| dc.description.abstract | Increased human population has led to increased vulnerabilities to hunger and reduced sources of affordable food. Sweet potato (Ipomoea batatas L.) is a root vegetable with large, starchy, tuberous roots, consumed worldwide. It is a potential food security crop, with high nutritional and economic value. Production of sweet potatoes in Kenya is low due to disease constraints such as sweet potato leaf spot (SPLS). Fungal SPLS results in reduced tuber yield, since the pathogen attacks photosynthetic leaves, causing premature defoliation and senescence. Information on disease incidence, pathogen genetic variability and susceptibility of some locally cultivated varieties in western Kenya is not fully documented. A characterization and varietal susceptibility study of SPLS, presents an opportunity for increased production, improved food security and enhanced income. This study evaluated SPLS disease incidence, characterized the causative pathogens, assessed susceptibility of locally grown varieties to the infection and evaluated farmers’ indigenous knowledge
to sweet potato diseases. Infected leaf samples were obtained from farmers’ fields in Kabondo Kasipul and Rangwe Sub-Counties in Homa Bay County, and in Kajulu in Kisumu East Sub-County of Kisumu County where active cultivation of sweet potatoes is done. A multi-stage sampling design was used to identify exact sampling points at farmers’ fields based on acreage of sweet potato grown. At each site, disease incidence and severity was evaluated in quadrats thrown on prescribed scales within the habitable space of diseased plants. Diseased leaf samples were collected and transferred to the Botany laboratory at Jaramogi Oginga Odinga University of Science and Technology, where pathogen isolation and characterization experiments were arranged in Completely Randomized Design with three replicates. Controlled pot-experiments were conducted in a green house to test the susceptibility of 1 farmer-held and 2 improved sweet potato varieties to one isolated SPLS pathogen (NF4 - Accession No. OK560339.1). The experiments were arranged in Randomized Complete Block Design with three replicates. A structured questionnaire was administered to 66 farmers to survey farmer’s indigenous and perception of the disease. Data on disease incidence, severity and susceptibility were transformed into percentages and subjected to Analysis of Variance using General Linear Model and means separated using Least Significant Difference (LSD0.05) on Scientific Analysis System (SAS) version 9.4. Morphological data was numerically transformed on MS Excel and hierarchical relationships determined using a dendogram. Genomic DNA was extracted from pure samples, and the Internal Transcribed Spacer (ITS) gene amplified by Polymerase Chain Reaction (PCR), followed by sequencing at Macrogen, UK. Molecular data were assembled and trimmed on CLC Main Workbench (CLC Bio, Version 6.8.3). Assembled sequences were transferred to MEGA Version 6 and aligned using CLUSTAL W. Data on farmer indigenous knowledge was analyzed using Chi-Square (χ2 ) test on SPSS version 25. Results on disease incidence ranged from 11% to 30.38% at Kakelo and Kamollo villages respectively, while SPLS severity was significantly (p<0.0001) highest at Kokwanyo (28.37%) and lowest at Rapogi (15.27%). A total of 12 morphologically different fungal pathogens were isolated on Potato Dextrose Agar. Molecular identification of the fungi revealed Fusarium chlamydosporum, Fusarium proliferatum and Fusarium verticillioides as agents of SPLS infection. Variety 2 (Odinga) was more susceptible to the fungal pathogen NF4, with 33.18% leaf spots while variety 3 (Mugande) had the lowest susceptibility. Most farmers (90.91%) reported occurrence of sweet potato diseases on their farms, but more females were able to differentiate between the diseases. Integrated disease management approach should be adopted for improved sweet potato yields and the less susceptible Mugande variety be adopted by farmers. Farmer awareness programs on SPLS management is recommended. Policy makers should adopt the findings of this study for production of disease-free quality tubers for food, export and value
addition to generate income. | en_US |
