Effect of severity and incidence levels of crown rust and stem rust on yield of oat genotypes

Germoplasm introduction represents an alternative to increase oat (Avena sa tiva L.) variability favoring selection. The objectives of this study were: a) to select oat lines with high grain yield and adaptation to State condi tions; b) to determine the relationship between crown and stem rust with gr ain yield; c) to estimate the relationship between severity and incidence r ules as tools to diagnose disease intensity. Fifty seven oat lines were eva luated for grain yield and other characters. The lines were classified usin g the mean standard deviation and the data was submitted to correlation and regression analyses. Only three introduced lines leaked promising. The cor relation between crown rust and grain yield was significant, differently fr om stem rust. Severity to incidence regression of diseases showed quadratic behaviour, although linear relations were observed in low incidence levels . From disease reaction type, the selected lines are valuable to oat breedi ng programs. Incidence rule can efficiently replace the severity rule at lo w epidemic levels, facilitating field diagnostics.