Antifungal efficacy of Hyptis suaveolens and Rumex nepalensis extracts against Alternaria solani: An approach for bio-pesticides

Globally, early blight is one of the serious threats leading to significant reduction of potato yield. The use of plant extracts in the management of plant diseases is gaining global significance. Hence, the main objective of this study was to determine the antifungal activity of Rumex nepalensis and Hyptis suaveolens (L.) Poiteau extracts against the fungal pathogen (Alternaria solani) causing early blight in potato. The study employed experimental research method with completely randomized design wherein the plant extracts were tested against the pathogen through in vitro and in vivo studies. In the in vitro study, results from the poison food technique showed that the aqueous extracts of aerial parts of R.nepalensis (RnA) was the most efficient in reducing the diameter growth of the fungus than R.nepalensis roots (RnR) and H. suaveolens (HS). The efficacy of the extracts was in the decreasing order of RnA > RnR > HS at all concentrations (20%, 40% and 60%). The fungal biomass extraction showed similar trend with RnA having the highest Initial Activity on Biomass (IAB) followed by RnR and HS. Interestingly, the fungal biomass growth decreased with increase in concentration of all three extracts. In the in vivo technique, plants treated with RnA prior to infection exhibited better tolerance to the test pathogen. Comparatively, RnA showed less Disease Severity Index (DSI) than RnR and HS for both preventive and curative controls. Consequently, the percentage reduction of disease was recorded highest in RnA preventive control (71.43%) compared to other treatments. The preventive control showed lower DSI and higher reduction of disease compared to the curative control. Although all three extracts showed some degree of antifungal activity against Alternaria solani, RnA showed higher activity in both in vitro and in vivo treatments. Therefore, RnA extracts can be used as a potential bio-fungicide for the control of early blight in potato.