THE INFLUENCE OF DIURNAL TEMPERATURES ON THE POSTHARVEST SUSCEPTIBILITY OF POINSETTIA TO BOTRYTIS-CINEREA

The influence of day/night (DT/NT) temperatures of 16/16, 19/19, 22/22 16/19, 19/22, 16/22, 19/16, 22/19, and 22/16 degrees C during poinset tia production on postharvest bract and foliage susceptibility to Botr ytis cinerea was investigated. Plants were inoculated with 2.7 x 10(5) B. cinerea conidia per ml of water following a 3- or 6-week temperatu re treatment and incubated at 20 degrees C. Area under the disease pro gress curve (AUDPC) data indicated that the postharvest susceptibility of poinsettia bracts and foliage to B. cinerea, measured by the propo rtion of bracts and foliage infected and the proportion with sporulati ng B. cinerea, was not influenced by the difference in DT and NT but i ncreased as DT or NT during production increased. As plants matured, a s indicated by thermal time, AUDPC values increased (P = 0.001) more f or the proportion of bracts infected (R(2) = 0.73) than for the propor tion of bracts with sporulating B. cinerea (R(2) = 0.86) and the propo rtion of foliage with sporulating B. cinerea (R(2) = 0.74). Results su ggested that commercial growers using higher NT than DT to limit poins ettia height are not increasing the postharvest susceptibility of thei r crop to B. cinerea. However, the increased susceptibility of maturin g poinsettias suggests disease management strategies should be intensi fied during crop finishing and postharvest handling.