BLANK FRUITS IN HAZELNUT (CORYLUS-AVELLANA L) CVBUTLER - CHARACTERIZATION AND INFLUENCE OF CLIMATE

Seedless nuts, or blanks, are a serious problem in many hazelnut (Cory lus avellana L.) cultivars and represent an important economic loss to the commercial grower. To evaluate the growth and fruit production of hazelnut in the northern region of Portugal, a trial with II cultivar s was established in 1984. 'Butler' was the most productive cultivar a nd is well-suited to the in-shell market, but in eight years it produc ed 8.4% blanks. Blanks could not be fully described according to curre nt classifications and so we propose a new one in which ten types of b lanks are defined according to the appearance, number, and size of the ovules, aspect of funiculus, existence of internal fibre, and shell a ppearance. To investigate the causes of blanks, blank fruit rates were correlated with climatic factors (temperature, rainfall, sunshine, wi nd and relative humidity) in each year from April to July. The increas e in solar radiation and decrease of relative humidity in May, and hig her minimum temperatures in July, were correlated with a reduction in blank rates in 'Butler'.