The effects of temperature and wetness duration on the development of Guignardia psidii in guava fruit naturally infected

A survey conducted in SP state in 2005 and another in 2007 found that black spot (Guignardia psidii) incidence on guava reached 58 %. The aim of this study was to investigate the effects of temperature and wetness duration on the development of black spot symptoms in detached guava naturally infected under controlled conditions. Guava fruit cv. Kumagai from a production field with a history of occurrence of the disease were subjected to different temperatures (10, 15, 20, 25, 30 and 35 °C) with wetness periods of 6 and 24 h. Analyses of variance and nonlinear regression were employed to evaluate the combined effects of temperature and wetness duration on the disease incidence, the final disease severity, the rate of disease progression and incubation period. Black spot symptoms were observed at all temperatures, except at 10 and 35 °C. The first symptoms of black spot in guavas were observed 2 days after incubation at 25 and 30 °C with wetness duration of 6 h. All variables reached their maximum values close to 30 °C, regardless of wetness duration. This temperature combined with 24 h of wetness duration resulted in black spot incidence of 100 %, disease severity of 3.02 cm, progress rate of 6.9 mm/day and incubation period of 6 days, 10 days after incubation. The postharvest storage of fruits at 10 °C and other control methods based on low or high temperature can delay the black spot incidence on ‘Kumagai’ guavas and prolong the fruit shelf life.