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.