Category Archives: ORIGINAL ARTICLE

Plant growth stage and Phoma medicaginis inoculum concentration together determine severity of Phoma black stem and leaf spot and consequent phytoestrogen production in annual Medicago spp.

Posted on 11 September 2023 by

Studies highlighted how Phoma disease incidence and severity and resultant phytoestrogen production in annual Medicago depend on plant developmental stage, inoculum concentration and cultivar.

Abstract

Phoma black stem and leaf spot disease (Phoma medicaginis) not only destroys annual Medicago spp. forage and seed yield but also reduces herbage quality by consequent phytoestrogen production that reduces ovulation of grazing animals. Two controlled environment studies evaluated the effects of plant developmental stage in annual Medicago rugosa ‘Paraponto’ and M. scutellata ‘Sava’ and different inoculum concentrations of P. medicaginis in M. littoralis ‘Harbinger’ and M. polymorpha ‘Serena’ on disease development and coumestrol production. Disease incidence and severity and coumestrol production were dependent on plant developmental stage, cultivar and inoculum level (all p ≤ 0.001). Disease was least in 4-week-old plants; highest coumestrol was in inoculated 10-week-old Sava (1353 mg/kg) and least coumestrol in uninoculated 4-week-old Paraponto (87 mg/kg); and there was a positive correlation of disease incidence/severity factors with coumestrol across cultivars and plant growth stages (p < 0.001). Disease levels and coumestrol production were determined by inoculum concentration and cultivar (both p ≤ 0.001). Highest coumestrol was in Serena inoculated with 10⁷ conidia/mL (265 mg/kg); lowest coumestrol was in uninoculated Harbinger (6 mg/kg); and there was a significant positive correlation of disease incidence/severity factors with coumestrol across cultivars and inoculum concentrations (p < 0.001). These studies emphasize both the opportunity for farmers to better use annual Medicago spp. stands for grazing reproducing animals early in the growing season when both disease and coumestrol levels are lowest, and the need for heightened farmer vigilance at later growth stages with greater disease and consequent phytoestrogen risk for grazing animals.

Synergistic effects of Bacillus velezensis SDTB038 and phenamacril on Fusarium crown and root rot of tomato

Posted on 11 September 2023 by

Bacillus velezensis SDTB038 had strong antifungal activity. The combination of phenamacril and SDTB038 had the most effective in controlling Fusarium crown and root rot of tomato, while also improving tomato yields in greenhouse.

Abstract

Fusarium crown and root rot (FCRR) is a damaging ailment that can affect tomato production. It is caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL). The use of biological agents, in conjunction with fungicides, has become a practical strategy for combating fungal diseases in crops. Lipopeptide extracts from a potential biocontrol strain of Bacillus velezensis (SDTB038) exhibited an inhibitory effect on the mycelial growth of FORL; the EC₅₀ value was 59.95 mg/L, and at a concentration of 256 mg/L the inhibition rate reached 97.4%. The SDTB038 strain produces metabolites such as protease and siderophores. Additionally, it is capable of forming a biofilm and swimming. Phenamacril, an antifungal agent, also displayed an inhibitory effect on FORL, demonstrating an EC₅₀ value of 1.074 mg/L. The control effects of the combination of Bacillus velezensis SDTB038 and phenamacril against FORL on tomato plants were also studied in the greenhouse. The combination of phenamacril and 10⁸ CFU/mL SDTB038 fermentation broth exhibited a strong synergistic control effect on FORL, of up to 84.0%. The combination also led to a 35.6% increase in tomato yield compared to the control. These results demonstrate that SDTB038 possesses antifungal activity. Moreover, when combined with phenamacril, it exhibits a strong synergistic effect against FORL. This solution proves to be an effective means of controlling FCRR in tomato plants.

Grapevine yellows in Jordan: Associated phytoplasmas, putative insect vectors and reservoir plants

Posted on 11 September 2023 by

In Jordan, genetic diversity, distribution and ecology of phytoplasmas associated with grapevine yellows are more complex than previously known.

Abstract

Field surveys were conducted in wine and table grape vineyards from June to October 2020 in 13 locations belonging to five governorates in North and South Jordan. Typical grapevine yellows symptoms, including leaf reddening/yellowing and rolling were observed on 10% to 55% of vines. Nested PCR-based amplification of the 16S rRNA gene detected phytoplasmas in 22% and 15.7% of the analysed symptomatic wine and table grape cultivar plants, respectively. Amplicon nucleotide sequence analyses identified the detected phytoplasmas as “Candidatus Phytoplasma solani” (taxonomic subgroup 16SrXII-A), “Ca. P. omanense” (16SrXXIX-A and -B), “Ca. P. aurantifolia” (16SrII-C) and “Ca. P. asteris” (16SrI-R) in 72.4%, 17.2%, 6.9% and 3.4% of infected plants, respectively. Such phytoplasmas were found differentially distributed in wine and table grape cultivar vineyards surveyed. Further investigation identified “Ca. P. solani” in the putative insect vectors Orosius cellulosus (first report in Jordan), Euscelidius mundus, Laodelphax striatellus, and Circulifer sp., and in bindweed; “Ca. P. aurantifolia” in the insect O. cellulosus and in bindweed; “Ca. P. omanense” in the insect Psammotettix striatus; and “Ca. P. asteris” in the insects Arboridia adanae, Cicadulina bipunctata, Circulifer sp., L. striatellus, Hyalesthes obsoletus, and P. striatus. Based on this preliminary data, ecological cycles of such phytoplasmas are discussed. Results suggest that the diversity and ecology of grapevine yellows phytoplasmas in Jordan are more complex than previously known, leading to a potential risk of disease outbreaks.

Detection of tomato brown rugose fruit virus is influenced by infection at different growth stages and sampling from different plant parts

Posted on 11 September 2023 by

Detection of tomato brown rugose fruit virus is influenced by plant age at time of infection. Regardless of plant age, sepals and young leaves, where present, give the best chance of detection.

Abstract

Since the first report of the virus in 2014, tomato brown rugose fruit virus (ToBRFV) has spread widely through Europe, the Americas and Asia. Within Europe there is currently a requirement for annual surveillance for the virus. However, little is known about the relative impact of sampling strategy with respect to timing of infection and the detection of virus from different plant parts. To test reliably for ToBRFV in crops of unknown infection status, this issue needed to be addressed. To do this, two different approaches were followed: (1) inoculation experiments were conducted at two institutes to look at the relative effects of time of infection, plant parts, cropping season and cultivar on detection of the virus; and (2) sampling and testing various plant parts were carried out during active outbreaks from two tomato production sites in the Netherlands to look at the effect of sampling plant parts on detection of the virus. In inoculation experiments, the greatest impact on detection was timing of infection, with plants infected early in the growth cycle showing a predictable development of infection. In plants infected later, infection was detectable in sepals (calyx) earlier than in older leaves. In the studies carried out on commercial crops during ToBRFV outbreaks, the highest virus concentrations were obtained from testing sepals and young leaves. Thus, in a young crop where sepals and fruit are not yet developed, sampling should focus on the young leaves; in a mature crop it may be better to sample sepals and/or fruit.

Genetic variation and population differentiation in North American, central Asian and European isolates of Venturia inaequalis

Posted on 11 September 2023 by nIan Mellon, nJugpreet Singh, nHana Feulner, nAwais Khann

Genome sequence of 123 global Venturia isolates shows genetic diversity and population structure but does not find population genetic differentiation between North America and Europe/central Asia due to geographic separation.

Abstract

Venturia inaequalis, the causal fungal pathogen of apple scab, has evolved with its Malus hosts during apple domestication. This co-evolution has resulted in a genetic structure in V. inaequalis populations from Europe and central Asia based on host species and geographic isolation. However, it is not yet clear if geographic isolation has led to population differentiation in North American isolates. We resequenced the genomes of 54 V. inaequalis isolates from North America and analysed them with publicly available genome sequences of 90 European and central Asian isolates for variant discovery and population structure. A total of 204,566 high-quality single-nucleotide polymorphisms (SNPs) were identified and used to assess population genetic structure and genomic diversity across 123 Venturia spp. isolates from around the world. Population genetic analysis identified four clusters based on Malus and non-Malus hosts and Venturia species; this differentiation was supported by genetic diversity parameters including F _ST, Nei's π and Tajima's D. Genetic structure analysis did not reveal a distinct subpopulation of North American V. inaequalis isolates within the global isolates. Additionally, structure was not observed in V. inaequalis isolates collected on M. × domestica between North America and Europe. These observations indicate that geographical isolation has not contributed to the population differentiation between North America and Europe/central Asia. These results will enhance our understanding of the evolution of V. inaequalis, the emergence of virulent isolates and their implications for managing apple scab effectively.

Double trouble: Co‐infection of potato with the causal agents of late and early blight

Posted on 11 September 2023 by

Alternaria solani directly inhibits Phytophthora infestans growth in vitro and co-inoculation of potato with both pathogens favours A. solani, even when P. infestans arrives first/simultaneously.

Abstract

Global potato production is plagued by multiple pathogens, amongst which are Phytophthora infestans and Alternaria solani, the causal agents of potato late blight and early blight, respectively. Both these pathogens have different lifestyles and are successful pathogens of potato, but despite observations of both pathogens infecting potato simultaneously in field conditions, the tripartite interactions between potato and these two pathogens are so far poorly understood. Here we studied the interaction of A. solani and P. infestans first in vitro and subsequently in planta both in laboratory and field settings. We found that A. solani can inhibit P. infestans in terms of growth in vitro and also infection of potato in both laboratory experiments and in an agriculturally relevant field setting. A. solani had a direct inhibitory effect on P. infestans in vitro and compounds secreted by A. solani had both an inhibitory and disruptive effect on sporangia and mycelium of P. infestans in vitro. In planta infection bioassays revealed that simultaneous co-inoculation of both pathogens resulted in larger necrotic lesions than single inoculations; however, consecutive inoculations only resulted in larger lesions when A. solani was inoculated after P. infestans. These results indicate that the order in which these pathogens attempt to colonize potato is important for the disease outcome and that the influence of plant pathogens on each other should be accounted for in the design of future disease control strategies in crops such as potato.

Damage on grapevine cv. Niagara Rosada leaves caused by the combined effect of temperature and Asian grapevine leaf rust (Neophysopella tropicalis)

Posted on 11 September 2023 by

Inoculated plants kept at 30°C presented cell alterations that blocked colonization, reducing lesion density and severity. However, accelerated leaf senescence due to temperature raise may increase leaf damage and reduce yield.

Abstract

Asian grapevine leaf rust (AGLR), caused by Neophysopella tropicalis, is a problem for viticulture, especially in latitudes lower than 25° S, which include the most significant production regions in Brazil. Climate change has raised new concerns in agriculture as temperature can affect the resistance of plants to pathogens. With the aim of understanding how air temperature rise affects the AGLR pathosystem, measurements of leaf gas exchange and epidemiological and histopathological analyses were carried out on control and inoculated leaves of Vitis labrusca ‘Niagara Rosada’ grown at 25°C and 30°C. The lesion density and rust severity were higher at 25°C than 30°C, and the ratio between adaxial surface necrosis and the abaxial surface area occupied by pustules was >1 only at 30°C, presenting a necrosis not associated to the pathogen lesion. In fact, leaf necrosis was identified on control plants kept at 30°C and associated with gerontoplasts, representing accelerated leaf senescence. The AGLR pathogen reduced gas exchange and photosystem II activities at 25°C, with no difference between control and inoculated plants at 30°C. Our results indicate that AGLR is sensitive to increasing air temperature. However, the accelerated leaf senescence caused by the combination of N. tropicalis infection and temperature on Niagara Rosada can lead to high leaf damage.

Transmission of Furcraea necrotic streak virus (FNSV) by Olpidium virulentus

Posted on 11 September 2023 by

Fique plants are source of natural fibre. Furcraea necrotic streak virus (FNSV) causes the most detrimental disease in fique plants, affecting fibre production, and is transmitted by Olpidium virulentus.

Abstract

Furcraea necrotic streak virus (FNSV) is the causative agent of necrotic streak disease, also known as macana in fique crops (Furcraea spp.) resulting in damage to leaf fibres and economic losses. The rhizospheric fungus Olpidium spp. is present in the roots of affected plants and may play a role in the disease transmission. FNSV infection and the role of fungi were examined in macanavirus-diseased plants in Colombia. Spherical, and icosahedral (24.7 ± 1.98 nm), non-enveloped virions with a granular surface were isolated from field fique plants showing signs of macana disease, and the viral genome was completely sequenced. Taxonomic status was assigned through sequence analysis (Macanavirus genus in Tombusviridae family). The variability of the virus pangenome was evaluated in diseased fique plants from ecologically different Andean regions that showed low gene flow. Olpidium virulentus zoospores, identified by internal transcribed spacer (ITS) sequencing and microscopic analysis, were associated with viral particles and resting spores in diseased fique roots. An in vitro virion–zoospore binding assay showed that FNSV and O. virulentus zoospores interacted. Transmission assays in lettuce (Lactuca sativa), a model plant used to study this virus, showed 100% infection when a preincubated mixture of zoospores and FNSV was added to roots, whereas only 33% infection occurred when FNSV was added alone. This demonstrated the ability of O. virulentus to act as a vector for FNSV, potentially enhancing viral transmissibility in field fique crops. This is the first report of FNSV being transmitted by O. virulentus, a rhizosphere fungus.

Genetic loci associated with Fusarium wilt resistance in tomato (Solanum lycopersicum L.) discovered by genome‐wide association study

Posted on 9 September 2023 by

Abstract

Fusarium wilt (FW), caused by Fusarium oxysporum f. sp. lycopersici (Fol), has impacted global tomato production. This study aims to identify single nucleotide polymorphisms (SNPs) and candidate genes associated with FW resistance against different Fol isolates in tomato accessions using genome-wide association studies (GWAS). Ninety-four tomato accessions were evaluated for FW resistance and subjected to GWAS analysis. Broad-spectrum tomato accessions demonstrated resistance to Fol in at least two isolates, exhibiting a disease severity index (DSI) of 0%. Thirty-two SNP loci were significantly linked to the DSI of Fol isolates TFPK401, BK2269 and NP-T4, clustering on chromosome 6. Among these, 12 common significant SNPs were associated with the DSI of at least two Fol isolates, while four unique SNPs were specific to TFPK401 or NP-T4. Furthermore, candidate genes associated with disease response to Fol infection were identified within a 37.9–41 Mb region flanking the SNPs. These findings contribute to a deeper understanding of resistance mechanisms against Fol infection in tomatoes, potentially aiding the development of effective breeding strategies for Fusarium wilt resistance.

Development of KASP fingerprinting panel for clonal identification in red raspberry (Rubus idaeus L.)

Posted on 7 September 2023 by

Abstract

Red raspberry is an economically important horticultural crop that is known for its fruit's sweet flavour and nutritional value. A reliable and economic genotyping platform is needed to facilitate clonal/variety identification. Previous attempts for clonal identification utilized morphological traits or low-throughput, difficult to score dinucleotide-containing simple sequence repeat molecular markers. Single nucleotide polymorphisms (SNPs), despite having lower allelic diversity, are numerous across the genome and more easily converted to high-throughput assays restoring differential power. In this study, we use the kompetitive allele-specific PCR (KASP™) chemistry, an affordable and high-throughput platform, to develop a panel of SNPs to distinguish a diverse collection of red raspberry accessions for clonal identification. The panel consists of 48 KASP assays that show high concordance with whole genome sequencing, allelic balance, and recovery rate and a minimal set of 24 assays that distinguished the same accessions differentiated by the larger panel.