Yearly Archives: 2023

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

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

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.

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

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

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.

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

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

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.

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

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

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.

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

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

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.

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.

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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.

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.

Trichoderma gamsii T6085, a biocontrol agent of Fusarium head blight, modulates biocontrol‐relevant defence genes expression in wheat

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Trichoderma gamsii T6085, a biocontrol agent of Fusarium head blight, modulates biocontrol-relevant defence genes expression in wheat

Modulation of plant defence genes could be included within the arsenal of mechanisms used by Trichoderma gamsii T6085 when applied on wheat, an additional feature of interest in the management of Fusarium head blight.


Abstract

To enhance the framework of the mechanisms of action used by Trichoderma gamsii T6085 for the control of Fusarium head blight (FHB), this work investigated its ability to modulate the expression of defence-related genes of wheat (Triticum aestivum ‘Apogee’) in response to endophytic colonization of plant tissues. Changes in relative expression of pal1, pr1, pgip2 and lox1 genes were assessed over time in wheat roots, in spikes colonized by T6085 alone and both T6085 and Fusarium graminearum, and in leaves from wheat seedlings root-inoculated with T6085. Results indicate the ability of T6085 to induce local and systemic defence responses in wheat plants in the presence of one of the causal agents of FHB. There was a general significant up-regulation of the plant defence-related genes analysed, especially in the first days after the application of T6085. According to these results, modulation of plant defence genes could be included within the arsenal of mechanisms used by T6085 when applied to wheat, an additional feature of interest in the management of FHB. To evaluate the effect of the plant genotype on the ability of T6085 to endophytically colonize roots, root colonization was assessed on four cultivars of T. aestivum and two cultivars of T. durum. Data showed that roots of only two T. aestivum cultivars were endophytically colonized by T6085, similar to cv. Apogee used here as control, thus demonstrating an effect of the host genotype on the endophytic ability of T6085.

HCPro affects heterologous virus infection through salicylic acid and auxin pathways

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HCPro affects heterologous virus infection through salicylic acid and auxin pathways

Transgenic Nicotiana tabacum plants expressing HCPro of chilli veinal mottle virus respond to the infection by tobacco mosaic virus or cucumber mosaic virus via salicylic acid and auxin pathways.


Abstract

Mixed infection by plant viruses is common in nature, but how a key viral protein of one virus affects the infection by heterologous viruses is not yet fully understood. The helper component proteinase (HCPro) is a widely studied RNA silencing suppressor encoded by viruses of the family Potyviridae. Here, we investigated the defence response of Nicotiana tabacum plants overexpressing HCPro of chilli veinal mottle virus (HCPro-OX) to tobacco mosaic virus and cucumber mosaic virus infection. We monitored the physiological and molecular changes of HCPro-OX plants in response to virus infection. The results showed that HCPro-OX plants under virus infection exhibited higher susceptibility at the early stage but stronger tolerance at the later stage compared to wild-type plants. The tolerance to heterologous virus infection of HCPro-OX plants corresponded to a lower level of reactive oxygen species accumulation and higher activities of several antioxidant enzymes. Reverse transcription-quantitative PCR assays showed that the expression of genes related to salicylic acid (SA) pathways was significantly upregulated, but the expression of genes related to the auxin pathways was downregulated at the late stage of virus infection in HCPro-OX plants compared to wild-type plants. By contrast, the situation in the early stage of virus infection was reversed. In addition, pretreatment with SA, the auxin naphthylacetic acid (NAA) and their respective inhibitors 1-aminobenzotriazole (ABT) and naphthalam (NPA) further confirmed the antagonistic effects of SA and NAA in the response of HCPro-OX plants to heterologous virus infection. Thus, our results demonstrate that HCPro affects heterologous virus infection through SA and auxin pathways.

A review on common root rot of wheat and barley in Australia

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A review on common root rot of wheat and barley in Australia

This article comprehensively reviews common root rot (Bipolaris sorokiniana) in Australia, covering the disease cycle, economic loss, management, traditional and emerging detection methods and research focus in the last 50 years.


Abstract

Common root rot (CRR) caused by the soilborne pathogen Bipolaris sorokiniana (teleomorph Cochliobolus sativus) is becoming increasingly prevalent worldwide. Identification of CRR is difficult and time-consuming for human assessors due to the non-distinctive above-ground symptoms, with browning of subcrown internodes and roots the most distinguishing symptom of infection. CRR disease has been recognized as a significant disease for cereal crops in many countries. In 2009, CRR in Australia was estimated to cause $30 million average annual yield loss for wheat and $13 million for barley. Recent evidence indicates CRR may be more prevalent than expected in Australian wheat cropping areas due to lack of research on this disease. Low levels of B. sorokiniana survive in the soil for up to 10 years and attack plants at early stages of growth. Therefore, mitigating CRR in wheat and barley may not be practical at the late stages of infection due to lack of effective methods; however, early detection might be viable to alleviate the impact of this disease. A comprehensive overview of CRR caused by B. sorokiniana, including disease background, worldwide economic losses, management methods, potential CRR detection using multispectral and hyperspectral sensors and the research focus over the past 50 years is provided in this article. This review paper is expected to provide thorough supplemental information for current studies about CRR and proposes recommendations for whole-of-field disease scouting methods to farmers, enabling reduced time and cost for CRR management and increasing wheat and barley production worldwide.

Banana bunchy top disease in Africa—Predicting continent‐wide disease risks by combining survey data and expert knowledge

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Banana bunchy top disease in Africa—Predicting continent-wide disease risks by combining survey data and expert knowledge

Visualizing and mitigating the growing risks of BBTD spread across Africa, leveraging a decade's worth of survey data and expert insights for strategic decision-making.


Abstract

Across Africa, banana bunchy top disease (BBTD) severely impacts banana production and livelihoods of millions of smallholder farmers. Mapping vulnerability of landscapes to monitor BBTD establishment and spread is crucial for proactive measures of disease exclusion. To highlight current and future risks of BBTD in Africa, the relationship between 1160 field observations from 14 BBTD surveys and environmental covariate maps was determined using logistic regression. From these relationships, we inferred the environmental suitability of the African landscape for the possible wider spread of BBTD. Using this information and expert knowledge, we generated a map highlighting the main banana production areas at risk of BBTD entry and establishment. We combined these maps to create a priority map that highlights the areas that need most attention in combating BBTD through surveillance and measures to prevent its spread. Our analysis shows that BBTD is widespread across tropical Africa, with dispersal over several hotspots. Central and Western Africa are most favourable for the development of BBTD. Central, West and South-East Africa are most at risk of BBTD entry and initial establishment. Areas in West and Central Africa, in the Great Lakes Region in Eastern Africa and in South-East Africa, particularly in Malawi and Mozambique, score high on the prioritization index for surveillance and mitigation efforts. Recent reports of BBTD presence in north-western Uganda and western Tanzania support these risk predictions. For these and other not-yet-infected areas, measures for close surveillance and proactive management of the disease are needed.