Cassava Brown Streak Disease Response and Association With Agronomic Traits in Elite Nigerian Cassava Cultivars

Abstract

Cassava mosaic geminiviruses (CMGs) and cassava brown streak viruses (CBSVs) cause the highest yield losses in cassava production in Africa. In particular, cassava brown streak disease (CBSD) is and continues to be a significant constraint to optimal cassava production in Eastern and Southern Africa. While CBSD has not been reported in West Africa, its recent rapid spread and damage to cassava productivity in Eastern, and Southern Africa is alarming. The aim of this study was to evaluate Nigerian cassava genotypes in order to determine their responses to CBSD, in the event that it invades Nigeria, the world’s largest cassava producer. The study gathered information on whether useful CBSD resistance alleles are present in the elite Nigerian cassava accessions. A total of 1,980 full-sib cassava seedlings from 106 families were assessed in the field at the seedling stage for a year. A subset of 569 clones were selected and assessed for another year at the clonal stage in Namulonge, central Uganda, a known hotspot for CBSD screening. Results indicated that foliar and root incidences and severities varied significantly (p ≤ 0.01, p ≤ 0.001) except for CBSD foliar incidence at 6 months (CBSD6i). Highest and lowest plot-based heritability estimates for CBSD were registered for CBSD root severity (CBSDrs) (0.71) and CBSD6i (0.5). Positive and highly significant correlations were noted between CBSD root incidence (CBSDri) and CBSDrs (r = 0.90***). Significant positive correlations were also noted between CBSD foliar severity at 3 months (CBSD3s) and CBSD foliar incidence at 6 months (CBSD6i) (r = 0.77***), CBSD3s and CBSDrs (r = 0.35***). Fresh root weight (FreshRW) negatively correlated with CBSDri and CBSDrs, respectively (r = −0.21*** and r = −0.22***). Similarly, CBSD3s correlated negatively with cassava mosaic disease severity at 3 (CMD3s) and 6 months (CMD6s), respectively (r = −0.25*** and r = −0.21***). Fifteen clones were selected using a non-weighted summation selection index for further screening. In conclusion, results revealed that the elite Nigerian accessions exhibited significant susceptibility to CBSD within 2 years of evaluation period. It is expected that this information will aid future breeding decisions for the improvement of CBSD resistance among the Nigerian cassava varieties.

Epidemiological Analysis of Cassava Mosaic and Brown Streak Diseases, and Bemisia tabaci in the Comoros Islands

“…Typical symptoms of both diseases were observed on all varieties indicating that they are all susceptible to CBSD and CMD. The low incidence (7.1%) of severe CBSD stem symptoms and dieback recorded in the current work suggests that the encountered varieties have a degree of tolerance to CBSD which is a common feature of cassava germplasm in East Africa, and which contrasts with germplasm introduced from West Africa which often has catastrophic root damage when affected by CBSD [ 46 ]. The scope of the current study did not include assessment of roots which can be used to ascertain the level of loss caused by CBSD which frequently results in corky dry necrotic rot that renders roots of susceptible varieties unfit for human consumption and marketing.…”

Utility of Ugandan genomic selection cassava breeding populations for prediction of cassava viral disease resistance and yield in West African clones

“…These cross validation predictions within the three populations were encouraging and thus highlighting the utility of GS for improving CBSD and CMD resistance, and fresh root weight. On the other hand, cross validation prediction accuracies in the validation set (west African clones) were much lower than that was observed in the Ugandan training set, and this could be attributed to the fact that west African clones might be deficient in CBSD resistance alleles ( Ano et al., 2021 ).…”

“…the training and validation populations were evaluated during different seasons. These low predictions could also be attributed to the fact that west African cassava populations were deficient in CBSD resistance alleles ( Ano et al., 2021 ). No consistent superior performance was observed for any of the prediction models that were assessed, and this was in good agreement with Heslot et al.…”

“…The leading biotic stress being cassava brown steak disease (CBSD) and cassava mosaic disease (CMD) ( Legg et al., 2014 ). While CMD is present in all cassava producing areas in Africa and Asia, CBSD is only endemic to Eastern and Southern and Central Africa and more recently the disease was reported in Angola, which is closer to West Africa especially Nigeria, the largest cassava producer and consumer in the world ( Ano et al., 2021 ). In highly susceptible varieties, yield losses of up to 100% have been reported ( Hillocks et al., 2002 ; Alicai et al., 2007 ).…”

“…From historical data, Uganda has registered significant gains for CMD and CBSD resistance breeding efforts ( Manze et al., 2021 ), and thus could offer CBSD resistant parents to west African cassava breeding programs such as Nigeria where CBSD is not yet a threat. However, because of the CBSD pandemic in Eastern, Southern and Central Africa, there is restriction on moving plant materials currently from Eastern, Central and Southern Africa to West Africa, where CBSD is non-existent ( Ano et al., 2021 ). Nonetheless, illegal movement of plant materials due to porous borders, besides the whitefly supported transmission could pose a risk of CBSD reaching to West Africa ( Legg et al., 2014 ).…”