The effect of chilling duration and temperature on asparagus spear growth

The aim of this study was to investigate the effect of different chilling periods at five different growth temperatures on bud break, relative spear growth rate (RSGR), and bud production. Five-year-old plants were placed in a coolstore at 5 degrees C to satisfy chilling for 0, 3 and 6 weeks. After the specified chilling time, the pots were placed into controlled environment growth cabinets at one of five temperatures (10 degrees C, 15 degrees C, 20 degrees C, 25 degrees C, and 30 degrees C) in dark conditions. The results showed that increasing the temperature from 20 degrees C to 30 degrees C had no significant effect on the time to bud break, but at 15 degrees C and below chilling had a positive effect on the timing of bud break. Asparagus plants that were not chilled and grown at 15 degrees C or below had a long period to bud break compared to the chilling treatment. The RSGR increased with increasing temperature from 10 degrees C to 30 degrees C irrespective of chilling treatment. The growth of spears was mainly exponential (constant RSGR) from 20 degrees C to 30 degrees C. At 15 degrees C, 56.9% of the spears showed exponential growth and 8.1% linear growth, while at 10 degrees C only 20% showed exponential growth and 20.7% linear growth. The maximum spear growth rate was achieved at 30 degrees C with non-chilled plants. Surprisingly during the spear harvest season new buds were produced but new buds per cluster were not influenced by temperatures between 15 degrees C to 30 degrees C, while at 10 degrees C bud production decreased. In summary, growing temperatures are important factors for spear production and growth, affecting RSGR, time to bud break and new bud initiation, but the effect may be modified by the amount of prior chilling.