Biocidal potential of Three Plant Extracts on Rhizopus stolonifer, Causal Organism of Irish Potato (Solanum tuberosum L.) Tuber Rot

Abstract

Research study was carried out to assess the biocidal effect of aqueous extracts of Curcuma longa, Zingiber officinale, Citrus limon peel and synthetic fungicide Mancozeb against Rhizopus stolonifer using the poisoned food technique on PDA. Various concentrations (50, 75, and 100%) of extracts from the rhizomes of C. longa, Z. officinale, the peel of C. limon and Mancozeb (0.002%) significantly inhibited the mycelia growth of R. stolonifer after 3 days. Effects of the synthetic fungicide (Mancozeb) comparative to the plant extracts were also determined. Although the extracts showed varying degrees of antifungal efficacy, 100% concentration of Z. officinale (58.96%) proved to be more potent against R. stolonifer than the other plant extracts but was lower and significantly different when compared with Mancozeb (73.31%) at (P≤0.05) after 3 days. Extracts of C. longa and C. limon peel showed a lower inhibition level ranging from 45.01% to 56.98% and 9.57% to 18.73% respectively and were significantly different when compared with Mancozeb at (P≤0.05). Inhibition of fungal growth increased with a corresponding increase in extract concentration and days. The plant leaf extracts effectively inhibited the mycelial growth of pathogen in vitro after 3 days. In vivo study was carried out using spore suspensions of R. stolonifer. Fresh, healthy and surface sterilized Irish potato tubers were inoculated with 6.4 x 104 spores/ml and treated with aqueous extracts of C. longa, Z. officinale and C. limon peel after 24 hours. The result showed that all plant extracts had significant effect on disease severity in tubers inoculated with R. stolonifer. However, 100% concentration of Z. officinale gave the best rot reduction caused by R. stolonifer with severity score of 0.33 but it was not significantly different at (p<0.05) from mancozeb which had a severity score of 0.67. However, they were significantly different at (p<0.05) from the inoculated control (3.33). There were variations in weight loss but no significant difference was observed among the various treatment methods adopted.