Department of Nuclear Agriculture and Radiation Processing

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    Biopesticide Control of Some Important Okra (Abelmoschus Esculentus (L.) Moench) Insect-Pests and Viral Diseases in Three Okra Cultivars
    (University of Ghana, 2020-10) Akama, C.K.A.
    The production, processing and marketing of Okra (Abelmoschus esculentus L. Moench), a vegetable valued for its rich nutritional and medicinal benefits, serves as an important means of employment and income generation to many peasant farmers. The production of the crop is, however, constrained by the incidence of pests (whitefly and flea beetle) and okra yellow vein mosaic virus [OYMV] and okra mosaic virus [OMV]) diseases. To overcome the health and environmental risks associated with the excessive use of synthetic agrochemicals, the predominant means of control of these pests and viral diseases, the efficacy of crude leaf extracts as biopesticides from Neem, Jathropha and Lemon grass on the incidence and severity of OMV and OYVMV as well as crop damage due to whitefly and flea beetle, were evaluated in three okra cultivars [F1 Kirene (F1K), FI Sahari (F1S) and Asontem (AST)]. Among the three plant extracts tested, Neem extract treatment induced significantly (p<0.05) the lowest mean count of whitefly [ASTNEM (18.91), F1KNEM (22.17), F1SNEM (24.49)] compared to Jathropha extracts [ASTJAT (27.99), F1KJAT (28.73), F1SJAT (28.74)] and Lemon grass extract treatments [ASTLEM (34.22), F1KLEM (32.77), F1SLEM (32.67)]. Similar results were obtained for mean population of flea beetle. With respect to insect pests damage to the okra cultivars, Neem extract caused significantly (p<0.05) the lowest severity of damage [F1KNEM (1.53), F1SNEM (1.58), ASTNEM (1.63)] compared to Jathropha extract treatment [F1SJAT (2.74), ASTJAT (2.75), F1KJAT (2.77)] and Lemon grass extract [F1SLEM (2.97), ASTLEM (3.64), F1KLEM (3.73)]. Similarly, the application of Neem extract significantly (p<0.05) reduced the mean incidence (21.84%) of the viral diseases than Lemon grass extract (25.28%), Jathropha extract (25.44%) and the Control (28.89%). In-vitro confirmation test using Enzyme-linked immunosorbent assay (ELISA) revealed that majority (86.67%) of the treatment combinations showed single infection of OMV disease while in 13.33% of the treatment combinations mixed-infection of OMV and OYVMV diseases was observed. In terms of yield levels, chemical pesticide treatment produced significantly (p<0.05) highest yield (186.92 kg/ha) compared to Neem extract treatment (144.81 kg/ha), Jathropha extract (139.06 kg/ha), Lemon grass extract (115.75 kg/ha) and the Control (94.02 kg/ha). However, Neem extract performed best among the tested plant extracts. Therefore, in a second experimental trial to ascertain the best efficacious dose for Neem extract application, varying concentrations of 20 ml/L, 30 ml/L and 40 ml/L were used and compared with the chemical “Akape” in the three okra cultivars (F1K, F1S and AST) instead of the 50ml/L applied in the first experimental trial. Treatment with “Akape” recorded significantly (p<0.05) the lowest mean whitefly populations than treatment with plant extracts. However, 20 ml/L Neem extract treatment produced significantly (p<0.05) lowest mean count of whitefly [F1KN1 (17.88), ASTN1 (23.95), F1SN1 (29.01)] compared to 40 ml/L Neem extract [F1KN3 (37.90), ASTN3 (39.57), F1SN3 (38.22)]. Similarly, although the application of the synthetic chemical (insecticide) “Akape” resulted in the best performance in reducing flea beetle populations, it was observed among the Neem extract concentrations, 20 ml/L treatment produced significantly (p < 0.05) lowest flea beetle mean count [F1KN1 (24.04), ASTN1 (25.61), F1SN1 (29.41)] compared to 30 ml/L [F1KN2 (49.89), ASTN2 (48.73), F1SN2 (51.92)] and 40 ml/L [F1KN3 (72.68), ASTN3 (65.88), F1SN3 (80.88)] treated okra cultivars. Okra cultivars treated with 20 ml/L Neem extract had significantly (p<0.05) lowest severity of insect pest damage compared to treatment with 40 ml/L Neem extract. Of the three concentrations of Neem extract applied, 20 ml/L (N1) significantly (p<0.05) reduced severity of mixed-infection of OMV and OYVMV) in all the three okra cultivars [ASTN1 (0.64), F1KN1 (0.84), F1SN1 (1.23)]. Yield of okra cultivars treated with chemical pesticide was significantly (p>0.05) highest (234kg/ha). However, yield obtained with 20 ml/L Neem extract treatment (207kg/ha) was significantly (p>0.05) highest compared to the other Neem extract doses. It is noteworthy that cultivar F1 Kirene recorded significant (p<0.05) the highest yield (207kg/ha) followed by F1 Sahari (139kg/ha) and Asontem (127kg/ha). From the obtained results, the cultivation of the okra cultivar F1 Kirene could be combined with Neem extract at a concentration of 20 ml/L to obtain effective disease and pests control for high yields.
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    Hybidization Studies in Okra (Abelmoschus spp (L.) Moench)
    (University of Ghana, 2016-07) Amitaaba, T
    Okra (Abelmoschus spp. L. Moench) is an important multi-purpose vegetable crop cultivated and consumed across all tropical and temperate regions of the world. In Ghana, it is popular in all ten regions and increasing quantities are exported to Europe in the fresh form. The crop has received little attention by way of breeding to produce varieties combining the most desirable qualities to boost local cultivation and export. Ten accessions of Abelmoschus spp., comprising two species, A. esculentus (T1, T2, T3, VT, ID and AG) and A. callei (KB, AM, YL and T4) collected from six geographical regions of Ghana were crossed in all possible combinations to assess inter-specific as well as intra-specific hybridisation between and within species. Reciprocal crosses were also carried out and the performances of their F1 offspring were evaluated against the respective parents for expression of heterosis for key quantitative traits including days to 50% germination, days to 50% flowering, plant height, fresh fruit weight, length of pod and number of seeds per pod. Genetic relatedness among the accessions and their progeny was established by way of a dendrogrom based on furthest neighbour method (Euclidean). All six accessions of Abelmoschus esculentus were able to hybridize with one another in both direct and reciprocal cross combinations with high degree of crossability index (CI) (45.71% to 90.32%). On the other hand, cross-compatibility among A. esculentus and A. callei was successful only in one direction when A. esculentus was used as females also with a CI between 34.48% and 60%. Parental lines T3 and T1 emerged as the most compatible female and male respectively. Crossability success was relatively high during early hours of the day but decreased continuously in subsequent hours. Ten parental accessions and 61 Fl progenies of A. esculentus and A.callei evaluated for 15 qualitative and 8 quantitative traits exhibited significant variations in all quantitative traits studied. Clustering pattern based on quantitative traits largely revealed no duplicates and clustering pattern especially among parental accessions, appears to reflect relationship based upon speciation as parental accessions belonging to A. caillei are clustered towards one end of the dendrogram, while members belonging to A. esculentus clustered towards the opposite end. Contributions of the three principal components were 45.98 %, 23.31 %, and 14.46% for the first (PC1), second (PC2) and third (PC3) respectively, with corresponding Eigen values of 3.21837, 1.63171 and 1.01212 respectively, cumulating into maximum of 83.75 % of total variance. These results demonstrate possibility of producing superior hybrids of okra through artificial cross-pollination. Key recommendations based on these findings include i) use of molecular markers to confirm results of morphological characterisation and also to better understand inheritance of qualitative traits. ii) Genes linked to agronomically important traits in okra should be genetically mapped through Quantitative Traits Loci (QTLs) to serve as a baseline data platform for researchers and breeders.iii) Further studies on inheritance of qualitative traits stretching to the F2 or even F3 generations should be carried out, preferably using molecular markers to fully understand the pattern of segregation with appropriate ratios.