Abundance, diversity and richness of natural enemies of the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), in Zambia.

The fall armyworm (FAW), Spodoptera frugiperda, an invasive pest originating from the Americas is a serious pest threatening cereal production and food security in Zambia. We studied the prevalence and abundance of natural enemies of FAW in three Agroecological regions (AERs I, II, and III) to identify those that could potentially serve as bio-control agents. Sampling of FAW parasitoids and predators was done along trunk roads at intervals of 10 km. Molecular sequence analysis and morphological characterization were used to identify natural enemies. Over 11 species of FAW natural enemies, including egg, egg-larval, and larval parasitoids, and predators, were identified in Zambia. The mean number of natural enemies and species richness was higher in AER I and IIa. Consequently, egg parasitism was highest in those two regions, at 24.5% and 12.2%, respectively. Larvae parasitism was highest in AER I (4.8%) and AER III (1.9), although no significant differences were observed. The most abundant and widely distributed parasitoid was Drino sp. (Diptera: Tachinidae), while Rhynocoris segmentarius (Germar) (Hemiptera: Reduviidae) and Belanogaster sp. (Hymenoptera: Vespidae) were the most prevalent predators. Our study reveals the presence of two natural enemies belonging to the genus Tiphia and Micromeriella, uncommon to FAW. Significant differences in the number of parasitoids were observed in polycropping, with the highest recovery of 12 ± 10% from maize + cowpeas + pumpkin and watermelon mixed cropping. The higher the rainfall, the lower the number of natural enemies recorded. Variations in rainfall patterns which affect FAW availability, cropping systems and the three AERs may explain natural enemies' species diversity in Zambia. The information provided in this study can aid the development of a national biological control programme for sustainable management of fall armyworm.

Survey for Virus Diversity in Common Bean (Phaseolus vulgaris) Fields and the Detection of a Novel Strain of Cowpea polerovirus 1 in Zambia.

The production of common bean (Phaseolus vulgaris L.) is adversely affected by virus-like diseases globally, but little is known about the occurrence, distribution, and diversity of common bean-infecting viruses in Zambia. Consequently, field surveys were conducted during the 2018 season in 128 fields across six provinces of Zambia and 640 common bean leaf tissue samples were collected with (n = 585) or without (n = 55) symptoms. The prevalence of symptomatic fields was 100%, but incidence of symptomatic plants ranged from 32 to 67.5%. Metagenomic analyses of nine composite samples and a single plant sample of interest revealed the occurrence of isolates of Bean common mosaic necrosis virus, Bean common mosaic virus, Cowpea aphid-borne mosaic virus, Peanut mottle virus, Southern bean mosaic virus (SBMV), Cucumber mosaic virus, Phaseolus vulgaris alphaendornavirus 1 (PvEV-1), PvEV-2, Ethiopian tobacco bushy top virus (ETBTV), and a novel strain of Cowpea polerovirus 1 (CPPV1-Pv) of 5,902 nt in length. While CPPV1-Pv was consistently detected in mixed infection with ETBTV and its satellite RNA molecule, based on results of mechanical transmission assays it does not appear to be involved in disease etiology, suggesting that its role may be limited to being a helper virus for the umbravirus. Screening of the survey samples by real-time PCR for the viruses detected by high-throughput sequencing revealed the prevalence of single (65.2% or 417/640) over mixed (1.9% or 12/640) infections in the samples. SBMV was the most frequently detected virus, occurring in ∼29.4% (188/640) of the samples and at a prevalence rate of 58.6% (75/128) across fields. The results showed that diverse virus species are present in Zambian common bean fields and the information will be useful for the management of common bean viral diseases.

Smallholder Cassava Planting Material Movement and Grower Behavior in Zambia: Implications for the Management of Cassava Virus Diseases.

Cassava (Manihot esculenta) is an important food crop across sub-Saharan Africa, where production is severely inhibited by two viral diseases, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), both propagated by a whitefly vector and via human-mediated movement of infected cassava stems. There is limited information on growers' behavior related to movement of planting material, as well as growers' perception and awareness of cassava diseases, despite the importance of these factors for disease control. This study surveyed a total of 96 cassava subsistence growers and their fields across five provinces in Zambia between 2015 and 2017 to address these knowledge gaps. CMD symptoms were observed in 81.6% of the fields, with an average incidence of 52% across the infected fields. No CBSD symptoms were observed. Most growers used planting materials from their own (94%) or nearby (<10 km) fields of family and friends, although several large transactions over longer distances (10 to 350 km) occurred with friends (15 transactions), markets (1), middlemen (5), and nongovernmental organizations (6). Information related to cassava diseases and certified clean (disease-free) seed reached only 48% of growers. The most frequent sources of information related to cassava diseases included nearby friends, family, and neighbors, while extension workers were the most highly preferred source of information. These data provide a benchmark on which to plan management approaches to controlling CMD and CBSD, which should include clean propagation material, increasing growers' awareness of the diseases, and increasing information provided to farmers (specifically disease symptom recognition and disease management options).[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Genetic Diversity of Mitochondrial DNA of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Associated with Cassava and the Occurrence of Cassava Mosaic Disease in Zambia.

Bemisia tabaci is an important vector of cassava brown streak viruses and cassava mosaic begomoviruses, the causal agents of cassava brown streak disease and cassava mosaic disease (CMD), respectively. A study was carried out to determine the genetic variability of B. tabaci associated with cassava and the occurrence of CMD in Zambia in 2013 and 2015. Phylogenetic analysis showed the presence of only the sub-Saharan Africa 1 (SSA1) genetic group in Zambia. The SSA1 population had three population subgroups (SGs): SSA1-SG1, SSA1-SG2 and SSA1-SG3. All three SSA1 population subgroups occurred in Western Province. However, only SSA1-SG3 occurred in Eastern Province, while only SSA1-SG1 occurred in North Western and Luapula Provinces. Adult B. tabaci were most abundant in Western Province in 2013 (11.1/plant) and 2015 (10.8/plant), and least abundant (0.2/plant) in Northern Province in both 2013 and 2015. CMD was prevalent in all seven provinces surveyed, with the highest incidence recorded in Lusaka Province in both 2013 (78%) and 2015 (83.6%), and the lowest in Northern Province in both 2013 (26.6%) and 2015 (29.3%). Although SSA1-SG1 occurred at greater abundances than the other subgroups, there was no direct association demonstrated between whitefly subgroup and incidence of CMD. Establishing which B. tabaci genetic groups and populations are associated with CMD and their distribution in the country is a key factor in guiding the development of CMD control strategies for cassava-dependent households.

A quick and sensitive diagnostic tool for detection of Maize streak virus.

Maize streak virus disease (MSVD), caused by Maize streak virus (MSV; genus Mastrevirus), is one of the most severe and widespread viral diseases that adversely reduces maize yield and threatens food security in Africa. An effective control and management of MSVD requires robust and sensitive diagnostic tests capable of rapid detection of MSV. In this study, a loop-mediated isothermal amplification (LAMP) assay was designed for the specific detection of MSV. This test has shown to be highly specific and reproducible and able to detect MSV in as little as 10 fg/µl of purified genomic DNA obtained from a MSV-infected maize plant, a sensitivity 105 times higher to that obtained with polymerase chain reaction (PCR) in current general use. The high degree of sequence identity between Zambian and other African MSV isolates indicate that this LAMP assay can be used for detecting MSV in maize samples from any region in Africa. Furthermore, this assay can be adopted in minimally equipped laboratories and with potential use in plant clinic laboratories across Africa strengthening diagnostic capacity in countries dealing with MSD.

Detection and characterization of fungus (Magnaporthe oryzae pathotype Triticum) causing wheat blast disease on rain-fed grown wheat (Triticum aestivum L.) in Zambia.

Wheat blast caused by Magnaporthe oryzae pathotype Triticum (MoT) is a threat to wheat production especially in the warmer-humid environments. In Zambia, wheat blast symptoms were observed for the first time on wheat (Triticum aestivum L.) grown in experimental plots and five farmers' fields in Mpika district of Muchinga Province during the 2017-18 rainy season. Infected plants showed the typical wheat blast symptoms with the spike becoming partially or completely bleached with the blackening of the rachis in a short span of time. Incidence of blast symptoms on nearly all wheat heads was high and ranged from 50 to 100%. Examination of diseased plant leaves showed the presence of elliptical, grayish to tan necrotic lesions with dark borders on the leaf often mixed with other foliar diseases. A study was conducted to isolate and identify the causal pathogen(s) using classical and molecular methods and determine the pathogenicity of the detected disease causal agent. Morphobiometrical determination of causal pathogen revealed conidia with characteristic pear shaped 2-septate hyaline spores associated with M. oryzae species. Preliminary polymerase chain reaction screening of six isolates obtained from wheat blast infected samples with diagnostic primers (MoT3F/R) was conducted at ZARI, Zambia, and subsequent analysis of two isolates with MoT3F/R and C17F/R was performed at USDA-ARS, USA. Both experiments confirmed that MoT is the causal agent of wheat blast in Zambia. Further, pathogenicity tests performed with pure culture isolates from samples WS4 and WS5 produced typical blast symptoms on all the six inoculated wheat genotypes. Results of this study indicate that MoT is causing wheat blast in rain-fed wheat grown in Zambia, thus making it the first report of MoT in Zambia and Africa. This inter-continental movement of the pathogen (disease) has serious implication for wheat production and trade that needs to be urgently addressed.

Konzo outbreak in the Western Province of Zambia.

OBJECTIVE: To identify the etiology of an outbreak of spastic paraparesis among women and children in the Western Province of Zambia suspected to be konzo. METHODS: We conducted an outbreak investigation of individuals from Mongu District, Western Province, Zambia, who previously developed lower extremity weakness. Cases were classified with the World Health Organization definition of konzo. Active case finding was conducted through door-to-door evaluation in affected villages and sensitization at local health clinics. Demographic, medical, and dietary history was used to identify common exposures in all cases. Urine and blood specimens were taken to evaluate for konzo and alternative etiologies. RESULTS: We identified 32 cases of konzo exclusively affecting children 6 to 14 years of age and predominantly females >14 years of age. Fourteen of 15 (93%) cases ≥15 years of age were female, 11 (73%) of whom were breastfeeding at the time of symptom onset. Cassava was the most commonly consumed food (median [range] 14 [4-21] times per week), while protein-rich foods were consumed <1 time per week for all cases. Of the 30 patients providing urine specimens, median thiocyanate level was 281 (interquartile range 149-522) µmol/L, and 73% of urine samples had thiocyanate levels >136 µmol/L, the 95th percentile of the US population in 2013 to 2014. CONCLUSION: This investigation revealed the first documented cases of konzo in Zambia, occurring in poor communities with diets high in cassava and low in protein, consistent with previous descriptions from neighboring countries.

Cassava mosaic disease: a review of a threat to cassava production in Zambia.

Cassava (Manihot esculenta Crantz) is one of the most important root staple crops in Zambia. An estimated 30% of Zambians, over 4 million people, consume cassava as part of their daily diet. Cassava is mostly grown by subsistence farmers on fields of less than 1 ha. Cultivation of cassava is hampered by several biotic constraints, of which cassava mosaic disease (CMD) is currently the most important factor limiting cassava production in Zambia. CMD occurs in all the cassava-growing provinces and accounts for 50% to 70% of yield losses countrywide. Strategies to counter CMD were initiated in the early 1990s and included the release of CMD-resistant cassava cultivars. However, efforts to control CMD are limited because few growers plant these cultivars. More recently, to address the CMD problem, regular disease monitoring and diagnostic capabilities have been strengthened, and there is increased support for screening breeders materials. CMD is a rising threat to cassava production in Zambia. This review of CMD research on disease surveillance, CMD spread, yield losses, awareness campaigns and control options in Zambia over the past 25 years informs future control efforts and management strategies.

Cassava Brown Streak Disease and Ugandan cassava brown streak virus Reported for the First Time in Zambia.

A diagnostic survey was conducted in July 2017 in two northern districts of Zambia to investigate presence or absence of cassava brown streak disease (CBSD) and its causal viruses. In total, 29 cassava fields were surveyed and cassava leaf samples were collected from 116 plants (92 symptomatic and 24 nonsymptomatic). CBSD prevalence was approximately 79% (23 of 29) across fields. Mean CBSD incidence varied across fields but averaged 32.3% while mean disease severity was 2.3 on a 1-to-5 rating scale. Reverse-transcription polymerase chain reaction screening of all 116 samples with one generic and two species-specific primer pairs yielded DNA bands of the expected sizes from all symptomatic plants with the generic (785 bp) and Ugandan cassava brown streak virus (UCBSV)-specific (440 bp) primers. All 24 nonsymptomatic samples were negative for UCBSV and all samples tested negative with primers targeting Cassava brown streak virus. The complete genome of a representative isolate of UCBSV (WP282) was determined to be 9,050 nucleotides in length, minus the poly A tail. A comparative analysis of this isolate with global virus isolates revealed its nature as a sequence variant of UCBSV sharing 94 and 96% maximum complete polyprotein nucleotide and amino acid identities, respectively, with isolates from Malawi (MF379362) and Tanzania (FJ039520). This is the first report of CBSD and UCBSV in Zambia, thus expanding the geographical distribution of the disease and its causal virus and further reinforcing the need to strengthen national and regional phytosanitary programs in Africa.

Spatial dynamics and control of a crop pathogen with mixed-mode transmission.

Trade or sharing that moves infectious planting material between farms can, for vertically-transmitted plant diseases, act as a significant force for dispersal of pathogens, particularly where the extent of material movement may be greater than that of infected vectors or inoculum. The network over which trade occurs will then effect dispersal, and is important to consider when attempting to control the disease. We consider the difference that planting material exchange can make to successful control of cassava brown streak disease, an important viral disease affecting one of Africa's staple crops. We use a mathematical model of smallholders' fields to determine the effect of informal trade on both the spread of the pathogen and its control using clean-seed systems, determining aspects that could limit the damage caused by the disease. In particular, we identify the potentially detrimental effects of markets, and the benefits of a community-based approach to disease control.

Survey, Molecular Detection, and Characterization of Geminiviruses Associated with Cassava Mosaic Disease in Zambia.

A survey was conducted from April to May 2014 in 214 farmers' fields located across six major cassava-producing provinces (Western, Northwestern, Northern, Luapula, Lusaka, and Eastern) of Zambia to determine the status of cassava mosaic disease (CMD) and the species diversity of associated cassava mosaic geminiviruses (CMG). Mean CMD incidence varied across all six provinces but was greatest in Lusaka Province (81%) and least in Northern Province (44%). Mean CMD severity varied slightly between provinces, ranging from 2.78 in Eastern Province to 3.00 in Northwestern Province. Polymerase chain reaction discrimination of 226 survey samples, coupled with complete DNA-A genome sequence analysis, revealed the presence of African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), and East African cassava mosaic Malawi virus (EACMMV) as single or mixed infections of different proportions. Single-virus infections were predominant, occurring in 62.8% (ACMV), 5.8% (EACMMV), and 2.2% (EACMV) of samples relative to mixed-virus infections, which occurred in 19.5% (ACMV + EACMMV), 0.4% (ACMV + EACMV), and 0.9% (ACMV + EACMV + EACMMV) of samples. Phylogenetic analysis revealed the segregation of virus isolates from Zambia into clades specific to ACMV, EACMV, and EACMMV, further confirming the presence of all three viruses in Zambia. The results point to a greater diversity of CMG across major cassava-growing provinces of Zambia and implicate contaminated cassava cuttings in disease spread.

Biology and management of Bemisia whitefly vectors of cassava virus pandemics in Africa.

Cassava mosaic disease and cassava brown streak disease are caused by viruses transmitted by Bemisia tabaci and affect approximately half of all cassava plants in Africa, resulting in annual production losses of more than $US 1 billion. A historical and current bias towards virus rather than vector control means that these diseases continue to spread, and high Bemisia populations threaten future virus spread even if the extant strains and species are controlled. Progress has been made in parts of Africa in replicating some of the successes of integrated Bemisia control programmes in the south-western United States. However, these management efforts, which utilise chemical insecticides that conserve the Bemisia natural enemy fauna, are only suitable for commercial agriculture, which presently excludes most cassava cultivation in Africa. Initiatives to strengthen the control of B. tabaci on cassava in Africa need to be aware of this limitation, and to focus primarily on control methods that are cheap, effective, sustainable and readily disseminated, such as host-plant resistance and biological control. A framework based on the application of force multipliers is proposed as a means of prioritising elements of future Bemisia control strategies for cassava in Africa.