Antifungal activity of metabolites obtained from microbial cultures against Cercospora kikuchii, causal agent of soybean purple seed stain

ROMERO, M.E.; CLAPS, M.P.; DIAZ, M.; MAGNAGO, S.; GONZALEZ ANTA, G.; GONZALEZ, V.; PLOPER, L.D.

Durban

Congreso; World Soybean Research Conference IX (WSRC IX); 2013

Protein Research Foundation

Soybean is considered the most important crop in Argentina. At present, this country is the third producer of soybean in the world, and the leading world exporter of soybean oil and soybean meal. Approximately 40 infectious diseases have been reported on soybean in Argentina. Some of them are endemic and usually do not produce damage, whereas others can cause important losses under favorable conditions. Disease management techniques include the use of resistant cultivars and fungicide applications. The ‘late-season disease complex’, a combination of various fungal diseases that affect soybean foliage, stems, pods, and seeds during the mid- to late-reproductive growth stages, has been shown to cause significant yield losses in Argentina, especially in the northwestern and eastern part of the country. Included in this complex is Cercospora blight, leaf spot and purple seed stain, caused by Cercospora kikuchii. In an effort to find alternatives to traditional pesticides, a project was started to evaluate the use of natural compounds to control soybean diseases. The fungicide activity of a microbial culture broth (CP1) was first tested in vitro against C. kikuchii cultures. Previous research had shown that CP1 was active against various bacteria and fungi. Minimum Inhibitory Concentration (MIC) was determined by occlusion of several concentrations of CP1 [Antimicrobial Units (AU) /mL] in 2% potato dextrose agar (PDA). CP1 effects on soybean seeds with purple stain symptoms were also studied. Seeds were first surface-disinfested, then treated with CP1 at concentrations of 0, 40 and 80 AU/mL during 15 min, and plated on PDA in 9-cm culture plates (ten seeds per plate). After incubation for 7 days at 27 ± 2ºC, C. kikuchii recovery and germination percentages were recorded. The experiment was repeated four times and means were compared with the Tukey test. C. kikuchii in vitro MIC was determined to be 8 AU/mL, which was similar to the value obtained with the commercial rate of a fungicide containing pyraclostrobin and thiophanate-methyl. Seed germination values of 96, 90, and 90% were recorded for symptomatic seeds treated with CP1 concentrations of 0, 40 and 80 AU/mL, respectively. Compared with the untreated control (0 AU/mL), treatments with 40 and 80 AU/mL significantly decreased C. kikuchii levels by 81 and 83%, respectively. These results show that the active compounds present in CP1 have fungicide activity against C. kikuchii and have the potential of being used in integrated management programs with low environmental impact.