Studies of apple bud dormancy and branching under conditions of inadequate winter chilling

[摘要] ENGLISH ABSTRACT:In order to study the dormancy of apple buds in conditions of inadequate chilling anumber of trails were done during 2000 and 2001.Year-old, unbranched shoots of 'Royal Gala', 'Braeburn', 'Cripps' Pink' and 'GrannySmith' apple were harvested randomly from bearing commercial orchards in theKoue Bokkeveld [33°S, 945m, ca.1300 Utah model chili units (CU)) and Elgin (34 S,305m, ca.750CU) regions of the Western Cape, South Africa, respectively. Shootswere chilled at 5-rC. Two replicate bundles were removed from the cold room,prepared and forced at 25°C with continuous illumination until budburst had occurredon at least 25% of the shoots per bundle. The change in the rate of budburst overtime was calculated for each orchard and to this response; either a linear or aquadratic function was fitted. Poorly correlated variables were selected that bestdescribe these functions. Using these variables, the orchards were separated intocluster groupings that represented a dormancy pattern. The first split separated thelower chilling requirement cultivars from the higher cultivars. The second and thirdsplit separated the orchards according to area differences. The clusters representingthe warmer area orchards initially entered deeper into dormancy before exiting. Theclusters for the colder area immediately had an increased budburst rate. This dataconfirm that the chilling requirement includes a period of dormancy induction. Animportant genotype and environment interaction, other than cold unit accumulation,was observed that could be responsible for terminating bud dormancy.Terminal apple buds from 'Royal Gala' Braeburn', 'Cripps' Pink' and 'Granny Smith'apples were cut from orchards in the Koue Bokkeveld and Elgin regions of theWestern Cape, South Africa. Buds were harvested every two weeks during thedormant period. The buds were cut in half and leaf scales removed before the waterpotential were measured. Fresh and dry weights of the buds were also determined.The data presented confirms the changes in availability of free water in dormant budsand that it could be measured in this way. A definite influence of temperature wasillustrated. The water potential from buds in a cold production area (Koue Bokkeveld)behaved more normally - water is in a bound form during most of the winter andchange to an available form later in winter - whereas buds from a warmer productionarea did not change much in water potential or content.In the trial, two-year-old proleptic-branched shoots, ca. 500mm long, were selectedfrom a 'Royal Gala' orchard in the Koue Bokkeveld region in the Western Cape,South Africa. During the dormancy period of 2000, shoots received two coldtreatments; chilling in a cold room at 5-7°C and the natural chilling received in thefield. In 2001, the trail was repeated, but only with the field chilling. The shootsreceived five dormant pruning treatments: control (not pruned), pruning back to thefourth lateral (heading) before or after chilling; and removal of the 2nd and 3rd laterals(thinning) before or after chilling. After pruning and chilling treatments, the shootswere removed from the orchard or cold room every two weeks and forced in a growthchamber. The rate of bud burst (1/days to 50% bud burst) was calculated for theterminal buds of the lateral shoots. Laterals were categorisation according toposition: the terminal extension shoot, the 4th lateral, and all other laterals werepooled. Removing distal tissue by pruning (heading more than thinning) promotedbud burst on laterals. Pruning before chilling was more effective than after chilling.The correlative phenomena that inhibit bud burst on proximal shoots within two-yearoldbranches were manipulated by pruning.The branching response of one-year-old unbranched shoots, 0.5m long, from 'RoyalGala' and 'Cripps' Pink' apple and 'Rosemary' pear were studied after physicalmanipulation treatments. Shoots for treatment a to d were re-orientated from either ahorizontal or vertical position or left in the original position as control, treatment e to hinvolved the same re-orientation of shoots and were headed. The amount of growth(in mm) from each node was recorded as well as the position from the terminal bud.The 'Cripps' Pink' had a definite shift in the acrotonic branching pattern (for headedand unheaded), towards a more basitonic response. The reduced effect on 'RoyalGala' and 'Rosemary' suggest a difference in genotype response to the treatmentsas well as time of treatment.

[发布机构] Stellenbosch University