Patterns of urediniospores release and development of rose apple rust

This research was conducted to evaluate some epidemiological features of the rose apple (Syzygium jambos) rust (Puccinia psidii Winter) under field conditions at the Universidade de Brasilia, Brasilia, DF, Brazil, from March 29 through December 31, 1988. Data for the amount of airborne urediniospores were collected in ten plants, using a Burkard's seven-day volumetric spore trap set between two rose apple trees. Most of the airborne urediniospores were collected between June 23 and July 6, from 10 a.m. to I p.m. The major quantity of S. jambos affected shoots occurred between April 28 and July 20. There was a positive correlation between the amount of trapped urediniospores and infected young shoots. A negative correlation was shown between temperature (12h) and number of airborne urediniospores. The number of days with relative humidity (RH) greater than or equal to 80% was positively correlated to the amount of deformed shoots. Also, the amount of urediniospores and infected young shoots were positively correlated to the number of days with night (24h) temperature less than or equal to 20 degreesC or night RH greater than or equal to 80%. These data show that this disease was favored by low temperatures (less than or equal to 20 degreesC), high night RH (greater than or equal to 80%) and high levels of airborne urediniospores.