Examination of Heating Condition for Promotion of Bud Burst on Japanese Persimmon (<i>Diospyros kaki</i> Thunb.) &lsquo;Tonewase&rsquo; in the Forced Culture

Abstract

This study investigated forcing conditions for promoting bud bursting in the forced culture of the 'Tonewase' persimmon. Bud burst occurred earlier with the advance of the forcing starts when cuttings, with the Development Index (DVI) for endodormancy breaking of 'Tonewase' persimmon greater than 0.60, were forced at 18 or 24 . Furthermore, bud burst occurred earlier with the advance of forcing starts when cuttings, with the DVI were greater than 0.91, were forced at 11 or 15 . Pre-heating to 5 or 8 , most effective temperatures for endodormancy breaking before forcing at 15 , similarly promoted bud burst of cuttings. The bud burst rate of cuttings was examined using pre-heating at 8 for 9-40 days before 15 forcing between 13 December and 12 January from 2003 to 2005. Pre-heating at 8 for 20 days before 15 forcing, to render the DVI as greater than 1, promoted bud burst of cuttings five days earlier compared with no pre-heating. Pre-heating of 'Tonewase' persimmon trees in the air temperature range between 6-8 and 10-15 in a greenhouse for 17-29 days induced the bud burst stage two to five days earlier compared with no pre-heating. These results suggest that, in the forcing culture of the 'Tonewase' persimmon, the forcing start date and set temperature can be determined according to the degree of endodormancy completion based on the DVR model, and that bud break can be further advanced by pre-heating at temperatures effective for endodormancy completion before forcing.