Non-destructive measurement of dormant bud respiration rates

Abstract

The lack of an indicator of the state of bud development during the dormant period has been a major difficulty in studying the effects of winter 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 individual dormant buds of kiwifruit (Actinidia deliciosa). A closed configuration gas exchange system was used. The low R(D) of dormant buds required the use of an unusually small system volume. As a consequence, it was necessary to modify the conventional closed system so that most of the system volume could be sampled for analysis. Increases in CO2 concentration during a measurement were determined by injecting gas samples into a stream of air flowing through an infrared gas analyser. The technique 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 coefficient of variation was approximately 3%. With two operators, measurements could be made at the rate of one bud every four minutes. The ability to make non-destructive measurements has the advantage of enabling us to make sequential measurements on individual buds and monitor subsequent development. The system could be readily adapted to other woody fruit species, providing that gas-tight seals can be established on individual buds. Use of the system is illustrated by measuring the temperature 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 °C. Buds which had grown in the coolest region, where bud break is usually the earliest, had the highest R(D) when measured during early spring.