Hi welcome to Taiga Bonzai, in this post we discuss the outbreak of new diseases recently found in 2024.

Introduction – according to Wiley on behalf of the British Society for Plant Pathology. New Disease Reports provide a platform for publication of significant new and emerging plant disease outbreaks. These, cover diseases caused by bacteria, fungi, nematodes, oomycetes, phytoplasmas, viruses and viroids.

This article focusses on Fusarium solani a species complex of at least 26 closely related filamentous fungi in the division Ascomycota, family Nectriaceae. It is the anamorph of Nectria haematococca and is a common soil inhabiting mold. It thrives at temperatures between 8.5–34.3C. More so in greenhouses and polytunnels where the temperature is higher, this fungal pathogen is on the increase.

The genus Fusarium was introduced in 1809–1935, much of the work on Fusarium was focused on identification of Fusarium species and diagnosis of Fusarium diseases.

Historically, Fusarium is an factor important because the taxonomy of Fusarium species has been a controversial issue. Due to the fact that Fusarium species are among the most important plant pathogens in the world. Moreover, many Fusarium species produce mycotoxins that cause animal and human diseases.

The following scientists Edel-Hermann, V., Gautheron, N., Durling, M.B., Kolseth, A.-K., Steinberg, C. et al. (2016) conducted Genus-specific primers for study of Fusarium communities in field samples. Applied and Environmental Microbiology, 82, 491–501. https://doi.org/10.1128/AEM.02748-15

In July 2023, symptoms of foliage wilting, yellowing and cortical rot of stems were observed on cucumber Cucumis sativus cv., in a commercial greenhouse located in Mamusha, Kosovo. The disease incidence was estimated to be approximately 30%.

Diseased material (stem and root fragments) were collected from affected plants. Samples were surface sterilised using 75% ethanol for one minute and rinsed in sterile distilled water.

The sterilised fragments were then placed on potato dextrose agar (PDA) and incubated at 27°C in the dark for seven days. Colonies had white mycelial growth with an orange to purple pigmentation in the centre. (shown below)

Macroconidia were slightly curved with three to five septa, with the morphology of two representative isolates, DLS2081 (stem) and DLS2082 (root), was consistent with Fusarium solani (Li et al., 2010). Macroconidia and microconidia of the isolated Fusarium solani. The size of macroconidia averaged 26–36 × 5–8 µm. Microconidia, with 0–1 septum, measured 8–22 × 2.5–5 µm on average. (shown below)

The scientists point out that single spore isolates of DLS2081 and DLS2082 were used for DNA extraction using a CTAB-based method.

The internal transcribed spacer (ITS) region, translation elongation factor (TEF1α) and second largest subunit of nuclear RNA polymerase II (RPB2) from both isolates, were amplified and sequenced with primer pairs ITS1/ITS4 (White et al., 1990).

EF-1/EF-2 (Karlsson et al., 2016) and 5F2/7cR (Liu et al., 1999), respectively. Sequences were deposited in GenBank under Accession Nos. PP940094 and PP940095 (ITS), PP963514 and PP963515 (TEF1α), PQ119501 and PQ119502 (RPB2) for DLS2081 and DLS2082 isolates, respectively.

A BLAST analysis of ITS sequences showed 100% identity with F. solani (MT371374.1, HQ384397.1), TEF1α sequences showed 99–100% identity with F. solani (HQ731056.1, MT305228.1), and RPB2 sequences showed 100% identity with F. solani (MF276966.1, MF276931.1). Phylogenetic analysis revealed that both DLS2081 and DLS2082 isolates clustered with F. solani strains.

Fighting the infection – synthetic fungicides are widely used to control wilt diseases. Katyayani Coc 50 and Katyayani Samarth are considered to be the two best fungicide for control of Fusarium wilt. Remove and burn the affected plants, do not compost this garden refuse. Remove and replace fusarium-infected garden soil if at all possible.

Fusarium species on humans – this well-known plant pathogen although normally seen in soil and water worldwide, has been causing invasive infections in immunocompromised patients, especially in bone marrow transplantation and long-term steroid therapy patients.

The main route of acquisition of the pathogen is through direct inoculation or inhalation of the spores. Fusarium is known to cause keratitis, onychomycosis, endophthalmitis, and even skin infection. On microscopic examination of the clinical specimens, septate fungal hyphae with acute angle branching similar to Aspergillus are seen.

The fungal culture on Sabourad’s Dextrose Agar (SDA) grew a mold with characteristic pink pigment, which on microscopy had fusiform septate macroconidia, specific for Fusarium genus of mold. Here, we present a case of chronic diabetic ulcer of the left lower limb from which Fusarium solani was isolated.

A 62-year-old taxi driver, on regular treatment for type II diabetes mellitus since 10 years, had a large ulcer on his left lower limb for 8 months following minor trauma at the heel. The patient was on antibacterial drugs for 2 months, yet the ulcer did not heal. There exists a gruesome image of the diseased limb that was eventually amputated.

We are not going to display it here for obvious reasons, but for the inquisitive, here is the link where it can be found. https://pmc.ncbi.nlm.nih.gov/articles/PMC3147084/

F. solani is a common but serious threat as the above few paragraphs have shown especially in people in their older years therefore, it is prudent to seek medical advice should problems occur. Amphotericin B (AmB) and voriconazole (VRC) alone or in combination have been frequently used to treat human diseases caused by Fusarium spp.

In the next article we continue to bring to light more diseases that are either relatively new strains of existing ones, or those completely new, which is important knowledge for horticulturists. Until next time, BW, Nik.

Statement – towards the end of 2024 we stated that our desire was to move to a new platform, after being with WordPress since 2016. (9 years) We have the new platform and already have been posting articles there. A platform where journalists and academics can post their content with ease. The platform is Substack.com – Taiga Bonzai.com we will post this article on WordPress then we will cease.

Hi welcome to Taiga Bonzai, in this article we revisit the article 62 – ‘New diseases’ 2 due to the comments received and the request for further information.

Introduction – the above mentioned article focussed it’s attention on Fusarium solani, a complex species of at least 26 closely related filamentous fungi in the division Ascomycota, family Nectriaceae. It is the anamorph of Nectria haematococca and a common soil inhabiting mold.

Fusarium solani is implicated in plant diseases as well as in serious human diseases such as fungal keratitis (Summerell, Brett A.; Laurence, Matthew H.; Liew, Edward C. Y.; Leslie, John F. (14 September 2010). (“Biogeography and phylogeography of Fusarium: a review.“)

History and taxonomy – the genus Fusarium was described in the 1930s, by Wollenweber and Reinking who organized the genus Fusarium into sections, including Martiella and Ventricosum, Lesli, John., Summerell, Brett, A. (2006) ^{The Fusarium Laboratory Manual. Ames: Blackwell. pp. 250–254.}

In the 1940s, these were collapsed together by Snyder and Hansen to form a single species, Fusarium solani; one of nine Fusarium species they recognized based on morphological features. 

The current concept of F. solani is as a complex species consisting of multiple, closely related and morphologically poorly distinguishable, “cryptic” species with characteristic genetic differences. There is a proposed concept for the entire genus – widely subscribed by specialists – that would include this complex. (Geiser, David M; Al-Hatmi, Abdullah; Aoki, Takayuki; Arie, Tsutomu (2020-11-17)

Like other species in its genus, Fusarium solani produces colonies that are white and cottony. However, instead of developing a pink or violet centre like most Fusarium species, it can become blue-green or bluish brown. (as shown below) 

On the underside, they may be pale, tea-with-milk-brown, or red-brown. Yet, some clinical isolates have been blue-green or ink-blue on the underside. Colonies are low-floccose, loose, slimy, and sporadic. When grown on potato dextrose agar (PDA), this fungus grows rapidly, but not as rapidly as Fusarium oxysporum. In PDA, F. solani colonies reach a diameter of 64–70 mm in 7 days.

F. solani is found in soil worldwide. However, a given species within the complex may not be as widespread and may not have the same ecology as others in the complex. In general, as a soil fungus, F. solani is associated with the roots of plants and may be found as deep in the ground as 80 cm. It is frequently isolated in tropic, subtropic, and temperate locations, and less frequently isolated from alpine habitats. 

The pH of soil does not have a significant effect on F. solani, but soil fumigation causes an increase in occurrence. F. solani is typically sensitive to soil fungicides. F. solani has been found in ponds, rivers, sewage facilities, and water pipes. 

F. solani has it’s chlamydospores that overwinter on plant tissue/seed or as mycelium in the soil. The pathogen enters the host through developing roots, where it can infect it. After infection, F. solani produces asexual macro and microconidia which are dispersed via the elements. The pathogen can persist in the soil for a decade and if left unchecked can cause complete crop loss.

The fungal pathogen rots the roots of its host plant. It also causes soft rot of plant tissues by penetrating plant cell walls and destroying the torus. It is implicated along with Pythium myriotylum, in pod rot of the pods of groundnuts. 

It can cause damping off, corn rot, and root rot, as well as sudden death of soybeans (SDS). It is a very generalistic fungal species and has been known to infect peas, beans, potatoes, and many types of cucurbits. Symptoms include general plant decline, wilting, and large necrotic spots on tap roots. Recently the pathogen has also done serious damage to olive trees throughout the Mediterranean region.

F. solani is largely resistant to typical antifungal agents. The most effective antifungals in treating F. solani infections are amphotericin B and natamycin; however, these agents have only modest success in the treatment of serious systemic infection.

Effect on humans – as of 2006, there has been increasing evidence that F. solani  can act as a causal agent of mycoses in humans, it has been implicated in the following diseases: disseminated disease, osteomyelitis, skin infection, fungemia, and endophthalmitis. 

Half of human disease involving Fusarium is caused by F. solani and is involved in most cases of systemic fusariosis and corneal infections. In immunocompromised patients, F. solani is one of the most common agents in disseminated and cutaneous infections.

In the southern USA, fungal keratitis has been most commonly caused by F. solani, as well as F. oxysporum. Cases occur most frequently during harvest season as a result of corneal trauma from dust or plant material. Fungal spores come into contact with the damaged cornea and grow.

Without treatment, the hyphae can grow into the cornea and into the anterior chamber of the eye.^] F. solani is also a major cause of fungal keratitis in HIV positive patients in Africa.

An investigation into a meningitis outbreak of 79 cases since October 2022, that had killed 35 people (34 of them women who had undergone cesarean section) in Durango (Mexico city) revealed the contamination of bupivacaine with Fusarium solani in 4 batches, used by an anesthesiologist.

As of June 1, 2023, a multistate outbreak of meningitis due to F. solani was ongoing among patients who underwent epidural anesthesia at two clinics in the Mexican city of Matamoros, Tamaulipas a Mexican state, with a total of 212 residents in 25 US states identified as being at risk, two of whom had died.

There will be more scholarly on new plant disease be it fungal pathogens borne on the wind or wing, or via entomology invasion. We will continue to add them on our new platform Substack.com where you can find us using our name Taiga Bonzai.com. We thank our readers and followers from around the world whom have been with us since 2016, until next time, BW, Nik.