Evaluation of three plant species to control black scurf disease of Irish potato (Solanum tuberosum Linn.)

Abstract

Irish potato (Solanum tuberosum) is an important worldwide food crop and one of the most popular in Nigeria. Its abundance and successful yield have been immensely affected by black scurf disease caused by Rhizoctonia solani. Harnessing a cost-effective management of this pathogenic fungus, three botanical species Acalypha wilkesiana, Moringa oleifera and Carica papaya leaves, each at concentrations of 0 mg ml-1 (control), 25 mg ml-1, 50 mg ml-1 and 75 mg ml-1 were evaluated in vitro. The plant leaf extracts were prepared using methanol and were evaluated for their toxicity using agar well diffusion method. The fungus was isolated from spoilt Irish potato with black scurf symptoms. The results showed the presence of some phytochemicals in leaf extract of each of the plants tested. The three leaves extract independently inhibited mycelial growth of R. solani. The potency of all the plant extracts increased with the increase in concentration. The highest concentration (75 mg ml-1) of M. oleifera and C. papaya evaluated, gave the highest inhibitory effect of 0.81 mm and 1.63 mm respectively, which were not significantly different (p> 0.05), but was obviously different from A. wilkesiana (2.81 mm). Furthermore, M. oleifera extract gave the highest percentage of mycelial growth inhibition of the fungus in all grades of the concentrations evaluated, whereas A. wilkesiana showed the least. The leaves of the three species are therefore recommended for in vivo control of this fungus, owing to their proven efficacy and to their cheap availability.