Elvis Asare-Bediako

Violet diode laser-induced chlorophyll fluorescence: a tool for assessing mosaic disease severity in cassava (Manihot esculenta Crantz) cultivars

Violet diode laser-induced chlorophyll fluorescence was used in agronomical assessment (disease severity and average yield per plant). Because cassava (Manihot esculenta Crantz) is of economic importance, improved cultivars with various levels of affinity for cassava mosaic disease were investigated. Fluorescence data correlated with cassava mosaic disease severity levels and with the average yield per plant.

Characterising shoot and root system trait variability and contribution to genotypic variability in juvenile cassava (Manihot esculenta Crantz) plants

The development of cassava genotypes with root system traits that increase soil resource acquisition could increase yields on infertile soils but there are relatively few work that has quantified cassava root system architecture (RSA). We used an easily adaptable and inexpensive protocol to: (i) measure genotypic variation for RSA and shoot traits of a range of cassava genotypes; and (ii) identify candidate variables that contribute the largest share of variance. Cassava genotypes were grown in soil-filled pots, maintained at 70% field capacity. Shoot and RSA traits were measured on plants grown up to 30, 45 and 60 days. Multivariate analysis was used to determine major traits contributing to variation. The study showed that cassava roots are adventitious in origin consisting of a main root axis and orders of lateral roots, and therefore the historically used term “fibrous roots” are redundant currently not contributing to clarity. There were significant differences (P < 0.05) for traits evaluated. The highest relative root growth rate occurred over the first 30 days and ranged from 0.39 to 0.48 cm day−1. Root fresh weight was significantly correlated with other traits, including root length (r = 0.79), leaf area (r = 0.72), number of lower nodal roots (r = 0.60), indicating that direct selection based on these traits might be sufficient to improve root biomass. Up to the first six principal components explained over 80% of the total variation among the genotypes for the traits measured at 30, 45 and 60 days. Leaf area, root diameter and branching density-related traits were the most important traits contributing to variation. Selection of cassava genotypes based on shoot and root biomass, root diameter and branching density at juvenile growth stage could be successful predictors of nutrient and water-use efficiency in the field. Further studies are required to relate studied juvenile cassava root traits with the performance of field-grown-mature plant with regard to drought, nutrient-use efficiency and yield.

Effects of Gamma Irradiation on Agromorphological Characteristics of Okra (Abelmoschus esculentus L. Moench.)

Cultivation of okra in Ghana is challenged by low yield due to lack of improved varieties. Gamma irradiated okra seeds can generate genetic variability to improve the crop. Samples of 150 seeds, each of okra genotype, UCCC6, were irradiated with 400 Gy to 1000 Gy using cobalt 60 source at a dose rate exposure of 121.58 Gy/hr. There were 40 stands comprising single plant per stand in three replications per treatment in a randomized complete block design outlay. Seedling survival, plant height, number of leaves, stem diameter, number of branches, leaf length and width, days to 50% flowering, number of fruits, length and weight of fruit, number of seeds, and 100-seed weight decreased significantly ( ) with increasing doses of gamma rays. Seedling survival was highest (88%) at 400 Gy, followed by control (81%). However, 600 Gy, 800 Gy, and 1000 Gy had 61%, 41%, and 17% seedling survival, respectively, with LD50 at 720 Gy. Significant ( ) correlations existed between growth and yield components. Optimum growth and yield in okra were induced by 400 Gy but the higher doses had growth retardation effects and the induced variability can be assessed at M2 generation.

Farmers and Agricultural Extension Officers Perception of Striga gesnerioides (Willd.) Vatke Parasitism on Cowpea in the Upper East Region of Ghana

Cowpea [Vigna unguiculata (L.) Walp] is an important food security crop in Sub-Saharan Africa. However, cowpea production in some parts of this region is constrained by Striga gesnerioides (Willd.) Vatke infestation resulting in yield losses. This study assessed the farmers and agricultural extension officers (AEOs) perception of S. gesnerioides parasitism on cowpea in the Upper East Region of Ghana. In all, 200 respondents—179 cowpea farmers and 21 AEOs—in five cowpea growing districts were randomly sampled to answer closed- and opened-ended questions coupled with visit to cowpea farms. Majority of the farmer respondents were males between the ages of 21 and 60 with very little or no formal education. Almost all of the respondents could identify the parasitic weed, S. gesnerioides, but they lacked adequate knowledge of the parasitic effects on the host, cowpea plant. S. gesnerioides infestation was widespread and devastating in almost all the fields surveyed. Its effects on the host plants (cowpea) included stunted growth, leaf senescence, chlorosis, death of the crop, and reduced yield. Different management strategies employed by the farmers to contain the spread of the parasite include weeding (90%), application of manure (5.5%), and crop rotation and fallowing (4.0%). Both farmers and extension officers had very little knowledge on existence of S. gesnerioides resistant cowpea genotypes for cultivation. Farmers expressed the desire to cultivate Striga-resistant cowpea varieties when made accessible, since it is the most reliable and environmentally friendly method of controlling the parasitic weed.

Status of Begomoviruses in Ghana: The Case of Vegetables and Root and Tuber Crops

In developing countries, including Ghana, a greater proportion of the population depends on small-scale farming for their income and livelihood. Crops are frequently affected by a wide array of virus diseases showing varying degrees and kinds of symptoms including leaf curling and distortion, green or yellow foliar mosaic, stunting of plants, and reduced yields. An emerging and economically important group of plant viruses belonging to the genus Begomovirus, family Geminiviridae, are known to cause extreme yield reduction in a number of economically important crops in Ghana. These begomoviruses have a very wide host range, infecting dicotyledonous plants, and are transmitted by the whitefly vector, Bemisia tabaci (Genn.). Vegetable crops such as tomato, okra, and pepper and root and tuber crops such as cassava and sweet potato are greatly affected by begomoviruses resulting in substantial yield losses. Begomoviruses associated with tomato yellow leaf curl disease in Ghana include tomato leaf curl Kumasi virus (ToLCKuV), tomato leaf curl Ghana virus (ToLCGHV), tomato leaf curl Mali virus (ToLCMLV), and tomato leaf curl virus (TYLCuV). Pepper leaf curl diseases have been observed in pepper fields in several parts of Ghana, but begomoviruses associated with these diseases have not been characterized even though pepper veinal mottle virus (PVMV) and tomato yellow leaf curl virus (TYLCV) are the most widespread in the Western Africa subregion. The coat protein gene of cotton leaf curl Gezira virus (CLCuGV) and the DNA-β of satellite DNA have been amplified from diseased okra leaf samples collected from the Central Region of Ghana with characteristic leaf curl disease symptoms. Viruses are the second most important constraint to the production of sweet potato (Ipomoea batatas) after weevils, resulting yield losses by up to 90%. Sweet potato leaf curl virus has been detected in Ghana using both PCR and disease symptoms. Cassava mosaic disease (CMD), caused by cassava mosaic geminiviruses mainly African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV), is the most important constraint to the production of cassava in Ghana. In view of the increasing economic importance of begomoviruses in Ghana and worldwide, there is an urgent need for their effective management in order to improve yields and quality of crop plants. This requires accurate detection and identification procedures, stimulating intensive research efforts focused on virus biology, diversity, and epidemiology to develop successful control strategies. Inadequate plant virologists with requisite skills and knowledge in plant virology together with inadequate logistical and financial supports coupled with low institutional and governmental supports hinder the efforts in developing effective management strategies against the numerous viral diseases confronting the country.