Cassava Mosaic Disease Incidence Research Articles

Assessment of yield components of some cassava (Manihot esculenta Crantz) genotypes using multivariate analysis such as path coefficients

Abstract Cassava, which is a tropical storage root crop, serves as a veritable source of carbohydrate for people living in Sub-Saharan Africa. It is also an important source of industrial starch, biopolymers, animal feeds and ethanol. However, the genetic improvement of the crop is impeded by dearth in information on its genetic variability. A field experiment was carried out at the National Root Crops Research Institute, Umudike (05° 29′ N; 07° 33′ E; 122 m a.s.l.), Nigeria, aimed at assessing the interrelationship between fresh root yield and thirteen quantitative yield-related characters of twenty-eight (28) newly developed cassava genotypes. The rain-fed experiment was laid out in a randomized complete block design with dual replications in 2016/2017 cropping seasons. The results indicated that the newly developed cassava genotypes [2] NR110315 followed by [20] B1-5 and [1] NR110238 exhibited (P < 0.05) highest fresh root yield among the twenty-eight genotypes tested. The fresh root yield of [2] NR110315 (18.77 Mt ha−1) was relatively higher compared with [18] NR050080, which gave the least root yield of 5.38 Mt ha−1. The correlation coefficients obtained from the associations among the variables were positive and exhibited highly significant (P ≤ 0.01) association, especially between leaf area index (LAI) and root diameter as well as with fresh root yield of cassava. Among the nine variables subjected to the path analysis, LAI, starch content, above ground dry matter (AGDM), weight of fresh marketable roots per plant and root length that contributed positively and directly to higher fresh root yield require greater attention during selection and breeding in cassava studies. The direct effect of the variables indicating their magnitudes in decreasing order showed that LAI exhibited the greatest effect followed by starch content, AGDM, weight of fresh marketable roots plant−1, root length, % cassava bacterial blight incidence and % Cassava mosaic disease incidence, which had the lowest direct effect on root yield of cassava. Cyanide potential exhibited a direct, weak and negative effect on fresh root yield. The results further suggested that cassava improvement could be achieved through these characters that have positive and highly significant magnitude effect on fresh root yield.

Evaluation of Cassava Genotypes for Agronomic Performance, Correlation with CMD and CBSD Parameters and Stability across Alupe, Kakamega and Kibos in Western Kenya

Cassava (Manihot esculenta Crantz) production in sub-Saharan Africa (SSA) is constrained by the two biotic constraints namely, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). The aim of this study was to evaluate elite cassava genotypes for variation in agronomical traits, correlate them to CMD and CBSD parameters and identify stable genotypes in Alupe, Kakamega and Kibos in Western Kenya. Twenty three (23) elite cassava genotypes that had shown resistance to either one or both of CMD and CBSD in Eastern Africa were evaluated. The trial was conducted using an alpha lattice balanced design with twenty three (23) genotypes, replicated three times at Alupe, Kakamega and Kibos in Western Kenya for an extended cropping cycle between 2016 and 2017. Results showed significant differences (P ≤ 0.05) between genotypes and location (or agro-ecology), but not interaction (P ≥ 0.05), for all the agronomic performance parameters evaluated. All the 23 cassava genotypes evaluated across the three locations had mean cyanide potential levels ranging from of 3.00–6.00 and were therefore, sweet and not bitter. The significant but negative relationship between CMD and CBSD incidence and severity with agronomic performance implied that their relationship was inverse. Confirmation of stability for agronomic performance was achieved through AMMI analysis, using AMMI stability value (ASV). Stable genotypes based on AMMI stability values (ASV) for fresh root yield across Alupe, Kakamega and Kibos were KBH/2002/066, Kibandameno (a local standard check), NASE-18, Kizimbani and NASE-3. These genotypes need to be further evaluated in more environments to assess their wider adaptability and stability.

Cassava Mosaic Disease and Associated Gemini Viruses in Bauchi State, Nigeria: Occurrence and Distribution

Cassava mosaic disease is one of the most important biotic constraint affecting Cassava limiting the production potential of the crop in Northern Nigeria. This study was carried out to evaluate the current status of Cassava mosaic disease incidence, severity, infection type, whitefly abundance in the farmers’ field as well as to determine the virus strains causing the disease in Bauchi State, North eastern Nigeria. A total of thirty three (33) farmers’ fields were surveyed and in each field, thirty plants were assessed along the two diagonals with respect to disease incidence, severity, infection type and whitefly abundance and leaf samples were collected from each field for the virus diagnosis. The results revealed that Cassava mosaic disease incidence was highest in Ganjuwa (88.66%) and lowest in Darazo (43.33%). The disease symptom severity was generally mild. It was also highest in Ganjuwa (2.85) and lowest in Darazo (1.34). Whitefly infection is most prevalent (59.73%) than cutting borne infection (2.67%) in the Districts. Adult whitefly (<i>Bemisia tabaci</i>) population was highest in Ganjuwa (56.33) followed by Kirfi (40.93) and lowest in Toro (27.63). Polymerase chain reaction (PCR) results using specific primers for African Cassava mosaic virus (ACMV) and East African Cassava mosaic virus (EACMV) detected single infections of ACMV and EACMV in 62.4% and 12.9% of the positive samples respectively. Co-infections of ACMV and EACMV were detected in 10.6% of the tested samples. Continuous monitoring of Cassava Mosaic Viruses and whiteflies population is required to provide appropriate management strategies of the disease in Nigeria.

Incidence and severity of cassava mosaic disease in farmer’s fields in Ghana

A survey of cassava mosaic disease (CMD) was carried out in Ghana from 2007-2008 to assess CMD incidence, infection type, severity and adult whitefly population. A total of 136 farmers’ fields across major cassava producing areas in the Brong Ahafo, Western, Northern, Ashanti and Volta regions were assessed. CMD was prevalent in most of the 136 fields surveyed. Frequently encountered local landraces were susceptible to the disease. CMD incidence reached 100% in farmers’ fields. Mean disease incidence ranged from 46% in the Ashanti region to 90% in the Western region of the country. CMD incidence averaged 66.0%, with cutting-borne infection and Whitefly-borne infections being 54.0% and 12.0%, respectively. CMD shoot symptom severity ranged from 2.0 to 3.7 in the farmers’ fields, with a mean of 2.9. Mean adult whitefly population was 0.47. The high prevalence of CMD requires a concerted effort in the management of CMD in the country.

AMMI analysis of cassava response to contrasting environments: case study of genotype by environment effect on pests and diseases, root yield, and carotenoids content in Cameroon

Genotype by environment interaction remains a substantial issue in all breeding programs. Crop genotypes are generally developed in a central breeding location, but always require the evaluation of breeding products in different environments. This is particularly relevant in countries that have a wide range of climates. Eighteen cassava genotypes were evaluated in Cameroon in eight environments—varying in seasonal rainfall and temperature patterns and soil characteristics—over two cropping seasons. Soil nutrient content was analyzed and trials were established in a randomized complete block design in three replications. Response of genotypes to major cassava pests and diseases, yield and carotenoids content was evaluated. It was observed that four genotypes did not show cassava mosaic disease (CMD) symptoms irrespective of the environments. The local check had highest CMD incidence and severity across all environments. Average number of whitefly per plant across all environments was highest on TMS 96/0023. Average cassava green mite (CGM) infestation was low on all the genotypes. Fresh root yield of five genotypes ranged between 25 and 30 tons per ha for both years. Significant and positive correlation was found across locations between fresh root yield and soil K, P and Mg. AMMI analysis revealed highly significant differences among genotypes and environments and significant genotype × environment interaction for most of the estimated traits, indicating variability in genotypes performance with environment.

Survey of farmers\u2019 knowledge of cassava mosaic disease and their preferences for cassava cultivars in three agro-ecological zones in Benin

BackgroundCassava is an important crop in Africa that is widely cultivated for its starchy tuberous root, which constitutes a major source of dietary carbohydrates. Cassava mosaic disease (CMD) is the most devastating disease affecting cassava in Africa and causes enormous losses in yield. In Benin, specifically, cultivars resistant to CMD are not commonly planted, and even when CMD is observed in fields, farmers do not implement control measures, presumably because they lack proper knowledge and training. Our study aimed to evaluate farmers’ knowledge of CMD to determine whether there is consistency between farmers’ criteria for selecting cassava cultivars and the currently CMD-recommended cassava varieties.MethodsWe conducted structured interviews with 369 farmers in 20% of townships in each of three agro-ecological zones in Benin between November 2015 and February 2016. Farmers were selected randomly in each household, and their fields were assessed for CMD incidence and severity.ResultsAll farmers surveyed, representing a broad demographic pool with regard to education level, age group, and years of experience in cassava production, successfully recognized CMD symptoms in photos, but most (98.60%) said they did not know the causes and vectors of the disease. Most farmers (93.51%) reported that they obtain planting material from neighboring fields or their own fields. In total, 52 unique cultivars were identified, of which 3 (5.76%) were preferred based on their yield and precocity and 3 (5.76%) were preferred based on taste or ability for transformation. The assessment of disease incidence and severity showed that the areas most affected by CMD were Comè Township (37.77% of fields affected) and agro-ecological zone VIII (26.33%).ConclusionFarmers already know how to recognize the symptoms of CMD and could implement control measures against it if they are trained by researchers. Across all surveyed areas, we identified six preferred cultivars based on the four most commonly stated preference criteria (precocity, yield, gari, and taste. Our results suggest that farmers will be more likely to use CMD-resistant cultivars and clean plant material if the plants meet their existing preference criteria. We suggest that CMD-resistant cultivars will be embraced only if the recommended cultivars are strategically aligned with the characteristics desirable to the cassava farmers in each region.

Spatial Analysis of Temporal Changes in the Pandemic of Severe Cassava Mosaic Disease in Northwestern Tanzania.

To improve understanding of the dynamics of the cassava mosaic disease (CMD) pandemic front, geospatial approaches were applied to the analysis of 3 years' data obtained from a 2-by-2° (approximately 222-by-222 km) area of northwestern Tanzania. In total, 80 farmers' fields were assessed in each of 2009, 2010, and 2011, with 20 evenly distributed fields per 1-by-1° quadrant. CMD-associated variables (CMD incidence, CMD severity, vector-borne CMD infection, and vector abundance) increased in magnitude from 2009 to 2010 but showed little change from 2010 to 2011. Increases occurred primarily in the two westernmost quadrants of the study area. A pandemic "front" was defined by determining the values of CMD incidence and whitefly abundance where predicted disease gradients were greatest. The pandemic-associated virus (East African cassava mosaic virus-Uganda) and vector genotype (Bemisia tabaci sub-Saharan Africa 1-subgroup 1) were both present within the area bounded by the CMD incidence front but both also occurred ahead of the front. The average speed and direction of movement of the CMD incidence front (22.9 km/year; southeast) and whitefly abundance front (46.6 km/year; southeast) were calculated, and production losses due to CMD were estimated to range from US$4.3 million to 12.2 million.

Evaluation of Cassava Cultivars for Resistance to Cassava Mosaic Disease and Yield Potential in Central African Republic

AbstractEleven cassava genotypes were tested against cassava mosaic disease (CMD) and compared to a local susceptible cultivar in field conditions from June 2011 to July 2012 in Central African Republic (CAR) at two sites representative of the savanna (Damara) and forest (Pissa) zones of the country. The mean number of whiteflies observed on plants varied among genotypes within each site, but was found nearly three times higher at Damara than at Pissa, resulting in a CMD incidence nearly five times higher at Damara than at Pissa. However, no relation was observed between the number of insect on the plants and the level of susceptibility/resistance of the genotypes. The difference of disease pressure between the two sites revealed high level of resistance in several genotypes, while some other ones indicated rather only a partial resistance. Nevertheless, none of the genotypes tested was found immune, in the end, the virus being detected at least in one site in every genotype, including those ones presenting no symptoms in both sites. The impact of CMD on yield components was assessed on the local susceptible check and three partially resistant genotypes, showing that the disease has no significant effect on the tuberous roots number as well as their weight in both sites. The yield potential varied among different genotypes and between the two sites, the mean number of tuberous roots as well as their mean weight being higher in Damara than in Pissa. This study identified highly resistant genotypes such as ‘Gabon’ that performed well in both sites, and ‘91/02322’ that was symptomless and presented a yield potential equivalent to the local check. These genotypes could be distributed to growers with the main advantage to be resistant to CMD and, therefore, reducing the risk to spread sources of inoculum all over the cassava cropping areas in the country.

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.

Survey, Molecular Detection, and Characterization of Geminiviruses Associated with Cassava Mosaic Disease in Zambia.

A survey was conducted from April to May 2014 in 214 farmers' fields located across six major cassava-producing provinces (Western, Northwestern, Northern, Luapula, Lusaka, and Eastern) of Zambia to determine the status of cassava mosaic disease (CMD) and the species diversity of associated cassava mosaic geminiviruses (CMG). Mean CMD incidence varied across all six provinces but was greatest in Lusaka Province (81%) and least in Northern Province (44%). Mean CMD severity varied slightly between provinces, ranging from 2.78 in Eastern Province to 3.00 in Northwestern Province. Polymerase chain reaction discrimination of 226 survey samples, coupled with complete DNA-A genome sequence analysis, revealed the presence of African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), and East African cassava mosaic Malawi virus (EACMMV) as single or mixed infections of different proportions. Single-virus infections were predominant, occurring in 62.8% (ACMV), 5.8% (EACMMV), and 2.2% (EACMV) of samples relative to mixed-virus infections, which occurred in 19.5% (ACMV + EACMMV), 0.4% (ACMV + EACMV), and 0.9% (ACMV + EACMV + EACMMV) of samples. Phylogenetic analysis revealed the segregation of virus isolates from Zambia into clades specific to ACMV, EACMV, and EACMMV, further confirming the presence of all three viruses in Zambia. The results point to a greater diversity of CMG across major cassava-growing provinces of Zambia and implicate contaminated cassava cuttings in disease spread.

Combating viral mosaic disease of cassava in the Lake Zone of Tanzania by intercropping with legumes

Cassava (Manihot esculenta Crantz) production is constrained by many factors, including the viral cassava mosaic disease (CMD). This study was conducted to explore the potential of intercropping cassava with legumes to reduce CMD effects on cassava production. Local (Lyongo Kwimba) and improved (Suma) cassava varieties were intercropped with three types of grain legumes (groundnut, Arachis hypogea L. var. Upendo; cowpea, Vigna unguiculata (L.) Walp. var. Vuli; and green gram, Vigna radiata (L.) R. Wilczek var. Imara). Monocrops of cassava with and without NPK fertilizer were included as controls. The experiment was established using a randomized complete block design with four replications in a split-plot arrangement for three seasons. Cassava varieties intercropped with cowpeas, green gram, and groundnuts and cassava monocrops with and without NPK fertilizer constituted the main plot and sub-plots, respectively. Whitefly population counts and CMD severity and incidence were measured at regular intervals. Cropping system had a significant effect (P < 0.05) on whitefly populations and CMD severity. Small whitefly populations (0–7.5 individuals per leaf) and low CMD severity (1–2.4 on a 5-point scale) were recorded in improved and local cassava varieties intercropped with green gram. The local cassava variety intercropped with green gram showed low CMD incidences (0%–40%) in all seasons. Generally, growing cassava with green gram proved effective in reducing whitefly populations and CMD incidence and severity. Intercropping cassava with grain legumes may improve cassava production and food security in CMD-prone areas of the Lake Zone of Tanzania and areas with similar environments.

Farmer’s Perception of Cassava Mosaic Disease, Preferences and Constraints in Lupaula Province of Zambia

Cassava is the principal staple root crop, providing a major source of calories for rural and urban households in Luapula province of Zambia. However, the yields on smallholder farms are relatively low largely due to disease infections. The study was therefore conducted to establish farmers’ perceptions, knowledge and management of cassava mosaic disease (CMD), which is one of the major diseases of cassava, and to establish farmers’ preferred traits, constraints and assess sources of cassava cuttings for planting. Focus group discussions (FGD) and structured interviews involving 156 farmers in Mwense, Mansa and Samfya districts were conducted from December 2008 to March 2009. Knowledge of CMD was limited among the respondents. Only 2.4% of the respondents were aware of the disease despite high CMD incidence in farmers’ fields. The majority of the farmers were aware of the importance of insect pests; however, they could not differentiate between damages due to diseases or insect pests. High yield and early bulking traits were highly ranked. Most of the farmers planted local landraces on small-fields (<1 ha). It was evident that a local breeding programme aimed at developing locally adapted disease and pest resistant cassava cultivars was a pressing requirement.

English

Cassava mosaic disease is the most important disease affecting cassava in Zambia. A study was conducted through a survey to determine the status of cassava mosaic disease incidence, severity and whitefly abundance in farmers&rsquo; fields in six provinces: Lusaka, Northern, North-Western, Luapula, Eastern and Western between March and May 2014. The study reveals that cassava mosaic disease incidence was highest in Lusaka (70.0%) and Eastern (69.2%) and lowest in Luapula (45.1%) and Northern (48.5%) provinces. Disease symptom severity was moderate to severe in Lusaka (3.48) and Eastern (3.14) and low in the rest of the provinces. Adult whitefly (Bemisia tabaci) populations were highest in Western Province (2.71) and lowest in Luapula Province (0.02). Polymerase chain reaction results using specific primers for African cassava mosaic virus and East African cassava mosaic virus detected single infections of African cassava mosaic virus and East African cassava mosaic virus in 67.9 and 6.8% of the positive reactions, respectively. Dual infections of African cassava mosaic virus and East African cassava mosaic virus were detected in 25.6% of the samples tested. Cassava brown streak virus was not detected in any of the samples and no symptoms suggestive of cassava brown streak disease were observed in the surveyed fields. &nbsp; Key words: Disease, incidence, severity, whitefly.

Field Evaluation of the Effectiveness of Thermotherapy against Cassava Mosaic Disease in Central African Republic

Aim: The effectiveness of thermotherapy in managing cassava mosaic disease (CMD) was studied on a susceptible local cultivar in the field in the epidemiological conditions. Study Design: The field was laid out in randomized complete block design Place and Duration: Field experiment was conducted in forest zone at Kapou located in south west of Central African Republic according to University of Bangui during August 2010 and July 2011. Methodology: Diseased cassava cuttings were treated in a heated water bath at temperatures ranging from 43oC to 51oC for 30 min before being grown for 12 months in the field. Results: Temperatures from 43oC to 49oC were found to have no deleterious effect on either the survival of cuttings or on plant regeneration. One month after planting (MAP), up to 40% of the cuttings treated at 47oC to 49oC had regenerated a plant with no CMD symptoms compared to 7% of untreated cuttings. Between two and five MAP, cassava cuttings treated at 49oC produced plants with a significantly lower incidence of CMD than plants produced from untreated cuttings. All plants grown from treated cuttings developed significantly less severe CMD symptoms than untreated cuttings between 8 and 12 months after planting. The highest tuberous root yield was obtained with diseased cuttings treated at 49oC (4.7kg/plant), equivalent to the yield from untreated symptomless cuttings (4.6kg/plant). Conclusion: Our data clearly demonstrate the value of thermotherapy to maintain a high level of production using local cultivars under severe CMD epidemic conditions.(Resume d'auteur)

Status and diversity of the cassava Mosaic disease causal agents in Sierra Leone

Cassava is the most important root and tuber crop in Sierra Leone. Its low yield can be attributed to several production-limiting factors including cassava mosaic disease (CMD). This study examined in a much wider scope the diversity, prevalence, distribution, incidence and level of severity of the CMD within the cassava farming communities across major agro ecologies in Sierra Leone. A survey was conducted October, 2010. Field assessment was also conducted on farms evaluated. Data was collected on the spot and complimented with group discussions and interviews. Field coordinates were determined using a global positioning system (GPS) recorder. This study showed a countrywide prevalence of 85.2% out of 156 sites visited using GPS mapping. The rain forest ecology had the highest prevalence of 97.2% while the coastal plain had the lowest disease prevalence. Incidence of CMD per district was generally high. Tonkolili district recorded the highest incidence of 99.2% followed by Kailahum and Pujehun. Bonthe district had the lowest severity score, while pujehun district had the highest severity score. Difference in CMD infection was also observed in terms of agro-ecology. Test using polymerase chain reaction (PCR) detected African cassava mosaic virus (ACMV) and also for the first time the East African cassava mosaic virus (EACMV) in two locations in the Moyamba district, southern Sierra Leone. The result from this study indicates the need for an increased adoption of CMD resistant cassava genotypes that are high yielding, has good cooking quality and with the ability to replace the local choice variety without significantly altering the cultural and aesthetic quality of the generally accepted local cultivar.

English

The effect of mosaic virus diseases on dry matter content and starch yield of five local accessions of cassava, &ldquo;Ankrah&rdquo;, &ldquo;AW/17, &ldquo;Tomfa&rdquo;, &ldquo;Dagarti&rdquo; and &ldquo;Tuaka&rdquo; was evaluated. Tomfa showed the highest (95%) incidence of the disease, index of severity of symptoms for all plants (ISSAP) of 3.70, as well as, for diseased plants (ISSDP) (3.84) while Dagarti did not show any phenotypic expression of the disease throughout the study period. Most of the accessions displayed mosaic disease symptoms two months after planting but by the fifth month had fully recovered. However, PCR-based testing at 12 months after planting revealed the presence of ACMV in all the accessions while EACMV was observed in Ankrah, Dagarti and AW/17.&nbsp; Mean tuber (fresh root weight) and starch yield at 12 months after planting (MAP) was significantly (P &le; 0.05) high in Ankrah while percentage dry matter was significantly higher in Dagarti than the other accessions. A negative correlation between starch yield and cassava mosaic disease incidence implies that a high mosaic incidence particularly in the first three months results in lower tuber and starch yields. Key words:&nbsp;Mosaic virus diseases, dry matter, starch yield, PCR, disease incidence

Genetic variability of cassava progenies developed through introgression of cassava mosaic disease resistance into Ghanaian landraces

Availability of genetic diversity is important in selecting suitable cultivars for crop improvement. Progenies of crosses between 19 farmer-preferred cassava landraces and Cassava Mosaic Disease (CMD)-resistant cultivar TME 11 were evaluated and compared with their maternal parents to assess their genetic variability and genetic gains based on CMD tolerance, some growth variables and root yield. The combined analysis of variance for the traits showed significant genotypic differences amongst the progenies and the parents. Apart from a few instances, the differences in replications and years were also significant. Genetic variability components showed high heritability ranging from 92.3 to 99.6% and moderately high genetic gains of 54.1 to 99.6% for the parental cultivars. Apart from canopy spread and plant height, heritability and genetic gains of the progenies were slightly lower than the parents indicating high variability within families of the progenies. The phenotypic coefficient of variation was slightly greater than genotypic coefficient of variation indicating minimal influence of environment on the genotypes. For most of the characters evaluated, the mean performance of the progenies was higher than their corresponding parental lines. Although the genotypes differed significantly (P < 0.001) for all traits evaluated, cultivars such as Afebankye, Bosome nsia, Cedi bankye, 262 Debor, Kwadaso 25, Nkaakom 57 and Sisipe were found to constitute a pool of germplasm with adequate variability. The negative correlation between CMD incidence and other traits evaluated showed significant progress made in the breeding program.

Cassava mosaic disease and associated viruses in Zambia: occurrence and distribution

Cassava mosaic disease (CMD) is caused by cassava mosaic begomoviruses (CMBs), which are transmitted by the whitefly (Bemisia tabaci) in sub-Saharan Africa. CMD and the pathogenic viruses associated with cassava were assessed in a country-wide survey in seven provinces of Zambia between April and May 2009. CMD incidence was highest in Northwestern (71.2%) and lowest in Western (34.3%) provinces. Disease symptoms were severe in Eastern (3.94) and Lusaka (3.88), moderate in Central (3.54), Luapula (3.48) and Northern (3.31) and mild in Northwestern (3.01) and Western (2.50) provinces. In addition, the numbers of adult whitefly were assessed on cassava fields, and found to be highest in Lusaka (2.12) and lowest in Central (0.02) province. Polymerase chain reaction detected two virus species: African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV), that occurred as single and dual infections in 65.4% (ACMV), 25% (EACMV) and 9.6% (ACMV + EACMV) of the positive reactions. None of the samples were positive for EACMV-Ug. This is the first comprehensive report of CMD and the pathogenic viruses infecting cassava in Zambia.

Assessing Reactions of Genetically Improved and Local Cassava Varieties to Cassava Mosaic Disease (CMD) Infection in a Savannah Region of the DR-Congo

The responses of eight genetically improved and eight local cassava varieties to cassava mosaic disease (CMD) were evaluated under field conditions at two sites, in Eastern Kasa?, region of the DR-Congo). The varieties were planted using randomized complete block design with three replications. The rate of cuttings sprouted varied significantly from variety to variety and from location to location. Local varieties were severely infected than improved varieties throughout the trial period. In general, the level of CMD incidence for genetically improved varieties was below 15% while it reached 100% for the local cassava varieties six months after planting (MAP). This trend was also observed for the CMD severity and gravity. The mean scores for CMD severity were 2 and 3.6 for genetically improved and local varieties, respectively at 6 MAP. CMD gravity for improved varieties was below 21% for genetically improved varieties and exceeded 85% for local varieties at the end of trials. Area Under the Severity index Progress Curve (AUSiPC) and Area Under Disease Progress Curve (AUDPC) estimates confirmed that improved varieties were moderately infested comparatively to local varieties. Molecular analysis is being conducted to determine the genetic variability and complexity of the cassava mosaic virus strains involved.

Effect of NPK Fertilization on Cassava Mosaic Disease (CMD) Expression in a Sub-Saharan African Region

The influence of NPK fertilizer on the incidence, severity and gravity of cassava mosaic disease (CMD) was investigated using eight genetically improved cassava varieties and eight local farmer’s varieties. The study was carried out in a savannah region (Gandajika) in D.R. Congo at two locations. The varieties were planted with and without NPK fertilization. Application of NPK fertilizer significantly (P<0.05) increased CMD incidence, severity (AUDPC) and gravity overtime compared to the trials without fertilizers for all the improved cassava varieties evaluated. The CMD incidence remained below 30% of infected plants for improved cassava varieties and reached 100% of plants for local varieties during the six months trial. The same trend was observed for CMD gravity (number of infected leaves per plant) that was below 50% for improved varieties while reaching 100% for all the local varieties at 6 MAP. High incidence and gravity of CMD were observed on local varieties just one month after planting. NPK fertilizers increased significantly the CMD incidence and gravity compared to control site during the first month after plantation. Thereafter, the effect of NPK fertilizer on CMD symptom expression was not noticeable since all the plants from local varieties were infected regardless of the fertilization regimen. Research Article