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.

They state that “We aim to provide a repository for such records to support the work of field advisers, diagnosticians, researchers, and plant health policy makers. We are proud to be a fully open access journal, published by Wiley on behalf of the British Society for Plant Pathology.“

https://bsppjournals.onlinelibrary.wiley.com/journal/20440588

According to P. Kong, R. Ioos and C. X. Hong in their New Disease Reports Volume 49, Issue 2 e12278. ‘First report of ‘Calonectria henricotiae’ that causes ‘box blight’ in Spain first published: 02 May 2024 https://doi.org/10.1002/ndr2.12278.

Box blight – is caused by two closely related fungi, Calonectria pseudonaviculata (Cps) and/or C. henricotiae (Che) (Gehesquière et al., 2016). Cps is widespread globally (Daughtrey, 2019) while Che is limited to eight central European countries. (Hong, 2023) To determine whether Che is present in southern Europe, we visited ten large boxwood gardens and street plantings in Madrid and Toledo, Spain and in Bordeaux, Lyon and Sainte-Foy-la-Grande, France.

Boxwood Buxus spp. twigs with black streaks were only observed in Madrid, Toledo, and Sainte-Foy-la-Grande. Diseased twigs were collected in sealed triple bags and brought to the laboratory under the USDA permit. (P526P-21-05960)

After surface sterilization with 10% bleach for two minutes and three rinses in deionised water, twigs were placed on a mesh with wet paper towels underneath in closed plastic containers at 23°C. They were sprayed with sterile distilled water every two days until white mould appeared on leaves. The mould was suspended in 15 µL sterile distilled water then transferred onto a glass slide for microscopy.

Following observations of rod-shaped conidia, typical of Calonectria spp., 1-µL drops of the suspensions were pipetted from slides onto acidified potato dextrose agar (PDA) for isolation (Kong et al., 2023). Clean colonies were only obtained from the Madrid and Sainte-Foy-la-Grande samples and were sub-cultured on regular PDA.

Colony PCR (Kong et al., 2005) was performed from a total of 159 colonies grown from three-day PDA cultures, using Cps– and Che-specific primers (Guo & Pooler, 2021). Also included in the PCR were three French isolates from the ANSES collection: LSVM0960 collected by Department Île-de-France in 2013, LSVM1007 by Department Meurthe-et-Moselle in 2014, and LSVM1235 by Department Finistère in 2015.

All 99 isolates from Spain were identified as Che while 63 isolates from France were Cps. Seven Spanish and nine French isolates were sub-cultured in potato dextrose broth for DNA extraction. Their identities were confirmed by PCR of the DNA and PCR product sequencing (GenBank Accession Nos. PP632113-19 For Che isolates and PP632120-28 for Cps isolates) with the same primer pairs.

The same isolates were tested for temperature tolerance. The Spanish isolates had an average colony diameter of 1.6 cm in PDA at 28.5°C for 10 days, while the French isolates did not grow under the same conditions, further confirming their identities (Gehesquière et al., 2016)

To our knowledge, this is the first report of Calonectria henricotiae causing box blight in Spain. Knowing the actual distribution of the fungus is critical to preventing its further spreading to other countries and areas currently not affected by this pathogen, promoting safe plant trade.

This work was funded by the USDA National Institute of Food and Agriculture – Specialty Crop Research Initiative (2020-51181-32135).

New Disease Reports – Volume 49, Issue 2 e12265 ‘Current epidemiological situation of mealybug wilt of pineapple disease in Ecuador’. J. F. Cornejo-Franco, A. Olmedo-Velarde, D. F. Quito-Avila. First published 02 April 2024.

https://doi.org/10.1002/ndr2.12265

Mealybug wilt of pineapple (MWP) is the most important virus-associated syndrome affecting pineapple worldwide. The wide range of symptoms including bronze-to-red colouring of leaves, tip dieback, leaf downward-curving and wilting has obscured the aetiology of MWP. (Dey et al., 2018) At least five ampeloviruses (family Closteroviridae), Pineapple mealybug wilt-associated virus 1 (PMWaV-1), PMWaV -2, -3, -5 and -6 have been associated with MWP.

Recently, additional viruses have been reported in pineapple including, Pineapple secovirus A (PSV-A), PSV-B, -C, and -D, all members of the Sadwavirus genus (family Secoviridae), Pineapple bacilliform CO virus (PBCOV) and Pineapple bacilliform ER virus. (PBERV)

These are both members of the Badnavirus genus family Caulimoviridae (Larrea-Sarmiento et al., 2022). In Ecuador, PMWaV-1 is the only virus reported from plants showing MWP-like symptoms. (Alvarez-Quinto et al., 2015) This study aimed to determine the prevalence of MWP and the viruses potentially associated with the disease in the largest pineapple-producing area of Ecuador.

In 2023, a total of 400 pineapple MD-2 hybrid plants were randomly sampled and inspected for disease symptoms to estimate the prevalence of MWP in a planting located in Santo Domingo, Ecuador (Figure. 1). Sampling was done in 36-week-old fields. Only 30 plants (8%) showed the typical tip dieback symptoms characteristic of MWP and these were found on the edge of plantations. Virus testing was done on all symptomatic plants (n = 30) and also on 30 symptomless plants.

Total RNA extraction and RT-PCR for virus testing was done as described by Cornejo-Franco et al. (2023) using primers and PCR conditions detailed by Larrea-Sarmiento et al. (2022) and Alvarez-Quinto et al. (2015). Virus identity was confirmed by Sanger sequencing of cloned amplicons (GenBank Accession Nos. PP479943, PP479944, PP489387-PP489390)

Virus indexing showed a strong association between the observed MWP symptoms and co-infections of PMWaV-2 and PMWaV-1 (73%), while single infections of these two viruses were also found (<53%) in symptomless plants. PMWaV-3 and PSV-B were found in both symptomatic and symptomless plants in similar proportions, while PSV-A was detected in one third of symptomatic and 13% of symptomless plants.

PBCOV was found in 20% of symptomatic plants. All viruses showed high nucleotide identity (>95%) with Hawaiian homologs, except for PSV-A and -B which showed <88% nucleotide identity. No clear association was observed between the occurrence of PMWaV-3, PSV-A, PSV-B, or PBCOV and MWP PMWaV-5 and -6, PSV-C and -D and PBERV were not detected during this study.

Pineapple mealybugs (Dysmicoccus spp.) were present in all pineapple plants sampled in this study. Hence, the aetiology of MWP remains to be further studied. These findings are consistent with those previously reported in Hawaii, where PMWaV-2 and mealybugs were present on plants with MWP symptoms. (Sether et al., 2002)

This study was funded by Centro de Investigaciones Biotecnológicas del Ecuador, CIBE, through a seed funding call, under project code CIBE-0004-2023. The authors would like to thank Mr. Jhonny España from Cibe for field assistance.

As we have often stated pests and disease are not only spread via wind and wing they are distributed by mankind as well. Now the globe has shrunk due to the various modes of transportation, which is a free ‘ticket’ to ride, pests and diseases are on the increase. This problem is getting worse with no way to sustain or permanently eradicate it’s onslaught.

Plants that are vulnerable will quickly perish, because their defence mechanisms are inadequate moreover, countless pests and disease are immune to many pesticides and fungicides and other chemical compounds. In the next article we look at some more diseases of 2024, until next time, BW, Nik.

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.