Cassava Mosaic Disease Research Articles

Cutting Dipping Application of Flupyradifurone against Cassava Whiteflies Bemisia tabaci and Impact on Its Parasitism in Cassava.

The cassava whitefly Bemisia tabaci causes damage in cassava through the feeding and vectoring of plant viruses that cause cassava mosaic and cassava brown streak diseases. This study sought to explore the efficacy of cutting dipping in flupyradifurone for whitefly control and the impact of the mode of application on whitefly parasitism under farmer field conditions. The insecticide treatment significantly reduced adult whiteflies by 41%, nymphs by 64%, and cassava mosaic disease (CMD) incidence by 16% and increased root yield by 49%. The whitefly parasitism rate by Encarsia spp. parasitoids was 27.3 and 21.1%, while Eretmocerus spp. had 26.7 and 18.0% in control and flupyradifurone, respectively, and these differences were not significant. Electropenetrography recordings of whitefly feeding behaviour on flupyradifurone-treated plants showed significantly reduced probing activity and a delay in reaching the phloem as compared to the control. The findings from this study demonstrated that cassava cutting dipping in flupyradifurone significantly reduces whitefly numbers and cassava mosaic disease incidence, thus contributing to a significant root yield increase in cassava. Flupyradifurone applied through cutting dips does not significantly impact parasitism rates in cassava fields. Routine monitoring of parasitoids and predators in insecticide-treated versus control fields should be emphasized to determine the impact of pesticides on these beneficial non-target organisms.

Comparative analysis of salicylic acid levels and gene expression in resistant, tolerant, and susceptible cassava varieties following whitefly-mediated SLCMV infection

Sri Lankan cassava mosaic virus (SLCMV), the primary pathogen responsible for cassava mosaic disease in cassava plantations, is transmitted via infected cutting stems and the whitefly vector, Bemisia tabaci. To obtain better insights into the defense mechanism of cassava against SLCMV, whiteflies were used to induce SLCMV infection for activating the salicylic acid (SA) signaling pathway, which triggers the innate immune system. The study aimed to investigate the specific interactions between viruliferous whiteflies and SA accumulation in resistant (C33), tolerant (Kasetsart 50; KU50), and susceptible (Rayong 11) cassava cultivars by infecting with SLCMV. Leaf samples were collected at various time points, from 1 to 7 days after inoculation (dai). The SA levels were quantified by gas chromatography–mass spectrometry and validated by quantitative reverse transcription polymerase chain reaction. The SA levels increased in KU50 and C33 plants at 2 and 3 dai, respectively, but remained undetected in Rayong11 plants. The expression of PR-9e, PR-7f5, SPS1, SYP121, Hsf8, and HSP90 increased in infected C33 plants at 4 dai, whereas that of KU50 plants decreased immediately at 2 dai, and that of Rayong11 plants increased at 1 dai but gradually decreased thereafter. These findings strongly indicate that SA plays a crucial role in regulating antiviral defense mechanisms, especially in SLCMV-resistant plants. Altogether, the findings provide valuable insights into the mechanisms underlying the activation of SA-mediated anti-SLCMV defense pathways, and the resistance, tolerance, and susceptibility of cassava, which can aid future breeding programs aimed at enhancing SLCMV resistance.

Field Screening of Elite Cassava (Manihot esculenta) Mutant Lines for their Response to Mosaic and Brown Streak Viruses

Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD) have been major limiting biotic factors to the productivity of cassava farming in Kenya. Development of resistant cassava varieties is most effective way. The study was to determine response of elite cassava lines to CBSD and CMD under field conditions on different agro-ecological zones in Kenya. Screening was done under hot-spot field conditions where five lines together with their parents were evaluated in Randomized Complete Block Design with three replications at University of Eldoret (UoE), Solai and Marakwet sites in Kenya. Severity assessment done on 1-5 rating scale where 1 very resistant and 5 most susceptible. Elite cassava lines had significant differences in their response (p < 0.05) to CBSD and CMD. Additionally, genotypes, site and time interval were also significant (p < 0.05). The three elite lines (CAS1, CAS2 and CAS3) had better tolerance to both diseases compared to their parents (KME3 and KME4) with KME4 showing visible brown rings on the root typical of CBSD The elite lines CAS1, CAS2 and CAS3 identified to have better adaptability to both CBSD and CMD could be further exploited in breeding for new cassava varieties for Kenya and other countries in the region with similar ecology.

Viruses associated with cassava mosaic disease and their alternative hosts along Nigeria-Cameroon border

Cassava mosaic disease (CMD) threatens cassava production across the African continent. Because CMD is widespread in sub-Saharan Africa (SSA), it is particularly important to monitor border regions to prevent the introduction of other cassava (Manihot esculenta Crantz) viruses and strains into regions otherwise considered still free of the viruses. The objective of this study was to establish the occurrence of viruses associated with CMD and their alternate host plants along the Nigeria-Cameroon border. One hundred leaf samples from cassava plants and weed species were collected across 21 locations, along the border regions of Cross River State; and assessed for CMD incidence and severity. Nucleic acid extracts were obtained and used to test for African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV), using polymerase chain reactions. Plants from ten, seven and four locations had mild, moderate and severe CMD symptoms, respectively. Of the 100 samples collected, 68 were symptomatic and 32 were asymptomatic for CMD; while five weed species were symptomatic. ACMV alone was detected in six symptomatic and three asymptomatic cassava leaves. EACMV was singly detected in one symptomatic and two asymptomatic cassava leaves; while 13 cassava leaves from ten locations had mixed ACMV/EACMV infections. One asymptomatic cassava leaf from Ikang tested positive for ACMV and EACMV. EACMV alone was detected on a symptomatic weed species, Sclerocarpus africanus. The occurrence of viruses causing CMD in Nigeria, including the border regions, has now been further documented, and S. africanus is now verified as a host of EACMV. There is a need for further studies on other plants that may be putative reservoirs for cassava mosaic viruses, towards the development of integrated management strategies.

Cassava mosaic disease in South and Southeast Asia: current status and prospects

Cassava is one of the most important food and industrial crops in Asia, Africa, and South America. Cassava mosaic disease (CMD), caused by cassava mosaic geminivirus, is one of the major constraints to cassava cultivation. In Asia, the disease is caused by the Indian cassava mosaic virus and Sri Lankan cassava mosaic virus. Phytosanitation, vector control, breeding, and genetic engineering strategies have been widely adopted to manage the disease. This study provides a comprehensive review of the disease spread, the development of diagnostic methods, and various approaches employed for the management of CMD in South and Southeast Asia.

Effect of Wolbachia as biocontrol agent on fecundity and survival of cassava whitefly in northwest Nigeria

Whitefly (Bemisia tabaci Genn.) is known to vectored Cassava mosaic virus (CMV) and Cassava brown streak virus (CBSV), these viruses caused major diseases of cassava in Africa. An experiment was conducted to determine the effect of Wolbachia as biocontrol agent on fecundity and survival of whitefly infesting cassava. Whiteflies infesting cassava were captured and reared using rearing cages. Wolbachia was isolated from infected cassava whiteflies, cultured and used for the inoculations. The experiment was conducted under control conditions using glass cages. Results of this research revealed that number of eggs lay by Bemisia tabaci inoculated with Wolbachia significantly (P = 0.05) reduced weeks after inoculation which significantly differ among the cassava genotypes. Number of eggs lay by B. tabaci free of Wolbachia was significantly higher (964.35) than those inoculated with Wolbachia (46.541) at 4 weeks after inoculation (4WAI). The genotype ‘Dan Aliero’ had the highest number (4WAI 82.33), while, ‘Farin rogo’ had the lowest number of eggs (4WAI 23.33). Number of whitefly nymphs and adults also significantly reduced when B. tabaci was inoculated with Wolbachia. ‘Dan Aliero’ had the highest number of whitefly nymphs and adults (4WAI = 59.00) and (4WAI = 51.00), respectively. ‘Farin rogo’ recorded the lowest number of whitefly nymphs (17.67) and adults (13.00) at 4WAI, respectively. For the first time, Wolbachia were evaluated for whiteflies management. From the finding of this study, Wolbachia can be used as biocontrol agent to suppress whiteflies infestation on cassava and other vegetable crops.

Genome segment ratios change during whitefly transmission of two bipartite cassava mosaic begomoviruses

Cassava mosaic disease is caused by a complex of whitefly-transmitted begomoviruses, which often occur in co-infections. These viruses have bipartite genomes consisting of DNA-A and DNA-B that are encapsidated into separate virions. Individual viruses exist in plants and whitefly vectors as populations comprising both genome segments, which can occur at different frequencies. Both segments are required for infection, and must be transmitted for virus spread to occur. Cassava plants infected with African cassava mosaic virus (ACMV) and/or East African cassava mosaic Cameroon virus (EACMCV), in which the ratios of DNA-A:DNA-B titers differed between plants, were used to examine how titers of the segments in a plant relate to their respective probabilities of acquisition by whiteflies and to the titers of each segment acquired and subsequently transmitted by whiteflies. The probabilities of acquiring each segment of ACMV did not reflect their relative titers in the source plant but they did for EACMCV. However, for both viruses, DNA-A:DNA-B ratios acquired by whiteflies differed from those in the source plant and the ratios transmitted by the whitefly did not differ from one – the ratio at which the highest probability of transmitting both segments is expected.

Time series and power law analysis of crop yield in some east African countries.

We carry out a time series analysis on the yearly crop yield data in six east African countries (Burundi, Kenya, Somalia, Tanzania, Uganda and Rwanda) using the autoregressive integrated moving average (ARIMA) model. We describe the upper tail of the yearly crop yield data in those countries using the power law, lognormal, Fréchet and stretched exponential distributions. The forecast of the fitted ARIMA models suggests that the majority of the crops in different countries will experience neither an increase nor a decrease in yield from 2019 to 2028. A few exceptional cases correspond to significant increase in the yield of sorghum and coffee in Burundi and Rwanda, respectively, and significant decrease in the yield of beans in Burundi, Kenya and Rwanda. Based on Vuong's similarity test p-value, we find that the power law distribution captured the upper tails of yield distribution better than other distributions with just one exceptional case in Uganda, suggesting that these crops have the tendency for producing high yield. We find that only sugar cane in Somalia and sweet potato in Tanzania have the potential of producing extremely high yield. We describe the yield behaviour of these two crops as black swan, where the "rich getting richer" or the "preferential attachment" could be the underlying generating process. Other crops in Burundi, Kenya, Somalia, Tanzania, Uganda and Rwanda can only produce high but not extremely high yields. Various climate adaptation/smart strategies (use of short-duration pigeon pea varieties, use of cassava mosaic disease resistant cassava varieties, use of improved maize varieties, intensive manuring with a combination of green and poultry manure, early planting, etc) that could be adapted to increase yields in east Africa are suggested. The paper could be useful for future agricultural planning and rates calibration in crop risk insurance.

Cassava Witches' Broom Disease in Southeast Asia: A Review of Its Distribution and Associated Symptoms.

Cassava witches' broom disease (CWBD) is one of the main diseases of cassava in Southeast Asia (SEA). Affected cassava plants show reduced internodal length and proliferation of leaves (phyllody) in the middle and top part of the plant, which results in reduced root yields of 50% or more. It is thought to be caused by phytoplasma; however, despite its widespread distribution in SEA still little is known about CWBD pathology. The overarching goal of this study was to review and corroborate published information on CWBD biology and epidemiology considering recent field observations. We report the following: (1) CWBD symptoms are conserved and persistent in SEA and are distinct from what has been reported as witches' broom in Argentina and Brazil. (2) In comparison with cassava mosaic disease, another major disease of cassava in SEA, symptoms of CWBD develop later. (3) Phytoplasma detected in CWBD-affected plants belong to different ribosomal groups and there is no association study available indicating phytoplasma as the causing agent of CWBD. These findings are essential clues for designing surveillance and management strategies and for future studies to better understand the biology, tissue localization and spatial spread of CWBD in SEA and other potential risk areas.

Cassava begomovirus species diversity changes during plant vegetative cycles.

Cassava is a root crop important for global food security and the third biggest source of calories on the African continent. Cassava production is threatened by Cassava mosaic disease (CMD), which is caused by a complex of single-stranded DNA viruses (family: Geminiviridae, genus: Begomovirus) that are transmitted by the sweet potato whitefly (Bemisia tabaci). Understanding the dynamics of different cassava mosaic begomovirus (CMB) species through time is important for contextualizing disease trends. Cassava plants with CMD symptoms were sampled in Lake Victoria and coastal regions of Kenya before transfer to a greenhouse setting and regular propagation. The field-collected and greenhouse samples were sequenced using Illumina short-read sequencing and analyzed on the Galaxy platform. In the field-collected samples, African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), East African cassava mosaic Kenya virus (EACMKV), and East African cassava mosaic virus-Uganda variant (EACMV-Ug) were detected in samples from the Lake Victoria region, while EACMV and East African mosaic Zanzibar virus (EACMZV) were found in the coastal region. Many of the field-collected samples had mixed infections of EACMV and another begomovirus. After 3 years of regrowth in the greenhouse, only EACMV-like viruses were detected in all samples. The results suggest that in these samples, EACMV becomes the dominant virus through vegetative propagation in a greenhouse. This differed from whitefly transmission results. Cassava plants were inoculated with ACMV and another EACMV-like virus, East African cassava mosaic Cameroon virus (EACMCV). Only ACMV was transmitted by whiteflies from these plants to recipient plants, as indicated by sequencing reads and copy number data. These results suggest that whitefly transmission and vegetative transmission lead to different outcomes for ACMV and EACMV-like viruses.

Genetic diversity, distribution, and structure of Bemisia tabaci whitefly species in potential invasion and hybridization regions of East Africa.

Outbreaks of whitefly, Bemisia tabaci species in East and Central Africa, have become increasingly prevalent during the previous 25 years and are responsible for driving the spread of plant-virus diseases, such as cassava mosaic disease and cassava brown steak disease. Epidemics of these diseases have expanded their ranges over the same period, spreading from Uganda into other sub-Saharan African countries. It was hypothesised that a highly abundant 'invader' population of B. tabaci was responsible for spreading these diseases from Uganda to neighbouring countries and potentially hybridising with the resident cassava B. tabaci populations. Here, we test this hypothesis by investigating the molecular identities of the highly abundant cassava B. tabaci populations from their supposed origin in Uganda, to the northern, central, eastern and coastal regions of Tanzania. Partial mitochondrial cytochrome oxidase I (mtCOI) barcoding sequences and nuclear microsatellite markers were used to analyse the population genetic diversity and structure of 2734 B. tabaci collected from both countries and in different agroecological zones. The results revealed that: (i) the putative SSA1 species is structured according to countries, so differ between them. (ii) Restricted gene flow occurred between SSA1-SG3 and both other SSA1 subgroups (SG1 and SG2), even in sympatry, demonstrating strong barriers to hybridization between those genotypes. (iii) Not only B. tabaci SSA1-(SG1 and SG2) was found in highly abundant (outbreak) numbers, but B. tabaci SSA1-SG3 and the Indian Ocean (IO) species were also recorded in high numbers in several sites in Tanzania. (iv) The SSA1-(SG1 and SG2) species was distributed in both countries, but in Tanzania, the B. tabaci IO and SSA1-SG3 species predominated. These data confirm that multiple, local Tanzanian B. tabaci species produce highly abundant populations, independent of the spread of the putative invasive B. tabaci SSA1-(SG1 and SG2) populations.

Insecticide Use by Small-Scale Ugandan Cassava Growers: An Economic Analysis

Cassava is the second most important source of calories in Sub-Saharan Africa. It is subject to economically important yield losses from viral diseases, including cassava brown streak disease and cassava mosaic disease. These diseases are vectored by cassava whitefly, so improved approaches for whitefly and disease control are needed to enable smallholder farmers to protect their cassava crops. To investigate the economic viability of insecticide applications against whitefly, the effect of four insecticide application regimes on three cassava genotypes (NASE 3, NASE 12, MKUMBA) and a local landrace were evaluated, for different farmer groups. Data were collected from researcher–farmer managed fields and descriptive statistics were analyzed. Insecticide and personal protective equipment were the major costs for those farmers that applied insecticide and the dipping treatment had a marginal rate of return of 1.66 (166%), demonstrating that this option was the most profitable and effective. While insecticide users incurred more production costs, they also accrued more profit than non-insecticide users, especially if insecticide was applied at early stages of cassava growth. There is a clear need, therefore, to strengthen the commercialization of cassava crop through plant protection measures such as judicious insecticide application on susceptible varieties, so as to increase yield and crop quality.

Metabolic profiles of Sri Lankan cassava mosaic virus-infected and healthy cassava (Manihot esculenta Crantz) cultivars with tolerance and susceptibility phenotypes

BackgroundCassava mosaic disease (CMD) of cassava (Manihot esculenta Crantz) has expanded across many continents. Sri Lankan cassava mosaic virus (SLCMV; family Geminiviridae), which is the predominant cause of CMD in Thailand, has caused agricultural and economic damage in many Southeast Asia countries such as Vietnam, Loas, and Cambodia. The recent SLCMV epidemic in Thailand was commonly found in cassava plantations. Current understanding of plant–virus interactions for SLCMV and cassava is limited. Accordingly, this study explored the metabolic profiles of SLCMV-infected and healthy groups of tolerant (TME3 and KU50) and susceptible (R11) cultivars of cassava. Findings from the study may help to improve cassava breeding, particularly when combined with future transcriptomic and proteomic research.ResultsSLCMV-infected and healthy leaves were subjected to metabolite extraction followed by ultra-high-performance liquid chromatography high-resolution mass spectrometry (UHPLC-HRMS/MS). The resulting data were analyzed using Compound Discoverer software, the mzCloud, mzVault, and ChemSpider databases, and published literature. Of the 85 differential compounds (SLCMV-infected vs healthy groups), 54 were differential compounds in all three cultivars. These compounds were analyzed using principal component analysis (PCA), hierarchical clustering dendrogram analysis, heatmap analysis, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation. Chlorogenic acid, DL-carnitine, neochlorogenic acid, (E)-aconitic acid, and ascorbyl glucoside were differentially expressed only in TME3 and KU50, with chlorogenic acid, (E)-aconitic acid, and neochlorogenic acid being downregulated in both SLCMV-infected TME3 and KU50, DL-carnitine being upregulated in both SLCMV-infected TME3 and KU50, and ascorbyl glucoside being downregulated in SLCMV-infected TME3 but upregulated in SLCMV-infected KU50. Furthermore, 7-hydroxycoumarine was differentially expressed only in TME3 and R11, while quercitrin, guanine, N-acetylornithine, uridine, vorinostat, sucrose, and lotaustralin were differentially expressed only in KU50 and R11.ConclusionsMetabolic profiling of three cassava landrace cultivars (TME3, KU50, and R11) was performed after SLCMV infection and the profiles were compared with those of healthy samples. Certain differential compounds (SLCMV-infected vs healthy groups) in different cultivars of cassava may be involved in plant–virus interactions and could underlie the tolerance and susceptible responses in this important crop.

Parasitism of the whitefly Bemisia tabaci by aphelinid parasitoids on cassava across five agro-ecological zones of Cameroon

The whitefly Bemisia tabaci (Gennadius) is the vector of cassava mosaic viruses causing cassava viral diseases, which are the most important biotic constraints of cassava production in sub-Saharan Africa (SSA). Presently, B. tabaci management in cassava fields calls for the development of an integrated approach that relies on host plant resistance and biological control. Data on B. tabaci's natural enemies, particularly parasitoids, in Central Africa are limited. Field surveys were conducted from 2015 to 2017 to identify parasitoids associated with B. tabaci in 5 Cameroon agro-ecological zones. Additionally, population dynamics studies were conducted in replicated fields experiments were conducted from 2016 to 2018 to identify cassava genotypes that can best promote B. tabaci parasitism. Two parasitoids, Encarsia sophia (Girault & Dodd) and Encarsia lutea (Masi) were found parasitizing B. tabaci nymphs with higher parasitism by E. lutea compared with E. sophia. The average parasitism rate during the survey was 33.4% for E. lutea and 8.4% for E. Sophia, regardless of AEZ. The highest parasitism rates by E. lutea (48.2% and 24.2% from field trials and surveys, respectively) were observed in the Western Highlands (AEZ 3) while parasitism by E. sophia was less than 12.4%. Four cassava genotypes (I090590, I011797, I090574, and I070593) promoted higher parasitism rates of B. tabaci by E. lutea and E sophia. The contributions of the two parasitoids and their integration with cassava genotypes for the management of B. tabaci in cassava fields are discussed.

Occurrence of cassava mosaic begomoviruses in national cassava germplasm preserved in two agro‐ecological zones of Ivory Coast

AbstractCassava production in Ivory Coast is hampered by cassava mosaic disease (CMD), which is caused by several begomovirus species. To increase cassava production and conserve genetic resources, the Centre National de Recherche Agronomique (CNRA) maintains a germplasm collection of 610 cassava accessions of various origins, which is kept in open fields in Bouaké and Man. We carried out an epidemiological assessment of the collection and a molecular characterization of the viruses infecting the CNRA cassava germplasm. The field in Man was less affected by CMD (incidence 49.78%, severity 2.23, whitefly infection 2.23%), despite the abundant whitefly populations (1.34 per plant), compared to Bouaké (incidence 74.54%, severity 2.92, whitefly infection 8.04% and whitefly population of 0.34 per plant). However, the predominant mode of CMD transmission was through infected cassava cuttings at both sites. PCR analysis showed that the East African cassava mosaic Cameroon virus (EACMCMV) was always found in co‐infection with African cassava mosaic virus (ACMV), which also occurred in single infection. Co‐infections of EACMCMV and ACMV were more prevalent in Bouaké (52.64%) than Man (13.87%). Eleven complete genome sequences of cassava mosaic begomoviruses infecting the CNRA germplasm were obtained, and phylogenetic analysis showed that they are closely related to ACMV and EACMCMV isolates from Ghana, Burkina Faso and Nigeria. The results of this study will assist breeders to screen accurately for CMD resistance in progeny resulting from parental lines, enabling the strategic distribution of new clean cassava planting materials to reduce the impact of CMD.

Integrated Proteomic and Metabolomic Analysis of Cassava cv. Kasetsart 50 Infected with Sri Lankan Cassava Mosaic Virus

Cassava mosaic disease (CMD) is a major disease affecting cassava production in Southeast Asia. This study aimed to perform an integrated proteomics and metabolomics analysis of cassava cv. Kasetsart 50 infected with Sri Lankan cassava mosaic virus (SLCMV). Proteomics analyses revealed that 359 proteins were enriched in the plant–pathogen interaction, plant hormone signal transduction, and MAPK signaling pathways. A total of 79 compounds were identified by metabolomics analysis of the healthy and SLCMV-infected cassava plants. Integrated omics analysis revealed that 9 proteins and 5 metabolites were enriched in 11 KEGG pathways. The metabolic pathways, plant hormone signal transduction, and plant–pathogen interaction pathway terms were specifically investigated. The findings revealed that caffeic acid and chlorogenic acid were associated with the plant–pathogen interaction pathway, histidine (HK3) was involved in plant hormone signal transduction, while citric acid and D-serine were associated with the metabolic pathways. KEGG functional enrichment analysis revealed that plant–pathogen interaction, plant hormone signal transduction, and metabolic pathways were linked via the enriched protein (protein phosphatase 2C) and metabolites (cyclic nucleotide-binding (AT2G20050) and D-serine). The available information and resources for proteomics and metabolomics analyses of cassava can elucidate the mechanism of disease resistance and aid in cassava crop improvement programs.

What Can Be Learned by a Synoptic Review of Plant Disease Epidemics and Outbreaks Published in 2021?

A synoptic review of plant disease epidemics and outbreaks was made using two complementary approaches. The first approach involved reviewing scientific literature published in 2021, in which quantitative data related to new plant disease epidemics or outbreaks were obtained via surveys or similar methodologies. The second approach involved retrieving new records added in 2021 to the CABI Distribution Database, which contains over a million global geographic records of organisms from over 50,000 species. The literature review retrieved 186 articles, describing studies in 62 categories (pathogen species/species complexes) across more than 40 host species on six continents. Pathogen species with more than five articles were Bursaphelenchus xylophilus, 'Candidatus Liberibacter asiaticus', cassava mosaic viruses, citrus tristeza virus, Erwinia amylovora, Fusarium spp. complexes, F. oxysporum f. sp. cubense, Magnaporthe oryzae, maize lethal necrosis co-infecting viruses, Meloidogyne spp. complexes, Pseudomonas syringae pvs., Puccinia striiformis f. sp. tritici, Xylella fastidiosa, and Zymoseptoria tritici. Automated searches of the CABI Distribution Database identified 617 distribution records new in 2021 of 283 plant pathogens. A further manual review of these records confirmed 15 pathogens reported in new locations: apple hammerhead viroid, apple rubbery wood viruses, Aphelenchoides besseyi, Biscogniauxia mediterranea, 'Ca. Liberibacter asiaticus', citrus tristeza virus, Colletotrichum siamense, cucurbit chlorotic yellows virus, Erwinia rhapontici, Erysiphe corylacearum, F. oxysporum f. sp. cubense Tropical race 4, Globodera rostochiensis, Nothophoma quercina, potato spindle tuber viroid, and tomato brown rugose fruit virus. Of these, four pathogens had at least 25% of all records reported in 2021. We assessed two of these pathogens-tomato brown rugose fruit virus and cucurbit chlorotic yellows virus-to be actively emerging in/spreading to new locations. Although three important pathogens-'Ca. Liberibacter asiaticus', citrus tristeza virus, and F. oxysporum f. sp. cubense-were represented in the results of both our literature review and our interrogation of the CABI Distribution Database, in general, our dual approaches revealed distinct sets of plant disease outbreaks and new records, with little overlap. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Silencing suppressor protein PRT of rice tungro bacilliform virus interacts with the plant RNA silencing-related protein SGS3

BackgroundRice tungro bacilliform virus (RTBV) is a double stranded DNA containing virus which causes the devastating tungro disease of rice in association with an RNA virus, rice tungro spherical virus. RNA silencing is an evolutionarily conserved antiviral defence pathway in plants as well as in several classes of higher organisms. Many viruses, in turn, encode proteins which are termed Viral Suppressor of RNA Silencing (VSR) because they downregulate or suppress RNA silencing. ResultsUsing an RNA silencing suppressor assay we show that RTBV protease (PRT) acts as a mild VSR. A truncated version of PRT gene abolished the silencing suppression activity. We also show in planta interaction of PRT with the SGS3 protein of Solanum tuberosum and Arabidopsis thaliana using bimolecular fluorescence complementation assay (BIFC). Transient expression of PRT in Nicotiana benthamiana caused an increased accumulation of the begomovirus Sri Lankan cassava mosaic virus (SLCMV) DNA-A, which indicated a virulence function imparted on an unrelated virus. ConclusionThe finding supports the idea that PRT acts as suppressor of RNA silencing and this action may be mediated by its interaction with SGS3.

High throughput sRNA sequencing revealed gene regulatory role mediated by pathogen-derived small RNAs during Sri Lankan Cassava Mosaic Virus infection in Cassava.

The online version contains supplementary material available at 10.1007/s13205-023-03494-2.

In Silico Identification of Cassava Genome-Encoded MicroRNAs with Predicted Potential for Targeting the ICMV-Kerala Begomoviral Pathogen of Cassava.

Cassava mosaic disease (CMD) is caused by several divergent species belonging to the genus Begomovirus (Geminiviridae) transmitted by the whitefly Bemisia tabaci cryptic species group. In India and other parts of Asia, the Indian cassava mosaic virus-Kerala (ICMV-Ker) is an emergent begomovirus of cassava causing damage that results in reduced yield loss and tuber quality. Double-stranded RNA-mediated interference (RNAi) is an evolutionary conserved mechanism in eukaryotes and highly effective, innate defense system to inhibit plant viral replication and/or translation. The objective of this study was to identify and characterize cassava genome-encoded microRNAs (mes-miRNA) that are predicted to target ICMV-Ker ssDNA-encoded mRNAs, based on four in silico algorithms: miRanda, RNA22, Tapirhybrid, and psRNA. The goal is to deploy the predicted miRNAs to trigger RNAi and develop cassava plants with resistance to ICMV-Ker. Experimentally validated mature cassava miRNA sequences (n = 175) were downloaded from the miRBase biological database and aligned with the ICMV-Ker genome. The miRNAs were evaluated for base-pairing with the cassava miRNA seed regions and to complementary binding sites within target viral mRNAs. Among the 175 locus-derived mes-miRNAs evaluated, one cassava miRNA homolog, mes-miR1446a, was identified to have a predicted miRNA target binding site, at position 2053 of the ICMV-Ker genome. To predict whether the cassava miRNA might bind predicted ICMV-Ker mRNA target(s) that could disrupt viral infection of cassava plants, a cassava locus-derived miRNA-mRNA regulatory network was constructed using Circos software. The in silico-predicted cassava locus-derived mes-miRNA-mRNA network corroborated interactions between cassava mature miRNAs and the ICMV-Ker genome that warrant in vivo analysis, which could lead to the development of ICMV-Ker resistant cassava plants.