SHADE AVOIDANCE RESPONSE REGULATES APRICOT VARIETIES CANOPY DEVELOPMENT AND ROOT SYSTEMS OF ROOTSTOCK

The phenotypic behaviour with respect to light shade conditions, in response to the proximity of neighbouring plants, was studied in three genotypes of apricot: ‘Pisana’, ‘Portici’ and ‘A. Errani’. Plants were grown in mixed stands, formed by two cultivars in a chessboard grid, to simulate a dense community canopy. Although all genotypes showed the typical shade-avoidance response with the escape from the competitive stress for light, a degree of shade tolerance was observed among them. Shoot elongation and LAI development were highest for the moderate and deep shade-intolerant genotype, cv. ‘Pisana’. ‘Portici’ did not tolerate very deep shade conditions, as detected in the very high, dense canopies. ‘A. Errani’ was the most shade-tolerant, even though it produced the highest dry weight per unit of developed shoot. The root system also changed in all genotypes, with an inverse relation to the decrease in the active fraction of phytochrome detected in the canopies. Whole-plant development modification, to prevent shading by neighbouring competitors, has been observed, showing that apricot is a shade-sensitive species and that different response strategies to shade conditions are found within its germplasm.