Tratamentos químicos e biológicos de sementes de soja para o controle de Phytophthora sojae

Abstract

The expansion of areas cultivated with soy in Brazil combined with its intensive cultivation favors the survival of soil pathogens, such as Phytophthora sojae, a causal agent of root rot. Resistant soy cultivars already exist on the market, however, this resistance is not always durable. Combining disease control methods are more effective and sustainable strategies. Thus, seed treatment stands out as the second line of defense against the disease. Chemical seed treatments are common among producers, however, due to cases of resistance and the mitigation of the use of biologicals in agriculture, more and more studies are being sought to assess the viability of fungi such as Trichoderma spp. as seed treatment. Thus, this study aimed to evaluate: i) the fungitoxic effect of Maxim Advanced ® and Apron RFC® on P. sojae isolates Ps.2.4 and 34.1 in vitro and, ii) the antagonistic effect of different strains of Trichoderma spp., in the control of P.sojae isolated Ps.2.4 and 34.1 in vitro. iii) the partial resistance of six commercial soybean cultivars and; iv) the efficiency of control of chemical and biological treatments in seeds for P.sojae isolates (Ps.2.4 and Ps.34.1) and its effect on the physiological Quality® of seeds. For this, five experiments were developed at the Federal University of Santa Maria, campus of Frederico Westphalen / RS. In the first experiment, the fungitoxicity of chemical products in different concentrations in culture medium was evaluated for the inhibition of mycelial growth of P. soye isolates. The second trial involved direct confrontation, as well as exposure of the pathogen to volatile, non-volatile and non-volatile thermostable compounds of different strains of Trichoderma spp. to isolates of P.sojae. The third experiment evaluated the partial resistance of six soybean cultivars (55I57RSF IPRO, NS 5445 IPRO, 53I54 IPRO, 58I60RSF IPRO, 57HO121 RR and Conrad) for P.sojae inoculum (isolated Ps.2.4; Ps.34.1 and without inoculum) ). In the fourth experiment, the physiological Quality® of three soybean cultivars (55I57RSF Ipro, NS 5445 Ipro and Conrad) treated with chemical products (Apron RFC® and Maxim Advanced®) and biological (Trianum®, Quality®, Organic® ® and Stimucontrol®) was evaluated. In the last experiment, the effect of seed treatment with chemical and biological products on the control of two isolates of P. soye for different soybean cultivars was analyzed. The chemicals Maxim Advanced® and Apron® were fungitoxic for the two isolates of P.sojae, in in vitro tests. The growth of P.sojae isolates is inversely proportional to the dose of the fungicides used, that is, the higher the dose of the fungicide, the lower the mycelial growth of the isolate. The isolate of P.sojae Ps 2.4 was more sensitive to the tested fungicides. The different commercial formulations based on Trichoderma spp. have an inhibitory effect on the growth of P.sojae isolates, Ps 2.4 and Ps 34.1, in vitro. The bioproducts Stimucontrol® (T. harzianum) and Organic® ® (T. asperellum) were the most effective in controlling P.sojae, as their isolates were able to act by more than one antagonistic mechanism, giving advantage to the biocontrol agent when released into the environment . Thermostable non-volatile metabolites did not show consistent results in the tests conducted, requiring further studies. The soybean cultivars 55I57RSF IPRO, NS 5445 IPRO, 53I54 IPRO, 58I60RSF IPRO, 57HO121 RR have high partial resistance to root rot of Ps.2.4 and Ps.34.1 isolates from P.sojae. The cultivar Conrad was susceptible to the isolate Ps.34.1 of P.sojae. Seed treatments with Apron RFC® and Maxim Advanced® ensured the vigor and germination of soybean seeds. The biological products did not show a negative effect on the physiological Quality® of the tested soybean cultivars, except for Trianum®. The chemical treatments with Apron RFC® and Maxim Advanced® are efficient in the control of P.sojae isolates in soybean cultivars. The biological treatments Quality®, Organic® ® and Stimucontrol® are promising in the control of root rot in soybean by P.sojae.