The role of tree architecture in super high density olive orchards

• Does tree architecture play a role in cultivar suitability for super high density olive orchards??
• We found that the most suitable cultivars have greater branching and thinner structures.
• This implies more producing sites and reduced supporting structure per unit of canopy volume.
• This is essential in super high density orchards where canopy volume has to be small.
• These findings are important for cultivar choice and breeding for super high density orchards.

Analyzing plant architecture is important for the understanding of plant growth, branching pattern, yield, and for the development of crop models. In other species tree architecture has been studied in detail, but not in olive. In this species, super high density (SHD) orchards (>1500 trees per hectare) have been extensively planted in recent years, using only a few cultivars (i.e. Arbequina, Arbosana and Koroneiki) considered suitable for this system. What makes these cultivars suitable for SHD orchards is not clear. In this work it is hypothesized that tree architecture plays an important role in this respect. We studied several tree architectural and reproductive parameters on different olive cultivars, including Arbequina, Arbosana and 19 others, mostly Italian. The impact of the architectural parameters on tree productivity was also studied. The architectural parameters studied were: diameter and node number of the trunk; number, diameter and angle of insertion of the lateral branches departing from the central leader; diameter, length, node number and average angle of fruiting shoots. On fruiting shoots, inflorescence and fruit number were also recorded respectively at bloom and at harvest. Branching frequency was calculated as the average number of lateral branches per bud. Arbequina and Arbosana differed from other cultivars for a greater branching frequency. The latter was negatively correlated to the diameter of lateral branches as well as to the diameter of one-year-old shoots. Consequently, Arbequina and Arbosana produced a greater number of smaller lateral branches and shoots, both parameters being desirable for SHD olive orchards. Combining branching and fruiting characteristics, we developed yield indices which segregated these cultivars from most others. The results suggest that high branching and small diameters are important architectural characteristics to increase yield efficiency, and affect the cultivar suitability for SHD orchards.