Effects of air pollution on tomato plants (Lycopersicon esculentum) grown along Waiyaki highway in Nairobi County, Kenya

Vehicle exhaust fumes emission, as one of leading major source among smoke producing air pollutants, was examined in this study. Nairobi, a mega-city with increasingly high levels of air pollution was studied with special emphasis on one of its roads, Waiyaki Highway. Objectives were to find if there is air pollution, air pollution effects growth and stress of plants. This road was investigated to gain scientific understanding of the effects of vehicle fumes on plants. Hotspots (ICEA building, ABC Place, and Kangemi Market), had unique characteristics, which included moribund trees or plants, dark tree trunks and leaves due to air pollution. Lycopersicon esculentum Mill., (1768), tomato plants that is highly susceptible to air pollution was exposed to the air at selected sites along the highway. Four experiments were set, (three as test experiments and one, control) using a raised platform containing twelve plants in polythene bags and irrigated frequently. For the study analysis, data was collection on pollution level, seed germination rate, height growth, leaf length, flower count, biomass, stress and stomata account for three months. The data was analysed using Analysis of Variance (ANOVA), Kruskal Wallis and Poisson distribution in Genestat software. Means were separated by use of Least Significant Difference (LSD) α = 0.05. The Waiyaki Highway had consistence air pollution, for whole period of this study (averaging PM10 42.6µgm/m3 for test sites). The control experiment at NARL had similar environmental conditions but no significant air pollution (PM10 0.6µgm/m3). The control experiment was protected from air pollution related to vehicle fumes by long distance away from the road plus canopies of trees thriving in between to shield experimental plants. Seed germination rate results, showed that, there were no significant differences at (P < 0.05). Growth pattern was determined using height, which proved significantly different at P < 0.05. Leaf length of tomato plants was not significantly different where P < 0.05. Results of flower count showed significantly difference (P < 0.05). Stress was significantly different where P < 0.05. Plants biomass was not significantly different between experiments (P < 0.05). Open stomata in upper epidermis was significantly different. Air pollution affects plants as evidenced by significance noticed on height growth, number of flowers, plant stress and distribution and status of stomata. Leaves elongation is independent of air pollution. Plants in air pollution had different height to control, more flowers and were stressed more due air pollution. Plants in air polluted environment had high stomata density underneath leaf than control and no open stomata on the upper epidermis. Stomata number, position and, if open or closed on leaves of plants is a quick way of determining air pollution. Three months was not enough for air pollution to affect biomass production. It is important for precise threshold levels of air pollution effects to plants be determined. Comprehensive study on effects of air pollution on seed germination, height growth, leaf growth, biomass and plants physiological behaviour in heavily air polluted environment be instituted on long term basis.