Effects of Triazole and Strobilurin-Based Fungicides on Fusarium culmorum on Wheat

Fusarium culmorum is an important pathogen, that causes pre and post-emergence death in seedlings from both seed and soil-borne sources, in addition to causing root, crown root and wheat head infections on wheat. Treatment of seeds with fungicides is especially important to inhibit seed originated seedling infections when cultural methods are ineffective against the infection of the pathogen in root and crown root and the lack of completely resistant wheat cultivars against this pathogen. The efficiency of fungicides with prothioconazole + tebuconazole and triticonazole + pyraclostrobin active ingredients, licensed on Fusarium spp. in seeds, on seed originated seedling infections of F. culmorum is determined in vitro and in vivo conditions. Seeds of Flamura-85 bread wheat cultivar, naturally infected with F. culmorum S-14, were used in this study. The effect of treating seeds naturally infected with F. culmorum S-14 with fungicides on seed germination, root length, coleoptile length and disease severity was determined in the experiment in vitro. Germination rate of the seed was determined as 68% for triticonazole + pyraclostrobin and 43% for prothioconazole + tebuconazole, while disease severity was 42.70% and 61.30%, respectively. While both fungicides were determined to be effective on the disease severity, the effect of triticonazole + pyraclostrobin on disease severity was found to be higher than prothioconazole + tebuconazole. Because of the higher rate of effectiveness of triticonazole + pyraclostrobin to prevent seed-borne infections in vitro conditions, it was determined that the fungicide causes an increase in germination rate with wet and dry weight of the seed, while significantly decreasing the disease severity, in the tests to determine the effectiveness of the fungicide in vivo conditions.


Introduction
Fusarium culmorum (W.G.Smith) Saccardo is an important soil/seed borne pathogen and causes head blight, root and root crown rot in wheat (Scherm et al., 2013).With the germination of conidies or long living chlamydospores in the period from wheat seed germination to spike emergence, infections might occur in the root, root crown and stem.Infections in seedling period mostly occur in coleoptile and/or root crown, because of 3-4 year longevity of pathogen chlamydospores in the soil.Infection symptoms, proceeding with the development of the plant, can also be observed after the tillering period.Bleached heads start to form on the plants with water stress related to the increase in the transpiration speed of plants.In Turkey, 50% crop loss is sometimes recorded in regions with high disease severity (Akgül, 2008;Anonymous, 2008).In highly humid Thrace region, it is the cause of economical losses in wheat by causing pre and post-emergence deaths originating from soil/seed-borne seedling infections.Cultural practices are not sufficient to control F. culmorum and natural conditions are suitable for disease development and there is no fully resistant cultivar against the agent (Scherm et al., 2013;Arıcı, 2006).Thus, it is obligatory to use fungicides to control the agent.Fungicide treatment of seeds against root and root crown infections of the pathogen is important to prevent seed-borne infections (Cook, 1986).When the fungicides from triazole group fungicides in Sterol biosynthesis inhibitors (SBI) fungicides such as prothioconazole, tebuconazole, and triticonazole and carboxin from succinate dehidrogenase inhibitor (SDHI), with systemic impact mechanism, are applied on the seed surface, they can effectively protect the seeds from soil/seed borne infections of F. culmorum by moving to cotyledon, embryo, rootlet and endosperm using the humidity in the soil (Delen, 2016)

Statisti
Effect of f NY).significant, wet weight of the seedling after fungicide treatment was found to be higher than negative control.When the effect of fungicide on dry weight of the seedlings was investigated, it was determined that the dry weight of the seedling was 0.06 g in negative control, 0.04 g in positive control and 0.06 g after triticonazole + pyraclostrobin treatment, with a significant difference between positive control and triticonazole + pyraclostrobin (P < 0.05).Disease severity was 6.18% in negative control, 32.03% in positive control and 8.75% in triticonazole + pyraclostrobin treatment.The effect of the fungicide on the disease was found to be 72.68% and there was a significant difference between the fungicide and positive control (P < 0.05).Fungicide treatment was found to be very effective at decreasing the develpment of the disease and there was no significant difference between the fungicide and negative control.Pathogen was obtained from the re-isolation of necrosis on the root and root crown of the seedlings.Note.* Differences between means with different letters in the same column are significant according to Tukey multiple comparison test (P < 0.05).

Discussion
F. culmorum causes regression in development of root and stem, decrease in tillering, head formation and kernel formation by limiting water and nutrition movement in the plant with relation to infection severity (Wojciechowski et al., 1997;Bağcı et al., 2001;Hekimhan et al., 2005;Mert-Türk et al., 2013;Scherm et al., 2013).Crop losses are economically important because of the severe infections especially in seedling period, in our country (Finci, 1979;Demirci, 2003;Arıcı, 2006;Araz et al., 2009;Köycü & Özer, 2014).Thus, knowing the effectiveness of fungicides used against F. culmorum on disease severity is important to prevent plant deaths from seed-borne infections especially in pre and post-emergence in infected seeds.Hence, treatment of the seeds infected with F. culmorum by fungicides with carboxin, difenoconazole, diniconazole, tebuconazole, thiabendazole, fludioxonil + metalaxyl-M and tebuconazole + metalaxyl-M active ingredients is known to be effective on disease severity and increases product quality (Arslan & Baykal 2002;Balmas et al., 2006;Hekimhan et al., 2007;Pariyar et al., 2014;Toçan, 2014;Köycü & Sukut, 2018), while the effectiveness of the fungicides can change in relation to the sensitivity of the cultivar and different isolates of the pathogen (Akgül 2008;Spolti et al., 2013;Serfling & Ordon, 2014).Likewise, Akgül (2008) has found that the effect of prothioconazole + tebuconazole (Lamardor FS 400, Bayer Crop Science) on seedlings developed from treated seeds against F. culmorum has changed between 11-12%.In our study, we found that the same fungicide's effectiveness was around 27% on the pathogen.
Water content of the wheat seedlings can be determined with wet weight measurement, while the organic and inorganic compounds (nutritinal elements like phosphorus, potassium, calcium, copper, magnesium) without water can be determined with dry weight measurement (Karman, 2012).According to the results of our study, we concluded that the increase in wet and dry weight of the seedlings caused by the positive effect of triticonazole + pyraclostrobin would also increase the yield in field conditions.

Conclusion
In conclusion, fungicide with triticonazole + pyraclostrobin active ingredient is effective at the seed-borne infections of the pathogen on seedling development.Also, it was determined that the effect of the fungicides on the pathogen may change with the virulence of the pathogen, active ingredient of the fungicide used on the seed, weath cultivar and the seed infection method of the pathogen.
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