Microbiology and Biotechnology
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Item INDUCTION OF SYSTEMIC ACQUIRED RESISTANCE AGAINST Ralstonia solanacearum IN IRISH POTATO(Chuka University, 2023-10) ATIENO MARGARET FAITHIrish potato (Solanum tubesorum) is an economically important crop throughout the world with large-scale production and consumption. Irish potato is rich in carbohydrates, vitamins and minerals, especially iron, magnesium and potassium. Irish potato production has been plagued by constraints such as lack of certified seeds, pests and diseases. Bacterial wilt caused by Ralstonia solanacearum is the major bacterial disease of potato resulting to 50 - 100% crop losses. Management of R. solanacearum is difficult since it has a wide host range and the fact that it is a soil borne pathogen. Several methods including biocontrol, chemical control, cultural practices, host resistance and phytosanitation have been used to manage R. solanacearum. However, there is no method that has been found to effectively control the disease but a combination of different methods have been reported to reduce the impact of the disease. Inducing systemic acquired resistance is another alternative to control bacterial wilt. Systemic acquired resistance is the response of a plant to a pathogen attack and confers long-lasting protection against a broad spectrum of microorganisms. Thus, this study determined the induction of systemic acquired resistance against bacterial wilt in Irish potato through injection of attenuated pathogen and non-pathogens. The ability of Escherichia coli, Saccharomyces cerevisiae and attenuated R. solanacearum to induce systemic acquired resistance against bacterial wilt of Irish potato was tested in the greenhouse. Attenuation assay was conducted using four levels of formaldehyde concentrations and incubation duration for attenuation of R.solanacearum using randomized complete block design. Randomised complete block design was also used to evaluate in-vivo effect of different treatments and varieties on R. solanacearum in the greenhouse. Bacterial wilt symptoms were observed and a rating scale of 0 - 6 was used to score for disease severity. Leaves of the treated plants were collected for salicylic acid quantification in the laboratory. Disease severity, colony count, amount of salicylic acid and tuber yield data were analysed using statistical analysis software version 9.4 to determine induction of systemic acquired resistance. Significant means were separated using Least Significant Difference test at 5% probability level. Result from this study showed that there was statistically significant effect (p < 0.05) of formaldehyde concentrations and incubation duration for attenuation of R. solanacearum. The results from attenuation of R. solanacearum showed that colony count ranged from 0.67 colony forming units (in 0.6% formaldehyde concentration and incubation duration of attenuation of two hours) to 233 colony forming units (in 0% formaldehyde concentration and incubation duration of attenuation of two hours). There was significant (p < 0.05) treatment effect on disease severity, salicylic acid levels and tuber yield of Irish potato. Higher disease severity was recorded in S. cerevisiae treatments (80%) followed by E. coli treatments (40%) while least disease severity was recorded in attenuated R. solanacearum treatments. Attenuated R. solanacearum induced the highest level of salicylic acid (3409.64 mg/kg of Irish potato leaves) while R. solanacearum induced the lowest (1222.74 mg/kg of Irish potato leaves). Irish potato plants with attenuated R. solanacearum treatment had the highest yield of tubers (0.5772 kg/plant) while those treated with S. cerevisiae treatments had the lowest (0.4840 kg/plant). This study concluded that attenuated R. solanacearum and E. coli triggered systemic acquired resistance in Irish potato plants thereby increasing the levels of salicylic acid, which reduced the negative impact of the disease in the plants. Induction of systemic acquired resistance is a viable method for induction of resistance against bacterial wilt in Irish potato. The study recommends the identification of the specific molecules involved in induction of resistance from attenuated R. solanacearum and E. coli and their utilization in the control of bacterial wilt in order to mitigate the huge loses that are caused by this disease.Item INCIDENCE AND PREVALENCE OF FUSARIUM WILT AND PHYTOCHEMICAL ANALYSIS OF CRUDE EXTRACTS OF Tithonia diversifolia (Hemsl.) A.Gray AND Kigelia africana (Lam.) Benth AND THEIR ANTIMICROBIAL ACTIVITIES AGAINST Fusarium oxysporum IN TOMATOES(Chuka University, 2020-12) Awere, Collince OmondiKenya is one of the leading countries in Africa in tomato production. Production of tomato is 14% of the total vegetable and 6.72% of the horticultural crops produced in the country. It is a source of food, foreign exchange earnings and source of employment and income. The major factor that reduces the growth and yield of tomato production in Kenya are pathogenic microorganisms. For instance, Fusarium oxysporum is among the fungal pathogens that destroy the xylem of the plant hence causing Fusarium wilt due to poor transportation of water to various parts of the plant. Besides, it persists in the soil environment for a long period thus continuously infecting healthy plants grown in the site. The management practices that are mostly used to control the pathogen are ineffective and environmentally unfriendly. Therefore, plant products with antimicrobial properties present an affordable alternative solution to control such persistent pathogens. The objective of this study was to determine the incidence and prevalence of Fusarium wilt and the phytochemical composition of Tithonia diversifolia and Kigelia africana and their antimicrobial activity against fungal pathogen F. oxysporum in tomatoes. Tithonia diversifolia and Kigelia africana plants were selected because of their wide medicinal use, distribution and availability. A preliminary survey was carried out in Mwea, Kirinyaga County which is among the most common areas where tomatoes are grown. Questionnaires were used to evaluate the farmers` knowledge, perception and management practices of Fusarium wilt disease. A total of 80 respondents were interviewed. K. africana and T. diversifolia plant samples were collected for phytochemical analysis. The samples were ground into a fine powder and extracted using water. Phytochemical screening of the crude extract was done. Soil was used for F. oxysporum pathogen isolation. Antimicrobial test disc soaked with plant extract was placed on to the media cultured with F. oxysporum and incubated at 28 oC for a week to allow growth. Analysis of the collected data was done using SAS version 9.4 for analysis of variance and further subjected to a post adhoc test with 𝛼 = 0.05 being considered significant. The results showed that the Rio Grande was the tomato variety widely grown; the preference for this variety was attributed due to its high marketability, high production, high quality, and early maturity. From the response, 92.5 % of the farmers had seen the symptoms of the pathogen while the rest had not seen the symptoms of the pathogen in tomatoes. The application of chemicals was widely used to control the pathogen, which contributes to environmental pollution. Screening of the plant extract revealed the presence of tannins, alkaloids, flavonoids, saponins, terpenoids, and glycosides. Each of the plant extract used had antimicrobial activity against F. oxysporum; this was due to the presence of phytochemicals that had an effect on the growth of the pathogen. K. africana exhibited the highest zone of inhibition while T. diversifolia had the lowest zones of inhibition. When each crude extract was used singly and in combination against the F. oxysporum, the zone of inhibition was found to be statistically significant at P< 0.05. The combined crude extract showed an increased antimicrobial activity against F. oxysporum. The results provide a potential application of the crude extract as an antifungal agent against F. oxysporum. It also provides scientific evidence that K. africana and T. diversifolia extract possess antifungal activity that can be used as a broad-spectrum in managing microbial diseases.