Distribution and diversity of pythium spp. in indigenous forests and adjacent farm lands in Taita and Embu districts in Kenya

Abstract

Pythium is a water mould fungus which survive as a parasite, saprophyte or both. Pythium spp. play important ecological services like recycling of both Carbon and mineral nutrients for continued plant growth. Members of this genus are ubiquitous and found in soil, water, plants and animal substrate. Spatial distribution and species diversity of Pythium were studied with aim of determining the effects of intensive agricultural practices on distribution and diversity. Agricultural intensification interferes with the natural processes occurring within the soil and destroys useful bacteria and fungi, and other organisms leading to increase in parasitic species like Pythium. Application of agrochemicals like fertilizers, pesticides and fungicides as well as continuous cropping interferes with natural processes in the soil ecosystem leading to change in the number of Pythium species in the soil (Burge, 1988). The possibility of using Pythium as environmental quality indicator is considered as one important aspect of the study since their distribution is associated with a particular environmental condition, that the presence or absence of such condition means its presence or absence (Paoletti et al.,1991). Land use practices in the two benchmark sites form a gradient of land use intensities drawn from the inputs which is perfect for testing the significance on the difference in distribution and diversity. Each benchmark site was divided into windows, sampling plots and sampling points where soil samples were collected. Using the soil samples collected from Embu in lrangi forest and Taita in Ngangao forest, the presence of Pythium species propagules were tested by attempting to isolate species of the genera using baiting techniques. The growing mycelium were verified directly by water mounts in a Microscope or transferred from the bait to the isolation media CMA (Com Meal Agar) amended with antibiotic Chloramphenicol (20mg/L) and Benomyl (10mg/L). To get data on distribution of Pythium at each sampling point, soil was collected at different depths. The isolates were characterized using morphological features in order to identify them tospecies level as guided by 'Monograph of genus Pythium' (Van Der Plaats - Niterink 1983). Eighteen Pythium species were collected in Embu and ten species in Taita. This shows that Embu has a richer diversity than Taita. Over 20 morpho species whose identification was not certain were isolated also in both Embu and Taita. ANa VA analysis of deviance table shows that dispersion of Pythium in Taita based on land use system is significant at p~0.04927 at a=O.05. Also, it was found that Chances of encountering Pythium increases significantly ith increase in carbon in Embu (p ~0.01830) (fig.7), and nitrogen concentration (~0.0003518).