Effect of temperature and leaf wetness duration on infection of sweet oranges by Asiatic citrus canker

Abstract

Asiatic citrus canker, caused by Xanthomonas smithii ssp. citri , formerly X. axonopodis pv. citri , is one of the most serious phytosanitary problems in Brazilian citrus crops. Experiments were conducted under controlled conditions to assess the influence of temperature and leaf wetness duration on infection and subsequent symptom development of citrus canker in sweet orange cvs Hamlin, Natal, Pera and Valencia. The quantified variables were incubation period, disease incidence, disease severity, mean lesion density and mean lesion size at temperatures of 12, 15, 20, 25, 30, 35, 40 and 42 ° C, and leaf wetness durations of 0, 4, 8, 12, 16, 20 and 24 h. Symptoms did not develop at 42 ° C. A generalized beta function showed a good fit to the temperature data, severity being highest in the range 30-35 ° C. The relationship between citrus canker severity and leaf wetness duration was explained by a monomolecular model, with the greatest severity occurring at 24 h of leaf wetness, with 4 h of wetness being the minimum duration sufficient to cause 100% incidence at optimal temperatures of 25-35 ° C. Mean lesion density behaved similarly to disease severity in relation to temperature variation and leaf wetness duration. A combined monomolecular-beta generalized model fitted disease severity, mean lesion density or lesion size as a function of both temperature and duration of leaf wetness. The estimated minimum and maximum temperatures for the occurrence of disease were 12 ° C and 40 ° C, respectively.

Transgenic Sweet Orange (Citrus sinensis L. Osbeck) Expressing the attacin A Gene for Resistance to Xanthomonas citri subsp. citri

“…Experimental plants were individually spray-inoculated on both sides of the young leaves with a 10 6 cfu mL −1 Xcc suspension and covered with a clear plastic bag for 72 h in order to keep high humidity (Dalla Pria et al 2006;Pavan et al 2007). Plants were then transferred to a growth chamber (Conviron® model PGW 36, Winnipeg, Canada) with restricted access due to biosafety regulations, in a 12-h photoperiod, at 28°C.…”

Modelling the progress of Asiatic citrus canker on Tahiti lime in relation to temperature and leaf wetness

“…However, a recent study showed citrus canker develops best at 30-35°C ). In addition, temperature influences the symptom expression and length of incubation period, reducing or increasing it (Koizumi 1976;Dalla Pria et al 2006). In each citrus species, the bacterium can express unique behaviour under the same environmental conditions (Peltier 1920).…”

Outcome of the public consultation on the draft Scientific Opinion on the risk to plant health of Xanthomonas citri pv. citri and Xanthomonas citri pv. aurantifolii for the EU territory

“…The model of suitable weather presented in Figure F.1 in Appendix F is heavily flawed for the following reasons: 1) The model used a minimum temperature of 5°C. While bacteria can survive at lower temperatures, infection is not supported until temperatures reach at least 12-15oC (Dalla Pria et al, 2006), although the optimal temperature range for infection is 20-35°C (Peltier, 1920;Peltier and Frederich, 1926;Dalla Pria et al, 2006). If the temperature scale was adjusted to raise the minimum temperature to 15°C, much of the suitable weather conditions depicted during the colder months of October, November, December, January, February, and March would be eliminated.…”

“…The existence of climatic events leading to disease dispersal, as shown in Figure 8, could then No Organisation Country Chapter Comment EFSA PLH Panel reply for infection needs to reach at least 12-15oC (Dalla Pria et al, 2006), although the optimal temperature range for infection is 20-35°C (Peltier, 1920;Peltier and Frederich, 1926;Dalla Pria et al, 2006). Multiplication of the bacteria within infected plants may occur at temperature as low as 12°C, but there is no documented evidence that infection can occur below 12-15oC.…”