Sustaining Production in Marginal Climates

Winter chill is the amount of ‘cold’ that dormant buds are exposed to from leaf fall until dormancy is broken and buds burst. Cherry varieties vary in the range of temperatures that contribute to chill and to uniform bud burst. This study confirmed in both the laboratory and the field that the variety ‘Kordia’ has a much higher chill requirement than the variety ‘Sweetheart’. It also highlighted that the different methods (chill hours, chill portions) for calculating chill need to be understood by growers if chill requirement is to be used to determine regional suitability for varieties. In the field Sweetheart achieved 100% bud burst in around 10 days whereas it took 16 days for Kordia to achieve maximum bud burst; some Kordia buds did not burst at all. This study additionally investigated a potential link between bud carbohydrate storage and bud break in cherries. The study found that sucrose concentration in buds increased from summer to winter in both varieties, whereas starch levels in buds increased from summer to winter for Sweetheart but decreased in Kordia. Sweetheart trees had potentially more carbohydrate storage reserves; they had larger trunk size than Kordia. Deciduous tree trunks can store carbon during dormant periods which can be remobilised to other tree parts when required in Spring. Decreasing trunk size in Kordia was associated with decreasing bud sucrose levels. This study suggests that to manipulate bud carbohydrate reserves by pruning, tree training or tree nutrition it may be possible to improve the rate and uniformity of bud burst, and sustain production in marginal climates.