African Crop Science Journal

Viruses associated with cassava mosaic disease and their alternative hosts along Nigeria-Cameroon border

L.A. Ezeji — 2023-08-14

Cassava mosaic disease (CMD) threatens cassava production across the African continent. Because CMD is widespread in sub-Saharan Africa (SSA), it is particularly important to monitor border regions to prevent the introduction of other cassava (Manihot esculenta Crantz) viruses and strains into regions otherwise considered still free of the viruses. The objective of this study was to establish the occurrence of viruses associated with CMD and their alternate host plants along the Nigeria-Cameroon border. One hundred leaf samples from cassava plants and weed species were collected across 21 locations, along the border regions of Cross River State; and assessed for CMD incidence and severity. Nucleic acid extracts were obtained and used to test for African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV), using polymerase chain reactions. Plants from ten, seven and four locations had mild, moderate and severe CMD symptoms, respectively. Of the 100 samples collected, 68 were symptomatic and 32 were asymptomatic for CMD; while five weed species were symptomatic. ACMV alone was detected in six symptomatic and three asymptomatic cassava leaves. EACMV was singly detected in one symptomatic and two asymptomatic cassava leaves; while 13 cassava leaves from ten locations had mixed ACMV/EACMV infections. One asymptomatic cassava leaf from Ikang tested positive for ACMV and EACMV. EACMV alone was detected on a symptomatic weed species, Sclerocarpus africanus. The occurrence of viruses causing CMD in Nigeria, including the border regions, has now been further documented, and S. africanus is now verified as a host of EACMV. There is a need for further studies on other plants that may be putative reservoirs for cassava mosaic viruses, towards the development of integrated management strategies.

Enset landrace diversity in major enset growing regions of Southern Ethiopia

G. Blomme — 2023-08-14

Enset [Ensete ventricosum (Welw.) Cheesman] is an important food security crop of the Southern Ethiopian highlands. The cultivation of enset is characterised by a wide variety of landraces, suitable to varying agro-ecological conditions and with multiple uses by households. The objective of this paper is to present enset landrace diversity, characteristics and uses in Ethiopia. The study was done through interviews with 375 households covering 20 communities (kebeles) and eight ethnic groups, along an altitudinal range of 1,500 to 3,000 masl across the main enset-producing belt in Southern Ethiopia. A total of 296 locally named enset landraces were recorded. Landrace presence was mostly constrained at the kebele and zone levels, with limited overlap in landrace names across these boundaries. Moderate to high enset landrace diversity was observed on farms across the entire study region. Cultivating a variety of landraces not only allowed for diversified uses, but increases the likelihood of retained yield and food security under variable environmental circumstances. Farmer experience and indigenous knowledge allow for the selection of specific landraces suited to prevalent agro-ecological conditions. We identified a perception bias in the attribution of landrace agro-ecological characteristics, with farmer insight often dependent on the environmental conditions that the local community was exposed to. We underscore the importance of research-based characterisation of enset landraces, to ensure optimal cultivation of this food security crop in changing climatic conditions.

Insecticidal activities of volatile oils of lime fruit peels and African black pepper seeds on adult kola weevil and their chemical compositions

O.Y. Alabi — 2023-08-14

Balanogastris kolae reduces the quality of stored kolanuts; yet, plants with insecticidal properties could be used to manage this insect pest. The objective of this study was to evaluate the efficacy of plant oils against B. kolae, a storage pest of kolanuts. The Citrus aurantifolia fruit peel and Piper guineense seed volatile oils obtained via hydro-distillation of the dried, pulverised samples were tested. Their chemical composition was determined using Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Adult mortality was generally low (0.0%) across treatments and exposure times, though not significant (P > 0.05) in the fumigant tests The highest mortality (47.5%) was recorded at 24 hours in 1.0% P. guineense, while the mortality was 13.1% occurred at 12 hours in the 15.0% C. aurantifolia concentration. In contact toxicity tests, none of the weevils treated with 10.0% C. aurantifolia survived after 24 hours of exposure. The highest mortality (85.0%) was obtained from the 10.0 and 15.0% P. guineense volatile oil after 96 hours. Citrus aurantifolia elicited contact toxicity against the weevil more than P. guineense across all concentrations. The GC-MS analysis gave 33 compounds in C. aurantifolia and 43 in P. guineense volatile oil samples. The prominent compounds were limonene (3.222%), linalyl isobutyrate (2.484%), gamma-caryophyllene (1.197%) and Patchoulene (6.529%). Therefore, C. aurantifolia fruit peel and P. guineense seed volatile oils are efficacios in controlling Balanogastris kolae insect pest infestation on kolanuts, though C. aurantifolia fruit peel oil is the best as it compares closely with the synthetic pesticide (2,2-dimethyl dichlorovinyl phosphate (DDVP)).

Prevalence of yam nematodes in diverse soil communities, and their morphometrics in the Krachi-Nchumuru District of Ghana

A.k. Enchill — 2023-08-14

Yam (Dioscorea spp.) is susceptible to dry rot disease, which limits its yields in farmers fields in West Africa.The objective of this study was to assess the occurrence and characteristics of the plant-parasitic nematode (Scutellonema bradys) on yam from the Volta Region of Ghana. A survey was conducted in KrachiI-Nchummuru District in the Volta region in Ghana, using a semi-structured questionnaire in ten communities. Majority of the farmers (62%) were unaware of nematodes and their damage caused to yam. Most interviewees (84%) mentioned the ‘pona’ yam variety as the most susceptible genotype to rot, especially in storage. Twelve nematode genera were identified in soils, and eight under storage conditions. Soil samples had, for relative abundance, 31.5% of nematodes as Scutellonema bradys and 16.8% as Meloidogyne spp. On the other hand, relative abundances in yam peels for S. bradys, Meloidogyne spp. and Pratylenchus spp. were 88.4, 6.0 and 3.3%, respectively. Body lenghts of female S. bradys ranged from 747.3 to 861.9 um. There was a strong positive correlation between tail length and head region diameter (r = 0.81); and stylet knob height and vulva position (r= 0.68). Agglomerative hierarchical clustering (AHC) showed 5 major groups at a dissimilarity of 90%, with sub-groups formed at dissimilarity value of 50%. In-depth survey of communities in the Krachi Nchumuru district revealed that, Scutellonema bradys is a threat to yam production in this region, and results in considerable dry rot disease and yield losses.

Farmer knowledge, management practices and occurrence of tomato root knot nematodes in Kenya

R.K. Birithia — 2023-08-14

Root-knot nematodes (RKNs) (Meloidogyne spp.) is a major constraint to tomato (Solanum lycopersicum L.) production in sub-Saharan Africa; yet there is low adoption of recommended nematode control measures in regions like east Africa due to inadequate farmer knowledge about the pest and associated diseases. The objective of this study was to assess farmers’ knowledge status, and intensity of damage of root-knot nematodes and their management practices in Kenya. A survey was conducted in Kenya, during February to August 2021; using a semi-structured questionnaire administered to 282 randomly selected household heads of actively growing tomato farmers, at two elevations in three counties. Most farmers (98.9%) could not identify the disease precisely. They mostly attributed its symptoms to moisture stress and nutrient deûciencies. Most farmers (63%) practiced mono-cropping; while only 4.3% of farmers amended soils with manure. Respondents preferred growing RKN susceptible tomato varieties, mainly Rio-Grande, Cal J, Onyx and Kilele FI. A total of 92% expressed willingness to shift to RKNs resistant varieties, if recommended varieties match their desirable characteristics. Majority of the respondents lacked knowledge on nematode characteristics and its associated disease control. A total of 37.9% of the respondents did not use control measures against the RKNs. There was high disease incidence, severity and galling index in the surveyed areas.

Analysis of sorghum social seed network in Tigray, Northern Ethiopia

S. Welderufael — 2023-08-14

Proper understanding of the nature of seed exchange among farming communities is fundamental to achieving a sustainable seed system and maintaining crop genetic resources. The objective of this study was to investigate sorghum (Sorghum bicolor) seed sources and analyse their network flow among farmers in Tigray in Northern Ethiopia. A survey was conducted using a semi-structured questionnaire, involving 153 sorghum household farmers selected randomly from six villages; namely Gezaadara, Medabe, Gezameker, Waekel, Munira and Gandostela. Farmers who plaid major roles in the sorghum seed exchange network were identified using social seed network analysis. Results showed that bartering and own-saved seeds were the dominant sources of sorghum seed for farmers throughout the study area; and sorghum seed flow was more confined within villages than beyond. Social capital such as cultural norms, trust and farmers’ desire to increase sorghum production in the communities were the fundamental drivers for farmer sorghum seed exchange. Individuals distinguished as nodal farmers who had high bridging roles could also act as entry points for improved sorghum seed exchange interventions in Tigray.

Using AquaCrop model to derive deficit irrigation schedules for improved irrigation water management for tomato production in Zimbabwe

G. Muroyiwa — 2023-08-14

Increasing scarcity and unreliability of rainfall, and the absence of irrigation schedules are challenges to decision-making, particularly for viable tomato (Lycopersicon esculentum Mill) production in Zimbabwe. The objective of this study was to determine water requirements of tomato as a basis for developing generic calendar guidelines for a more efficient irrigation management in Harare, Zimbabwe. We explored the options of improving the traditional, dry and supplementary wet season irrigation practices. By considering the archived climate data of thirty years (1991-2021) for Harare; and model-simulated consumptive water use from 2014 to 2017 at Thornpark Research Station, together with the crop and soil characteristics; and the irrigation method; an irrigation calendar was developed using the AquaCrop model 5.0. The improved irrigation schedule for dry season tomato cultivation at 60% ETc, resulted in water use of 471.6 mm, with a yield of 3.40 t ha-1; compared to water use of 820 mm and a yield of 1.118 t ha-1; for the wet season. Through this model, we have been able to estimate the time interval between the previous irrigation and the next irrigation for any date in the growing season. Therefore, year-round irrigated tomato production may be feasible with an added yield advantage of 2.28 t ha-1 obtainable using water and rainy periods.