Varietal response of cassava root yield components and root necrosis from cassava Brown streak disease to time of harvesting in Uganda

Cassava is consumed in the Democratic Republic of Congo (DRC) as a staple food for the majority of the Congolese population. This crop is used in several forms: as fufu, chikwangue and pondu; cassava leaves are the most consumed vegetable in the country. In 2002, cassava root symptoms similar to cassava brown streak disease (CBSD) were reported for the first time in western DRC. PCR assays, using primers specific to Cassava brown streak virus (CBSV), failed to detect or identify any viral pathogens in diseased cassava samples from western DRC. Therefore, next generation sequencing (NGS) techniques were used as they are able to sequence full organism genomes and are widely used for the identification of pathogens responsible for new diseases. The main objective of this study was to identify the pathogens causing root necrosis in western DRC. Whatman®FTA™ cards were used to collect 12 cassava leaf samples from plants with symptoms indicative of very severe root necrosis, as well as two asymptomatic samples. These 12 samples were sent to Australia at the University of Western Australia in Perth for next generation sequencing (NGS) using the Illumina HiSeq platform. Additional bioinformatics tools included Geneious, CLC workbench, ParaKraken and Kaijou software for short DNA sequences. No viruses (including CBSV) were found in any of the DRC samples. These preliminary results confirm all the previous negative results obtained using PCR and CBSV primers. However, NGS analyses did reveal the presence of a number of bacterial and fungal taxa. These will require further investigation and tests such as the Koch Postulates, to establish their specific pathogenic role in cassava. This is the first scientific evidence that no currently known virus is responsible for the disease which had been referred to previously as ‘CBSD-like disease’. Consequently, the disease found in DRC cassava samples has been designated ‘Cassava Root Necrosis Disease’ or CRND.

Download Full-text

Analysis of Interactions Between Cassava Brown Streak Disease Symptom Types Facilitates the Determination of Varietal Responses and Yield Losses

Plant Disease ◽

10.1094/pdis-11-15-1274-re ◽

2016 ◽

Vol 100 (7) ◽

pp. 1388-1396 ◽

Cited By ~ 8

Author(s):

I. L. Ndyetabula ◽

S. M. Merumba ◽

S. C. Jeremiah ◽

S. Kasele ◽

G. S. Mkamilo ◽

...

Keyword(s):

Plant Root ◽

Sources Of Resistance ◽

Novel Approach ◽

Lake Zone ◽

Root Necrosis ◽

Two Factors ◽

Cassava Brown Streak Disease ◽

Total Plant ◽

Brown Streak

Cassava brown streak disease (CBSD), caused by cassava brown streak viruses, is recognized as one of the most important plant disease threats to African food security. This study describes the incidence and severity of the different symptom types caused by CBSD, derived from extensive surveys in the country most severely affected by the disease: Tanzania. Total plant incidence and mean root severity of CBSD, recorded from 341 farmers’ fields, were both greater in the Coast Zone (49.5% and 3.05), than in the Lake Zone (32.7% and 2.57). Overall, the differing incidences recorded declined in the following order: total plant incidence (39.1%), plant shoot incidence (33.4%), plant root incidence (19.3%), root incidence (10.5%), and unusable root incidence (5.4%). The much lower-than-anticipated loss due to the root necrosis that is characteristic of CBSD was offset by large reductions of root number in plants expressing foliar symptoms of CBSD (15.7% in the Coast Zone and 5.5% in the Lake Zone). These data suggest that the effects of CBSD on the growth of affected plants are greater than those due to root spoilage. Based on these two factors, annual losses due to CBSD in the parts of Tanzania surveyed were estimated at >860,000 t, equivalent to more than U.S.$51 million. A novel approach to using farm-derived data on the responses of the most frequently cultivated varieties to CBSD infection allowed the grouping of the varieties into four categories, based on their relative resistance or tolerance to infection. This tool should be of value to breeders in identifying and selecting for sources of resistance or tolerance in both local and exotic germplasm, and should ultimately contribute to enhancing the management of one of Africa’s most damaging crop diseases.

Download Full-text

Outlook of Cassava Brown Streak Disease Assessment: Perspectives of the Screening Methods of Breeders and Pathologists

Frontiers in Plant Science ◽

10.3389/fpls.2021.648436 ◽

2021 ◽

Vol 12 ◽

Author(s):

Alfred A. Ozimati ◽

Williams Esuma ◽

Titus Alicai ◽

Jean-Luc Jannink ◽

Chiedozie Egesi ◽

...

Keyword(s):

Resistance Breeding ◽

Assessment Method ◽

Disease Assessment ◽

Screening Methods ◽

Computation Method ◽

Breeding Populations ◽

Root Necrosis ◽

Cassava Brown Streak Disease ◽

The One ◽

Brown Streak

Cassava production and productivity in Eastern, Central, and Southern Africa are ravaged by cassava brown streak disease (CBSD), causing yield losses of up to 100% when susceptible varieties are grown. Efforts to develop CBSD-resistant clones are underway. However, the methods for screening CBSD resistance currently vary between breeders and pathologists, with the limited empirical data to support their choices. In this study, we used the empirical CBSD foliar and root necrosis data from two breeding populations, termed cycle zero (C0) and cycle one (C1), to assess and compare the effectiveness of the CBSD screening methods of breeders vs. pathologists. On the one hand, the estimates of broad-sense heritability (H2) for the CBSD root necrosis assessment of breeder ranged from 0.15 to 0.87, while for the assessment method of pathologists, H2 varied from 0.00 to 0.71 in C0 clones. On the other hand, the marker-based heritability estimates (h2) for C0 ranged from 0.00 to 0.70 for the assessment method of breeders and from 0.00 to 0.63 for the assessment method of pathologists. For cycle one (C1) population, where both foliar and root necrosis data were analyzed for clones assessed at clonal evaluation trials (CETs) and advanced yield trials (AYTs), H2 varied from 0.10 to 0.59 for the assessment method of breeders, while the H2 values ranged from 0.09 to 0.35 for the CBSD computation method of pathologists. In general, higher correlations were recorded for foliar severity from the assessment method of breeders (r = 0.4, p ≤ 0.01 for CBSD3s and r = 0.37, p ≤ 0.01 for CBSD6s) in C1 clones evaluated at both clonal and advanced breeding stages than from the approach of pathologists. Ranking of top 10 C1 clones by their indexed best linear unbiased predictors (BLUPs) for CBSD foliar and root necrosis showed four overlapping clones between clonal and advanced selection stages for the method of breeders; meanwhile, only a clone featured in both clonal and advanced selection stages from the CBSD assessment method of pathologists. Overall, the CBSD assessment method of breeders was more effective than the assessment method of pathologists, and thus, it justifies its continued use in CBSD resistance breeding.

Download Full-text

Optimum Time for Harvesting Cassava Tubers to Reduce Losses Due to Cassava Brown Streak Disease in Northeastern DRC

Journal of Agricultural Science ◽

10.5539/jas.v12n5p70 ◽

2020 ◽

Vol 12 (5) ◽

pp. 70

Author(s):

Honoré Muhindo ◽

François Wembonyama ◽

Odette Yengele ◽

Médard Songbo ◽

Willy Tata-Hangy ◽

...

Keyword(s):

Negative Relationship ◽

Harvest Time ◽

Optimum Time ◽

Whitefly Population ◽

Tuber Necrosis ◽

Foliar Symptoms ◽

Root Necrosis ◽

Foliar Symptom ◽

Cassava Brown Streak Disease ◽

Brown Streak

The present study aimed to determine the appropriate time to harvest cassava tuberous root which minimize the losses due to cassava brown streak disease (CBSD) in the region of Yangambi, DRC. To achieve the aim of the study, 38 cassava cultivars were evaluated in Yangambi INERA’s Research Center for CBSD in the roots at harvest time between 9 and 13 months after planting (MAP). All the 38 cultivars tested showed CBSD root necrosis symptoms. Foliar symptoms occurred on 37.6% of the evaluated cultivars while CBSD root necrosis varied significantly among cultivars (7.0% to 82.5%) depending on susceptibility and the age of plant. This indicates the differential response of the cultivars to CBSD infection. Whitefly population density decreased with age of cassava, it was of 3 whiteflies per plant (9 MAP) to 1 (10 MAP). We noticed that in older plants, whitefly population decreased from 1 at 11 MAP to none at 13 MAP. Although, some cultivars did not show CBSD symptoms up to 12 MAP, they were not necessarily less attractive to whitefly. Negative relationship (r = -0.08 and r = -0.25) has been found between whitefly number and foliar symptom severity or between whitefly and tuber necrosis severity. Beyond 12 MAP, CBSD necrosis (severity score 4) was present in the tubers of 3 cultivars (EUR/2011/0148, Yafelamonene and Ybi/2011/258). Our study shows that in order to mitigate the losses due to CBSD necrosis, the optimum harvesting time for cassava tubers in Yangambi is 9 MAP.

Download Full-text

Gene action controlling cassava brown streak disease resistance and storage root yield in cassava

Euphytica ◽

10.1007/s10681-018-2196-1 ◽

2018 ◽

Vol 214 (7) ◽

Author(s):

Michael M. Chipeta ◽

Rob Melis ◽

Paul Shanahan

Keyword(s):

Disease Resistance ◽

Gene Action ◽

Storage Root ◽

Root Yield ◽

Cassava Brown Streak Disease ◽

And Storage ◽

Brown Streak

Download Full-text

Response to Cassava Brown Streak Disease Infections in Local and Improved Cassava Genotypes under Field and Greenhouse Assays in Lower Eastern Kenya

International Journal of Pathogen Research ◽

10.9734/ijpr/2018/v1i329616 ◽

2018 ◽

pp. 1-14

Author(s):

I. N. Koima ◽

C. O. Orek

Keyword(s):

Field Experiment ◽

Disease Incidence ◽

Graft Infection ◽

Rt Pcr ◽

Local Varieties ◽

Root Necrosis ◽

Cassava Brown Streak Disease ◽

Cassava Production ◽

Greenhouse Assay ◽

Brown Streak

Cassava brown streak disease (CBSD) is caused by two cassava brown streak viruses (CBSVs) transmitted by whiteflies (Bemisia tabaci). CBSD significantly inhibits cassava production in Kenya through losses of up to 100% in farmer-preferred but susceptible varieties. As a management strategy, the present study evaluated the effect of CBSD on two local varieties (Thika-5 & Serere) and 15 improved genotypes in lower Eastern Kenya. Between October 2016 and June 2017, the genotypes were infected with CBSVs through whitefly transmission under field experiment at SEKU research farm (1.31ºS, 37.75ºE) and chip-bud grafting at KALRO-Katumani (1.35ºS, 37.14ºS) greenhouse conditions. RCBD and CRD experimental designs were respectively applied in field and greenhouse assays. CBSD symptoms were quantified through disease incidence (DIC) and severity (DSY) every 3 months for the field experiment and weekly for greenhouse assay. At harvest, storage root necrosis (SRN) was scored and non-necrotic roots weighed as marketable root yield (MRY). Molecular diagnostics was accomplished through duplex RT-PCR. Results revealed significantly (P≤0.01) higher foliar field DIC (81- 100%) and SRN (2.3 – 5.0) recorded in Thika-5 and Serere compared to all the improved genotypes that were foliarly asymptomatic (0% DIC and mean SRN of 1.0). Concomitantly and substantially lower (P≤0.01) MRY (1.99 – 2.16 t/ha) were bulked by Thika-5 and Serere compared to 10 improved genotypes that bulked 5.81 – 9.21 t/ha MRY. Upon chip-bud graft infection, Thika-5 and Serere showed higher DIC of 81 – 90% compared to four improved genotypes with 20 - 35% DIC. Correlations between MRY, DIC and SRN were inverse and significant (P≤0.01). RT-PCR detected pre-dominantly CBSV. In conclusion, the natural whitefly-based transmission of CBSVs was ineffective compared to chip-bud grafting. The inverse correlations between CBSD symptoms and yield corroborated the deleterious impact of CBSD on cassava production. The ten improved, high yielding and asymptomatic genotypes identified in the current study could potentially be used to confer resistance against CBSD into farmer-preferred but often sensitive varieties.

Download Full-text

Differential Tropism in Roots and Shoots of Resistant and Susceptible Cassava (Manihot esculenta Crantz) Infected by Cassava Brown Streak Viruses

Cells ◽

10.3390/cells10051221 ◽

2021 ◽

Vol 10 (5) ◽

pp. 1221

Author(s):

Samar Sheat ◽

Paolo Margaria ◽

Stephan Winter

Keyword(s):

Virus Replication ◽

Central Africa ◽

Streak Virus ◽

Virus Infections ◽

Long Distance ◽

Manihot Esculenta Crantz ◽

Cassava Brown Streak Virus ◽

Cassava Brown Streak Disease ◽

Long Distance Movement ◽

Brown Streak

Cassava brown streak disease (CBSD) is a destructive disease of cassava in Eastern and Central Africa. Because there was no source of resistance in African varieties to provide complete protection against the viruses causing the disease, we searched in South American germplasm and identified cassava lines that did not become infected with the cassava brown streak viruses. These findings motivated further investigations into the mechanism of virus resistance. We used RNAscope® in situ hybridization to localize cassava brown streak virus in cassava germplasm lines that were highly resistant (DSC 167, immune) or that restricted virus infections to stems and roots only (DSC 260). We show that the resistance in those lines is not a restriction of long-distance movement but due to preventing virus unloading from the phloem into parenchyma cells for replication, thus restricting the virus to the phloem cells only. When DSC 167 and DSC 260 were compared for virus invasion, only a low CBSV signal was found in phloem tissue of DSC 167, indicating that there is no replication in this host, while the presence of intense hybridization signals in the phloem of DSC 260 provided evidence for virus replication in companion cells. In neither of the two lines studied was there evidence of virus replication outside the phloem tissues. Thus, we conclude that in resistant cassava lines, CBSV is confined to the phloem tissues only, in which virus replication can still take place or is arrested.

Download Full-text