The Screening And Safety Evaluation Of The Fungicide Seed Coating Formula And Its Effects On Damping-off In Tomato Seedlings

Tomato (Solanum lycopersicone) is one of the most popular vegetables in the world,widely cultivated in our country. Seedling damping-off is a serious and worldwide diseasein tomato, causing severe damage every year. In this paper, with seeds of a tomato cultivar‘Hezuo903’, we investigated the effect of fungicides coating treatment on seed vigor,seedling quality and the control of seedling damping-off disease. The main contents andresults were as follows:1. The pathogen of tomato seedling damping-off was isolated through general tissueseparation. It was identified as Pythium aphanidermatum by morphological observation,polymerase chain reaction (PCR) of ribosomal DNA internal transcribed spacer (ITS)regions as well as pathogenicity test. This pathogen exhibiting radiate colonial morphologyon potato dextrose agar (PDA) medium, had hyaline, nonseptate and branched hyphae,smooth archegonium and aplerotic oospore, which are accorded as the typicalcharacteristics of Pythium aphanidermatum. The sequence of its ITS region was99%homology with that of Pythium aphanidermatum accessed in GenBank.2. The laboratory toxicities of several fungicides widely used in controllingdamping-off disease were tested with the method of mycelial growth rate. Mefenoxam andpyraclostrobin were screened out for seed coating to control seedling damping-off causedby Pythium aphanidermatume. Effective concentration reducing mycelial growth to50%(EC50) of mefenoxam and pyraclostrobin to Pythium aphanidermatum was0.0003and3.4027μg·mL-1respectively. When combined these two fungicides at1:1ratio EC50reduced to0.0002μg·mL-1.3.The safety of coating seeds was evaluated by the Q2oxygen sensing technology,paper bed germination test, and the pot germination experiment. Film coating with0.6%mefenoxam significantly increased seed vigor and promoted seedling growth(P<0.05).Seed coating with low concentration pyraclostrobin inhibited seedling height whilepromoted stem diameter, which showed a slight effect for cultivating strong seedling. As awhole, seed coating with a combination of mefenoxam and pyraclostrobin at1:1ratio inhibited seedling growth.4. The control effect on seedling damping-off disease caused by Pythiumaphanidermatum was studied through an artificial inoculation test. In the artificialinoculation condition, the average emergence rate, incidence percentage of seedlingdamping-off disease and seedling rate for mefenoxam0.6%, were88%,2.3%and86.0%,respectively; which had reached an extremely remarkable level(P<0.01) compared withuntreated control36%,42.6%and20.7%. The seedling rates for pyraclostrobin0.1%,0.2%and0.4%were all below80%, which meant unsatisfactory effect for controllingdamping-off disease and keeping seedlings.