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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.

The objectives of this work were (i) to determine the influence of temperature on infection of citrus by ‘Candidatus Liberibacter asiaticus’ and ‘Candidatus Liberibacter americanus’, the two bacterial species associated with citrus huanglongbing (HLB) in Brazil, and (ii) to determine the influence of temperature on citrus colonization by ‘Ca. L. asiaticus’, which has taken over from ‘Ca. L. americanus’ as the predominant species in Brazil since 2008. Two experiments were carried out with graft-inoculated Valencia oranges on Rangpur lime rootstocks. Immediately after inoculation the plants were maintained for 423 days in growth chambers under the following night ⁄day temperature conditions: 17 ⁄22, 22 ⁄27 or 27 ⁄32� C, with a dark ⁄light photoperiod of 8 ⁄16 h. Infection and colonization of plants were determined using quantitative PCR (qPCR). ‘Candidatus Liberibacter americanus’ did not infect the plants maintained at 27 ⁄32� C; however, infection by ‘Ca. L. asiaticus’ occurred at all studied temperatures. Two months after inoculation, ‘Ca. L. asiaticus’ was distributed throughout the inoculated plants, with mean Ct values in the range of 30‐31 for leaves and 25‐28 for roots. Over time, ‘Ca. L. asiaticus’ reached the highest titres in mature leaves (mean Ct value = 26AE7) of citrus plants maintained at 22 ⁄27� C. ‘Candidatus Liberibacter asiaticus’ colonization of citrus plants was negatively affected by the daily temperature regime of 27 ⁄32� C( meanCt value in mature leaves = 33AE6).