The Efficiency of Noni (Morinda citrifolia L.) Essential Oil on the Control of Leaf Spot Caused by Exserohilum turcicum in Maize Culture

Abstract

The objective of this work was to evaluate the efficiency of noni essential oil on the control of Exserohilum turcicum, a causative agent of Exserohilum spot in maize culture. In the sanitary test 400 seeds were incubated using the blotter test method. For the transmissibility test, the fragments of damaged leaves of seedlings were removed and put into a potato, dextrose and agar (PDA) culture environment. To verify the pathogenicity, Koch´s postulates were performed. In the phytotoxicity test different concentrations of noni oil were applied in maize seedlings. E. turcicum conidia were submitted to different concentrations of noni oil. In the preventive and curative tests noni essential oils were applied before and after the conidia inoculation, respectively. The results revealed the presence of fungi of the genres Aspergillus, Penicillium, Rhizopus, Fusarium, and Exserohilum in the maize seeds. The pathogenicity of E. turcicum and also the transmission of this fungus from the seeds to the maize seedlings was confirmed. The inhibition of conidia germination was proportional to the concentration increase. The preventive application of noni essential oil was the most efficient on the control of Exserohilum spot.

Enzymatic Activity in Essential Oil-Treated and Pathogen-Inoculated Corn Plants

“…In maize, essential oil of Cymbopogon citratus reduced the progress of the Curvularia leaf spot when applied preventively and it was also showed to inhibit 100% of conidia germination, but not mycelial growth of Curvularia lunata (Mourão et al, 2017). In addition, we have demonstrated that essential oil of Morinda citrifolia inhibited conidia germination of E. turcicum and reduced area under the disease progress curve in preventive applications in corn (Silva et al, 2017).…”

“…B. maydis and E. turcicum were chosen because their importance in limiting corn yield in the region of Gurupi (TO, Brazil). M. citrifolia was selected because we demonstrated previously its potential to control E. turcicum (Silva et al, 2017).…”

“…Total inhibition of urediniospore germination of Phakopsora pachyrhizi was also found after treatment with essential oils of Hyptis marrubioides, Aloysia gratissima and Cordia verbenacea and their curative application reduced area under the Asian rust curves by 33-41% (Silva et al, 2014). In maize, essential oil of Cymbopogon citratus reduced the progress of the Curvularia leaf spot when applied preventively and it was also showed to inhibit 100% of conidia germination, but not mycelial growth of Curvularia lunata (Mourão et al, 2017). In addition, we have demonstrated that essential oil of Morinda citrifolia inhibited conidia germination of E. turcicum and reduced area under the disease progress curve in preventive applications in corn (Silva et al, 2017).…”

“…Despite the reports of their effectiveness against several diseases, mechanisms of the action of essential oils remain elusive. Although a direct effect in pathogen is well documented (Pereira et al, 2012;Nguefack et al, 2013;Silva et al, 2014Silva et al, , 2017Mourão et al, 2017), an indirect effect, by inducing plant defenses, cannot be ruled out. Therefore, this work aimed to assess the effect of B. maydis and E. turcicum as well as the essential oil of M. citrifolia in the activity of defense enzymes in corn plants.…”

Potencial do óleo essencial de noni no controle preventivo e curativo da an-tracnose da mangueira

“…O fungo fitopatogênico foi obtido a partir do isolamento de lesões características de plantas de manga, cultivar "Manga Rosa". Sua patogenicidade foi comprovada através dos postulados de Koch, conforme Silva et al (2017).…”