Eleven years of breeding efforts to combat cassava brown streak disease

Kawuki, Robert; Kaweesi, Tadeo; Esuma, Williams; Pariyo, Anthony; Kayondo, Siraj Ismail; Ozimati, Alfred; Kyaligonza, Vincent; Abaca, Alex; Orone, J; Tumuhimbise, Robooni; Nuwamanya, Ephraim; Abidrabo, Philip; Amuge, Teddy; Ogwok, Emmanuel; Okao, Geoffrey; Wagaba, Henry; Adiga, Gerald; Alicai, Titus; Omongo, Christopher; Bua, A.; Ferguson, Morag; Kanju, Edward; Baguma, Yona

doi:10.1270/jsbbs.16005

Cited by 75 publications

(109 citation statements)

References 36 publications

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“…Cassava is known to suffer from inbreeding depression (Rojas et al, 2009;Kawuki et al, 2016;Ramu et al, 2017). These values should be interpreted to mean that the clones were less inbred than might be expected on the basis of the marker allele frequencies (i.e., the heterozygous marker genotypes were more frequent than expected under Hardy-Weinberg equilibrium).…”

Section: Estimates Of Phenotypic and Genetic Correlations Among Traitsmentioning

confidence: 99%

Genetic Variation and Trait Correlations in an East African Cassava Breeding Population for Genomic Selection

et al. 2019

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Cassava (Manihot esculenta Crantz) is a major source of dietary carbohydrates for >700 million people globally. However, its long breeding cycle has slowed the rate of genetic gain for target traits. This study aimed to asses genetic variation, the level of inbreeding, and trait correlations in genomic selection breeding cycles. We used phenotypic and genotypic data from the National Crops Resources Research Institute (NaCRRI) foundation population (Cycle 0, C0) and the progeny (Cycle 1, C1) derived from crosses of 100 selected C0 clones as progenitors, both to evaluate and optimize genomic selection. The highest broad‐sense heritability (H2 = 0.95) and narrow‐sense heritability (h2 = 0.81) were recorded for cassava mosaic disease severity and the lowest for root weight per plot (H2 = 0.06 and h2 = 0.00). We observed the highest genetic correlation (rg= 0.80) between cassava brown streak disease root incidence measured at seedling and clonal stages of evaluation, suggesting the usefulness of seedling data in predicting clonal performance for cassava brown streak root necrosis. Similarly, high genetic correlations were observed between cassava brown streak disease severity (rg= 0.83) scored at 3 and 6 mo after planting (MAP) and cassava mosaic disease, scored at 3 and 6 MAP (rg= 0.95), indicating that data obtained on these two diseases at 6 MAP would suffice. Population differentiation between C0 and C1 was not well defined, implying that the 100 selected progenitors of C1 captured the diversity in the C0. Overall, genetic gain for most traits were observed from C0 to C1.

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Section: Estimates Of Phenotypic and Genetic Correlations Among Traitsmentioning

confidence: 99%

Genetic Variation and Trait Correlations in an East African Cassava Breeding Population for Genomic Selection

et al. 2019

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“…The resistance conferred by p5001 and ranking of events accumulating lower levels of CP-derived siRNAs at this location may suggest differences in virulence of the CBSD causal pathogens and/or a combination of the environment and CBSD pressure. Year-to-year variation in CBSD incidence and severity has been reported at the same location (Kawuki et al, 2016). Indeed, data generated from the diversity study reported here indicates presence of a cluster of CBSV isolates at Namulonge (Cluster I) (Figure 8) that was not found at the Mtwapa location (Figure 8).…”

Section: Discussionmentioning

confidence: 80%

“…In order to determine the impact of CBSD on marketable/usable root yields, CBSD symptom severity data was re-analyzed, defining usable storage roots as those with scores of 1–2 on the severity scale of 1–5, similar to breeders' practices employed for line selection (Kawuki et al, 2016). Based on this assessment, the wild-type TME 204 and local controls had between 0% and 25% usable storage roots at 12 MAP while 11 of the 25 transgenic TME 204 lines had 98–100% of their roots defined as usable (Table 2).…”

Section: Resultsmentioning

confidence: 99%

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Field Level RNAi-Mediated Resistance to Cassava Brown Streak Disease across Multiple Cropping Cycles and Diverse East African Agro-Ecological Locations

et al. 2017

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Cassava brown streak disease (CBSD) presents a serious threat to cassava production in East and Central Africa. Currently, no cultivars with high levels of resistance to CBSD are available to farmers. Transgenic RNAi technology was employed to combat CBSD by fusing coat protein (CP) sequences from Ugandan cassava brown streak virus (UCBSV) and Cassava brown streak virus (CBSV) to create an inverted repeat construct (p5001) driven by the constitutive Cassava vein mosaic virus promoter. Twenty-five plant lines of cultivar TME 204 expressing varying levels of small interfering RNAs (siRNAs) were established in confined field trials (CFTs) in Uganda and Kenya. Within an initial CFT at Namulonge, Uganda, non-transgenic TME 204 plants developed foliar and storage root CBSD incidences at 96–100% by 12 months after planting. In contrast, 16 of the 25 p5001 transgenic lines showed no foliar symptoms and had less than 8% of their storage roots symptomatic for CBSD. A direct positive correlation was seen between levels of resistance to CBSD and expression of transgenic CP-derived siRNAs. A subsequent CFT was established at Namulonge using stem cuttings from the initial trial. All transgenic lines established remained asymptomatic for CBSD, while 98% of the non-transgenic TME 204 stake-derived plants developed storage roots symptomatic for CBSD. Similarly, very high levels of resistance to CBSD were demonstrated by TME 204 p5001 RNAi lines grown within a CFT over a full cropping cycle at Mtwapa, coastal Kenya. Sequence analysis of CBSD causal viruses present at the trial sites showed that the transgenic lines were exposed to both CBSV and UCBSV, and that the sequenced isolates shared >90% CP identity with transgenic CP sequences expressed by the p5001 inverted repeat expression cassette. These results demonstrate very high levels of field resistance to CBSD conferred by the p5001 RNAi construct at diverse agro-ecological locations, and across the vegetative cropping cycle.

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“…Unlike CMD, where sources of inherent resistance have been identified (Akano et al, 2002; Lokko et al, 2005; Okogbenin et al, 2012; Rabbi et al, 2014), most farmer-preferred cassava cultivars are susceptible, or highly susceptible, to CBSD. Breeding programs targeting introgression of CBSD resistance from resistant/tolerant cultivars are ongoing (Kawuki et al, 2016), but such efforts are time consuming and face challenges in combining effective resistance to CBSD and CMD with good storage root quality and other attributes preferred by farmers and consumers. To date, the best varieties deployed to control CBSD are tolerant to the disease and rapidly degenerate under high virus inoculum pressure after 2–3 cropping cycles.…”

Section: Introductionmentioning

confidence: 99%

A Virus-Derived Stacked RNAi Construct Confers Robust Resistance to Cassava Brown Streak Disease

et al. 2017

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Cassava brown streak disease (CBSD) threatens food and economic security for smallholder farmers throughout East and Central Africa, and poses a threat to cassava production in West Africa. CBSD is caused by two whitefly-transmitted virus species: Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) (Genus: Ipomovirus, Family Potyviridae). Although varying levels of tolerance have been achieved through conventional breeding, to date, effective resistance to CBSD within East African cassava germplasm has not been identified. RNAi technology was utilized to integrate CBSD resistance into the Ugandan farmer-preferred cassava cultivar TME 204. Transgenic plant lines were generated expressing an inverted repeat construct (p5001) derived from coat-protein (CP) sequences of CBSV and UCBSV fused in tandem. Northern blots using probes specific for each CP sequence were performed to characterize 169 independent transgenic lines for accumulation of CP-derived siRNAs. Transgenic plant lines accumulating low, medium and high levels of siRNAs were bud graft challenged with the virulent CBSV Naliendele isolate alone or in combination with UCBSV. Resistance to CBSD in the greenhouse directly correlated to levels of CP-derived siRNAs as determined by visual assessment of leaf and storage root symptoms, and RT-PCR diagnosis for presence of the pathogens. Low expressing lines were found to be susceptible to CBSV and UCBSV, while medium to high accumulating plant lines were resistant to both virus species. Absence of detectable virus in the best performing p5001 transgenic lines was further confirmed by back-inoculation via sap or graft challenge to CBSD susceptible Nicotiana benthamiana and cassava cultivar 60444, respectively. Data presented shows robust resistance of transgenic p5001 TME 204 lines to both CBSV and UCBSV under greenhouse conditions. Levels of resistance correlated directly with levels of transgene derived siRNA expression such that the latter can be used as predictor of resistance to CBSD.

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Eleven years of breeding efforts to combat cassava brown streak disease

Cited by 75 publications

References 36 publications

Genetic Variation and Trait Correlations in an East African Cassava Breeding Population for Genomic Selection

Genetic Variation and Trait Correlations in an East African Cassava Breeding Population for Genomic Selection

Field Level RNAi-Mediated Resistance to Cassava Brown Streak Disease across Multiple Cropping Cycles and Diverse East African Agro-Ecological Locations

A Virus-Derived Stacked RNAi Construct Confers Robust Resistance to Cassava Brown Streak Disease

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