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High-throughput sequencing (HTS) application in the field of plant virology started in 2009 and has proven very successful for virus discovery and detection of viruses already known. Plant virology is still a developing science in most of Africa; the number of HTS-related studies published in the scientific literature has been increasing over the years as a result of successful collaborations. Studies using HTS to identify plant-infecting viruses have been conducted in 20 African countries, of which Kenya, South Africa and Tanzania share the most published papers. At least 29 host plants, including various agricultural economically important crops, ornamentals and medicinal plants, have been used in viromics analyses and have resulted in the detection of previously known viruses and novel ones from almost any host. Knowing that the effectiveness of any management program requires knowledge on the types, distribution, incidence, and genetic of the virus-causing disease, integrating HTS and efficient bioinformatics tools in plant virology research projects conducted in Africa is a matter of the utmost importance towards achieving and maintaining sustainable food security.

Criniviruses accumulate in the phloem tissue and damage crops by reducing chlorophyll which is essential for plant growth and development. Tomato chlorosis crinivirus (ToCV) is vectored by several whitefly species that damage tomato crops throughout the world. In South Africa, ToCV is a poorly studied pathogen of global economic importance. Therefore, a national survey was initiated to investigate the occurrence and distribution of criniviruses infecting tomato crops in South Africa. Whitefly infested tomato crops exhibiting interveinal leaf chlorosis and chlorotic flecking symptoms were assayed for crinivirus infections using a multiplex reverse transcription polymerase reaction (RT-PCR) approach to assess for the presence of crinivirus species that are known to infect solanaceous hosts. Next-generation sequencing (NGS) was used to generate the complete genome of ToCV from South Africa. Results from the survey indicated that ToCV is presently the only crinivirus species infecting tomatoes in South Africa. Blast analysis showed that the RNA-1 segment of ToCV from South Africa (ToCR1-186) matched 99% to Spanish isolates. On the other hand, the RNA-2 (ToCR2-186) segment matched 98% to a South Korean isolate and three Spanish isolates. Although recombination events were not detected, phylogenetic studies showed inconsistencies in the grouping of RNA-1 and RNA-2 segments for some of the ToCV isolates analyzed in this study. Therefore, we suggest the possibility of intraspecific reassortment. This is the first comprehensive study and full genome sequence of ToCV from South Africa. The information generated from this study is intended to raise awareness of ToCV infections on tomato crops in South Africa.

Emerging pests and diseases are a major threat to food production worldwide. In a recent survey, Tomato torrado virus (ToTV) was identified on tomato crops in the Limpopo province of South Africa and a first report of the disease was published. In this follow-up study, the full genome sequence of a tomato-infecting isolate of ToTV from South Africa was elucidated. High-throughput sequencing was used to generate the full genome of ToTV infecting tomato crops in South Africa. The longest contig obtained for the RNA-1 and RNA-2 genome of ToTV was comprised of 7420 and 5381 nucleotides (nt), respectively. Blast analysis of the RNA-1 sequence of ToTV from South Africa (ToT-186) matched 99% to a Spanish and Polish isolate; the RNA-2 segment of ToTV from South Africa (ToT-186) matched 99% to ToTV isolates from Italy and Poland, respectively. The information presented in this study will go a long way towards better understanding the emergence and spread of ToTV and devising sustainable management of ToTV diseases.

Objectives Plant-infecting viruses remain a serious challenge towards achieving food security worldwide. Cucurbit virus surveys were conducted in Zimbabwe during the 2014 and 2015 growing seasons. Leaf samples displaying virus-like symptoms were collected and stored until analysis. Three baby marrow samples were subjected to next-generation sequencing and the data generated were analysed using genomics technologies. Zucchini shoestring virus (ZSSV), a cucurbit-infecting potyvirus previously described in South Africa was one of the viruses identified. The genomes of the three ZSSV isolates are described analysed in this note. Results The three ZSSV isolates had the same genome size of 10,297 bp excluding the polyA tail with a 43% GC content. The large open reading frame was found at positions 69 to 10,106 on the genome and encodes a 3345 amino acids long polyprotein which had the same cleavage site sequences as those described on the South African isolate except for the P1-pro site. Genome sequence comparisons of all the ZSSV isolates showed that the isolates F7-Art and S6-Prime had identical sequence across the entire genome while sharing 99.06% and 99.34% polyprotein nucleotide and amino acid sequence identities, respectively with the isolate S7-Prime.

ABSTRACTA tomato-infecting tomato mosaic virus (ToMV) isolate was detected in Zimbabwe using lateral flow kits and double-antibody sandwich enzyme-linked immunosorbent assay. Next-generation sequencing and de novo assembly were subsequently performed to determine its genome sequence. The ToMV genome of the Zimbabwe isolate is the second to be reported in Africa.

Tomato spotted wilt virus (TSWV), the type species of the genus Tospovirus in the family Bunyaviridae , is one of the most economically important emerging plant viruses worldwide. It causes over US$1 billion losses annually in open field and greenhouse-grown crops. A study was carried out to determine the geographical distribution, host range and phylogeny of TSWV in Zimbabwe. Disease surveys were conducted in 18 districts over a three-year period using tospovirus immunostrips. Virus-infected leaf samples were collected on FTA cards and in RNA later solution. TSWV was characterized by double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) and reverse transcription polymerase chain reaction (RT-PCR) followed by sequencing and phylogenetic analysis. The virus was detected in 50% of the districts surveyed, mostly in the country’s prime agricultural region. It was confirmed to be present by DAS-ELISA and RT-PCR. In addition to some previously reported hosts, TSWV was detected for the first time in Cucurbita moschata , Cucurbita pepo, Cucumis sativus and Gyposphila elegans . Molecular analysis of the TSWV nucleocapsid gene showed that Zimbabwean TSWV isolates were highly similar (≥93.99%) and identical (99.02%) to each other at nucleotide and amino acid sequence levels. When compared to isolates from the rest of the world, Zimbabwean TSWV isolates were most closely related to isolates from Italy, Montenegro, New Zealand and Serbia. The study lays the foundation for future TSWV studies by providing protocols and procedures that could be used. Information generated in this study will be useful in formulating effective TSWV control measures.

The complete nucleotide sequences of Beet pseudoyellows virus (BPYV)-MI (cucumber isolate; Matsuyama, Idai) genomic RNAs 1 and 2 were determined and compared with the previously sequenced Japanese cucumber strain (BPYV-JC) and a strawberry strain (BPYV-S). The RNA 2 of BPYV-MI showed 99 % nucleotide sequence identity with both BPYV-JC and -S having highly conserved eight ORFs. In contrast, the RNA1 of BPYV-MI showed sequence identities of 98 and 86 % with BPYV-JC and -S, respectively. Phylogenetic analysis of RNA-dependent RNA polymerase (RdRp) coding sequences from three fully sequenced BPYV strains and five partially sequenced cucurbit-infecting BPYV strains from Japan and South Africa has shown that cucurbit-infecting strains are closer to each other than to BPYV-S. In addition, the strawberry strain BPYV-S has an ORF2 in the downstream of RdRp gene in RNA1, but all the cucumber strains, BPYV-JC, -MI, and those from South Africa, lacked the ORF2 of RNA1, highlighting the difference between common BPYV cucumber strains and a unique strawberry strain.

Criniviruses accumulate in the phloem tissue and damage crops by reducing chlorophyll which is essential for plant growth and development. Tomato chlorosis crinivirus (ToCV) is vectored by several whitefly species that damage tomato crops throughout the world. In South Africa, ToCV is a poorly studied pathogen of global economic importance. Therefore, a national survey was initiated to investigate the occurrence and distribution of criniviruses infecting tomato crops in South Africa. Whitefly infested tomato crops exhibiting interveinal leaf chlorosis and chlorotic flecking symptoms were assayed for crinivirus infections using a multiplex reverse transcription polymerase reaction (RT-PCR) approach to assess for the presence of crinivirus species that are known to infect solanaceous hosts. Next-generation sequencing (NGS) was used to generate the complete genome of ToCV from South Africa. Results from the survey indicated that ToCV is presently the only crinivirus species infecting tomatoes in South Africa. Blast analysis showed that the RNA-1 segment of ToCV from South Africa (ToCR1-186) matched 99% to Spanish isolates. On the other hand, the RNA-2 (ToCR2-186) segment matched 98% to a South Korean isolate and three Spanish isolates. Although recombination events were not detected, phylogenetic studies showed inconsistencies in the grouping of RNA-1 and RNA-2 segments for some of the ToCV isolates analyzed in this study. Therefore, we suggest the possibility of intraspecific reassortment. This is the first comprehensive study and full genome sequence of ToCV from South Africa. The information generated from this study is intended to raise awareness of ToCV infections on tomato crops in South Africa.

Avocado sunblotch viroid (ASBVd) is found in many avocado-growing regions of the world, where it affects fruit yield and quality. The trees develop two types of infections: symptomatic and symptomless infections. Symptoms are most obvious as yellow streaks on leaves, fruit and green stems of symptomatic trees and symptomless carrier trees do not display any such symptoms. Symptomless carrier trees are considered the primary source of disease transmission in orchards. Hence, this study investigated the impact of ASBVd-infected symptomless carrier trees on tree morphology, fruit maturity, yield and quality of ‘Hass’ avocado from 2019 until 2021. Differences were observed in the orchard between infected and healthy trees; trees with medium and high viroid concentrations excessively produced flowers, lost leaves during flowering and ultimately bore few to no fruit at the end of the season. The dry matter content results showed that ASBVd did not affect the rate of maturity of the fruit, as fruit from infected and healthy trees matured at the same time. Yield counts indicated that medium and highly infected trees produced between 83 and 96% lower yields compared to healthy trees. Postharvest studies showed that medium and highly infected fruit significantly lost firmness and coloured up more rapidly than healthy fruit. Infected, non-stored fruit also developed external rots and shrivels, however, these disorders were reduced in fruit stored at 5 °C for 28 days. Therefore, flower overbearing with the shedding of leaves and lower yields can be used as indicators of ASBVd infection in ‘Hass’ orchards but confirmation with molecular testing is required. These observations can be incorporated into an ASBD management strategy in ‘Hass’ orchards.

Sweetpotato (Ipomoea batatas L.) is an important staple crop cultivated in over 100 countries, and the storage roots and vines provide food for humans and livestock. Sweetpotato consumption and demand for its value‐added products have increased significantly in the last two decades and have led to new cultivar development, expansion in acreage, and increased demand in the United States and its export markets. Despite the known nutritional components and other health benefits, further research is needed to characterize the genetic diversity and chemical composition related to their storage root qualities, essential in developing consumer‐preferred cultivars that offer host plant resistance against pests and pathogens. There is a critical need for research on non‐pesticidal control approaches that can provide safe, effective, economical, sustainable, and environmentally sound pest and disease management techniques, especially for socially disadvantaged small farmers in the United States. Moreover, climate change can significantly impact future production practices and yield and may directly or indirectly affect crop pests, weeds, and diseases. In this review, we discuss the current status, challenges, and future approaches associated with sweetpotato production practices; health‐promoting properties of sweetpotato cultivars; value‐added products; genetic diversity and germplasm; pest and disease management; weed and water management; pollination ecology; and other agronomic and cultural practices that may impact sustainable sweetpotato production by small‐scale, organic, and large‐scale growers. Core Ideas Sweetpotato (Ipomoea batatas L.) is an important staple crop cultivated in over 100 countries. US sweetpotato industry faces many production challenges, including pest and diseases, as well as climate change extremes. A comprehensive review by subject matter experts on the challenges of US sweetpotato industry is not available. This review evaluates the current situation, challenges, and future approaches for improving sweetpotato production. Also, current and future impacts of climate change on global sweetpotato production and demand are discussed.