Browsing by Author "Marfo, Esther Agyemang"

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    Prevalence and identification of yam viruses responsible for seed yam degeneration in the Ejurasekyedumase and Atebubu-Amantin Districts of Ghana
    (November, 2018) Marfo, Esther Agyemang;
    Yam viruses are reported to be widespread in all areas where yam is grown. In Ghana, viral diseases are known to cause about 50% of yield reduction on yam. It was for this reason that this research was carried out to manage yam viruses in Ghana. Surveys were conducted in the 2015 and 2016 cropping seasons in two major growing districts, Ejura-Sekyedumase and AtebubuAmantin of Ghana to determine the prevalence of yam virus. There was the need to identify the specific viruses producing the symptoms that were observed during the survey, as such symptomatic leaf samples were taken for analysis at the laboratory using RT-PCR. Out of the 40 leaf samples collected from each district, Ejura-Sekyedumase District had six mixed infections for both Yam mosaic virus (YMV) and Yam mild mosaic virus (YMMV) while eight single infections were recorded for YMMV. Atebubu-Amantin District had 10 mixed infections for both viruses and eight single infections for YMV. Molecular-based diagnostics techniques were also employed to monitor the health status of seven plants (Diosecorea rotundata Poir) established from positive selection, of which five of them did not amplify for any of the two viruses tested while two amplified for both viruses that were tested. Seed yams (‘Dente’, ‘Pona’ and ‘Laribako’) selected in 2015 from symptomless or mildly infected plants (positive selection), as well as those purchased from the Ejura market (farmer practice) and those selected from field diseased plants were established in field experiments in 2016 and 2017 cropping seasons at Ejura and Fumesua using a 3 x 3 factorial in randomized complete block design. The performances of the three seed yam sources were compared for their reaction to yam mosaic virus infection and tuber yield. The three white yam (D. rotundata) varieties used were; ‘Dente’, ‘Pona’ and ‘Laribako’. Plants raised from positive selection performed significantly (P<0.05) better with least virus percentage infection and disease severity scores irrespective of the variety. Positiveiii selection Dente out-yielded farmer practice Dente and diseased Dente by 35 and 66.7% respectively in the 2016 cropping season at Ejura. Similar result was obtained at Fumesua with positive selection Dente out-yielding farmer practice and diseased seed yams by 32.6 and 60.7% respectively. In the 2017 cropping season, even though there was general yield reduction indicating loss of seed yam quality with time, similar trend occurred with positive selection plants performing significantly (P<0.05) better with least virus incidence and severity scores at both locations. Positive selection Laribako produced the highest yield at both locations. With farmers’ current practice of recycling seed yams from one season to another, this study showed that positive selection was a good approach to reducing virus load in farmers’ farms as well as reducing seed yam degeneration while maintaining fairly good yields.