Abstract:
Irish potato (Solanum tuberosum L.) is the second most important food crop in Kenya after maize and a source of employment and income for many families. In 2015, potato cyst nematode (Globodera rostochiensis) was first reported in Kenya. This nematode is a quarantine pest in many countries because of its adverse effects on potato production. The current study was carried out to manage the nematode using host plant resistance, plant extracts of Datura stramonium and chicken manure. Cysts of G. rostochiensis were extracted from infested soil collected from Molo and Njoro sub Counties. Six commonly grown potato varieties ie Shangi, Kenya Karibu, Sherekea, Tigoni, Kenya Mpya and Dutch Robjin were screened for resistance against the nematode using pot experiments. Each pot with a tuber was inoculated with 25 cysts. Each variety was replicated 4 times and arranged in a Completely Randomised Design (CRD) on raised benches. After 10 weeks the cysts from each pot were counted and compared to the susceptible standard variety (Desiree). All the tested varieties were susceptible with a relative susceptibility score of either 2 or 3. However there was a significant difference in cyst population among the test varieties (F (5, 18) = 6.138; P = 0.002). The effects of aqueous extracts of leaves, roots and seeds of D. stramonium on mortality of second stage juveniles (J2s) of G. rostochiensis was tested in vitro in Egerton University, Department of Biological Sciences laboratory. Twenty freshly hatched J2s were exposed to 5 ml of each extract at
dilutions of 100, 50, 25 and 12.5% while distilled water was used as a control. The 100 and 50% dilutions were the most effective, achieving 100% mortality within 24 h of exposure. The root extract was more effective as compared to the seed and leaf extracts after 24 and 48 h of exposure, however there was no significant difference among the three extracts after 72 h of exposure. Chicken manure was mixed with sterilized soil at a rate of 1:2 w/w manure to soil and used to plant the susceptible standard variety, Desiree. Unamended soil was included as a control. The population of G. rostochiensis in the amended soil was significantly low when compared to the unamended soil at (t (6) =4.138, p< 0.006). The performance of the test varieties was subjected to one way ANOVA using SPSS program (version 24). The effect of the aqueous extracts was determined by a two way ANOVA using SPSS program (version 24) while the amended and unamended soils were compared using two tailed t- test. This study established that extracts of D. stramonium had nematicidal effects on the J2s. the extracts can be explored for formulation of a bionematicide. The chicken manure was effective in reduction of G. rostochiensis cysts and therefore can be recommended for integrated pest management on the farm.
