Mitochondrial Genetic Diversity of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Associated with Cassava in Lao PDR

Molecular Diversity and Distribution of Whiteflies (Bemisia tabaci) in Cassava Fields Across South West and North Central, Nigeria

Whitefly Bemisia tabaci (Gennadium, Hemiptera) causes severe damage to cassava plants through excessive feeding on leaves and transmitting viruses, such as African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), and ipomoviruses that cause cassava brown streak disease. Currently, little is known about the molecular diversity and distribution of whitefly species in the major cassava-growing zones of Nigeria. This study aimed to address the knowledge gap by assessing the genetic diversity, distribution, and associated cassava mosaic begomoviruses (CMBs) in whiteflies across South West and North Central, Nigeria. Whitefly samples were systematically collected from cassava plants during georeferenced epidemiological surveys in 2017, 2020, and 2022. The samples were genotyped using the mitochondrial cytochrome oxidase I (mtCOI) marker, and CMBs were detected by PCR with virus-specific primers. Phylogenetic analyses revealed four distinct genetic groups of B. tabaci: Sub-Saharan Africa 1 (SSA1; 84.8%), SSA2 (1.4%), SSA3 (13.1%), and Mediterranean (MED) (0.7%). The SSA1 group was the predominant and most widely distributed genotype across the surveyed zones, with three subgroups identified: SSA1-SG1, SSA1-SG3, and SSA1-SG5. The second most frequently identified genotype, SSA3, was restricted to the North Central zone, along with the SSA2 group, which was only identified in two North Central states (Niger and Plateau). African cassava mosaic virus (ACMV) was detected in SSA1-SG1, SSA1-SG5, and SSA3, whereas EACMV was found in only the SSA1-SG3. The findings of this study will aid in developing better whitefly management strategies to reduce the impact of CMD on cassava production in Nigeria.

Diversity and functional characteristics of culturable bacterial endosymbionts from cassava whitefly biotype Asia II-5, Bemisia tabaci

Whitefly Bemisia tabaci, a carrier of cassava mosaic disease (CMD), poses a significant threat to cassava crops. Investigating culturable bacteria and their impact on whiteflies is crucial due to their vital role in whitefly fitness and survival. The whitefly biotype associated with cassava and transmitting CMD in India has been identified as Asia II 5 through partial mitochondrial cytochrome oxidase I gene sequencing. In this study, bacteria associated with adult B. tabaci feeding on cassava were extracted using seven different media. Nutrient Agar (NA), Soyabean Casein Digest Medium (SCDM), Luria Bertani agar (LBA), and Reasoner's 2A agar (R2A) media resulted in 19, 6, 4, and 4 isolates, respectively, producing a total of 33 distinct bacterial isolates. Species identification through 16SrRNA gene sequencing revealed that all isolates belonged to the Bacillota and Pseudomonadota phyla, encompassing 11 genera: Bacillus, Cytobacillus, Exiguobacterium, Terribacillus, Brevibacillus, Enterococcus, Staphylococcus, Brucella, Novosphingobium, Lysobacter, and Pseudomonas. All bacterial isolates were tested for chitinase, protease, siderophore activity, and antibiotic sensitivity. Nine isolates exhibited chitinase activity, 28 showed protease activity, and 23 displayed siderophore activity. Most isolates were sensitive to antibiotics such as Vancomycin, Streptomycin, Erythromycin, Kanamycin, Doxycycline, Tetracycline, and Ciprofloxacin, while they demonstrated resistance to Bacitracin and Colistin. Understanding the culturable bacteria associated with cassava whitefly and their functional significance could contribute to developing effective cassava whitefly and CMD control in agriculture.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03949-0.

Ceratobasidium sp. is associated with cassava witches' broom disease, a re-emerging threat to cassava cultivation in Southeast Asia

Cassava witches' broom disease (CWBD) is a devastating disease of cassava in Southeast Asia (SEA), of unknown etiology. Affected plants show reduced internodal length, proliferation of leaves and weakening of stems. This results in poor germination of infected stem cuttings (i.e., planting material) and significant reductions in fresh root yields and starch content, causing economic losses for farmers and processors. Using a metagenomic approach, we identified a fungus belonging to the Ceratobasidium genus, sharing more than 98.3-99.7% nucleotide identity at the Internal Transcribed Spacer (ITS), with Ceratobasidium theobromae a pathogen causing similar symptoms in cacao. Microscopy analysis confirmed the identity of the fungus and specific designed PCR tests readily showed (1) Ceratobasidium sp. of cassava is strongly associated with CWBD symptoms, (2) the fungus is present in diseased samples collected since the first recorded CWBD outbreaks in SEA and (3) the fungus is transmissible by grafting. No phytoplasma sequences were detected in diseased plants. Current disease management efforts include adjustment of quarantine protocols and guarantee the production and distribution of Ceratobasidium-free planting material. Implications of related Ceratobasidium fungi, infecting cassava, and cacao in SEA and in other potential risk areas are discussed.

New Technologies Provide Innovative Opportunities to Enhance Understanding of Major Virus Diseases Threatening Global Food Security

Plant viruses pose a continuous and serious threat to crop production worldwide, and globalization and climate change are exacerbating the establishment and rapid spread of new viruses. Simultaneously, developments in genome sequencing technology, nucleic acid amplification methods, and epidemiological modeling are providing plant health specialists with unprecedented opportunities to confront these major threats to the food security and livelihoods of millions of resource-constrained smallholders. In this perspective, we have used recent examples of integrated application of these technologies to enhance understanding of the emergence of plant viral diseases of key food security crops in low- and middle-income countries. We highlight how international funding and collaboration have enabled high-throughput sequencing-based surveillance approaches, targeted field and lab-based diagnostic tools, and modeling approaches that can be effectively used to support surveillance and preparedness against existing and emerging plant viral threats. The importance of national and international collaboration and the future role of CGIAR in further supporting these efforts, including building capabilities to make optimal use of these technologies in low- and middle-income countries, are discussed. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Translating virome analyses to support biosecurity, on-farm management, and crop breeding

Virome analysis via high-throughput sequencing (HTS) allows rapid and massive virus identification and diagnoses, expanding our focus from individual samples to the ecological distribution of viruses in agroecological landscapes. Decreases in sequencing costs combined with technological advances, such as automation and robotics, allow for efficient processing and analysis of numerous samples in plant disease clinics, tissue culture laboratories, and breeding programs. There are many opportunities for translating virome analysis to support plant health. For example, virome analysis can be employed in the development of biosecurity strategies and policies, including the implementation of virome risk assessments to support regulation and reduce the movement of infected plant material. A challenge is to identify which new viruses discovered through HTS require regulation and which can be allowed to move in germplasm and trade. On-farm management strategies can incorporate information from high-throughput surveillance, monitoring for new and known viruses across scales, to rapidly identify important agricultural viruses and understand their abundance and spread. Virome indexing programs can be used to generate clean germplasm and seed, crucial for the maintenance of seed system production and health, particularly in vegetatively propagated crops such as roots, tubers, and bananas. Virome analysis in breeding programs can provide insight into virus expression levels by generating relative abundance data, aiding in breeding cultivars resistant, or at least tolerant, to viruses. The integration of network analysis and machine learning techniques can facilitate designing and implementing management strategies, using novel forms of information to provide a scalable, replicable, and practical approach to developing management strategies for viromes. In the long run, these management strategies will be designed by generating sequence databases and building on the foundation of pre-existing knowledge about virus taxonomy, distribution, and host range. In conclusion, virome analysis will support the early adoption and implementation of integrated control strategies, impacting global markets, reducing the risk of introducing novel viruses, and limiting virus spread. The effective translation of virome analysis depends on capacity building to make benefits available globally.