soil. They sit there, insoluble and tantalizingly out of reach of plant roots.

A review of scientific literature reveals that most, as in 75 - 95%, of the phosphorus fertilizer applied to crops is not taken up by the plants. It will mostly stay in the soil. However, significant amounts are washed or eroded away into adjacent streams where they wreck havoc with aquatic systems causing large algae blooms killing lakes.

Despite this, our crops still don't have adequate phosphorus. They may be surrounded by reserves of phosphorus, but these reserves are either inaccessible or insoluble so not suitable for plants to uptake.

9 Ways To Help The Beneficial Fungi In Your Soil

Without sufficient beneficial microbes on (and in) our bodies, we get sick very fast.

Perhaps the most beneficial fungi for plant health is a group of fungi you may have heard me talk about before called mycorrhizal fungi.

This week, I received a fresh batch of mycorrhizal inoculant, a powder that brings these fungi onto the roots of my plants.

In addition to my regular inoculant, I now have a new inoculant that contains not only endomycorrhizal fungi, but also the ectomycorrhizal fungi that are needed by some trees such as oaks, some nuts and many conifers.

Personally, I use a mycorrhizal inoculant whenever I plant or sow seeds – indoors or outdoors.

It’s so affordable to use a pinch of powder each time I plant that I always do it.

That’s what this article is about today – how to maintain your garden to encourage the beneficial fungi in the soil to be as healthy as they can, because they do a lot of work for us in the garden.

Mycorrhizal fungi live in the soil in partnership with plants. The beneficial effects of these fungi are that they:

  • Seek out phosphate and other nutrients and then bring them to plants
  • Connect many plants together, allowing for nutrient exchange between plants
  • Supply water to plants
  • Protect plants from fungal diseases and other root-feeding microorganisms
  • Improve soil structure, so it’s less compacted, with more spaces for air and water

Here are my main tips for keeping your soil’s beneficial fungi happy so you don’t have to keep buying an inoculant every year…

1. Phosphorus fertilizer. Don’t use too much, especially chemical phosphorus.

When plants have ample access to soluble phosphorus (soluble means it dissolves in water, so is easier to take up by plants), they aren’t as reliant on mycorrhizal fungi, so they don’t allow the fungal infection to occur with their roots as much.

That means by using soluble phosphorus fertilizer, we’re interfering with how nature provides plants with phosphorus, so we’ll need to take over the job of the fungi and continue to fertilize our plants every year. Even fresh manure can oversupply phosphorus.

Rock phosphate is okay because it’s insoluble – it actually needs to be worked on by microbes such as these beneficial fungi in order for plants to most effectively use it.

2. Other fertilizer. Other than phosphorus, overfertilizing in general can inhibit mycorrhizal fungi, so it’s good to fertilize just a little at a time.

That’s why I often take the fertilizer recommendations from my organic soil lab and split it up into 2-4 applications during the year instead of all at once.

Too much nitrogen seems to be the next big issue after phosphorus, and sulfur is another big one too because it’s antimicrobial.

Many soils are deficient in sulfur, but if we use gypsum or potassium sulfate (both contain about 18% sulfur), that’s going to be less damaging to fungi than elemental sulfur (90% sulfur), which is much more soluble.

3. Organic fertilizer. One reason organic fertilizers are nice is because they tend to either be rock fertilizers (such as rock dust) that are slow-releasing and therefore won’t cause as many problems, or are broad-spectrum biological fertilizers (such as ocean water) that supply just small amounts of many different nutrients and therefore won’t oversupply any one nutrient.

It’s still possible to overapply organic fertilizers, but they’re more forgiving.

4. Pesticides. ‘Cide’ means to kill. Fungicides kill fungi, so using them can harm mycorrhizal fungi. But so can herbicides, insecticides and other pesticides.

Just spraying a pesticide once isn’t going to knock out your whole fungal network, but repeated applications, especially of certain pesticides such as methyl bromide, will kill most of your microbial soil life (most countries stopped allowing methyl bromide use years ago, but the U.S. still allows it as of this writing).

Anyway, I know I don’t have to speak much to this point on this site, because most of you are interested in organic gardening practices already.

5. Mulch. Maintaining a consistent mulch of leaves, straw and perhaps some wood chips will provide protection and habitat for the fungi.

I don’t like to use too many wood chips, but they do encourage fungi, so I will use them around trees and shrubs, which want a more fungal-dominated soil.

A living mulch (a groundcover or cover crop) is also useful to give beneficial fungi more plants to partner with.

6. Diversity. Mycorrhizal fungi benefit from having other microbes around, including beneficial bacteria, so while compost doesn’t provide the fungi itself, it does support them, as does using compost tea and effective microorganisms.

Plant diversity is also beneficial, which is one reason why crop rotation can be helpful, and why leaving some weeds and wild areas to grow is, too.

7. Water. Like us, fungi need water, but they also need air, so if your soil is so wet that there’s not enough air, the fungi will suffer.

But even if your soil is just consistently moist (perhaps from your irrigation system watering for 15 minutes every morning), that’s also an issue because the fungi won’t have any reason to go searching deeper in the soil for moisture. We face the same issue with plant roots. We want roots and fungi to spread out and go down, so we need to let the soil dry out a little between waterings.

8. Tilling. Tilling, plowing and double digging will slice your fungi up into pieces. It can sometimes be useful to do one of these when you’re first establishing a garden, but in the long run, it’s better to limit them to only when the benefits outweigh the downsides, which may be occasionally, or may be never. Sometimes they’re useful to lightly incorporate a cover crop or control weeds, but otherwise, less soil disturbance is usually better.

9. Other soil disturbance. Topsoil removal during construction is devastating to fungi. Compaction is detrimental as well, as is erosion. On a farm, there’s usually more bacteria than fungi in terms of biomass (weight). In a forest, there’s 5, 10, 100, even 1000 times more fungal biomass than bacteria!

The main reasons for this big difference are the lack of tilling/plowing, compaction and erosion in a forest, plus the lack of pesticides being sprayed, and the plant species growing there.

So yes, applying an inoculant to your garden to bring in these beneficial fungi for plants can be very useful, as long as you’re addressing the above factors as well.

Once you’ve done that, you generally don’t have to keep using the inoculant, although if I have some around, I still tend to when I’m planting and seeding new plants.

If you have any questions about mycorrhizal fungi, you can head over to my main mycorrhizae page below and scroll down to the comments area to ask them there – that way we can keep all myco questions in the same place.

Or if you want to learn more about these fungi, my main mycorrhizae page has more detailed information on that too:

The Effects of Mycorrhizal Fungi Inoculum on Vegetables

The Master Gardeners at Elkus Ranch designed a study to compare the yield and vigor of a variety of vegetables grown with and without mycorrhizal fungi plant inoculum. Products claim to increase size and health of plants have been made by a number of suppliers of inoculate, without providing much supportive data. The goal of this trial was to document the planting, comparative growth and yields of six vegetables planted in two beds, one bed inoculated and the other non inoculated, so that the results would help the home gardener make an educated choice on whether or not to use a mycorrhizal inoculum. The study was conducted in a Zone 17 coastal climate.

Vegetables grown with endomycorrhizal fungi plant inoculum will be more vigorous and produce higher yields than vegetables grown without inoculum.

Background: What is ‘endomycorrhizal fungi plant inoculum’?
A mycorrhiza, from the Greek ‘mykos’ meaning fungus and ‘riz’ meaning roots refers to a symbiotic association between a fungus and the roots of a vascular plant. They form an important component of soil life and soil chemistry.

In a mycorrhizal association, the fungus colonizes the host plant's roots, either intracellular as in endomycorrhizal fungi, or extracellular as in ectomycorrhizal fungi. This study is concerned with the former.

Mycorrhizal fungi form a mutual relationship with the roots of most plant species.

This association provides the fungus with relatively constant and direct access to carbohydrates, such as glucose and sucrose. The carbohydrates are transferred from their source (usually leaves) to root tissue and on to the plant's fungal partners. In return, the plant gains the benefits of the mycelium's higher absorptive capacity for water and mineral nutrients due to the comparatively large surface area of mycelium to root ratio. This improves the plant's mineral absorption capabilities.

The mechanisms of increased absorption are both physical and chemical. Mycorrhizal mycelia are much smaller in diameter than the smallest root, and thus can explore a greater volume of soil, providing a larger surface area for absorption. Mycorrhizal fungi are especially beneficial for plants in nutrient-poor soils.

Mycorrhizal plants are often more resistant to diseases, such as those caused by microbial soil-borne pathogens, and are also more resistant to the effects of drought. This is an important thing to consider in the rain challenged Bay Area.

Seeds of the following plants were started in one inch cells in a green house on March 3, 2011: golden chard, strawberry spinach, double red orach spinach, epazote (Mexican culinary herb), edible Japanese chrysanthemum garland round leaved and cardoon (related to the artichoke). On March 23rd, the seedlings were transplanted into four inch containers. On April 5th the seedlings were planted, half of each variety, into two beds at Elkus Ranch Research Garden. The soil in both beds consisted of a combination of 50% Elkus compost and 50% Elkus dirt.

On planting:
Bed A was given a root inoculant consisting of a blend of endomycorrhizal species selected by the manufacturer specifically for vegetables. A 1/2-ounce dry inoculum was mixed with &half gallon of water. A siphon mixer was attached to a standard garden hose bib, the hose screwed into the other end of the mixer, and the flexible mixer tubing fed into the container of inoculum. The &half gallon of soluble inoculum was automatically mixed into 8 gallons of water and applied directly to the soil resulting in a deep soak. (According to the manufacturer, the dry mix can also be sprinkled into rows prior to planting or under transplants as they are being placed in the soil.)

Bed B was given a good watering at planting using H2O straight from the hose.

Both beds received 10 minutes of drip irrigation every day for the first two weeks. On April 17th, irrigation was reduced to 10 minutes every other day due to cool, foggy spring weather.

The following measurements, recorded in inches, were taken on May 10th:

Inoculated Height Non-Inoculated Height
Cardoon 6" 6"
Golden Chard 10" 7"
Epazote 5" 5"
Japanese Chrysanthemum 10" 5"
Orach Spinach 16" 13"
Strawberry Spinach 9" 8"

The following measurements, recorded in inches, were taken on June 14th:

Inoculated Height Non-inoculated Height
Cardoon 28" 27"
Golden Chard 19" 19"
Epazote 20" 17"
Japenese Chrysanthemum 38" 36"
Orach Spinach 28" 26"
Strawberry Spinach 8" 10"

The vegetables that received inoculum grew slightly taller than those that did not receive inoculum (except for the strawberry spinach). We began harvesting and eating the plants mid June. A very informal ‘taste test’ was conducted on plants from the two beds. It consisted of asking volunteers to comment on what they noticed, if anything, between samples from Beds A and B. They were not told from which bed their samples came. Four of the five subjects thought that the samples of spinach, both strawberry and orach, were ‘sweeter’ from the beds receiving inoculum. No difference was noted for the other plants.

The golden chard grown in Bed B without inoculum, suffered severe leaf damage from leaf miners. These critters feed within the tissues of the leaves themselves, selectively eating only the layers that have the least amount of cellulose.

The cardoon plants in the inoculated beds grew to a massive height of over 8 feet by September:

The vegetables in the bed that received mycorrhizal fungi inoculum grew larger (cardoon, epazote and chrysanthemum), were more disease resistant (chard) and, according to a very small sample size, sweeter tasting (strawberry and orach spinaches) than the vegetables grown without inoculum.

I will continue to experiment with the use of mycorrhizal fungi plant inoculum in future plantings, and believe that it has great application in new beds and soils that may be nutrient poor. I would caution the home gardener that if they are interested in using mycorrhizal fungi, to purchase inoculum from a reputable source and do your homework first. Scientific analysis has shown that many of the ‘over the counter’ products that claim to contain live mycelium, do not in fact live up to that promise.

For more information, please contact the Master Gardener Help Line at (650) 726-9059 ext 107

Watch the video: 14 Nasty Citrus Diseases that You MUST Avoid