Abstract
Late blight is caused by Phytopthora infestans (Mont.) de Bary which establishes quickly in Solanum esculentum L. (tomato); as a result, it makes the pathogen one of the most devastating plant diseases across the world. The control of late blight is difficult because P. infestans has advanced and complex enzymes and effecter molecules coded by avirulence genes. As such, a study was carried out at the University of Zimbabwe, Department of Plant Production Sciences and Technologies, between August 2018 and May 2019 to evaluate the efficacy of Moringa oleifera Lour. (moringa), Eucalyptus nigra R.T. Baker (gumtree), and Lantana camara L. (sensu lato) (lantana) extracts as biofungicides on late blight development on S. esculentum. The effect of acetone, ethyl acetate, and water extracts of M. oleifera, E. nigra, and L. camara on percent inhibition and radial growth were evaluated in the laboratory. In addition, the efficacy of different extract concentrations of M. oleifera, E. nigra, and L. camara L. on defence enzymes, disease incidence, disease severity, and yield parameters of S. esculentum were assessed in the in vivo experiment. Increasing concentration of the botanical extracts significantly ( p ≤ 0.05 ) reduced radial growth and increased percent inhibition of P. infestans. In addition, increasing botanical extract concentration significantly ( p ≤ 0.05 ) increased peroxidase (PОD), phenylalanine ammonia lyse (PAL), and polyphenol oxidase (PPO) activity. Disease incidence and severity were significantly ( p ≤ 0.05 ) reduced as the concentration of the botanical extracts increased. Similarly, marketable and total yield significantly ( p ≤ 0.05 ) increased with increase in the botanical extract concentration. Gas chromatography mass spectrometry (GCMS) revealed the presence of furfural, 5-methyl-4- (trifluoromethyl) pyrido, dodecanamide, cyclopentasiloxane, and decamethyl. From the research, it can be concluded that M. oleifera ethyl acetate, E. nigra ethyl acetate, and L. camara water extracts contain antifungal compounds and can be used as biofungicides in late blight management.
Highlights
It is reported that late blight caused by Phytopthora infestans L (Mont.) de Bary is one of the most devastating diseases of Solanum esculentum L.. e pathogen led to the Irish potato famine in the mid-nineteenth century in Ireland which resulted in the death of approximately one million people and emigration of an additional three million from Ireland [1]. e pathogen affects all stages of plant development
E. nigra ethyl acetate, M. oleifera, and L. camara water extracts showed a concentration-dependent reduction of radial growth of P. infestans. ere was a significant increase of radial growth as time increased from 3 to 12 days after incubation
Nagar et al [1] reported that these antifungal compounds bind and penetrate the surface of P. infestans resulting in denaturation of enzymes and proteins. is concurs with the work done by Ghannoum and Rice [17] on imidazole derivatives which had a complex mode of action, inhibiting synthesis of several membrane-bound enzymes as well as membrane lipid biosynthesis of pathogens
Summary
It is reported that late blight caused by Phytopthora infestans L (Mont.) de Bary is one of the most devastating diseases of Solanum esculentum L. (tomato). e pathogen led to the Irish potato famine in the mid-nineteenth century in Ireland which resulted in the death of approximately one million people and emigration of an additional three million from Ireland [1]. e pathogen affects all stages of plant development. Late blight can affect large leaves, stems, and dark oblivious spots on tomato fruits [3]. All these symptoms reduce the rate of photosynthesis and concomitantly reduce crop productivity and, on the other hand, increase household food insecurity. Reports from Cameroon, Kenya, and Pakistan showed that P. infestans has developed resistance to synthetic fungicides with active ingredients such as metalaxyl and chlorothalonil [2, 5, 6] leading to persistence and surveillance of S. esculentum leaf blight. Botanical extracts contain antifungal compounds such as phenols, flavonoids, alkaloids, quinones, saponins, tannins, and steroids [2] Their fungicidal properties against P. infestans have not yet been reported. Their fungicidal properties against P. infestans have not yet been reported. e antifungal compounds have both direct and indirect effects on P. infestans as they create a conducive environment for the establishment of antagonistic microbes [9]
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