fusarium=death

[camille1585]

Originally Posted by mvmgems

Though as for fusarium occurrence, I'm not sure a low endemic rate in California necessarily rules it out? I only had this plant a few months and purchased from a grocery store who could have imported them from a tropical nursery (Hawaii or Taiwan). Given the short period of time I've had it, Occam's Razor would suggest it could have contracted an infection from the nursery and been asymptomatic until the multiple stresses involved in getting it to my home.

While I also don't think your plant has fusarium, I agree with this comment. While we must not be too quick suspect fusarium, we should also be careful about being too dismissive of it as a potential cause. Like you say, plants travel, and can come from places where the disease is an issue.

That being said, I found a nice information sheet some time ago about orchid diseases including fusarium in Phals and Paphs, put together by a large commercial orchid nursery in the Netherlands. It's in Dutch, but google translate will do the trick.
HARK Orchideen - Bacterie-, virus en schimmelziekten aan orchideeengeslachten

Here is a quick translation:

Fusarium is mainly a problem in Phals and Paphs and can be considered an opportunistic pathogen, infecting/spreading when the plant is in a weakened state mainly due to issues such as very high fertilizer concentration, low substrate temperature, excessively wet substrate or sterilized substrate (due to lack of beneficial micro-organisms).

On Phalaenopsis, infections are first visible as small yellow-brown to reddish lesions on the roots. The spots gradually become larger until forming typical dark rotten sections of root. The base of the plant usually has black, dry rot which gradually spreads upwards, and in high humidity, pink reproductive fungal spores will form. The youngest leaves take on a reddish tinge, then chlorosis appears which leads to defoliation and death.

In Paphs the infection usually starts at the point where the roots and base of plant meet. A wet rot then develops with individual leaves easy to pull out. Disease development is slow and plants often form new roots on the healthy parts of the plant. However, the combination with slow delayed growth is a sure indication of fusarium.

[Shadeflower]

Thx Camille,
that is quite informative and confirms my suspicions that fusarium is not always a death sentence.
Your info states the plants can still grow new roots, the fusarium just hinders this. This would indicate a couple of orchids I'm suspecting have had it/have it might have it.
As long as the black area is kept dry it doesn't spread but some people recommend cutting all the black away which is very extreme and would certainly set them back.
I just discovered the one case this week after peeling away some dried sheaths which were completely hiding it and I am suspecting the plant has had it for months already based on its recent slow growing behavior.

But the area is being kept dry and I was debating to do more but I will leave it and see what happens. The plant is still growing I think and is starting to develop new roots above the black area

[mvmgems]

Originally Posted by Roberta

Fusarium mostly occurs in tropical areas. In northern California, I doubt it very much. Root rot from bad sphagnum? Very likely. The wrinkly leaves are indicative of the plant not taking up water - which is what happens when the roots are dead. (Underwatering can do that too, but here, I think it was the bad roots making it impossible for the plant to get water, even if the medium was wet. ) Looking at the stubs of roots, I doubt very much whether it was salvageable, at any rate. If there WAS a viable root, cutting it removed that option, however. But if it was in poor condition when you got it, chances are that it was on its way out from the beginning, from poor culture long before you got it. Time for a new, healthy plant to give you pleasure and a good chance for success.

Hi Roberta,

I was pretty curious about the prevalence of fusarium in orchids after your comment, which surprised me since fusarium blight is a familiar issues here in California with many different species of ornamental, vegetable, and crop plants.

I did find a couple of useful scientific resources, though some are paywalled. Since I'm a molecular biologist by training, and with brief experience in a pathogen research lab, this is right up my alley for a fun evening's reading haha.

This open-access article from 2002 describes the incidence of fusarium infection in Phalaenopsis cultivated in greenhouses in Korea (which has a temperate climate) as up to 30%. If fusarium does indeed favor warm, humid tropical conditions, it's possible that the microclimate of a cultivation greenhouse promotes its pathogenicity.

This review of Fusarium in orchids from 2018 is much more comprehensive, though paywalled. Contact me if you'd like the full text copy. Notable highlights for me included:

"In 2015, the largest state producers of potted orchids were California ($118.5 million), Florida ($77.8 million), and Hawaii ($11.3 million), while for cut flower production California ($6.1 million) was the largest producer followed by Hawaii ($1.5 million)." I had no idea most modern orchid production in the US was in California! I would have guessed HI/FL.

"Fusarium is associated with orchids as both pathogens and non-pathogens throughout the world. The non-pathogenic Fusarium species associated with orchids are usually decomposers (Booth, 1971) and/or mutualists, which aid seed germination and seedling coloration (Vujanovic et al., 2000). Non-pathogenic species of Fusarium can be used to control Fusarium wilt on various crop." I hadn't fully appreciated the diversity of Fusarium species and strains, and how certain species are beneficial and may protect against pathogenic species/strains.

"The incidence of Fusarium diseases in orchids has been steadily increased worldwide, and pathogenic Fusarium spp. are now considered one of the major limiting factors for the production of high quality orchids (Wedge and Elmer, 2008)."

"Fusarium pathogens of orchids have been reported from locations around the world, although the majority of the reports originate from tropical and subtropical regions (Table 1)." Roberta, is this where you drew your information? The table draws from studies from 1996 to 2015, so it's relatively recent information.

"Fusarium oxysporum is a complex species composed of at least 150 host-specific, phytopathogenic species (refs) and a vast number of sapro- trophic strains. Due to a relatively high level of biodiversity in this species, it has the ability to adapt to environmental changes and form new pathogenic strains over a short period (White et al., 2001). It is also the most economically important species in the Fusarium genus, given its numerous hosts and the level of loss that is produces on infected plants." So as orchid cultivation centers shift to include temperate countries, it's quite plausible that orchid-specific strains would adapt to the new host-environment conditions.

"The recent rise in the popularity of orchids as a global crop, has been accompanied by a rise in disease incidence on the crop. Movement of orchids from countries where diseases are prevalent, to countries where they were previously not known to occur is an unintended consequence of the global trade. In many countries such as the United States, strict measures are in place to inspect imported plant material and prevent the entry of new pathogens. However, many plants produced in Taiwan and South-East Asia, that have been allowed into the United States, were contaminated with low levels of Fusarium (Kawate and Sewake, 2014)." Looks like my conjecture wasn't off-base!

Then there's a useful section on management techniques tailored to greenhouses, including setup, culture, breeding of resistance, and appropriate fungicides. But the coolest to me was using bugs to fight bugs: "Biological control is another area of disease management that needs further research for orchids. Pseudomonas fluorescens as an antagonistic agent in the soil, effectively suppressed F. oxysporum f. sp. vanillae. A combined inoculation of Trichoderma sp. and Pseudomonas spp. also was effective against Fusarium wilt of vanilla (Tombe et al., 1997; Sandheep et al., 2012)."

[estación seca]

Presence of pathogenic organisms on potential host organisms (or their DNA/RNA recovered by PCR) does not prove infection. Minor infections may not be harmful if organisms are healthy and not stressed by poor ambient conditions.

Orchids grown commercially in the US aren't growing in temperate climates - they're growing in tropical climates inside greenhouses situated in temperate climates.

Windowsill hobbyists simply do not have environments suitable for fungus to spread widely unless they live in hot, humid parts of Hawaii or southern Florida and don't have air conditioning. People who grow in tightly sealed terraria might have trouble with it. Many cacti evolved to grow in alkaline environments, and they are know to be susceptible to Fusarium when potted in acidic (high-organic) soil mixes.

Almost all problems with fungal diseases I have seen in cultivated plants are caused by inadequate cultural practices or conditions. Gardeners worried about fungus should ensure proper temperatures, relative humidity, light and air circulation. Fungicide won't help unless proper growing conditions are present.

[Ray]

This is precisely why I recommend the regular use of plant probiotics - the more diverse the population, the better.

That got me thinking about natural ecosystems. It has long been established and accepted that the more diverse they are the more robust they are - a “slackening” in one component is readily compensated for by another. I firmly believe that applies to all systems, whether they be ecological or social.

The commercial cultivation of orchids started with wild-collected plants. Over the years, with the application of pesticides and the use of aseptic propagation, the diverse collection of microflora and -fauna that occurs in wild plants has been pretty thoroughly wiped out. That leaves the plants more susceptible to those that remain or to which they are exposed.

Granted, we know more about orchid culture than did the original collectors, but I feel like we’re on a cultural “razor’s edge” - any mistake and the plants can easily succumb to something. If, on the other hand, a diverse microbial community is well-established within the plant, their competitive “balance” may not give the pathogens a significant chance to do much harm, so while the plant may be in the less-than-ideal conditions to thrive, it muddles through, rather than fails.

(OK, maybe that’s a bit of hyperbole, but you get the concept…)