Browsing by Author "Ocan, David"

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    Effect of Two Years of Conservation Agricultural Practices on Weed Seed Banks Evaluated Using Three Techniques
    (East African Nature and Science Organization, 2024-07-06) Otim, Godfrey Anyoni; Ocan, David; Kumakech, Alfred; Tumwebaze, Susan; Obia, Alfred
    Understanding the soil seed bank is very important when developing integrated weed management technologies and detecting the influence of crop management practices on weeds. In conventional weed control, farmers tend to focus on the above-ground, yet the above-ground vegetation is related to the below-ground soil seed bank. Several soil seed bank estimation methods have been used to estimate the soil seed bank, but varying results have been obtained under different field management practices and soil depths. In this study, we compared three methods for estimating the soil seed bank: seedling emergence method and two direct seed extraction methods (floatation and cloth bag) for determining weed seed density and diversity from different soil depths under conservation farming practices. The three methods had significant differences in estimating weed densities from the soil seed bank (p<0.001). The greenhouse seedling emergence method had a mean number of 5.06, cloth bag had 4.07 while floatation method had the lowest number of 3.38 per 300g of soil. The mean highest weed density was obtained from soil depth of 0-15 cm (5 weeds/300g vs 1.6 weeds/300g of soil from 15-30 cm depth). For soil seed bank diversity, cloth bag method had the highest mean value followed by greenhouse emergence and lastly floatation method with Simpsons diversity index of 2.72, 1.79 and 1.31, respectively. Shannon Weiner diversity index followed the same pattern for the three methods. The methods had different sensitivity to density and diversity and therefore greenhouse emergence method should always be combined with cloth bag method. The greenhouse emergency method detected a total of 26 weed species, cloth bag detected 22 weed species and Floatation method detected 18 weed species. Despite, the greenhouse emergence method detecting more species than the cloth bag at 26 and 22 weed species, respectively, it had a lower Simpson’s diversity index than the cloth bag method due to lower species evenness. Sampling of the entire soil plough layer of 0-30 cm depth for disturbed agricultural soils may produce the best results. Seasons significantly influenced soil seed bank diversity and not soil seed bank density where second season (B) significantly increased soil seed bank diversity. Soil cover practice through intercropping maize with soybean significantly reduced soil seed bank density and not diversity in both minimum and conventional tilled plots. This positive influence on weed density and diversity is a good indicator for integration into a weed management program
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    Influence of environment on soybean [Glycine max (L.) Merr.] resistance to groundnut leaf miner, Aproaerema modicella (Deventer) in Uganda
    (Journal of Plant Breeding and Crop Science, 2018) Pembele Ibanda, Angele; Karungi, Jeninah; Malinga, Geoffrey Maxwell; Adjumati Tanzito, Georges; Ocan, David; Badji, Arfang; Mwila, Natasha; Lapaka Odong, Thomas; Tukamuhabwa, Phinehas; Rubaihayo, Patrick
    Groundnut leaf miner (GLM) [Aproaerema modicella (Deventer)] is a serious problem for soybean cultivation in Uganda causing yield losses of up to 100%. The use of soybean [Glycine max (L.) Merr.] cultivars resistant to GLM attack is an important strategy in the integrated pest management program. The aim of this study was to determine the environment × genotype interaction influence on the soybean resistance traits to GLM attack. Eighteen soybean genotypes were evaluated for resistance to GLM attack. The experiment was set up using randomized complete block design replicated three times under natural pest infestation in Budaka (Eastern) and Arua (Northern) districts in Uganda. Data were subjected to analysis of variance, Pearson’s phenotypic correlation and cluster analysis. Highly significant (p < 0.001) differences among the genotypes were recorded for all the studied traits, except the number of pupae per plant which was significant (p < 0.05). GLM incidence and severity had significant negative correlations with rainfall and relative humidity. However, there were significant positive correlations between minimum temperature and GLM incidence as well as severity for most of the genotypes. Soybean genotypes VI046160 and VI046167 could be used as parents in breeding for resistance to GLM pest. Areas with high rainfall and humidity would be recommended for soybean production to minimize infestation by GLM.
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    Influence of environment on soybean [Glycine max (L.) Merr.] resistance to groundnut leaf miner, Aproaerema modicella (Deventer) in Uganda
    (Journal of Plant Breeding and Crop Science, 2018) Pembele Ibanda, Angele; Karungi, Jeninah; Malinga, Geoffrey Maxwell; Adjumati Tanzito, Georges; Ocan, David; Badji, Arfang; Mwila, Natasha; Lapaka Odong, Thomas; Tukamuhabwa, Phinehas; Rubaihayo, Patrick
    Groundnut leaf miner (GLM) [Aproaerema modicella (Deventer)] is a serious problem for soybean cultivation in Uganda causing yield losses of up to 100%. The use of soybean [Glycine max (L.) Merr.] cultivars resistant to GLM attack is an important strategy in the integrated pest management program. The aim of this study was to determine the environment × genotype interaction influence on the soybean resistance traits to GLM attack. Eighteen soybean genotypes were evaluated for resistance to GLM attack. The experiment was set up using randomized complete block design replicated three times under natural pest infestation in Budaka (Eastern) and Arua (Northern) districts in Uganda. Data were subjected to analysis of variance, Pearson’s phenotypic correlation and cluster analysis. Highly significant (p < 0.001) differences among the genotypes were recorded for all the studied traits, except the number of pupae per plant which was significant (p < 0.05). GLM incidence and severity had significant negative correlations with rainfall and relative humidity. However, there were significant positive correlations between minimum temperature and GLM incidence as well as severity for most of the genotypes. Soybean genotypes VI046160 and VI046167 could be used as parents in breeding for resistance to GLM pest. Areas with high rainfall and humidity would be recommended for soybean production to minimize infestation by GLM.
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    Relationship between 2-acetyl-1-pyrroline and aroma in Uganda rice populations with Oryza (barthi, glaberrima and sativa) backgrounds
    (African Journal of Biotechnology, 2019-11-30) Ocan, David; Odoch, Martin; Ibanda, Angele Pembele; Nuwamanya, Ephraim; Rubaihayo, Patrick Rutimbanzigu
    The sweet popcorn aroma conferred by 2-acetyl-1-pyrroline (2AP) is a highly economic trait of rice grain attracting premium price worldwide. This research study was conducted to determine the levels of 2AP in Ugandan rice lines with the aim of establishing a better understanding on the level and classes of 2AP and aroma phenotype. Concentration of 2AP was assayed using two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOF-MS) in tandem with sensory evaluation. Substantial variations in aroma intensity within and between the Uganda rice families were recorded. However, the levels of aroma variation were strongly influenced by the type of rice, and the breeding population it was derived from. Hence, three aroma based categories, namely, nonaromatic, moderately aromatic and highly aromatic were identified. GC with complementary sensory evaluation suggested a highly complex nature of rice aroma, as several rice lines were re-classified on the basis of this study. The 2AP contents and aroma intensity for genotypes with O. glaberrima were low compared to O. sativa and O. barthi. Genotypes of Supa 5, Supa 1052, Yasmin aromatic and MET 3 contained high 2AP levels whereas MET 16, MET 6, AGRA 78, AGRA 55, AGRA 41 and Sande TXD 306 exhibited moderate 2AP contents. Therefore, in developing an optimal breeding strategy aimed at improving the aroma in rice, quantitative information about 2AP and complementary sensory evaluation are a prerequisite.
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    Volatile Organic Compound Based Markers for the Aroma Trait of Rice Grain
    (Journal of Agricultural Science, 2020) Ocan, David; Rongrong, Zhang; Odoch, Martin; Nuwamanya, Ephraim; Ibanda, Angele P.; Odong, Thomas L.; Lamo, Jimmy; Fitzgerald, Anne M.; Daygon, Venea D.; Rubaihayo, Patrick R.
    A study was conducted to determine the volatile organic compounds (VOCs) associated with rice grain aroma in 37 commonly grown lines within Uganda, as well as elites. The aim of the study was to identify potential volatile biochemical markers, if any, for the rice grain aroma trait. Certified rice seeds were obtained from the Uganda National Crops Resources Research Institute germplasm collection. The seeds were sown into experimental plots, under field conditions and the mature paddy harvested. Polished rice grains were heated to 80 oC and the liberated VOCs subjected to untargeted metabolite analysis using gas chromatography-time-of-flight mass spectrometry. In total, nine functional groups were present; hydrocarbons, alcohols, ketones, aldehydes, N-containing compounds, S-containing compounds, esters, oxygen heterocycles and carboxylic acids. More specifically, 148 VOCs were identified across the 37 rice lines, of which 48 (32.4%) including 2-acetyl-1-pyrroline (2-AP) appeared to elucidate the difference between non-aromatic and aromatic rice. Furthermore, 41 (27.7%) VOCs were found to be significantly correlated with 2-AP abundance, the principle rice aroma compound. Amongst the 41 VOCs, only ten compounds were found to contribute highly towards variation in 2-AP abundance, indicative of their possible modulation roles in regard to rice aroma. Within the ten influential volatiles, three aroma active compounds; toluene, 1-hexanol, 2-ethyl and heptane, 2,2,4,6,6-pentamethyl- were established as the most reliable biochemical surrogates to the rice aroma trait. Thus, the aforementioned compounds may be used in rice breeding programme for enhancing development of the grain aroma trait.