The effects of chestnut apical bud positions on vegetative and reproductive annual growth

The growth and fruiting pattern of chestnut annual branches was investigated in a traditional sweet chestnut (Castanea sativa Mill. ‘Marrone di Castel del Rio’) orchard. The development of the annual apical shoot, from the top four apical buds, was described in one-year-old branches, randomly selected in the orchard. A total of 60 shoots were weekly measured in length and diameter from bud break (07 BBCH stage) to a week before burr fall (83 BBCH stage). On the same annual shoot, once female inflorescences were well differentiated and fully receptive (65 BBCH stage), the burr diametral growth was also weekly measured and the number of burrs, in each shoot, counted. At harvest, nut quality (fresh weight and diameter) was also assessed. For each annual shoot, length and burr diameter absolute growth rate (AGR) were calculated. The shoot vegetative growth showed a rapid increase in the first part of the season, reaching a peak, in absolute growth rate, in the middle of May. Later, their growth reduced and being constant throughout the rest of the season. Shoot showed a reduced vegetative vigour, form the apical to the bottom part of each branch, although a limited presence of burrs in the lower ones. Once shoot stop completely their growth (middle of June), burr started to increase their growth rate, likely acting as the major sink. The apical bud, although carrying the highest number of burrs per shoot, showed generally the highest growth rate along the season with also improved nut quality traits recorded at harvest. These preliminary results highlight the importance of the apical bud in sustaining chestnut yield and quality.