Occurrence of cucumber mosaic virus within tomato seed lots

Tomato (Solanum lycopersicum L.) is an important crop whose fruit is widely consumed globally. However, its yield is affected by cucumber mosaic virus (CMV) and can cause total crop failure. The virus is mainly transmitted by aphid vectors, but data on its spread via seeds are limited. Thus, the occurrence of CMV within tomato seed lots obtained from different sources was investigated. Seven tomato accessions and varieties were collected from five sources and evaluated for seed transmission of CMV. One hundred seeds each were sown in a plastic tray, and germination rates were recorded. The incidence and severity of virus symptoms were observed at 3, 6, and 9 weeks after sowing (WAS), while leaves were tested for CMV using antigen-coated plate enzyme-linked immunosorbent assay (ACP-ELISA). The germination percentage ranged from 60% in accession 'V4' to 92% in 'UC-82B'. Infection rates were 100%, 71.74%, 70.31%, 45.90%, and 8.33% in 'Roma-VF', 'UC-82B', 'NG/AA/SQ/09/053', 'V2', and 'V4', respectively. 'Kerewa' and 'Alausa-Long' exhibited zero infection rates and tested negative for CMV using ACP-ELISA. Eighty percent of test plants became symptomatic at 6 and 9 WAS, although accession 'NG/AA/SQ/09/053' tested positive for CMV despite showing no symptoms. Tomato seeds from commercial stores, research institutes, and farmers' fields tested positive for CMV, while seeds from the market were negative at 9 WAS. The results from this study confirm the transmissibility of CMV through seeds in tomatoes, although the rate of seed transmission is cultivar dependent

Mapping of QTLs associated with recovery resistance to streak virus disease in maize

Open Access Article; Published online: 10 June 2018Maize streak virus (MSV, genus Mastrevirus, family Geminiviridae), vectored by the leafhoppers (Cicadulina sp.), is the most economically important viral disease of maize endemic to Sub-Saharan Africa and its offshore islands. Yield losses due to MSV are mainly controlled through use of resistant varieties. ‘Recovery’ (ability of plants to reduce symptom severity), is one of the types of resistance being used to develop MSV resistant cultivars through breeding. This study was conducted to map Quantitative Trait Loci (QTLs) associated with recovery resistance to MSV in a mapping population comprising 250 S1 lines derived from a cross between two MSV resistant lines. The population was genotyped using single nucleotide polymorphism (SNP) markers at 269 loci. A genetic map of 11 linkage groups was constructed comprising 230 SNP markers. Four QTLs, two putative QTLs with significant effect on chromosome 3 and two other QTLs with reduced effect on chromosomes 7 and 9, were identified from the population. The two QTLs on chromosome 3 together accounted for 47 to 51% of the total phenotypic variance while the other two QTLs accounted for 28 to 32% of the total variation. These QTLs originated from the two parents of the mapping population had both additive and dominance effects but interaction among the four loci was not significant. Further validation of these QTLs associated with recovery resistance in other diverse populations will lead to the development of new genomic resources to enhance breeding for MSV resistant maize

Chromogenic detection of yam mosaic virus by closed-tube reverse transcription loop-mediated isothermal amplification (CT-RT-LAMP)

A closed-tube reverse transcription loop-mediated isothermal amplification (CT-RT-LAMP) assay was developed for the detection of yam mosaic virus (YMV, genus Potyvirus) infecting yam (Dioscorea spp.). The assay uses a set of six oligonucleotide primers targeting the YMV coat protein region, and the amplification products in YMV-positive samples are visualized by chromogenic detection with SYBR Green I dye. The CT-RT-LAMP assay detected YMV in leaf and tuber tissues of infected plants. The assay is 100 times more sensitive in detecting YMV than standard RT-PCR, while maintaining the same specificity

Whitefly Bemisia tabaci (Homoptera: Aleyrodidae) infestation on cassava genotypes grown at different ecozones in Nigeria

Large-scale screening of cassava, Manihot esculenta Crantz, genotypes for resistance to infestation by whitefly Bemisia tabaci Gennadius, the vector of cassava mosaic geminiviruses, is limited. A range of new cassava elite clones were therefore assessed for the whitefly infestation in the 1999/2000 and 2000/2001 cropping seasons in experimental fields of International Institute of Tropical Agriculture, Ibadan, Nigeria. On each scoring day, between 0600 and 0800 hours when the whiteflies were relatively immobile, adult whitefly populations on the five topmost expanded leaves of cassava cultivars were counted. All through the 6-mo scoring period, there was a highly significant difference in whitefly infestation among the new cassava elite clones. Vector population buildup was observed in Ibadan (forest–savanna transition zone) and Onne (humid forest), 2 mo after planting (MAP). Mean infestation across cassava genotypes was significantly highest (16.6 whiteflies per plant) in Ibadan and lowest in Zaria (0.2). Generally, whitefly infestation was very low in all locations at 5 and 6 MAP. During this period, cassava genotypes 96/1439 and 91/02324 significantly supported higher infestations than other genotypes. Plants of 96/1089A and TMS 30572 supported the lowest whitefly infestation across cassava genotypes in all locations. The preferential whitefly visitation, the differences between locations in relation to whitefly population, cassava mosaic disease, and the fresh root yield of cassava genotypes are discussed

Effect of detopping on disease incidence and symptom severity of African cassava mosaic virus disease (ACMD) on some newly developed cassava cultivars form landraces introgression

Twenty-five cassava genotypes were exposed to natural infection by African cassava mosaic disease (ACMD) in plots at the International Institute of Tropical Agriculture (IITA), Ibadan (forest-savanna transition zone), Nigeria. The effect of removing the shoot tips (detopping) of cassava plants on disease incidence and symptom severity was assessed fortnightly for 14 weeks, starting 8 weeks after planting (WAP). There were highly significant differences (P < 0.01) in disease incidence (DI) and symptom severity (ISS) among clones throughout the period of observation, indicating different levels of resistance to infection. Detopping produced a significant effect on disease incidence in clones 91/02322, 91/02324, 91/02327 and 92/0427. It also had a significant effect on symptom severity of clones 92/0342, M94/0177 and TMS 4(2) 1425. The interaction between the treatment (TRT) and clone was highly significant (P < 0.01) for DI and ISS throughout the period of observation, an indication that there are differential responses of the clones to detopping. Cassava genotypes M94/0121 and Isu were observed to be highly resistant and highly susceptible respectively to the disease, while plants of genotypes 82/00058 and 91/02322 showed moderate susceptibility. None of the genotypes was immune to the disease. There was also a highly significant and positive correlation between DI and ISS in both detopped and undetopped plants. A conclusion from this study is that removal of shoot tips from moderately resistant cassava clones for consumption should be discouraged as it increases the severity of ACMD infection in the regenerating shoots of these clone

Cassava mosaic disease and its causal agents: the Nigeria situation

Highlights are presented on the status of knowledge about cassava mosaic disease (CMD) and its causal agents in Nigeria. The disease occurs in all the agroecologies where cassava is grown, from the humid forest in the south to the semiarid and arid agroecologies in the north. The severity is generally moderate but can be very severe on susceptible genotypes. A severe outbreak of the disease was recorded in the late 1980s in Akwa Ibom State in southeastern Nigeria and was curtailed through the use of resistant genotypes. The causal agent had been African cassava mosaic virus but East African cassava mosaic virus (EACMV) was identifi ed in 1997 as an additional causal agent. EACMV was limited in distribution to the humid forest, derived/coastal, and southern Guinea savannas. The two viruses occur mainly in mixed infections. Bemisia tabaci, the whitefly vector of the viruses, is host-specifi c; those infesting cassava are different from those infesting other crops such as cowpea, tomato, and sweetpotato. The decrease in the rate of spread of CMD from the humid forest to the semiarid and arid regions reflects the gradients of whitefly population and cassava cultivation. Storage root yield loss ranges between 32 and 69%. Adoption of cultural control methods is limited. Some of the resistant cassava landraces are usually interplanted with the improved resistant genotypes to control the disease. Proposed areas of further work are suggested for effective control of the disease