Diversity of plant-parasitic nematodes associated with taro (Colocasia esculenta) under different agro-ecologies, soil-physico-chemical properties and agronomic practices in smallholder production in Central Kenya

Abstract

Summary Globally, tubers, including taro, are the main source of carbohydrates after cereals. Taro ( Colocasia esculenta (L.) Schott) is grown as a source of starch and income. However, production of taro is constrained by biotic factors especially plant-parasitic nematodes, which invade the corm compromising its quality. This study sought to determine the diversity of plant-parasitic nematodes affecting taro in relation to agroecological zones, soil physicochemical properties and agronomic practices in Murang’a and Kirinyaga regions of Central Kenya. A structured questionnaire was used to obtain data from taro farmers in three agroecological zones (AEZs), which included Lower Highland 1 (LH1), Upper Midland 2 (UM2), and Lower Midland 4 (LM4) within Murang’a and Kirinyaga Counties. Soil and diseased samples of roots and corms were obtained at depths of 15-30 cm in the taro rhizosphere for each of the selected farms for recovery of the nematodes. Shannon-Wienner ( H ’), Simpson ( λ ’) and Pielou ( J ’) indices were used to determine the community structure (diversity, richness, evenness) of the nematodes in the three agro ecologies and in the three sample types. The study established that 17 genera of nematodes were identified from the corms, soil and root samples. The order Tylenchida had the highest number of genera (86%) followed by Triplonchida and Dorylaimida orders with 7% each. The absolute frequency of the nematode genera differed significantly between the AEZs and the samples types except for the genus Trichodorus , Radopholus , Globodera and Longidorus . All the soil physicochemical parameters except nitrogen were negatively correlated with the nematode diversity indices. The information from this study is vital in the formulation of policies aimed at the control of plant-parasitic nematodes on taro to increase its yield.