He Efficacy of Selected Plant Extracts Against Aspergillus Flavus and Sitophilus Zeamais On Post-Harvest Management of Maize

Abstract

Maize (Zea mays L.) is the most important cereal crop in Kenya with 90% of the total population relying on it as the main staple food. Post-harvest losses in maize is caused by insect pests such Sitophilus zeamais and Fungi such Aspergillus and Fusarium among others. Post harvest losses by insect pests can sometimes be up to 90 percent. Synthetic chemicals are used to manage weevil infestation and control mould development in maize. However, chemical residues have been detected on the stored maize prior to consumption. Additionally, continuous uses of synthetic chemicals have led to development of pathogen/pest resistance reducing their effectiveness. This study therefore sought to evaluate a possible use of Ocimum kilimandscharicum essential oil to manage both Aspergillus flavus and Sitophilus zeamais. The study also determined the effect of pretreating baglets with aqueous extracts of A. indica and W. ugandensis to enhance efficacy of O. kilimandscharicum oil. Aspergillus flavus was isolated from maize samples using direct plating method, identified and pathogenicity tests done. Laboratory experiments were carried out to establish antimicrobial and insecticidal property of O. kilimandscharicum oil. Additionally on farm experiments were carried out to establish the oil’s effectiveness and longevity. Maize grains were treated with O. kilimandscharicum oil in the first experiment and in the second treated maize grains were put in miniature synthetic bags treated with aqueous extracts of A. indica and W. ugandensis and stored in a granary for six months. Ocimum kimandscharicum oil inhibited growth of A. flavus on petri dishes with concentration level above 100μl/ml of the essential oil having total inhibition. The size of zone of inhibition using disc diffusion method was significantly largest at 400μl/ml concentration level and lowest at 50μl/ml concentration level. However, the inhibition zones were significantly (p<0.0001) higher than in the control treatment. On-farm experiment revealed that O. kilimandscharicum oil doses were effective against S. zeamais as compared with untreated maize grains. However, 10 ml per 1kg of maize grains was the best dosage. Weight loss in maize grains was proportional to the number of holed grains. Replenishment of the oil after the third month (at 6 ml, 8 ml and 10 ml) reduced significantly (p<0.0001) the number of holed grains as well as weight loss. Pretreatment of baglets containing maize grains with aqueous extracts of A. indica and W. ugandensis significantly improved protection of maize grains treated with O. kilimandscharicum oil. From the results of this study it can be concluded that plant extracts can offer a possible substitute to synthetic chemicals in post harvest management of A. flavus and S. zeamais in stored maize. Use of essential oil of O. kilimandscharicum for post-harvest protection of maize grains against S. zeamais is therefore recommended.