Determining the chill requirement of important pear rootstocks available to the South African fruit industry

We endeavoured to determine the dormancy status of various pear rootstocks by assessing their Progression of Dormancy and Chill Requirements.

Twenty Dormancy Progression Curves (DPC) were quantified using 6 rootstocks grown in two locations over two years. In 2013 Chill Requirements (CR) of all the rootstocks available at both locations were determined.

From DPC it was determined that BP3, OH X F 40 and OH X F217 went into deeper dormancy than BP1, BA29 and C51. Dormancy in OH X F 40 and 217 as well as BA29 and C51 peaked early in the season while BP1 and BP3 showed a more gradual entrance into dormancy. OH X F 40 and 217 exited dormancy considerably later than the other rootstocks resulting in a much longer dormancy period.

CR results proved unreliable and contradictory. Differences in the dormancy status of the shoots used to determine CR proved to influence the results as did the location from which the shoots were sampled. Furthermore, the relatively low dormancy pattern of some of the pear rootstocks increased the possibility of inaccurate results.

Under conditions of inadequate chill, the method used to determine CR is not reliable in its entirety. The dormancy status of rootstocks must rather be assesed generally and ranked from low to high chill using both DPC and CR over numerous locations and seasons.