NONDESTRUCTIVE MEASUREMENT OF DORMANT BUD RESPIRATION RATES

The lack of an indicator of the state of bud development during the do rmant period has been a major difficulty in studying the effects of wi nter chilling on subsequent shoot growth and flowering. We considered that respiration rate (R-D) might provide such an index, so developed a technique for the non-destructive measurement of the R-D of individu al dormant buds of kiwifruit (Actinidia deliciosa). A closed configura tion gas exchange system was used. The low R-D of dormant buds require d the use of an unusually small system volume, As a consequence, it wa s necessary to modify the conventional closed system so that most of t he system volume could be sampled for analysis, Increases in CO2 conce ntration during a measurement were determined by injecting gas samples into a stream of air flowing through an infrared gas analyser. The te chnique was found to be reliable even at R-D as low as 20 pmol s(-1). Error analysis showed that under normal operating conditions the coeff icient of variation was approximately 3 %. With two operators, measure ments could be made at the rate of one bud every four minutes. The abi lity to make non-destructive measurements has the advantage of enablin g us to make sequential measurements on individual buds and monitor su bsequent development. The system could be readily adapted to other woo dy fruit species, providing that gas-tight seals can be established on individual buds. Use of the system is illustrated by measuring the te mperature response of the R-D of dormant buds grown under contrasting conditions. All buds showed increasing R-D with increasing temperature in the range 15 to 25 degrees C, Buds which had grown in the coolest region, where bud break is usually the earliest, had the highest R-D w hen measured during early spring.