Chemical control of Septoria lycopersici in vitro as first screening for fungicide efficacy studies

Abstract

The disease septoriose causes severe defoliation in tomato plants that can reach 100% leaf fall. Consequently, the losses are significant due to the decrease in photoassimilate production and sun scald on tomato fruits. To apply a fungicide the dose used must follow the fungicide label instructions to keep the resistance risk low and comply with current legislation. This work presents in vitro studies of 16 active ingredients (17 commercial products) at the recommended doses to control the tomato septoriose and the molecular identification of 26 Septoria lycopersici isolates performed with the ITS gene. In vitro test was performed at Petri dishes filled with 20 mL of maltextract medium (20 g/L malt extract and 20 g/L agar). 100 µL of spore suspension (105 spores/mL) were spread onto Petri dishes with the Drigalski loop. In their label dose, 10 µL of each fungicide was added at the centre of the Petri dishes to measure the inhibition halo formed. Petri dishes were incubated for 14 days at 25 ºC and 12h of photoperiod. Among the fungicides tested, 14 commercial products formed inhibition halo showing the dose used was able to control the spore germination which indicates efficacy of the fungicide and also an adequate dose to control the pathogen. Only cuprous oxide (1344 mg a.i./L), azoxystrobin (80 mg a.i./L) and thiophanate methyl (490 mg a.i. /L) were unable to prevent spore germination and did not form an inhibition halo. The Septoria isolates were identified as Septoria lycopersici and sequences were deposited at the Genbank. No variation was observed for the species when using ITS region.