Field and controlled temperature studies on the flowering of hazelnuts in Australia.

Observations on the date of commencement and the period of pollen shed and female bloom were recorded for a range of hazelnut genotypes at five field sites over an eight year period. Date of commencement of both pollen shed and female bloom varied between seasons and sites but the order of both pollen shed and female bloom for genotypes showed very little variation. The earlier the genotypes came into pollen shed, the longer the period that pollen was shed. The genotypes were protandrous. A study was undertaken using temperature controlled cabinets. Material from a range of genotypes was cut weekly and placed in cabinets where temperatures were maintained at 10°C and 15°C. Pollen shed was observed to occur in the cabinets up to nine weeks earlier than it occurred for the same genotype in the field but female bloom did not occur any earlier in the cabinets than in the field. It is hypothesised that there are two physiological processes affecting catkin extension: chilling, which causes a decline in a plant regulating substance preventing catkin extension and warmth, causing the production of a substance which stimulates catkin extension. Once the balance tilts in favour of the stimulating substance, catkin extension occurs. In the female flower, the principle factor is considered to be a decline in the retarding substance due to chilling; once this is at sufficiently low levels, flowering occurs. There is concern that with global warming, pollen shed may occur earlier, relative to female bloom, resulting in poor pollination for later blooming varieties.