Desempenho de fosfitos de potássio no manejo de mofo branco em soja

Soybean plays an important role in the Brazilian agriculture being one of the products most exported by the country. Its yield may be affected by diseases such as white mold, caused by the fungus Sclerotinia sclerotiorum Lib. de Bary, which, under favorable field conditions prevents the crop of expressing all its productive potential. The fungus is cosmopolitan and infects more than 400 species of plants. This disease is difficult to control, and the use of chemicals has not been sufficient to avoid significant losses, thus, this products are expensive and may cause environmental damage. Alternative methods, such as foliar fertilizers based on potassium phosphite, can also be used in the management of this disease. In this context, this work aimed to study different sources of potassium phosphite and its effects in the control of white mold in soybeans, as well as the time of application in culture, its action in inducing plants defense responses and/or its influence over the seeds quality. The effect of phosphites, over the pathogen, was evaluated in vitro, on mycelial inhibition, the mass of dry mycelium and germination of sclerotia. In all tests, the following phosphites were utilized: Phosphite A (P2O5-40%; K2O-20% - 1 L/ha); Phosphite B (P2O5-40%; K2O-28% - 1 L/ha); Phosphite C (P2O5-40%; K2O-20% - 1 L/ha) e Phosphite D (P2O5-30%; K2O-20% - 2,4 L/ha). At the induction of resistance tests were evaluated the synthesis of phytoalexin in soybean cotyledons and the enzymes FAL and POX evaluated in seedlings in growing chamber, sprayed with phosphites and the fungicide fluazinam. Field experiment was carried out at Coronel Domingos Soares-PR, in the 2012/2013 season, in an area with natural infestation of the pathogen. Soybean cultivar BMX Active was no-till seeded with 0,5m between rows. The experimental was laid out as a factorial 5 x 4 scheme (treatment x application time). Phosphites sources were used, as described above, and water was sprayed in the control treatment. Treatments were applied at four different growth stages: V4, V4 + R1, R1 and R2 at the rates recommended by the manufacturer. Soybean yield components and seeds and health and physiological quality were evaluated after harvesting. None of the tested phosphites affected mycelial growth and sclerotia germination or influenced phytoalexin synthesis. Phosphites C and D stood out due to an increasing in the phenylalanine ammonia-lyase activity 48 hours after its inoculation. These same products also induced the synthesis and peroxidases and phosphite C kept the levels of this enzyme elevated up to 72 hours after inoculation. At the field trials, phosphites C and D stood out in the control of white mold. There was no significant interaction of potassium phosphite on physiological and sanitary quality of the seeds.

Chorume de suíno no controle da rizoctoniose em beterraba

The fungus Rhizoctonia solani is a soil borne pathogen that causes damage to various crops. The chemical control, when managed incorrectly, can be harmful to the environment, which makes the study of alternative control important. This study aimed to evaluate the ability of different doses of Liquid swine manure (LSM), with and without the retention of gases, at different soil pH levels, to control R. solani in beet. An inoculum of the fungus R. solani was on rice grains, which had been previously sterilised. The experiments were set up in a greenhouse in a completely randomised block design, arranged in a three-factor 2 x 2 x 5 scheme, comprising of soil pH levels (4.8 and 7.2) x with and without gas retention x LSM dose (0, 5, 10, 15 and 20%), with four replications per treatment. To setup the experiments, 4 kg of soil of each pH level were packed separately into plastic bags. Subsequently, the soil of each bag was infested with 15 g of fungus inoculum/kg of soil, and moistened as necessary. After seven days of infestation of the soil with the pathogen the different doses of LSM were incorporated separately into the bags, the bags designated as the gas retention treatment were closed, while those designated as the gas release treatment were left open. After seven days, part of the soil from each bag was packed separately into 16 cells of 128 cell Styrofoam trays, which were then seeded with two beet seeds per cell. The other part of the soil was placed in 2 litre pots, to conduct the quantification of microbial activity, through the method of CO2 release, 21 days after the experiment was setup. Seedling emergence and damping-off evaluations were performed daily for 21 days consecutively. The data was submitted to analysis of variance, and when significant were submitted to regression analysis or Tukey at 5% probability of error. The experiments were repeated twice. According to the results obtained, there was a suppressive effect of LSM on R. solani. For the variable emergence, the 10% dose of LSM resulted in the largest number of emerging plants in the two soil pH levels studied, whether or not gas was retained. Seedling dampingoff decreased with increasing volumes of LSM incorporated into the soil. The soil with the pH level of 7.2 presented less seedling damping-off than the soil with a pH level of 4.8. The retention of gases provided greater control of R. solani in the higher LSM doses and in soil with a pH level of 7.2. Also noted in this study that there was a significant increase in microbial activity with increasing doses of LSM when applied to soil with pH levels of 4.8 and 7.2. Based on these results, it was concluded that the 10% dose of LSM provided the best control of R. solani without harming seedling emergence.