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Here we investigated the effect of the insect pest whitefly (Bemisia tabaci), cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) on cassava root yield and quality in two cropping seasons 2014–2015 and 2015–2016 on ten cassava varieties in Tanzania. ANOVA (sum of squares or SS) revealed that the time of planting (42.7%) and cassava variety (29.5%) had the largest effect on whitefly population. Not surprisingly, cassava varieties also had the highest effect (SS 39.8 to 70.4%) on both diseases and yield. An increase in whitefly population led to higher disease incidences and severity in 2015–2016 compared to 2014–2015. Some CBSD-resistant and tolerant cassava varieties like Namikonga and Kiroba, respectively, harboured high whitefly populations. The CMD, CBSD and whitefly-susceptible variety, Mreteta, showed highest yield losses of up to 60%, while the resistant variety NDL 2005/1471 had approximately 1% loss. Deployment of varieties resistant to both diseases and whitefly is thus necessary to safeguard cassava production and food security of vulnerable communities in the affected African countries. [ABSTRACT FROM AUTHOR]

Barley yellow dwarf viruses (BYDVs) are one of the most widespread and economically important plant viruses affecting many cereal crops. Growing resistant varieties remains the most promising approach to reduce the impact of BYDVs. A Recent RNA sequencing analysis has revealed potential genes that respond to BYDV infection in resistant barley genotypes. Together with a comprehensive review of the current knowledge on disease resistance in plants, we selected nine putative barley and wheat genes to investigate their involvement in resistance to BYDV-PAV infection. The target classes of genes were (i) nucleotide binding site (NBS) leucine-rich repeat (LRR), (ii) coiled-coil nucleotide-binding leucine-rich repeat (CC-NB-LRR), (iii) LRR receptor-like kinase (RLK), (iv) casein kinase, (v) protein kinase, (vi) protein phosphatase subunits and the transcription factors (TF) (vii) MYB TF, (viii) GRAS (gibberellic acid-insensitive (GAI), repressor of GAI (RGA) and scarecrow (SCR)), and (ix) the MADS-box TF family. Expression of genes was analysed for six genotypes with different levels of resistance. As in previous reports, the highest BYDV-PAV titre was found in the susceptible genotypes Graciosa in barley and Semper and SGS 27-02 in wheat, which contrast with the resistant genotypes PRS-3628 and Wysor of wheat and barley, respectively. Statistically significant changes in wheat show up-regulation of NBS-LRR, CC-NBS-LRR and RLK in the susceptible genotypes and down-regulation in the resistant genotypes in response to BYDV-PAV. Similar up-regulation of NBS-LRR, CC-NBS-LRR, RLK and MYB TF in response to BYDV-PAV was also observed in the susceptible barley genotypes. However, no significant changes in the expression of these genes were generally observed in the resistant barley genotypes, except for the down-regulation of RLK. Casein kinase and Protein phosphatase were up-regulated early, 10 days after inoculation (dai) in the susceptible wheat genotypes, while the latter was down-regulated at 30 dai in resistant genotypes. Protein kinase was down-regulated both earlier (10 dai) and later (30 dai) in the susceptible wheat genotypes, but only in the later dai in the resistant genotypes. In contrast, GRAS TF and MYB TF were up-regulated in the susceptible wheat genotypes while no significant differences in MADS TF expression was observed. Protein kinase, Casein kinase (30 dai), MYB TF and GRAS TF (10 dai) were all up-regulated in the susceptible barley genotypes. However, no significant differences were found between the resistant and susceptible barley genotypes for the Protein phosphatase and MADS FT genes. Overall, our results showed a clear differentiation of gene expression patterns in both resistant and susceptible genotypes of wheat and barley. Therefore, further research on RLK, NBS-LRR, CC-NBS-LRR, GRAS TF and MYB TF can lead to BYDV-PAV resistance in cereals. [ABSTRACT FROM AUTHOR]

Wheat dwarf virus (WDV) is one of the most important pathogens of cereal crops worldwide. To understand the molecular mechanism of resistance, here we investigated the comparative transcriptome of wheat genotypes with different levels of resistance (Svitava and Fengyou 3) and susceptibility (Akteur) to WDV. We found a significantly higher number of differentially expressed transcripts (DETs) in the susceptible genotype than in the resistant one (e.g., Svitava). The number of downregulated transcripts was also higher in the susceptible genotype than in the resistant one (Svitava) and the opposite was true for the upregulated transcripts. Further functional analysis of gene ontology (GO) enrichment identified a total of 114 GO terms for the DETs. Of these, 64 biological processes, 28 cellular components and 22 molecular function GO terms were significantly enriched. A few of these genes appear to have a specific expression pattern related to resistance or susceptibility to WDV infection. Validation of the expression pattern by RT-qPCR showed that glycosyltransferase was significantly downregulated in the susceptible genotype compared to the resistant genotypes after WDV infection, while CYCLIN-T1-3, a regulator of CDK kinases (cyclin-dependent kinase), was upregulated. On the other hand, the expression pattern of the transcription factor (TF) MYB (TraesCS4B02G174600.2; myeloblastosis domain of transcription factor) was downregulated by WDV infection in the resistant genotypes compared to the susceptible genotype, while a large number of TFs belonging to 54 TF families were differentially expressed due to WDV infection. In addition, two transcripts (TraesCS7A02G341400.1 and TraesCS3B02G239900.1) were upregulated with uncharacterised proteins involved in transport and regulation of cell growth, respectively. Altogether, our findings showed a clear gene expression profile associated with resistance or susceptibility of wheat to WDV. In future studies, we will explore the regulatory network within the same experiment context. This knowledge will broaden not only the future for the development of virus-resistant wheat genotypes but also the future of genetic improvement of cereals for resilience and WDV-resistance breeding. [ABSTRACT FROM AUTHOR]

Aphids severely affect crop production by transmitting many plant viruses. Viruses are obligate intracellular pathogens that mostly depend on vectors for their transmission and survival. A majority of economically important plant viruses are transmitted by aphids. They transmit viruses either persistently (circulative or non‐circulative) or non‐persistently. Plant virus transmission by insects is a process that has evolved over time and is strongly influenced by insect morphological features and biology. Over the past century, a large body of research has provided detailed knowledge of the molecular processes underlying virus‐vector interactions. In this review, we discuss how aphid biology and morphology can affect plant virus transmission. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Background: The phenylalanine ammonia lyase genes play crucial role in plant response to biotic and abiotic stresses. In this study, we characterized the role of PAL genes in increasing resistance to the Cassava brown streak virus that causes the economically important cassava brown streak disease (CBSD) on cassava in Africa. Methods: The whole transcriptomes of eight cassava varieties differing in resistance to CBSD were obtained at 1, 5 and 8 weeks after CBSV infection. Results: Analysis of RNA-Seq data identified the overexpression of PAL1, PAL2, cinnamic acid and two chalcone synthase genes in CBSD-resistant cassava varieties, which was subsequently confirmed by RT-qPCR. The exogenous application of Acibenzolar-S-Methyl induced PAL1 gene expression to enhance resistance in the susceptible var. Kalawe. In contrast, the silencing of PAL1 by RNA interference led to increased susceptibility of the resistant var. Kaleso to CBSD. Conclusions: PAL1 gene of the phenylpropanoid pathway has a major role in inducing resistance to CBSD in cassava plants and its early induction is key for CBSD resistance. [ABSTRACT FROM AUTHOR]

Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are two important biotic constraints affecting cassava (Manihot esculenta Crantz) production in sub‐Saharan Africa, and the deployment of cassava varieties dually resistant to both diseases is the most effective and realistic way of reducing losses. Crosses were carried out between a Tanzanian local cassava cultivar (Namikonga) and a South American cassava genotype (AR37‐80) to develop dual‐resistant progenies, and they were evaluated for two seasons at Naliendele in Southern Tanzania, which is a CMD and CBSD hot spot area. The CMD‐resistant progenies had low foliar severities (≤1.8), similar to the CMD‐resistant parent. The CBSD‐resistant progenies had minimal foliar (≤2.0) and root necrosis (≤1.2) severities, similar to the CBSD resistant parent, whereas CBSD‐tolerant progenies had severe foliar severities up to 3.3 but minimal root necrosis severities (≤1.2). Traits with minimal environmental influence also had high heritability (≥0.65) and high selection accuracy (≥0.70), and they included CMD foliar symptoms, CBSD foliar symptoms at 6 mo after planting, root necrosis, root necrosis incidence, root weight, root number per plant, and harvest index. Correlation analysis showed that the presence of disease reduces usable roots, root weight, root number per plant, and harvest index. Dual resistance can improve yield as observed in Namar 050 and Namar 371, which had high root weights of 27.5 and 28.2 t ha−1 with high genetic gains of 56.1 and 58.5%, respectively. Dual‐resistant progenies identified were Namar 050, Namar 100, Namar 130, Namar 200, Namar 334, Namar 371, and Namar 479, as they had minimal CMD and CBSD symptom severities (≤2.0) and could be used for breeding cassava varieties with superior characteristics. [ABSTRACT FROM AUTHOR]

Cassava brown streak disease ( CBSD) is arguably the most dangerous current threat to cassava, which is Africa's most important food security crop. CBSD is caused by two RNA viruses: Cassava brown streak virus ( CBSV) and Ugandan cassava brown streak virus ( UCBSV). The roles of the whitefly Bemisia tabaci (Gennadius) and farmer practices in the spread of CBSD were investigated in a set of field and laboratory experiments. The virus was acquired and transmitted by B. tabaci within a short time (5-10 min each for virus acquisition and inoculation), and was retained for up to 48 hr. Highest virus transmission (60%) was achieved using 20-25 suspected viruliferous whiteflies per plant that were given acquisition and inoculation periods of 24 and 48 hr, respectively. Experiments mimicking the agronomic practices of cassava leaf picking or the use of contaminated tools for making cassava stem cuttings did not show the transmission of CBSV or UCBSV. Screenhouse and field experiments in Tanzania showed that the spread of CBSD next to spreader rows was high, and that the rate of spread decreased with increasing distance from the source of inoculum. The disease spread in the field up to a maximum of 17 m in a cropping season. These results collectively confirm that CBSV and UCBSV are transmitted by B. tabaci semipersistently, but for only short distances in the field. This implies that spread over longer distances is due to movements of infected stem cuttings used for planting material. These findings have important implications for developing appropriate management strategies for CBSD. [ABSTRACT FROM AUTHOR]

Cassava brown streak disease (CBSD) is endemic to the coast of East Africa and the disease continues to spread to new areas in the Great Lakes region. In both these areas CBSD leaf symptoms occur at high incidences. However, it is the associated symptom of necrosis in the starch-bearing tissues that renders the root unfit for human consumption. Where root necrosis occurs, the economic viability of processing into flour is adversely affected. Surveys undertaken in Tanzania, Kenya, Uganda, and Malawi showed that CBSD leaf symptoms were present at high incidences but root necrosis incidence was lower than would be expected. It appears that a form of tolerance to CBSD occurs in which the plants are susceptible to infection by the virus but are less affected by the root symptom. Farmers practise selection for cassava varieties less prone to CBSD root necrosis leading to dependence on a decreasing number of varieties. [ABSTRACT FROM AUTHOR]