Evaluation of plant extracts for the management of Cercospora leaf spot of groundnut (Arachis hypogaea L.)

Abstract

Groundnut (Arachis hypogaea L.) is a leguminous crop with high economic and nutritional value. However, increased production is hampered by Cercospora leaf spot (CLS) caused by Cercospora arachidicola and Cercosporidium personatum. Studies were conducted in vitro and in vivo to evaluate the efficacy of aqueous extracts of desert date seed (DDSE), neem seed (NSE), jatropha seed (JSE) and tobacco leaf (TLE) for the management of CLS. The antifungal activities of 25, 50, 75 and 100 g/l concentrations of each of the plant extracts was assessed in vitro on potato dextrose agar using the food poison technique. The field study was a factorial experiment consisting of 18 treatments laid in a Randomised Complete Block Design with four replications over two cropping seasons. The in vitro results revealed that all the botanicals at 100 g/l recorded the highest inhibition percentages. DDSE at 100 g/l significantly (P < 0.001) inhibited the highest mycelia growths compared to other levels of plant extracts used with inhibition percentages of 90.33 and 84.96% in C. arachidicola and C. personatum, respectively. Three out of the four aqueous extracts (DDSE, NSE and JSE) at 100 g/l significantly (P < 0.05) lowered disease incidence, severity and defoliation in the field and increased yield. Pod yield was significantly (P < 0.05) higher in plants treated with JSE, NSE, DDSE and Topsin-M, compared to those treated with TLE and the negative control plants. For most of the parameters, DDSE produced similar results as Topsin-M followed by NSE and JSE. Farmers can adopt DDSE, NSE and JSE as alternatives to fungicides leading to minimal effect on the environment since they are biodegradable.    Key words: Cercospora leaf spot, plant extracts, groundnut, incidence, severity, aqueous.