Morphological and molecular identification of Pythium spp. isolated from common beans (Phaseolus vulgaris) infected with root rot disease

Common beans (Phaseolus vulgaris L.) is the main leguminous crop grown primarily by small-holder farmers in the East and South African countries. Pythium root rot disease is the major production constraints which results in yield losses of 70% to most commercial bean cultivars in eastern Africa. Study focused on ascertaining preliminary information on bean cultivation practices in Tanzania, morphological and molecular characterization and identification of Pythium species from infected beans plants and determining the relationship between soil pH and the occurrence and distribution of the Pythium spp. Soil samples and infected bean plants were collected by aseptic pathogenic isolation and DNA extraction. Universal primers (ITS1 and ITS4) were used for amplification and followed by sequencing. About 63.0% of farmers practiced sole beans cropping, 31.0% mixed cropping and 6.0% intercropping. Corn, banana, cassava, Irish potatoes and coffee were either mixed or intercropped with beans. Also, 52.4% of farmers use farm saved seeds and 92.9% do not use fertilizer in their bean fields. Eleven species of the Pythium spp. were identified: Pythium aphanidermatum, Pythium splendens, Pythium ultimum, Pythium attrantheridium, Pythium graminicola, Pythium oligandrum, Pythium dissotocum, Pythium irregurale, Pythium camurandrum, Pythium paroecandrum and Pythium acanthophoron. Phylogenetic analysis showed diversity and homogenity among the Pythium spp. across the collection area. A high incidence and wide distribution of Pythium species were recorded in soils in the 5.03 to 5.95 pH range. Key words: Incidence, internal transcribed spacer (ITS), leguminous, molecular characterization of pathogen.