Resistance Against Cassava Brown Streak Viruses From Africa in Cassava Germplasm From South America

Cassava brown streak disease (CBSD) is a severe virus disease of cassava and prevalent in the eastern regions of Africa. The disease is characterized by distinct vein chlorosis and streak symptoms on leaves and stems and necrosis of storage roots. This necrosis can encompass large areas of the root, rendering it inedible so that the entire cassava harvest can be lost. African cassava varieties are susceptible to either of the two viruses causing the disease, cassava brown streak virus (CBSV) and Uganda cassava brown streak virus, and while there are less sensitive varieties, all cassava eventually succumb to the disease. The lack of CBSD resistance in African cassava varieties prompted this search for new sources of virus resistance in the diversity of South American cassava germplasm held in the collection at International Center for Tropical Agriculture, Columbia. Our search for CBSD resistance in South American cassava germplasm accessions revealed that most of the 238 South American cassava lines infected with CBSV established systemic virus infections with moderate to severe disease symptoms on leaves and stems. Fifteen cassava accessions did not become virus infected, remained free of symptoms, and CBSV was undetected by qRT-PCR. When tuberous roots of those lines were examined, necrotic tissue was found in eight lines and CBSV was detected. The remaining seven cassava accessions remained clear of symptoms on all tissues and organs and were virus free. A broad spectrum of virus resistance also including other virus isolates was confirmed for the breeding lines DSC167 and DSC118. While detailed infection experiments with other cassava lines selected for resistance are still ongoing, this indicates that the resistance identified may also hold against a broader diversity of CBSVs. Taken together, we present the results of a comprehensive study on CBSV resistance and susceptibility in cassava germplasm accessions from South America. The virus resistance in cassava germplasm identified provides compelling evidence for the invaluable contribution of germplasm collections to supply the genetic resources for the improvement of our crops.

[1]  T. Alicai,et al.  Resistance of advanced cassava breeding clones to infection by major viruses in Uganda , 2019, Crop protection.

[2]  J. Legg,et al.  Exchanging and managing in-vitro elite germplasm to combat Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD) in Eastern and Southern Africa , 2018, Food Security.

[3]  R. Lozano,et al.  Genome-wide association mapping and genomic prediction for CBSD resistance in Manihot esculenta , 2018, Scientific Reports.

[4]  R. Hillocks,et al.  Genotype by environment interactions in identifying cassava (Manihot esculenta Crantz) resistant to cassava brown streak disease , 2018 .

[5]  D. Rokhsar,et al.  QTL Mapping for Pest and Disease Resistance in Cassava and Coincidence of Some QTL with Introgression Regions Derived from Manihot glaziovii , 2017, Front. Plant Sci..

[6]  D. Rokhsar,et al.  QTL associated with resistance to cassava brown streak and cassava mosaic diseases in a bi-parental cross of two Tanzanian farmer varieties, Namikonga and Albert , 2017, Theoretical and Applied Genetics.

[7]  S. Duffy,et al.  Variability in P1 gene redefines phylogenetic relationships among cassava brown streak viruses , 2017, Virology Journal.

[8]  N. Taylor,et al.  New opportunities and challenges to engineer disease resistance in cassava, a staple food of African small-holder farmers , 2017, PLoS pathogens.

[9]  L. Kubatko,et al.  Cassava brown streak virus has a rapidly evolving genome: implications for virus speciation, variability, diagnosis and host resistance , 2016, Scientific Reports.

[10]  Y. Baguma,et al.  Inbreeding enhances field resistance to cassava brown streak viruses , 2016 .

[11]  Y. Baguma,et al.  Eleven years of breeding efforts to combat cassava brown streak disease , 2016, Breeding science.

[12]  W. Gruissem,et al.  Characterization of Brown Streak Virus-Resistant Cassava. , 2016, Molecular plant-microbe interactions : MPMI.

[13]  Wenquan Wang,et al.  Validation of Reference Genes for Relative Quantitative Gene Expression Studies in Cassava (Manihot esculenta Crantz) by Using Quantitative Real-Time PCR , 2016, Front. Plant Sci..

[14]  N. Taylor,et al.  Comparative analysis of virus-derived small RNAs within cassava (Manihot esculenta Crantz) infected with cassava brown streak viruses , 2016, Virus research.

[15]  R. Hillocks,et al.  Disparity between leaf and root symptoms and crop losses associated with cassava brown streak disease in four countries in eastern Africa , 2016 .

[16]  L. Boykin,et al.  Analyses of Twelve New Whole Genome Sequences of Cassava Brown Streak Viruses and Ugandan Cassava Brown Streak Viruses from East Africa: Diversity, Supercomputing and Evidence for Further Speciation , 2015, PloS one.

[17]  B. L. Patil,et al.  Cassava brown streak disease: a threat to food security in Africa. , 2015, The Journal of general virology.

[18]  Y. Baguma,et al.  Field evaluation of selected cassava genotypes for cassava brown streak disease based on symptom expression and virus load , 2014, Virology Journal.

[19]  S. Cowell,et al.  Differential tropism in roots and shoots infected by Citrus tristeza virus. , 2014, Virology.

[20]  M. Gedil,et al.  High-resolution mapping of resistance to cassava mosaic geminiviruses in cassava using genotyping-by-sequencing and its implications for breeding. , 2014, Virus research.

[21]  R. Hillocks,et al.  Transcriptional Response of Virus-Infected Cassava and Identification of Putative Sources of Resistance for Cassava Brown Streak Disease , 2014, PloS one.

[22]  James B. Legg,et al.  A global alliance declaring war on cassava viruses in Africa , 2014, Food Security.

[23]  C. Fauquet,et al.  Efficient transmission of Cassava brown streak disease viral pathogens by chip bud grafting , 2013, BMC Research Notes.

[24]  Robert Kawuki,et al.  Genetic Relationships of Cassava Genotypes That are Susceptible or Tolerant to Cassava Brown Streak Disease in Uganda , 2013 .

[25]  T. Alicai,et al.  High throughput real‐time RT‐PCR assays for specific detection of cassava brown streak disease causal viruses, and their application to testing of planting material , 2013 .

[26]  Gration M. Rwegasira,et al.  Response of Selected Cassava Varieties to the Incidence and Severity of Cassava Brown Streak Disease in Tanzania , 2012 .

[27]  P. Ntawuruhunga,et al.  Progress in screening cassava genotypes for resistance to cassava brown streak Uganda virus , 2012 .

[28]  A. Dixon,et al.  Cassava Mosaic Disease in Sub-Saharan Africa: A Feasible Solution for an Unsolved Problem , 2010 .

[29]  S. Winter,et al.  Analysis of cassava brown streak viruses reveals the presence of distinct virus species causing cassava brown streak disease in East Africa. , 2010, The Journal of general virology.

[30]  B. L. Patil,et al.  Cassava mosaic geminiviruses: actual knowledge and perspectives. , 2009, Molecular plant pathology.

[31]  S. Offei,et al.  Genetic relationships among improved cassava accessions and landraces for resistance to the cassava mosaic disease , 2009 .

[32]  A. Dixon,et al.  Prospects for cassava breeding in Sub-Saharan Africa in the next decade , 2008 .

[33]  R. J. Hillocks,et al.  Re-emergence of Cassava Brown Streak Disease in Uganda. , 2007, Plant disease.

[34]  A. Dixon,et al.  Resistance profile of improved cassava germplasm to cassava mosaic disease in Nigeria , 2007, Euphytica.

[35]  R. Hillocks,et al.  Cassava brown streak disease: A review of present knowledge and research needs , 2003 .

[36]  Thomas D. Schmittgen,et al.  Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method. , 2001, Methods.

[37]  C. Hershey,et al.  Definition of a core collection for cassava , 1994 .

[38]  D. Jennings.  Further Studies in Breeding Cassava for Virus Resistance , 1957 .