Evaluation of Effects of Capsaicin in Suppression of Plant Pathogens in Tomatoes

Abstract

Chilies contain an active component known as capsaicin. It is hydrophobic and is the main capsaicinoid. Due to this component, chilies have obtained certain bioactive components such as antioxidants, phenolic and anti-microbial properties. Based on the mentioned characteristics, chilies exhibit bio pesticide characteristics which can be used to control pest and diseases in crops.In this study, four varieties of chilies were used, including habanero, bird’s eye, cayenne and bullet chilies. This was to assess the potential utilization of capsaicin in control of late blight fungal disease and bacteria speck in tomatoes To determine the capsaicin content in the four varieties, extraction of capsaicin from both oven-dried and fresh chilies was conducted using three different solvents at different amounts namely 100ml, 150ml and 200ml which included, methanol 99%, a mixture of methanol 99% and acetone and ethanol 99%. Evaluation of the antioxidant and total phenolic composition of capsaicin from the four varieties was analyzed using the Dipheny1-1-picrtyl-hydrazyl (DPPH) method and the absorbance at λmax 760nm measured on a spectrophotometer respectively. Determination of the sensitivity of capsaicin on late blight and bacterial speck in tomatoes was conducted using the agar dilution method. Moreover, determination of the antimicrobial properties of capsaicin from the four varieties of chilies was conducted by examining the minimum inhibitory concentration and the minimum bactericidal concentration. From extraction using different solvents at different amounts, the ideal solvent was said to be ethanol at 200ml giving an ideal extraction ratio of 1:10. Fresh habanero, bird’s eye, cayenne and bullet chilies had the highest amount of capsaicin respectively at an amount of 23.09 mg/g, 12.36mg/g, 7.37mg/g and 3.80mg/g respectively. Oven died habanero, bird’s eye, cayenne and bullet chilies had the highest amount of capsaicin respectively at an amount of 16.84mg/g, 9.60mg/g, 6.39mg/g and 3.21mg/g respectively. Therefore, fresh chilies had a higher amount of capsaicin than oven dried chilies. A positive correlation was observed between the amount of capsaicin present in the chili varieties and the bioactive components available in the chilies. Total phenolic was highest in both fresh and oven- dried habanero, bird’s eye, cayenne and bullet chilies respectively, having xi fresh chilies with a higher total phenolic than oven-dried chilies. Total phenolic ranged between 2923mg/g- 352mg/g in fresh chilies and 2274.5mg/g – 117mg/g in oven-dried chilies. Similarly, to total phenolic, there was a correlation between the amount of capsaicin in a variety and antioxidant activity in the same. Antioxidant activity was highest in both fresh and oven- dried habanero, bird’s eye, cayenne and bullet chilies respectively, having fresh chilies with a higher antioxidant activity than oven-dried chilies. Antioxidant activity ranged between 50%-86% in fresh chilies and 46%-74% in oven-dried chilies. Capsaicin from fresh chilies had a higher inhibition than oven-dried chilies. Bacterial speck was more susceptible to capsaicin than late blight across all varieties. Zone of inhibition for bacterial speck ranged between 0.96cm – 2.48cm in fresh chilies and 0.63cm – 1.95cm in oven-dried chili having habanero with highest zone of inhibition and bullet chili the lowest. Zone of inhibition for late blight ranged between 0.68cm – 2.22cm in fresh chilies and 0.56cm – 1.75cm in oven-dried chili having habanero with highest zone of inhibition and bullet chili the lowest as well. Capsaicin from fresh chilies had a higher MBC than oven-dried chilies. Late blight was more susceptible to the capsaicin than bacterial speck across all varieties. Minimum bactericidal concentration for late blight ranged between 0.01% - 0.18% in the first tube and 0.21% - 0.53% in the second tube incubate, using fresh chilies and 0.02% - 0.20 in the first tube and 0.29% - 0.55% in the second tube incubated, using oven-dried chili having habanero with highest minimum bactericidal concentration and bullet chili the lowest. Minimum bactericidal concentration for bacterial speck ranged between 0.01% - 0.19% in the first tube and 0.26% - 0.55% in the second tube incubate, using fresh chilies and 0.02% - 0.21% in the first tube and 0.30% - 0.61% in the second tube incubated, using oven-dried chili having habanero with highest minimum bactericidal concentration and bullet chili the lowest.as well. From the study, capsaicin from habanero exhibited the most preferred characteristics of bio pesticides from the four varieties tested. A positive correlation between amount of capsaicin and the efficiency of the bio active components characteristics as a bio pesticide was observed. Thus, the higher the amount of capsaicin, the higher the efficacy of capsaicin as a bio pesticide. More study of the efficacy of capsaicin in diseases in tomatoes under in vivo environment is recommended to evaluate the influence of environmental conditions in the bio pesticide properties