Potato productivity in Kenya has remained below the potential due to the use of infected seed tubers especially by seed borne viruses. A study was carried out to asses the effectiveness of Positive Selection (PS) in managing seed borne potato viruses. Sprouted seed potato tubers of nine genotypes; three commercial varieties and six advanced International Potato Center (CIP) clones were screened in the field for two seasons, Field Generation Three (FG3) and Field Generation Four (FG4), respectively. In each season, experimental plots were divided into two sub-plots in which one sub-plot was planted with seed tubers sourced through Random Seed Selection (RSS) and the other with seed tuber sourced through Positive Selection (PS). Positive selection plots had low visual virus incidences, high number of tubers per hill and yield (t/ha) in both FG3 and FG4 growing seasons irrespective of the genotypes. ELISA test also revealed that Potato Virus S (PVS) (78%) was the most predominant virus followed by Potato Virus Y (PVY) (20%), Potato Leaf Roll Virus (PLRV) (16%) and Potato Virus M (PVM) (9%) in RSS plots either with single or multiple infections. Positive Selection plots recorded low virus incidences of PVS (47%), and PVY, PLRV and PVM were absent in the tubers tested with ELISA. This study concludes that Positive Selection is a good management strategy to manage the seed borne potato viruses, and if adopted, small holder farmers can reduce the yield losses arising from use of virus infected seed tubers.
Potato viruses are one of the major biotic factors causing high yield losses in potato production fields. In contrast to other disease causing pathogens, potato viruses’ lack well documented chemical control strategy and hence difficult to control once established in the field. The aim of the study was to assess the reaction of different potato genotypes to natural virus infection in the field. The present study was carried out on 12 potato genotypes (7 CIP clones and 5 commercial varieties) at the Field Station of the University of Nairobi, Upper Kabete campus Kenya in two potato growth seasons. A Randomized Complete Block Design (RCBD) of 4 replications was adopted with 12 treatments. Data was collected on percent crop emergence, disease incidence, growth and yield performance. At the end of season 2, tubers were sampled randomly per genotype and tested for presence of viruses using CIP DAS-ELISA kit. Analysis of variance on different parameters revealed varied response of each genotype to virus infection in the field in both seasons. Four potato viruses: PVS (67%), PVY (20%), PLRV (12%) and PVM (7%), were detected infecting tested potato tubers either as single or as multiple infections. The results revealed that four clones: 392797.22, 393371.157, 398190.200 and 397073.7 had high levels of tolerance to virus infection. Therefore further studies should be done to understand whether they possess quantitative or qualitative resistant traits to specific potato viruses and other biotic factors.
Common guava (Psidium guajava) and Pelargonium (Pelargonium zonale) have shown in-vitro antibacterial activity against Ralstonia pseudosolanacearum sp. nov. in previous studies. However, their phytochemical constituents and bioactive compounds against the pathogen have not been identified. The present study investigated the phytochemical components of P. guajava and P. zonale leaf extracts by phytochemical screening and gas chromatography-mass spectrometry (GC-MS). Phytochemical screening was done using different solvents while 100 mg of the dried ethanolic extract pastes from each plant sample was subjected to GC-MS analysis. Automated mass spectral deconvolution and identification system software (AMDIS, US) was used to analyze chromatograms and spectra representing individual compounds. Compound identification was performed by comparing each of the mass spectra with the database of NIST 11 (Gaithersburg, MD, USA), Wiley 7N (John Wiley, NY, USA) and by comparing the calculated Kovats linear retention indices using retention times of n-alkane series against the values in the NIST webbook. Flavonoids, phenols, alkaloids, saponins, terpenoids and tannins were detected in both plant samples. GC-MS analysis revealed presence of 35 and 26 compounds from P. zonale and P. guajava respectively. Both P. zonale and P. guajava had 7 similar compounds with antibacterial properties; Fumaric acid, Phytol, Pyrogallol, 4-Hydroxybenzoic acid, Shikimic acid, Protocatechuic acid and 3, 4, 5-Trihydroxybenzoic acid ethyl ester but P. zonale had one additional antibacterial compound; Lactic acid. In both cases, Shikimic acid had the highest percent peak areas of 3.2% for P. zonale and 6.8% P. guajava respectively. Therefore, P. zonale and P. guajava can serve as alternative sources of active ingredients for formulation of commercial botanicals for the management of bacterial wilt of potato.
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