Mycorrhizal fungi are getting increasingly popular for improving plant health and growth naturally. Evidence has shown that it works well with succulents and cacti.
But does it also work with roses?
Mycorrhizal fungi benefit roses by increasing the water and nutrient uptake, improving drought resistance, increasing the rooting of cuttings, and increasing flower production.
In this article, we will find out how the fungi also work with roses.
How do mycorrhizal fungi benefit roses?
1. Improves water uptake and drought resilience
Mycorrhizal fungi benefit roses by improving water uptake, thereby making the rose plant more drought resistant.
This is shown in an experiment where damask roses (Rosa damascena) were inoculated with arbuscular mycorrhizal fungi and without the fungi and were subjected to four levels of drought stress (i.e. 100% of the water needed as control, 75%, 50%, and 25% of the water needed) (Abdel-Salam et al, 2018).
The results revealed that at every drought level, the roses with the fungi had higher water content than roses without the fungi.
This is because the long hyphae of mycorrhizal fungi stretch out in all directions and can reach farther into the soil than the plant’s root system, effectively doubling the moisture absorption zone of the plant.
Additionally, roses that were inoculated with the fungi were significantly less affected by the drought in terms of the growth in leaf size and root mass, nutrient content, and photosynthetic activities.
During wet seasons the increased water supply by the fungi positively influences plant growth in terms of root mass and leaf size. And in times of drought, mycorrhized roses do not suffer the typical effects of drought like wilting leaves, yellowing, stunted growth, and delayed flowering, as the mycorrhizae can still supply water to the plant even when the soil surrounding the plant roots is bone dry.
2. Increases nutrient uptake
Mycorrhizal fungi can increase the nutrient uptake of rose plants, resulting in better growth.
Results from the same Damask rose study showed that roses that were inoculated with Arbuscular mycorrhizal fungi had higher concentrations of nitrogen, phosphorus, potassium, calcium, and magnesium in the leaves shoots, and roots compared to the roses without the fungi.
Mycorrhizal fungi can transport nutrients to the plant from areas outside the reach of the plant’s root the same way they transfer water to the plant. Moreover, the hyphae of the fungi can also solubilize fixed nutrients like phosphorus and zinc in the soil, making them available to the plant.
Increased nutrients, particularly phosphorus (P) promote plant growth, as it’s one of the most important plant nutrients but is often in short supply in the soil. Increased P encourages photosynthesis, cell division, new growth, and increased flower formation.
3. Increases photosynthesis
Another way mycorrhizae benefit roses is by increasing the rate of photosynthesis, leading to better growth.
In the damask rose drought experiment, net photosynthesis of plants inoculated with the fungi was higher than those without the fungi at all drought levels and even when there was adequate water.
Increased photosynthesis also translates into better yield in terms of the number of flowers, as well as better overall growth of the plant in terms of leaf size, root length, and root weight.
4. Increases flower production
The ability of mycorrhizae in speeding up and increasing flower production is significant for flower farming.
Studies have shown that mycorrhizal fungi can increase the number of cut flowers in roses by 30% to 50% (Garmendia and Mangas, 2012).
Roses that are inoculated by mycorrhizal fungi produced more flowers with bigger diameters and greater dry and fresh flower weight than those without the fungi (Abdel-Salam et al, 2018).
Mycorrhizal fungi can also speed up flower production for roses. A study using Grand gala rose (Rosa hybrida ‘Grand gala’) found that even a small dose of the Arbuscular mycorrhizae fungi Glomus mosseae for 5 months was able to reduce the typical time for flower production by one month (Garmendia and Mangas, 2012).
5. Helps with propagation
Mycorrhizal fungi can also increase the quantity and quality of roots of rose cuttings during propagation, especially the cultivars that are hard to root.
This is shown in an experiment where a combination of rooting hormone and mycorrhizal fungi (Glomus intraradices) were given to cuttings from five cultivars of miniature roses (Jolly Cupido, Candy Sunblaze, White Miniwonder, Orange Cupido, Cherry Cupido) for four weeks.
The results revealed that the addition of the fungi increased the root quantity and quality of cuttings from two cultivars (Jolly Cupido, Candy Sunblaze) that typically take longer to root (Scalgel, 2001)
Which fungi benefit roses?
Endomycorrhizal fungi like the glomus species and some strains of Trichoderma species benefit roses, resulting in better flower yield, increased growth, and reduced diseases.
There are numerous types of fungi, but only a few are beneficial to roses. For example, ectomycorrhizal fungi aren’t compatible with roses, so they’re neither useful nor harmful to the plant.
On the other hand, fungi like Diplocarpon rosae and Podosphaera pannosa are pathogenic, resulting in the rose black spot disease and rose powdery mildew respectively, diseases that affect virtually all types of roses.
Only endomycorrhizal fungi like the Glomus and Trichoderma species are able to form symbiotic relationships that are beneficial to roses.
Glomus
Glomus mycorrhizae help plants by supplying water and nutrients to the plant. There are about 85 glomus species, and all should work with roses. But the most widely known species, proven to be good for roses include
- Glomus intraradices
- Glomus mosseae
- Glomus deserticola
These fungi help roses by sending out hyphae that reach farther into the soil to pull in water and nutrients to the plant.
Trichoderma
Trichoderma species like T. harzianum, T.viride, and T.virens help roses by acting as a biological control for pathogens in the soil. They may also improve flower yield.
Trichoderma is a genus of fungi found in all soils. They form symbiotic relationships with roses, by producing hyphae that parasitize any pathogens in the soil, or body of the plant.
In an experiment investigating the effectiveness of Trichoderma as biocontrol for rose plants, Three strains of Trichoderma – T. harzianum, T.viridi, and T.virens were applied to samples of a rose cultivar (Rosa hybrida ‘First red’) for two consecutive years.
At the end of the study, researchers found that Trichoderma significantly reduced the intensity of black spot and powdery mildew diseases to an average of 15.77% and 19.64% respectively, compared to the control plants which had disease intensities averaging 42.33% and 41.16% for black spot and powdery mildew respectively.
T. Harzianum was the most effective, while T.Virens was the least effective, but all strains of Trichoderma were effective biocontrol agents (Amin et al, 2018)
Powdery mildew and black leaf spot affect all types of roses, and are found everywhere roses are planted. These diseases do not outrightly kill the rose but can defoliate the plant, disfigure rose flowers, and reduce plant vigor. As such, by keeping these diseases in check, Trichoderma helps roses retain their beautiful flowers and leaves.
Are mycorrhizal fungi necessary only for poor soil?
Mycorrhizal fungi may only be necessary for poor soils, as under ideal conditions the plant’s natural roots and systems are sufficient for water and nutrient uptake, making hyphal networks of mycorrhizal fungi unnecessary.
In one study, three groups of Samantha rose (Rosa hybrida ‘Samantha’) were used to test the effect of mycorrhizae on phosphorus-rich soils.
One group was put in soils with low phosphorus and inoculated with Glomus intraradices, another group with the same low P soil was treated with Glomus deserticola, and a third group with a high P soil was left untreated.
After 6 months, the results showed noticeable differences in growth characteristics. The total dry weight and leaf area of high P, non-mycorrhizal plants were about 5 to 8% higher than the mycorrhizal plants with low P (Augé et al, 1986).
| Treatment | Total dry weight (g) | Leaf surface area (dm²) |
| High Phosphorus | 46.4 | 21.2 |
| Glomus deserticola + low phosphorus | 44.0 | 19.6 |
| Glomus intraradices + low phosphorus | 40.8 | 20.7 |
The study also investigated the effect of mycorrhizae combined with high levels of Phosphorus and found the results comparable with non-mycorrhizal plants with high phosphorus. It also found that Mycorrhizal fungi colonization was 63% lesser when the P levels were high.
This result shows that with roses and many other plants, mycorrhizal fungi colonization is considerably less when the soil has sufficient moisture and nutrient content, as the plant rejects the fungi. This is because, under optimum conditions, a mycorrhizal relationship isn’t beneficial to the plant, so it opts for the direct, non-symbiotic uptake using its root system (Balzergue et al, 2013).
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References
Abdel-Salam, E., Alatar, A., & El-Sheikh, M. A. (2018). Inoculation with arbuscular mycorrhizal fungi alleviates harmful effects of drought stress on damask rose. Saudi Journal of Biological Sciences, 25(8), 1772–1780. https://doi.org/10.1016/j.sjbs.2017.10.015
Amin, F., Banday, S., Dar, S., & Shahnaz, E. (2018). Biological control of powdery mildew and black spot diseases of rose. Journal of Pharmacognosy and Phytochemistry 2018;7(3):2826-2828.https://www.phytojournal.com/archives?year=2018&vol=7&issue=3&ArticleId=4599
Auge, R. M., Schekel, K. A., & Wample, R. L. (1986). Greater leaf conductance of well-watered VA Mycorrhizhal rose plants is not related to Phosphorus nutrition. New Phytologist, 103(1), 107–116. https://doi.org/10.1111/j.1469-8137.1986.tb00600.x
Balzergue, C., Chabaud, M., Barker, D. G., Bécard, G., & Rochange, S. F. (2013). High phosphate reduces host ability to develop arbuscular mycorrhizal symbiosis without affecting root calcium spiking responses to the fungus. Frontiers in Plant Science, 4. https://doi.org/10.3389/fpls.2013.00426
Garmendia, I., & Mangas, V. J. (2012). Application of arbuscular mycorrhizal fungi on the production of cut flower roses under commercial-like conditions. Spanish Journal of Agricultural Research, 10(1), 166. https://doi.org/10.5424/sjar/2012101-156-11
Scagel, C. (2001). Cultivar Specific Effects of Mycorrhizal Fungi on the Rooting of Miniature Rose Cuttings. Journal of Environmental Horticulture, 19(1), 15–20. https://doi.org/10.24266/0738-2898-19.1.15
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