Resistant Cassava Varieties Research Articles

Volatile Organic Compounds from Cassava Plants Confer Resistance to the Whitefly Aleurothrixus aepim (Goeldi, 1886).

Cassava is an essential tuber crop used to produce food, feed, and beverages. Whitefly pests, including Aleurothrixus aepim (Goeldi, 1886) (Hemiptera: Aleyrodidae), significantly affect cassava-based agroecosystems. Plant odours have been described as potential pest management tools, and the cassava clone M Ecuador 72 has been used by breeders as an essential source of resistance. In this study, we analysed and compared the volatile compounds released by this resistant clone and a susceptible genotype, BRS Jari. Constitutive odours were collected from young plants and analysed using gas chromatography-mass spectrometry combined with chemometric tools. The resistant genotype released numerous compounds with previously described biological activity and substantial amounts of the monoterpene (E)-β-ocimene. Whiteflies showed non-preferential behaviour when exposed to volatiles from the resistant genotype but not the susceptible genotype. Furthermore, pure ocimene caused non-preferential behaviour in whiteflies, indicating a role for this compound in repellence. This report provides an example of the intraspecific variation in odour emissions from cassava plants alongside information on odorants that repel whiteflies; these data can be used to devise whitefly management strategies. A better understanding of the genetic variability in cassava odour constituents and emissions under field conditions may accelerate the development of more resistant cassava varieties.

Field Screening of Elite Cassava (Manihot esculenta) Mutant Lines for their Response to Mosaic and Brown Streak Viruses

Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD) have been major limiting biotic factors to the productivity of cassava farming in Kenya. Development of resistant cassava varieties is most effective way. The study was to determine response of elite cassava lines to CBSD and CMD under field conditions on different agro-ecological zones in Kenya. Screening was done under hot-spot field conditions where five lines together with their parents were evaluated in Randomized Complete Block Design with three replications at University of Eldoret (UoE), Solai and Marakwet sites in Kenya. Severity assessment done on 1-5 rating scale where 1 very resistant and 5 most susceptible. Elite cassava lines had significant differences in their response (p < 0.05) to CBSD and CMD. Additionally, genotypes, site and time interval were also significant (p < 0.05). The three elite lines (CAS1, CAS2 and CAS3) had better tolerance to both diseases compared to their parents (KME3 and KME4) with KME4 showing visible brown rings on the root typical of CBSD The elite lines CAS1, CAS2 and CAS3 identified to have better adaptability to both CBSD and CMD could be further exploited in breeding for new cassava varieties for Kenya and other countries in the region with similar ecology.

Time series and power law analysis of crop yield in some east African countries.

We carry out a time series analysis on the yearly crop yield data in six east African countries (Burundi, Kenya, Somalia, Tanzania, Uganda and Rwanda) using the autoregressive integrated moving average (ARIMA) model. We describe the upper tail of the yearly crop yield data in those countries using the power law, lognormal, Fréchet and stretched exponential distributions. The forecast of the fitted ARIMA models suggests that the majority of the crops in different countries will experience neither an increase nor a decrease in yield from 2019 to 2028. A few exceptional cases correspond to significant increase in the yield of sorghum and coffee in Burundi and Rwanda, respectively, and significant decrease in the yield of beans in Burundi, Kenya and Rwanda. Based on Vuong's similarity test p-value, we find that the power law distribution captured the upper tails of yield distribution better than other distributions with just one exceptional case in Uganda, suggesting that these crops have the tendency for producing high yield. We find that only sugar cane in Somalia and sweet potato in Tanzania have the potential of producing extremely high yield. We describe the yield behaviour of these two crops as black swan, where the "rich getting richer" or the "preferential attachment" could be the underlying generating process. Other crops in Burundi, Kenya, Somalia, Tanzania, Uganda and Rwanda can only produce high but not extremely high yields. Various climate adaptation/smart strategies (use of short-duration pigeon pea varieties, use of cassava mosaic disease resistant cassava varieties, use of improved maize varieties, intensive manuring with a combination of green and poultry manure, early planting, etc) that could be adapted to increase yields in east Africa are suggested. The paper could be useful for future agricultural planning and rates calibration in crop risk insurance.

English

A farm survey was conducted in Kuria East and Suna West sub-counties to determine the incidence, severity and estimated losses of cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) on cassava crops in farmers’ fields. The results showed that cassava is the second most important staple crop after maize in Migori County. CMD incidence ranged from 0.0 to 56.7%) in Kuria East and 10.0 to 55.0% in Suna West. CBSD incidences were much higher at 5.0 to 74.0% in Kuria East and 10.0 to 77.5% in Suna West. Both CMD and CBSD had an effect on yield reduction and total root loss ranged from 10.7 to 47.2% in Kuria East and 11.5 to 33.2 in Suna West. The percent mean total root loss in Kuria East was 25.9%; equivalent to 1299.6 US dollars/ha while in Suna East was 24.7%; equivalent to 1259.5 US dollars/ha. The best performing variety with regards to low CBSD and CMD incidence, low root losses and high yield were TMS 30572 and MH95/0183. The findings of this study are expected to provide impetus for the development and promotion of new high yielding, locally adapted and resistant cassava varieties. Key words: Cassava, CBSD, incidence, root necrosis, yield loss.

Correlation of chemical compositions of cassava varieties to their resistance to Prostephanus truncatus Horn (Coleoptera: Bostrichidae).

The preference of cassava as a major host by Prostephanus truncatus Horn is a major constraint to ample production of cassava, Manihot esculenta Crantz and storage. This study analyzed the nutritional and secondary metabolite compositions in 15 cassava varieties, evaluated levels of damage and reproduction by P. truncatus, and assessed their resistance to attack. One hundred grams of dried cassava chips in 250-ml Kilner jars were infested with 10 adult larger grain borerof 0–10 days old and held for 3 months. The nutritional and secondary metabolites compositions of the dry cassava chips were determined using the method of Association of Analytical Chemists . Chip perforation rates in the cassava varieties ranged from 17.7 to 71.6%. The weight of cassava powder varied by about threefold. The final number of larger grain borer in the cassava varieties varied by about sixfold with 63 in 01/0040 and 379 in 01/1368. Hydrocyanic acid content content varied by over 10-fold and correlated negatively with number of larger grain borer. Flavonoid content varied by ∼10%. Tannins and saponin content of the cassava negatively correlated with number of adult P. truncatus. The cassava varieties 95/0166, 92/0326, 01/0040, 05/0024, and 34 91934 had selection index <0.8 and were classified as resistant to larger grain borer damage, while others with selection index >0.8 were classified as susceptible. The resistance to high damage in the resistant varieties was conferred by secondary metabolites such as tannins, saponins, alkaloids, and hydrocyanic acid content. The genetic variation in cassava varieties could be explored to breed resistant cassava varieties for use in larger grain borer-endemic areas.

Flood and cassave productivity in Kogi State, Nigeria: A quantitative analysis using cross-sectional data

The study assessed the effect of the 2012 flood disaster on cassava productivity in Kogi State and identified the adaptation measures and resilience capacity of the cassava farmers affected by the flood. To achieve the objectives of the study, the “with and without” approach involving the flood affected farmers and control group was employed to ascertain and compare the effect of the flood on cassava productivity. Simple descriptive statistics, productivity index, z-test of two means and multiple regression analysis were employed to analyse the data collected. The result indicated a significant cassava productivity differentials of about 56% between the flood affected farmers and the control population. The multiple regression analysis result further confirmed that flood had a significant effect on cassava productivity amongst the respondents at 5% level of significance. Against this backdrop, there is the need for farmers to continue to diversify their farming practices with a view to mitigating the effect of future flood occurrence, adopt drought resistant cassava varieties while the National Emergency Management Agency (NEMA) should in conjunction with the Nigerian Meteorological Agency (NIMET), Kogi State Government and the Media create effective climatic situation awareness for cassava farmers within the State with the view to containing and minimizing the adverse effect of flooding. Key Words: Flood, Disaster, Adaptation, Resilience, Cassava farmers, Productivity

Developing Cassava Mosaic Disease resistant cassava varieties in Ghana using a marker assisted selection approach

Cassava is a major staple and food security crop in Africa which can produce a crop under uncertain rainfall and low fertility conditions. However, it suffers from several pests and diseases, with Cassava Mosaic Disease (CMD) being the main biotic constraint in production in sub-Saharan Africa. It is caused by cassava mosaic geminiviruses. Plants infected with CMD usually produce a few or no storage roots. Markers associated with resistance genes to CMD have been mapped, including a major dominant gene, CMD2. Eight CMD resistant genotypes from CIAT were used in crosses with three cassava landraces and one IITA breeding genotype. CMD evaluation was done on the parents and 525 F1 progenies comprising of individuals pre-selected for CMD resistance based on average severity scores of 1 and 2. Multiple marker analysis was used to screen for the CMD2 gene, where four markers associated with this gene were used. Of the tested genotypes 83 % showed at least one marker allele for the CMD2 gene. Two CIAT genotypes (CR52A-31 and AR14-10) had all four marker alleles. TMEII had three alleles associated with CMD2 while Dabodabo had one marker allele. This suggests that Dababo may have alternative genes than CMD2 for CMD resistance. The F1 families showed segregation for the CMD2 gene. A total of 88 individuals (17 %) had all four marker alleles associated with the CMD2 gene. A total of 179 individuals had between one to three marker alleles each associated with CMD2. A total of 91 individuals had no marker allele associated with the CMD2 gene.

English

Development of high yielding and disease resistant cassava varieties, coupled with the promotion of efficient processing technologies, was the principal intervention aimed at changing the cassava sub-sector in Nigeria. National research and extension programs in Nigeria and IITA have been spearheading efforts to disseminate these varieties alongside improving farmer&rsquo;s access to processing machineries. Several Research-for-Development (R4D) projects were implemented to this effect between early 1980 to date. This paper investigated the effects of improved cassava varieties and processing technologies on adopting households. It also attempts to test and establish the link between adoption of improved cassava varieties and access to processing technologies. The data used in this paper come from a sample household survey of 952 households conducted in four regions of Nigeria. The results showed that in all the study sites farmers grow mixture of improved and local cassava varieties. They process cassava at home using small processing machines and also using services of commercial processors. The most common processed cassava products were found to be garri and fufu. Adopters of improved cassava varieties have higher cassava yield of 16 tons/ha compared to 11 ton/ha for non-adopters. There was also significant yield variation between villages that participated (15 tons/ha) in research for development (R4D) training and those which did not (13 tons/ha). The bivariate probit model estimates showed a strong relationship between adoption of improved cassava varieties and farmers&rsquo; access to grating machines. Moreover, farmers that were members of either community organizations or cooperative organizations had a higher tendency of using improved varieties than others, suggesting that the introduction of new cassava varieties would be enhanced by farmers&rsquo; access to processing facilities and services. Moreover, training of farmers and processors through R4D programs has led to increased use of improved technologies. Key words: Cassava, improved varieties, processing, bivariate probit.

Viscoelastic Properties and Physico-Functional Characterization of Six High Yielding Cassava Mosaic Disease-Resistant Cassava (Manihot Esculenta Crantz) Genotypes

Investigations were conducted to characterize six high yielding cassava mosaic disease (CMD) resistant cassava varieties (Ampong, Broni bankye, Sika, Otuhia, Amakuma and Bankye fitaa) that have been developed by the Crop Research Institute of Ghana in collaboration with the International Institute for Tropical Agriculture for their differences and similarities in viscoelastic properties and physico-functional characteristics. The viscoelastic properties (pasting temperature, peak viscosity, final viscosity, breakdown viscosity and setback viscosity), and physico-functional characteristics (swelling power, solubility and water binding capacity) were determined using standard analytical methods. The results showed wide variations in viscoelastic properties with values ranging from 270.67-380.67 BU for peak viscosity, 37.17-260 BU for final viscosity, 199.83-282.33 BU for breakdown viscosity, 21.83-98.66 BU for setback viscosity and 2.48-10.51 min time to pasting temperature. Similarly, variations in swelling power, solubility and water binding capacity were noted with values ranging between 14.34-17.04%, 73.04-79.98% and 234.53- 276.63% respectively for all the different cassava genotypes. Statistical analysis showed significant differences (P < 0.05) amongst the studied cassava genotypes with Sika (improved variety) having exceptionally high viscoelastic characteristics. The differences noted in the viscoelastic properties and physico-functional characteristics of the six CMD resistant cassava genotypes could be used in their selection for specific food and industrial processing applications.

Application of Multivariate Techniques for Characterizing Composition of Starches and Sugars in Six High Yielding CMD Resistant Cassava (Manihot esculenta Crantz) Varieties

High yielding and cassava mosaic disease (CMD) resistant cassava varieties have been developed by the Crop Research Institute of Ghana with varying compositions and concentrations of starches and sugars. This study characterized four of these improved cassava varieties (Ampong, Broni bankye, Sika and Otuhia) together with two traditional varieties (Amakuma and Bankye fitaa) for their composition of starches and sugars using principal component and cluster analyses. The concentration of total sugars, reducing and non-reducing sugars, sucrose, starches, amylose and amylopectin were determined using standard analytical methods. Results obtained were total sugar (4.04-18.47%), non-reducing sugar (2.08-16.21%), sucrose (1.98-15.40%), starch (15.39-31.07%) and amylose (30.57-40.33%) and these were significantly different (p < 0.05) amongst the studied cassava varieties. The improved varieties (Ampong, Broni bankye, Sika and Otuhia) had high total sugar levels ranging from 7.19 to 18.47 %. With the exception of Broni bankye (improved variety) all the improved and traditional varieties were high starch and amylose containing varieties. These differences in the biochemical composition of the traditional and improved cassava varieties could be used in their selection for specific food and industrial processing applications.

First report of the occurrence of East African cassava mosaic virus‐Uganda (EACMV‐UG) in Angola

Cassava mosaic disease (CMD) is the major production constraint on cassava ( Manihot esculenta ) in Angola. Previous reports derived from single samples recorded the presence of African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) in Angola. Regional CMD monitoring initiatives have predicted the spread into northern Angola of EACMV-Uganda (-UG), the unusually virulent (aggressive) recombinant strain associated with the African CMD pandemic (Legg et al ., 2006). In view of this threat, an assessment survey was conducted in north and central Angola in April 2008. Eighteen cassava fields were sampled in Bengo, Cuanza Norte, Malanje and Uige Provinces. Moderate to severe CMD symptoms were observed in most fields. Sixty-three of 65 samples obtained from these fields tested positive in TAS-ELISA using monoclonal antibody SCR 20. PCR was performed using primer pairs previously described for the specific identification of ACMV, EACMV, EACMV-UG, East African cassava mosaic Cameroon virus (EACMCV) and Indian cassava mosaic virus (ICMV) (Ogbe et al ., 2003), East African cassava mosaic Malawi virus (EACMMV) (Zhou et al ., 1998), East African cassava mosaic Zanzibar virus (EACMZV) (Were et al ., 2004) and South African cassava mosaic virus (SACMV) in mixed infections. This revealed the occurrence of ACMV, EACMV and EACMV-UG, but not EACMZV, EACMMV, SACMV or ICMV. Single infections of ACMV and EACMV were detected in 32·3 and 9% of samples, respectively. Mixed infections of ACMV with EACMV, EACMV with EACMV-UG and all three viruses were detected in 35·3, 1·5 and 16·9% of samples, respectively. ACMV, detected in 84·6% of samples, was the predominant species, followed by EACMV (63%) and EACMV-UG (18·5%). Significantly, EACMV-UG occurred most frequently in the northernmost part of the surveyed area (Uige Province) immediately to the south of the Bas Congo region of the Democratic Republic of Congo, already known to be affected by the pandemic. These findings significantly broaden the known geographical extent of the CMD pandemic and draw attention to the urgent need for the large-scale deployment of resistant cassava varieties, which have been used to reduce losses in pandemic-affected regions of East Africa.