-Phosphorous application effects were evaluated on ryegrass dry matter (DM) accumulation, root development and plant tissue concentration of phosphorus, nitrogen and carbon aiming to determinate the nutritional status of the pasture, as well as to verify the possibility to establish a phosphorus dilution curve for this pasture. Also, the development of phosphorus and ryegrass cultivated with the residual effect of phosphorus fertilization was determined. The experiment was carried out in Pinhais County -Paraná State on a Cambisol with very low phosphorus levels. The experiment was of random blocks design and treatments consisted of five phosphorus rates of triple superphosphate (0, 45, 90, 180 and 360 kg P 2 O 5 ha -1 ) applied to soil surface with four replications. Phosphorus fertilization promoted linear increments in the soil phosphorus availability and resulted, in the first year, in early pasture production and higher phosphorus content in the plant. Nitrogen and carbon contents were not affected. Phosphorous application increased ryegrass DM accumulation in all periods, ranging from 16 to 2826 kg DM ha -1 at flowering stage, for zero and 360 kg P 2 O 5 ha -1 , respectively. Root density was positively influenced by phosphorus supply, and the rate of 45 kg P 2 O 5 ha -1 was effective for maximum root development. The residual effect of phosphorus fertilizer provided enhancement of yield and phosphorus plant concentration for both sorghum and ryegrass in the second year.
Cotton blue disease (CBD) is the viral disease which poses the greatest threat to cotton in Brazil. One efficient way of controlling this disease is by using resistant cultivars. However, the recent emergence of an atypical form of CBD (ACBD), caused by a new virus genotype capable of overcoming these resistant cultivars, is causing concern. Thus, the aims of this study were to evaluate the distribution of ACBD in the states of Mato Grosso (MT) and Goiás (GO), to determine the relationship between vector infestation level, disease incidence and yield, and to check the reaction of cotton cultivars to two viral isolates. In both cotton production areas, 1128 plots were surveyed and 6.5% showed plants with the virus, 97.3% and 2.7% with ACBD and CBD, respectively. In cultivars susceptible to ACBD, a positive linear relationship between changes in the levels of aphid infestation and incidence of viral infection was indentified, and a negative linear relationship between infestation level and yield. The maximum acceptable level of aphids up to 80 days after sowing for susceptible cultivars was approximately 15%. Although 83% of the cultivars were shown to be resistant to CBD, only 19.2% were resistant to ACBD. There was also a number of cultivars with considerable resistance to both isolates.
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