Search for antifungal agents in extracts of Prosopis nigra useful in the control of Cercospora kikuchii and Septoria glycines

SEQUÍN, CHRISTIAN J.; SAMPIETRO, D.A.; SGARIGLIA, M.A.; SOBERÓN, J.R; CATALÁN, C.A.N.; ACEÑOLAZA, PABLO G.

Tucumán, Argentina

Congreso; IV JOINT MEETING OF THE BIOLOGY SOCIETIES OF ARGENTINA; 2020

TUCUMAN BIOLOGY ASSOCIATION

Soybean is affected by late season diseases produced by Cercospora kikuchii and Septoria glycines that lead to defoliation and yield losses due to a bad seed filling. These fungi are controlled with azole fungicides alone or in mixtures with strobilurins. The appearance of fungal resistance conducted to the increase in the doses and frequency of application of the fungicides. New antifungals are needed in order to overcome this problem. The aims of this work were: (1) The evaluation of the antifungal activity of extracts from Prosopis nigra against C. kikuchii and S. glycines. (2) The isolation and identification of the main metabolite responsible of the antifungal activity in the most bioactive extract. Leaves, bark and hearthwood of P. nigra collected in Paraná (Entre Ríos) were separated in portions that were extracted with methanol, ethyl acetate or dichloromethane. The extracts were evaporated to dryness and the residues tested on C. kikuchii and S. glycines by the disc diffusion method. Minimum inhibitory dose (MID) and diameter of inhibition at the MID were measured. The most bioactive extract was subjected to a bioassay guided isolation involving TLC bioautography, column chromatography (silica gel and Sephadex LH20) and preparative TLC. The identity of the bioactive metabolite was estblished by NMR. The anticercosporin activity was also evaluated. Difenoconazol was used as positive control. The leaf methanolic extract showed MID = 0.2 mg/disc on both fungi (DI = 18.5 mm, C. kikuchii; 20.5 mm, S. glycines). The remaining extracts were inactive or had higher MID values. Tryptamine was identified as the main antifungal constituent and had anticercosporin activity. It is promisory for control of C. kikuchii and S. glycines